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19-4634; 5/09
DS2780 Standalone Fuel Gauge IC
www.maxim-ic.com
GENERAL DESCRIPTION
The DS2780 measures voltage, temperature and current, and estimates available capacity for rechargeable Lithium Ion and Lithium Ion Polymer batteries. Cell characteristics and application parameters used in the calculations are stored in onchip EEPROM. The available capacity registers report a conservative estimate of the amount of charge that can be removed given the current temperature, discharge rate, stored charge and application parameters. Capacity estimation reported in mAh remaining and percentage of full.
FEATURES

Precision Voltage, Temperature, and Current Measurement System Internal Time Base is Accurate and Temperature Stable Absolute and Relative Capacity Estimated from Coulomb Count, Discharge Rate, Temperature and Battery Cell Characteristics Accurate Warning of Low Battery Conditions Automatic Backup of Coulomb Count and Age Estimation to Nonvolatile (NV) EEPROM Gain and Tempco Calibration Allows the Use of Low-Cost Sense Resistors 24-Byte Battery/Application Parameter EEPROM 16-Byte User EEPROM Unique ID and Multidrop 1-Wire Interface Tiny 8-pin TSSOP & 10-pin TDFN Package Embeds Easily in Battery Packs Using Thin Prismatic Cells
APPLICATIONS
Digital Still Cameras Sub-Notebook Computers Handheld PC Data Terminals 3G Multimedia Wireless Handsets
TYPICAL OPERATING CIRCUIT
PK+
PIN CONFIGURATION
DS2780
DATA
150 DQ PIO NC SNS 5.6V
500
1K
5 8 1 7
TSSOP-8
4 VDD 3 VIN 6 OVD 2 VSS
0.1uF Protection Circuit
1 Cell Li-Ion Battery
PK-
RSNS
ORDERING INFORMATION
PART DS2780E DS2780E/T&R DS2780E+ DS2780E+T&R DS2780G+ DS2780G+T&R MARKING 2780 2780 2780 2780 2780 2780 PACKAGE INFORMATION TSSOP TSSOP Tape-and-Reel TSSOP TSSOP Tape-and-Reel TDFN TDFN Tape-and-Reel
+Denotes lead(Pb)-free/RoHS-compliant package. 1-Wire is a registered trademark of Maxim Integrated Products, Inc. Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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DS2780 Standalone Fuel Gauge IC
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Pin Relative to VSS Voltage on VIN Relative to VSS Operating Temperature Range Storage Temperature Range Soldering Temperature (10s) -0.3V to +6.0V -0.3V to (VDD + 0.3V) -40C to +85C -55C to +125C See JEDEC J-STD-020
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to the absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED DC OPERATING CHARACTERISTICS
(VDD = 2.5V to 4.5V, TA = -20C to +70C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Supply Voltage OVD Voltage DQ, PIO Voltage Range SYMBOL VDD CONDITIONS (Note 1) (Note 1) (Note 1) MIN +2.5 -0.3 -0.3 TYP MAX +4.5 +4.5 +5.5 UNITS V V V
DC ELECTRICAL CHARACTERISTICS
(VDD = 2.5V to 4.5V, TA = -20C to +70C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER ACTIVE Current SLEEP Mode Current Input Logic High: DQ, PIO Input Logic Low: DQ, PIO Output Logic Low: DQ, PIO Pulldown Current: DQ, PIO Input Logic High: OVD Input Logic Low: OVD VIN Input Resistance DQ Capacitance DQ SLEEP Timeout Undervoltage SLEEP Threshold SYMBOL IACTIVE ISLEEP VIH VIL VOL IPD VIH VIL RIN CDQ tSLEEP VSLEEP CONDITIONS 2.5V VDD 4.2V 2.5V VDD 4.2V (Note 1) (Note 1) IOL = 4mA (Note 1) VDQ, VPIO = 0.4V (Note 1) (Note 1) 15 DQ < VIL (Note 5) (Note 1) 1.5 2.40 50 2.0 2.45 2.5 2.50 1.5 0.6 0.4 0.2 VDD - 0.2 VSS + 0.2 MIN TYP 65 1 MAX 95 105 3 UNITS A A V V V A V V M pF s V
ELECTRICAL CHARACTERISTICS: TEMPERATURE, VOLTAGE, CURRENT
(VCC = 2.5V to 4.5V, TA = -20C to +70C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Temperature Resolution Temperature Error Voltage Resolution Voltage Full-Scale Voltage Error Current Resolution SYMBOL TLSB TERR VLSB VFS VERR ILSB 2 of 31 1.56 0 4.88 4.992 50 CONDITIONS MIN TYP 0.125 3 MAX UNITS C C mV V mV V
DS2780 Standalone Fuel Gauge IC PARAMETER Current Full-Scale Current Gain Error Current Offset Error SYMBOL IFS IGERR IOERR (Note 2) 0C TA +70C, 2.5V VDD 4.2V (Note 4) 0C TA +70C, 2.5V VDD 4.2V VSNS = VSS, (Notes 3, 4) VDD = 3.8V, TA = +25C 0C TA +70C, 2.5V VDD 4.2V -7.82 CONDITIONS MIN TYP MAX 51.2 1 +12.5 UNITS mV % FullScale V Vhr/ day
Accumulated Current Offset
qOERR
-188
+0 1 2 3
Timebase Error
tERR
%
ELECTRICAL CHARACTERISTICS: 1-WIRE INTERFACE, STANDARD
(VCC = 2.5V to 4.5V, TA = -20C to +70C.) PARAMETER Time Slot Recovery Time Write-0 Low Time Write-1 Low Time Read Data Valid Reset Time High Reset Time Low Presence Detect High Presence Detect Low SYMBOL tSLOT tREC tLOW0 tLOW1 tRDV tRSTH tRSTL tPDH tPDL 480 480 15 60 960 60 240 CONDITIONS MIN 60 1 60 1 120 15 15 TYP MAX 120 UNITS s s s s s s s s s
ELECTRICAL CHARACTERISTICS: 1-WIRE INTERFACE, OVERDRIVE
(VCC = 2.5V to 4.5V, TA = -20C to +70C.) PARAMETER Time Slot Recovery Time Write-0 Low Time Write-1 Low Time Read Data Valid Reset-Time High Reset-Time Low Presence-Detect High Presence-Detect Low SYMBOL tSLOT tREC tLOW0 tLOW1 tRDV tRSTH tRSTL tPDH tPDL 48 48 2 8 80 6 24 CONDITIONS MIN 6 1 6 1 16 2 2 TYP MAX 16 UNITS s s s s s s s s s
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DS2780 Standalone Fuel Gauge IC
EEPROM RELIABILITY SPECIFICATION
(VCC = 2.5V to 4.5V, TA = -20C to +70C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER EEPROM Copy Time EEPROM Copy Endurance SYMBOL tEEC NEEC TA = +50C 50,000 CONDITIONS MIN TYP MAX 10 UNITS ms cycles
Note 1: All voltages are referenced to VSS. Note 2: Factory calibrated accuracy. Higher accuracy can be achieved by in-system calibration by the user. Note 3: Accumulation bias register set to 00h. Note 4: Parameters guaranteed by design. Note 5: The application must wait for the maximum DQ SLEEP Timeout to confirm that the IC has entered sleep mode.
PIN DESCRIPTION
NAME TSSOP PIN TDFN PIN FUNCTION
NC VSS VIN VDD DQ
1 2 3 4 5
1 2, 3 4 5 6
Not Connected. Pin not connected internally, float or connect to VSS. Device Ground. Connect directly to the negative terminal of the battery cell. Connect the sense resistor between VSS and SNS. Voltage Sense Input. The voltage of the battery cell is monitored through this input pin. Power-Supply Input. Connect to the positive terminal of the battery cell through a decoupling network. Data Input/Output. 1-Wire data line. Open-drain output driver. Connect this pin to the DATA terminal of the battery pack. This pin has a weak internal pulldown (IPD) for sensing pack disconnection from host or charger. 1-Wire Bus Speed Control. Input logic level selects the speed of the 1-Wire bus. Logic 1 selects overdrive (OVD) and Logic 0 selects standard timing (STD). On a multidrop bus, all devices must operate at the same speed. Not Connected. Pin not connected internally, float or connect to VSS. Sense Resistor Connection. Connect to the negative terminal of the battery pack. Connect the sense resistor between VSS and SNS. Programmable I/O Pin. Can be configured as input or output to monitor or control user-defined external circuitry. Output driver is open drain. This pin has an weak internal pulldown (IPD). Exposed Pad. Connect to VSS or leave floating. (Only present on TDFN package)
OVD NC SNS PIO PAD
6 -- 7 8 --
7 8 9 10 PAD
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DS2780 Standalone Fuel Gauge IC
Figure 1. Block Diagram
DETAILED DESCRIPTION
The DS2780 operates directly from 2.5V to 4.5V and supports single cell Lithium-ion battery packs. As shown in Figure 2, the DS2780 accommodates multicell applications by adding a voltage regulator for VDD and voltage divider for VIN. Nonvolatile storage is provided for cell compensation and application parameters. Host side development of fuel-gauging algorithms is eliminated. On-chip algorithms and convenient status reporting of operating conditions reduce the serial polling required of the host processor. For 2-cell applications, the DS2781 is recommended, since it includes a voltage regulator and accepts VIN up to 10V. Additionally, 16 bytes of EEPROM memory are made available for the exclusive use of the host system and/or pack manufacturer. The additional EEPROM memory can be used to facilitate battery lot and date tracking and non-volatile storage of system or battery usage statistics. A Dallas 1-Wire interface provides serial communication at the standard 16kbps or overdrive 140kbps speeds. It allows access to data registers, control registers and user memory. A unique, factory programmed 64-bit registration number (8-bit family code + 48-bit serial number + 8-bit CRC) assures that no two parts are alike and enables absolute traceability. The Dallas 1-Wire interface on the DS2780 supports multidrop capability so that multiple slave devices may be addressed with a single pin.
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DS2780 Standalone Fuel Gauge IC
Figure 2. Multicell Application Example
PK+
0.1uF 4.7uF 500
DATA PIO
150 DQ 150 PIO SNS RSNS VDD VIN OVD VSS 0.1uF R (n * R)
Multi-Cell Li-Ion Battery
(1)
(1)
Protection Circuit
PK-
(1) Components improve IEC1004 Air/Contact ESD compliance
Figure 3. Inside Protector Example
PK+
500
DATA PIO
150 DQ 150 PIO SNS RSNS VDD 1K
Li-Ion Battery
DS2780
VIN OVD VSS 0.1uF
(1)
(1)
PK-
Protection Circuit
(1) Precaution must be taken to ensure that a charge path is not created from PK+ to Data or PIO.
PROTECTOR CIRCUIT LOCATION
The battery protection circuitry can be located inside or outside the DS2780. Either location is acceptable but there are some advantages and disadvantages to both. With the protection circuit located inside, see Figure 2 and Typical Operating Circuit on page 1, the DS2780 will loose power in a circuit protection event. The DS2780 stores 6 of 31
DS2780 Standalone Fuel Gauge IC fuel gauge data to EEPROM, but some data loss can occur depending on the timing of the protection event and the backup. When the protection circuit is connected directly to the battery the protection is absolute, no charging will occur during a protection event. With the protection circuit located outside, see Figure 3, the DS2780 will remain powered up during a protection event. The disadvantage to this configuration is that you run the risk of overcharging the battery by creating an unintentional charge path from PK+ to DATA or PIO (VPK+ > VCELL + VDIODE). Communication to the DS2780 is broken during a protection event regardless of protector location.
POWER MODES
The DS2780 has two power modes: ACTIVE and SLEEP. On initial power up, the DS2780 defaults to ACTIVE mode. While in ACTIVE mode, the DS2780 is fully functional with measurements and capacity estimation continuously updated. In SLEEP mode, the DS2780 conserves power by disabling measurement and capacity estimation functions, but preserves register contents. SLEEP mode is entered under two different conditions and an enable bit for each condition makes entry into SLEEP optional. SLEEP mode can be enabled using the Power Mode (PMOD) bit or the Under Voltage Enable (UVEN) bit. The PMOD type SLEEP is entered if the PMOD bit is set AND DQ is low for tSLEEP (2s nominal). The condition of DQ low for tSLEEP can be used to detect a pack disconnection or system shutdown, in which no charge or discharge current will flow. A PMOD SLEEP condition transitions back to ACTIVE mode when DQ is pulled high. The second option for entering SLEEP is an under voltage condition. When the UVEN bit is set, the DS2780 transitions to SLEEP if the voltage on VIN is less than VSLEEP (2.45V nominal) AND DQ is stable at a low or high logic level for tSLEEP. An under-voltage condition occurs when a pack is fully discharged, where loading on the battery should be minimized. UVEN type SLEEP relieves the battery of the IACTIVE load until communication on DQ resumes. NOTE: PMOD and UVEN SLEEP features must be disabled when a battery is charged on an external charger that does not connect to the DQ pin. PMOD SLEEP can be used if the charger pulls DQ high. UVEN SLEEP can be used if the charger toggles DQ. The DS2780 remains in SLEEP on a charger that fails to properly drive DQ and therefore does not measure or accumulate current when a battery is charged.
INITIATING COMMUNICATION IN SLEEP
When beginning communication with a DS2780 in PMOD SLEEP, DQ must be pulled up first and then a 1-Wire Reset pulse must be issued by the master. In UVEN SLEEP, the procedure depends on the state of DQ when UVEN SLEEP was entered. If DQ was low, DQ must be pulled up and then a 1-Wire Reset pulse must be issued by the master as with PMOD SLEEP. If DQ was high when UVEN SLEEP was entered, then the DS2780 is prepared to receive a 1-Wire reset from the master. In the first two cases with DQ low during SLEEP, the DS2780 does not respond to the first rising edge of DQ with a presence pulse.
VOLTAGE MEASUREMENT
Battery voltage is measured at the VIN input with respect to VSS. It has a range of 0V to 4.992V (pin voltage limited to 4.5V) and a resolution of 4.88mV. The measurement is stored in the VOLTAGE register in two's compliment form and is updated every 440ms. Voltages above the maximum register value are reported at the maximum value; voltages below the minimum register value are reported at the minimum value. The format of the voltage register is shown in Figure 4.
Figure 4. Voltage Register Format
VOLT MSB--Address 0Ch S MSb
"S": sign bit(s), "X": reserved
Read Only LSB--Address 0Dh 24 23 LSb 22 MSb 21 20 X X X X X LSb
Units: 4.88mV
29
28
27
26
25
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DS2780 Standalone Fuel Gauge IC
VIN is usually connected to the positive terminal of a single cell Lithium-Ion battery via a 1k resistor. The input impedance is large enough (15M) to be connected to a high impedance voltage divider in order to support multiple cell applications. The pack voltage should be divided by the number of series cells to present a single cell average voltage to the VIN input. In Figure 2, the value of R can be up to 1M without incurring significant error due to input loading.
TEMPERATURE MEASUREMENT
The DS2780 uses an integrated temperature sensor to measure battery temperature with a resolution of 0.125C. Temperature measurements are updated every 440ms and placed in the temperature register in two's complement form. The format of the temperature register is shown in Figure 5.
Figure 5. Temperature Register Format
TEMP MSB--Address 0Ah S MSb
"S": sign bit(s), "X": reserved
Read Only LSB--Address 0Bh 24 23 LSb 22 MSb 21 20 X X X X X LSb
Units: 0.125C
29
28
27
26
25
CURRENT MEASUREMENT
In the ACTIVE mode of operation, the DS2780 continually measures the current flow into and out of the battery by measuring the voltage drop across a low-value current-sense resistor, RSNS. The voltage-sense range between SNS and VSS is 51.2mV. The input linearly converts peak signal amplitudes up to 102.4mV as long as the continuous signal level (average over the conversion cycle period) does not exceed 51.2mV. The ADC samples the input differentially at 18.6kHz and updates the Current register at the completion of each conversion cycle. The Current register is updated every 3.515s with the current conversion result in two's complement form. Charge currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum register value are reported at the minimum value (8000h = -51.2mV).
Figure 6. Current Register Format
CURRENT MSB--Address 0Eh S MSb
"S": sign bit(s)
Read Only LSB--Address 0Fh 29 28 LSb 27 MSb
Units:
214
213
212
211
210
26
25
24
23
22
21
20 LSb
1.5625V/Rsns
CURRENT RESOLUTION (1 LSB) VSS VSNS 1.5625V RSNS 20m 78.13A 15m 104.2A 10m 156.3A 5m 312.5A
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DS2780 Standalone Fuel Gauge IC
AVERAGE CURRENT MEASUREMENT
The Average Current register reports an average current level over the preceding 28 seconds. The register value is updated every 28s in two's complement form, and is the average of the 8 preceding Current register updates. The format of the Average Current register is shown in Figure 7. Charge currents above the maximum register value are reported at the maximum value (7FFFh = +51.2mV). Discharge currents below the minimum register value are reported at the minimum value (8000h = -51.2mV).
Figure 7. Average Current Register Format
IAVG MSB--Address 08h S MSb
"S": sign bit(s)
Read Only LSB--Address 09h 29 28 LSb 27 MSb
Units:
214
213
212
211
210
26
25
24
23
22
21
20 LSb
1.5625V/Rsns
CURRENT OFFSET CORRECTION
Every 1024th conversion, the ADC measures its input offset to facilitate offset correction. Offset correction occurs approximately once per hour. The resulting correction factor is applied to the subsequent 1023 measurements. During the offset correction conversion, the ADC does not measure the sense resistor signal. A maximum error of 1/1024 in the accumulated current register (ACR) is possible; however, to reduce the error, the current measurement made just prior to the offset conversion is displayed in the current register and is substituted for the dropped current measurement in the current accumulation process. This results in an accumulated current error due to offset correction of less than 1/1024.
CURRENT MEASUREMENT CALIBRATION
The DS2780's current measurement gain can be adjusted through the RSGAIN register, which is factory-calibrated to meet the data sheet specified accuracy. RSGAIN is user accessible and can be reprogrammed after module or pack manufacture to improve the current measurement accuracy. Adjusting RSGAIN can correct for variation in an external sense resistor's nominal value, and allows the use of low-cost, non-precision current sense resistors. RSGAIN is an 11 bit value stored in 2 bytes of the Parameter EEPROM Memory Block. The RSGAIN value adjusts the gain from 0 to 1.999 in steps of 0.001 (precisely 2-10). The user must program RSGAIN cautiously to ensure accurate current measurement. When shipped from the factory, the gain calibration value is stored in two separate locations in the Parameter EEPROM Block, RSGAIN which is reprogrammable and FRSGAIN which is read only. RSGAIN determines the gain used in the current measurement. The read-only FRSGAIN is provided to preserve the factory value only and is not used in the current measurement.
SENSE RESISTOR TEMPERATURE COMPENSATION
The DS2780 is capable of temperature compensating the current sense resistor to correct for variation in a sense resistor's value over temperature. The DS2780 is factory programmed with the sense resistor temperature coefficient, RSTC, set to zero, which turns off the temperature compensation function. RSTC is user accessible and can be reprogrammed after module or pack manufacture to improve the current accuracy when using a high temperature coefficient current-sense resistor. RSTC is an 8-bit value stored in the Parameter EEPROM Memory Block. The RSTC value sets the temperature coefficient from 0 to +7782ppm/C in steps of 30.5ppm/C. The user must program RSTC cautiously to ensure accurate current measurement. Temperature compensation adjustments are made when the Temperature register crosses 0.5oC boundaries. The temperature compensation is most effective with the resistor placed as close as possible to the VSS terminal. This will optimize thermal coupling of the resistor to the on-chip temperature sensor. The current shunt trace should be run under the DS2780 package, and it should be constructed with a copper PCB trace.
CURRENT ACCUMULATION
Current measurements are internally summed, or accumulated, at the completion of each conversion period and the results are stored in the Accumulated Current Register (ACR). The accuracy of the ACR is dependent on the 9 of 31
DS2780 Standalone Fuel Gauge IC current measurement and the conversion timebase. The ACR has a range of 0 to 409.6mVh with an LSb of 6.25Vh. Additional read-only registers (ACRL) hold fractional results of each accumulation to avoid truncation errors. Accumulation of charge current above the maximum register value is reported at the maximum register value (7FFFh); conversely, accumulation of discharge current below the minimum register value is reported at the minimum value (8000h). Charge currents (positive Current register values) less than 100V are not accumulated in order to mask the effect of accumulating small positive offset errors over long periods. This limits the minimum charge current, for coulombcounting purposes, to 5mA for RSNS = 0.020 and 20mA for RSNS = 0.005. Read and write access is allowed to the ACR. The ACR must be written MSByte first then LSByte. The write must be completed within 3.515s (one ACR register update period). A write to the ACR forces the ADC to perform an offset correction conversion and update the internal offset correction factor. Current measurement and accumulation begins with the second conversion following a write to the ACR. Writing the ACR clears the fractional values in the ACRL. The format of the ACR is shown in Figure 8, and the ACRL is shown in Figure 9. To preserve the ACR value in case of power loss, it is backed up to EEPROM. The ACR value is recovered from EEPROM on power-up. See the Memory Map in Table 2 for specific address location and backup frequency.
Figure 8. Accumulated Current Register Format, ACR
ACR MSB--Address 10h 215 MSb 214 213 212 211 210 29 28 LSb 27 MSb
Units:
R/W & EE LSB--Address 11h 26 25 24 23 22 21 20 LSb
6.25Vh/Rsns
Figure 9. Fractional/Low Accumulated Current Register Format, ACRL
ACRL MSB--Address 12h 211 MSb
"X": reserved
Read Only LSB--Address 13h 25 24 LSb 23 MSb 22 21 20 X X X X LSb
Units:1.526nVHr/RSNS
210
29
28
27
26
ACR LSb VSS VSNS 6.25Vh RSNS 20m 312.5Ah 15m 416.7Ah 10m 625Ah 5m 1.250mAh
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DS2780 Standalone Fuel Gauge IC
ACR RANGE VSS VSNS 409.6mVh RSNS 20m 20.48Ah 15m 27.30Ah 10m 40.96Ah 5m 81.92Ah
ACCUMULATION BIAS
The Accumulation Bias register (AB) allows an arbitrary bias to be introduced into the current-accumulation process. The AB can be used to account for currents that do not flow through the sense resistor, estimate currents too small to measure, estimate battery self-discharge or correct for static offset of the DS2780. The AB register allows a user programmed constant positive or negative polarity bias to be included in the current accumulation process. The user-programmed two's compliment value, with bit weighting the same as the current register, is added to the ACR once per current conversion cycle. The AB value is loaded on power-up from EEPROM. The format of the AB register is shown in Figure 10.
Figure 10. Accumulation Bias Register Formats
AB Address 61h S MSb
"S": sign bit Units:
EE
26
25
24
23
22
21
20 LSb
1.5625V/Rsns
CAPACITY ESTIMATION ALGORITHM
Remaining capacity estimation uses real-time measured values, stored parameters describing the cell characteristics, and application operating limits. The following diagram describes the algorithm inputs and outputs.
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DS2780 Standalone Fuel Gauge IC
Figure 11. Top Level Algorithm Diagram
MODELING CELL CHARACTERISTICS
In order to achieve reasonable accuracy in estimating remaining capacity, the cell performance characteristics over temperature, load current, and charge termination point must be considered. Since the behavior of Li-ion cells is non-linear, even over a limited temperature range of 10C to 35C, these characteristics must be included in the capacity estimation to achieve a reasonable accuracy. See Applications Note AN131 "Li+ Fuel Gauging with Dallas Semiconductor Devices" for general information on the FuelPackTM method used in the DS2780. To facilitate efficient implementation in hardware, a modified version of the method outlined in AN131 is used to store cell characteristics in the DS2780. Full and empty points are retrieved in a lookup process which re-traces a piece-wise linear model. Three model curves are stored: Full, Active Empty and Standby Empty. Each model curve is constructed with 4 line segments and spans from 0C to 40C. Operation outside the 0C to 40C model span is supported by the model with minimal loss of accuracy. Above 40C, the 40C fixed points are extended with zero slope. This achieves a conservative capacity estimate for temperatures above 40C. Below 0C, the model curves are extended using the slope of each 0C to 10C segment. If low temperature operation is expected, the 0C to 10C slopes can be selected to optimize the model accuracy. A diagram of example battery cell model curves is shown in Figure 12.
FuelPack is a trademark of Maxim Integrated Products, Inc.
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DS2780 Standalone Fuel Gauge IC
Figure 12. Cell Model Example Diagram
100%
Derivative [ppm / C]
FULL
Active Empty
Cell Characterization data points
Standby Empty
1 2 3
4
0C
10C
20C
30C
40C
Full: The Full curve defines how the full point of a given cell depends on temperature for a given charge termination. The application's charge termination method should be used to determine the table values. The DS2780 reconstructs the Full line from the cell characteristic table to determine the Full capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature increments. Active Empty: The Active Empty curve defines the variation of the Active Empty Point over temperature. The Active Empty Point is defined as the minimum voltage required for system operation at a discharge rate based on a high level load current (one that is sustained during a high power operating mode). This load current is programmed as the Active Empty current (IAE) and should be a 3.5s average to correspond to values read from the Current register. The specified minimum voltage, or Active Empty voltage (VAE), should be a 220ms average to correspond to values read from the Voltage register. The DS2780 reconstructs the Active Empty line from the cell characteristic table to determine the Active Empty capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature increments. Standby Empty: The Standby Empty curve defines the variation of the standby empty point over temperature. The standby empty point is defined as the minimum voltage required for standby operation at a discharge rate dictated by the application standby current. In typical PDA applications, Standby Empty represents the point that the battery can no longer support RAM refresh and thus the standby voltage is set by the RAM voltage supply requirements. In other applications, Standby Empty can represent the point that the battery can no longer support a subset of the full application operation, such as games or organizer functions on a wireless handset. The standby load current and voltage are used for determining the cell characteristics but are not programmed into the DS2780. The DS2780 reconstructs the Standby Empty line from the cell characteristic table to determine the Standby Empty capacity of the battery at each temperature. Reconstruction occurs in one-degree temperature increments.
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DS2780 Standalone Fuel Gauge IC
CELL MODEL CONSTRUCTION
The model is constructed with all points normalized to the fully charged state at +40C. All values are stored in the cell parameter EEPROM block. The +40C Full value is stored in uVhr with an LSB of 6.25uVhr. The +40C Active Empty value is stored as a percentage of +40C Full with a resolution of 2-10. Standby Empty at +40C is by definition zero and therefore no storage is required. The slopes (derivatives) of the 4 segments for each model curve are stored in the cell parameter EEPROM block as PPM/C. Segment endpoints are fixed at 0C, +10C, +20C, +30C and +40C. (See Application Note 3584 for more details on how values are stored.) An example of cell model data is shown in Table 1a. Table 1b shows the actual data values stored in memory.
Table 1a. Example Cell Characterization Table (Normalized to +40C)
Rated cell capacity: 1000mAh Charge Voltage: 4.2V Active Empty (V): 3.0V Sense Resistor: 0.020 +40C Nominal [mAh] Full 1051 Active Empty Standby Empty Terminating Current: 50mA Active Empty (I): 300mA
0C 0.927 0.051 0.013
+10C 0.951 0.040 0.0067
+20C 0.974 0.022 0.0038
+30C 0.991 0.012 0.001
+40C 1.0 0.008 0
Table 1b. Example Cell Characterization Table (Actual data values stored in EEPROM)
Rated cell capacity: 0C80h Charge Voltage: D7h Active Empty (V): 9Ah Sense Resistor: 32h +40C Nominal [mAh] Full 0D32h Active Empty Standby Empty Terminating Current: 14h Active Empty (I): 1Eh
0C 27h 12h 0Ah
+10C 26h 1Eh 05h
+20C 1Ch 10h 05h
+30C 0Fh 07h 02h
+40C 0D32h 08h
Figure 13. Lookup Function Diagram
Cell Model Parameters 15 bytes (EEPROM) Temperature FULL(T) Lookup Function AE(T) SE(T)
APPLICATION PARAMETERS
In addition to cell model characteristics, several application parameters are needed to detect the full and empty points, as well as calculate results in mAh units.
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DS2780 Standalone Fuel Gauge IC Sense Resistor Prime (RSNSP[1/): RSNSP stores the value of the sense resistor for use in computing the absolute capacity results. The resistance is stored as a 1-byte conductance value with units of mhos (1/. RSNSP supports resistor values of 1 to 3.922m. RSNSP is located in the Parameter EEPROM block. RSNSP = 1/RSNS (units of mhos; 1/
Charge Voltage (VCHG): VCHG stores the charge voltage threshold used to detect a fully charged state. The voltage is stored as a 1-byte value with units of 19.52mV and can range from 0V to 4.978V. VCHG should be set marginally less than the cell voltage at the end of the charge cycle to ensure reliable charge termination detection. VCHG is located in the Parameter EEPROM block. Minimum Charge Current (IMIN): IMIN stores the charge current threshold used to detect a fully charged state. It is stored as a 1-byte value with units of 50V (IMIN * RSNS) and can range from 0 to 12.75mV. Assuming RSNS = 20m, IMIN can be programmed from 0mA to 637.5mA in 2.5mA steps. IMIN should be set marginally greater than the charge current at the end of the charge cycle to ensure reliable charge termination detection. IMIN is located in the Parameter EEPROM block. Active Empty Voltage (VAE): VAE stores the voltage threshold used to detect the Active Empty Point. The value is stored in 1-byte with units of 19.52mV and can range from 0V to 4.978V. VAE is located in the Parameter EEPROM block. See the Cell Characteristics section for more information. Active Empty Current (IAE): IAE stores the discharge current threshold used to detect the Active Empty Point. The unsigned value represents the magnitude of the discharge current and is stored in 1-byte with units of 200V. It can range from 0 to 51.2mV. Assuming RSNS = 20m, IAE can be programmed from 0mA to 2550mA in 10mA steps. IAE is located in the Parameter EEPROM block. See the Cell Characteristics section for more information. Aging Capacity (AC): AC stores the rated cell capacity which is used to estimate the decrease in battery capacity that occurs during normal use. The value is stored in 2-bytes in the same units as the ACR (6.25Vh). When set to the manufacturer's rated cell capacity the Aging Estimation rate is approximately 2.4% per 100 cycles of equivalent full capacity discharges. Partial discharge cycles are added to form equivalent full capacity discharges. The default aging estimation results in 88% capacity after 500 equivalent cycles. The Aging Estimation rate can be adjusted by setting the AC to a value other than the cell manufacturer's rating. Setting AC to a lower value, accelerates the Aging Estimation rate. Setting the AC to a higher value, retards the Aging Estimation rate. The AC is located in the Parameter EEPROM block. Age Scalar (AS): AS adjusts the cell capacity estimation results downward to compensate for aging. The AS is a -7 1-byte value that has a range of 49.2% to 100%. The lsb is weighted at 0.78% (precisely 2 ). A value of 100% (128 decimal or 80h) represents an un-aged battery. A value of 95% is recommended as the starting AS value at the time of pack manufacture to allow the learning of a larger capacity on batteries that have an initial capacity greater than the rated cell capacity programmed in the cell characteristic table. The AS is modified by the Aging Estimation introduced under Aging Capacity and by the Learn function. The host system has read and write access to the AS, however caution should be exercised when writing it to ensure that the cumulative aging estimate is not over written with an incorrect value. Usually, writing the AS by the host is not necessary because it is automatically saved to EEPROM on a periodic basis by the DS2780. (See the Memory section for details.) The AS value stored in EEPROM is recalled on power-up.
CAPACITY ESTIMATION UTILITY FUNCTIONS
Aging Estimation As discussed above, the AS register value is adjusted occasionally based on cumulative discharge. As the ACR register decrements during each discharge cycle, an internal counter is incremented until equal to 32 times the AC. The AS is then decremented by one, resulting in a decrease in the scaled full battery capacity of 0.78% (approximately 2.4% per 100 cycles). Refer to the AC register description above for recommendations on customizing the age estimation rate. Learn Function Since Li+ cells exhibit charge efficiencies near unity, the charge delivered to a Li+ cell from a known empty point to a known full point is a dependable measure of the cell capacity. A continuous charge from empty to full results in a 15 of 31
DS2780 Standalone Fuel Gauge IC "learn cycle". First, the Active Empty Point must be detected. The Learn Flag (LEARNF) is set at this point. Then, once charging starts, the charge must continue uninterrupted until the battery is charged to full. Upon detecting full, LEARNF is cleared, the Charge to Full (CHGTF) flag is set and the Age Scalar (AS) is adjusted according to the learned capacity of the cell. ACR Housekeeping The ACR value is adjusted occasionally to maintain the coulomb count within the model curve boundaries. When the battery is charged to full (CHGTF set), the ACR is set equal to the age scaled full lookup value at the present temperature. If a learn cycle is in progress, correction of the ACR value occurs after the age scalar (AS) is updated. When an empty condition is detected (AEF or LEARNF set), the ACR adjustment is conditional. If AEF is set and LEARNF is not, then the Active Empty Point was not detected and the battery is likely below the Active Empty capacity of the model. The ACR is set to the Active Empty model value only if it is greater than the Active Empty model value. If LEARNF is set, then the battery is at the Active Empty Point and the ACR is set to the Active Empty model value. Full Detect Full detection occurs when the Voltage (VOLT) readings remain above the VCHG (Charge Voltage) threshold for the duration of two Average Current (IAVG) readings, where both IAVG readings are below IMIN (Terminating Current). The two consecutive IAVG readings must also be positive and non-zero. This ensures that removing the battery from the charger does not result in a false detection of full. Full Detect sets the Charge to Full (CHGTF) bit in the Status register. Active Empty Point Detect Active Empty Point detection occurs when the Voltage register drops below the VAE threshold and the two previous Current readings are above IAE. This captures the event of the battery reaching the Active Empty Point. Note that the two previous Current readings must be negative and greater in magnitude than IAE, that is, a larger discharge current than specified by the IAE threshold. Qualifying the Voltage level with the discharge rate ensures that the Active Empty Point is not detected at loads much lighter than those used to construct the model. Also, the Active Empty Point must not be detected when a deep discharge at a very light load is followed by a load greater than IAE. Either case would cause a learn cycle on the following charge to include part of the Standby capacity in the measurement of the Active capacity. Active Empty Point detection sets the Learn Flag (LEARNF) bit in the Status register. DO NOT confuse the Active Empty Point with the Active Empty Flag. The Active Empty Flag is set only when the VAE threshold is passed.
RESULT REGISTERS
The DS2780 processes measurement and cell characteristics on a 440ms interval and yields seven result registers. The result registers are sufficient for direct display to the user in most applications. The host system can produce customized values for system use, or user display by combining measurement, result and User EEPROM values. FULL(T) [ ]: The Full capacity of the battery at the present temperature is reported normalized to the 40C Full value. This 15-bit value reflects the cell model Full value at the given temperature. FULL(T) reports values between 100% and 50% with a resolution of 61ppm (precisely 2-14). The register is clamped to a maximum value of 100% even though the format permits values greater than 100%,. Active Empty, AE(T) [ ]: The Active Empty capacity of the battery at the present temperature is reported normalized to the 40C Full value. This 13-bit value reflects the cell model Active Empty Point at the given temperature. AE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2-14). Standby Empty, SE(T) [ ]: The Standby Empty capacity of the battery at the present temperature is reported normalized to the 40C Full value. This 13-bit value reflects the cell model Standby Empty value at the current temperature. SE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2-14). Remaining Active Absolute Capacity (RAAC) [mAh] - RAAC reports the remaining battery capacity under the current temperature conditions at the Active Empty discharge rate (IAE) to the Active Empty Point in absolute units of milli-amp-hours. RAAC is 16 bits. 16 of 31
DS2780 Standalone Fuel Gauge IC Read Only MSB--Address 02h 215 MSb 214 213 212 211 210 29 28 LSb 27 MSb 26 LSB--Address 03h 25 24 23 22 21 20 LSb
Units:1.6mAhr
RAAC
Remaining Standby Absolute Capacity (RSAC) [mAh] - RSAC reports the remaining battery capacity under the current temperature conditions at the Standby Empty discharge rate (ISE) to the Standby Empty point in absolute units of milli-amp-hours. RSAC is 16 bits. RSAC MSB--Address 04h 215 MSb 214 213 212 211 210 29 28 LSb 27 MSb 26 LSB--Address 05h 25 24 23 22 21 20 LSb
Units:1.6mAhr
Read Only
Remaining Active Relative Capacity (RARC) [%] - RARC reports the remaining battery capacity under the current temperature conditions at the Active Empty discharge rate (IAE) to the Active Empty Point in relative units of percent. RARC is 8 bits. RARC Address 06h 27 MSb
Units:
Read Only
26
25
24
23
22
21
20 LSb
1%
Remaining Standby Relative Capacity (RSRC) [%] - RSRC reports the remaining battery capacity under the current temperature conditions at the Standby Empty discharge rate (ISE) to the Standby Empty point in relative units of percent. RSRC is 8 bits. RSRC Address 07h 27 MSb
Units:
Read Only
26
25
24
23
22
21
20 LSb
1%
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DS2780 Standalone Fuel Gauge IC Calculation of Results RAAC [mAh] = (ACR[mVh] - AE(T) * FULL40[mVh]) * RSNSP [mhos]
Note: RSNSP = 1/RSNS
RSAC [mAh] = (ACR[mVh] - SE(T) * FULL40[mVh]) * RSNSP [mhos]
Note: RSNSP = 1/RSNS
RARC [%] = 100% * (ACR[mVh] - AE(T) * FULL40[mVh]) / {(AS * FULL(T) - AE(T)) * FULL40[mVh]} RSRC [%] = 100%* (ACR[mVh] - SE(T) * FULL40[mVh]) / {(AS * FULL(T) - SE(T)) * FULL40[mVh]}
STATUS REGISTER
The STATUS register contains bits which report the device status. The bits can be set internally by the DS2780. The CHGTF, AEF, SEF, LEARNF and VER bits are read only bits which can be cleared by hardware. The UVF and PORF bits can only be cleared via the 1-Wire interface.
Figure 14. Status Register Format Address
Field CHGTF
01h
Bit 7 Format Read Only
Bit Definition
Allowable Values Charge Termination Flag Set to 1 when: ( VOLT > VCHG ) AND ( 0 < IAVG < IMIN ) continuously for a period between two IAVG register updates ( 28s to 56s ). Cleared to 0 when: RARC < 90% Active Empty Flag Set to 1 when: VOLT < VAE Cleared to 0 when: RARC > 5% Standby Empty Flag Set to 1 when: RSRC < 10% Cleared to 0 when: RSRC > 15% Learn Flag - When set to 1, a charge cycle can be used to learn battery capacity. Set to 1 when: ( VOLT falls from above VAE to below VAE ) AND ( CURRENT > IAE ) Cleared to 0 when: ( CHGTF = 1 ) OR ( CURRENT < +100V/R ) OR ( ACR = 0 **) OR ( ACR written or recalled from EEPROM) OR ( SLEEP Entered ) Undefined Under-Voltage Flag Set to 1 when: VOLT < VSLEEP Cleared to 0 by: User Power-On Reset Flag - Useful for reset detection, see text below. Set to 1 upon Power-Up by hardware. Cleared to 0 by: User Undefined
AEF
6 5 4
Read Only Read Only Read Only
SEF
LEARNF
Reserved UVF
3 2 1 0
Read Only Read / Write * Read / Write * Read Only
PORF Reserved
* - This bit can be set by the DS2780, and may only be cleared via the 1-Wire interface. ** - LEARNF is only cleared if ACR reaches 0 after VOLT < VAE.
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DS2780 Standalone Fuel Gauge IC
CONTROL REGISTER
All CONTROL register bits are read and write accessible. The CONTROL register is recalled from Parameter EEPROM memory at power-up. Register bit values can be modified in shadow RAM after power-up. Shadow RAM values can be saved as the power up default values by using the Copy Data command.
Figure 15. Control Register Format Address
Field Reserved UVEN
60h
Bit 7 6 Format Read/Write
Bit Definition
Allowable Values Undefined Under Voltage SLEEP Enable 0: Disables transition to SLEEP mode based on VIN voltage 1: Enables transition to SLEEP mode if, VIN < VSLEEP AND DQ stable at either logic level for tSLEEP Power Mode Enable 0: Disables transition to SLEEP mode based on DQ logic state 1: Enables transition to SLEEP mode if DQ at a logic low for tSLEEP Read Net Address Opcode 0: Read Net Address Command = 33h 1: Read Net Address Command = 39h Undefined
PMOD
5 4 0:3
Read/Write Read/Write
RNAOP Reserved
SPECIAL FEATURE REGISTER
All Special Feature Register bits are read and write accessible, with default values specified in each bit definition.
Figure 16. Special Feature Register Format Address
Field Reserved PIOSC
15h
Bit 1:7 0 Format Read/Write
Bit Definition
Allowable Values Undefined PIO Sense and Control Read values 0: PIO pin Vil 1: PIO pin Vih Write values 0: Activates PIO pin open-drain output driver, forcing the PIO pin low 1: Disables the output driver, allowing the PIO pin to be pulled high or used as an input Power-up and SLEEP mode default: 1 (PIO pin is hi-Z) Note: PIO pin has weak pulldown
EEPROM REGISTER
The EEPROM register provides access control of the EEPROM blocks. EEPROM blocks can be locked to prevent alteration of data within the block. Locking a block disables write access to it. Once a block is locked, it cannot be unlocked. Read access to EEPROM blocks is unaffected by the lock/unlock status.
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DS2780 Standalone Fuel Gauge IC
Figure 17. EEPROM REGISTER FORMAT Address
Field EEC
1Fh
Bit 7 Format Read Only
Bit Definition
Allowable Values EEPROM Copy Flag Set to 1 when: Copy Data command executed Cleared to 0 when: Copy Data command completes Note: While EEC = 1, writes to EEPROM addresses are ignored Power-up default: 0 EEPROM Lock Enable Host write to 1: Enables the Lock command. Host must issue Lock command as next command after writing Lock Enable bit to 1. Cleared to 0 when: Lock command completes or when the Lock command is not issued immediately following the setting of the Lock Enable bit. Power-up default: 0 Undefined EEPROM Block 1 Lock Flag (Parameter EEPROM 60h - 7Fh) 0: EEPROM is not locked 1: EEPROM block is locked Factory default: 0 EEPROM Block 0 Lock Flag (User EEPROM 20h - 2Fh) 0: EEPROM is not locked 1: EEPROM block is locked Factory default: 0
LOCK
6
Read / Write to 1
Reserved BL1
2:6 1
Read Only
BL0
0
Read Only
MEMORY
The DS2780 has a 256 byte linear memory space with registers for instrumentation, status, and control, as well as EEPROM memory blocks to store parameters and user information. Byte addresses designated as "Reserved" return undefined data when read. Reserved bytes should not be written. Several byte registers are paired into twobyte registers in order to store 16-bit values. The most significant byte (MSB) of the 16 bit value is located at a even address and the least significant byte (LSB) is located at the next address (odd) byte. When the MSB of a two-byte register is read, the MSB and LSB are latched simultaneously and held for the duration of the read data command to prevent updates to the LSB during the read. This ensures synchronization between the two register bytes. For consistent results, always read the MSB and the LSB of a two-byte register during the same read data command sequence. EEPROM memory consists of the non-volatile EEPROM cells overlaid with volatile shadow RAM. The Read Data and Write Data commands allow the 1-Wire interface to directly access the shadow RAM only. The Copy Data and Recall Data function commands transfer data between the shadow RAM and the EEPROM cells. In order to modify the data stored in the EEPROM cells, data must be written to the shadow RAM and then copied to the EEPROM. In order to verify the data stored in the EEPROM cells, the EEPROM data must be recalled to the shadow RAM and then read from the shadow RAM.
USER EEPROM
A 16 byte User EEPROM memory (block 0, addresses 20h - 2Fh) provides non-volatile memory that is uncommitted to other DS2780 functions. Accessing the User EEPROM block does not affect the operation of the DS2780. User EEPROM is lockable, and once locked, write access is not allowed. The battery pack or host system manufacturer can program lot codes, date codes and other manufacturing, warranty, or diagnostic information and then lock it to safeguard the data. User EEPROM can also store parameters for charging to support different size batteries in a host device as well as auxiliary model data such as time to full charge estimation parameters.
PARAMETER EEPROM
Model data for the cells, as well as application operating parameters are stored in the Parameter EEPROM (block 1, addresses 60h - 7Fh). The ACR (MSB and LSB) and AS registers are automatically saved to EEPROM when 20 of 31
DS2780 Standalone Fuel Gauge IC the RARC result crosses 4% boundaries. This allows the DS2780 to be located outside the protection FETs. In this manner, if a protection device is triggered, the DS2780 cannot lose more that 4% of charge or discharge data.
Table 2. MEMORY MAP
ADDRESS (HEX) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C to 1E 1F 20 to 2F 30 to 5F 60 to 7F 80 to FF DESCRIPTION Reserved STATUS - Status Register RAAC - Remaining Active Absolute Capacity MSB RAAC - Remaining Active Absolute Capacity LSB RSAC - Remaining Standby Absolute Capacity MSB RSAC - Remaining Standby Absolute Capacity LSB RARC - Remaining Active Relative Capacity RSRC - Remaining Standby Relative Capacity IAVG - Average Current Register MSB IAVG - Average Current Register LSB TEMP - Temperature Register MSB TEMP - Temperature Register LSB VOLT - Voltage Register MSB VOLT - Voltage Register LSB CURRENT - Current Register MSB CURRENT - Current Register LSB ACR - Accumulated Current Register MSB ACR - Accumulated Current Register LSB ACRL - Low Accumulated Current Register MSB ACRL - Low Accumulated Current Register LSB AS - Age Scalar SFR - Special Feature Register FULL - Full Capacity MSB FULL - Full Capacity LSB AE - Active Empty MSB AE - Active Empty LSB SE - Standby Empty MSB SE - Standby Empty LSB Reserved EEPROM - EEPROM Register User EEPROM, Lockable, Block 0 Reserved Parameter EEPROM, Lockable, Block 1 Reserved READ/WRITE R R/W R R R R R R R R R R R R R R R/W* R/W * R R R/W * R/W R R R R R R -- R/W R/W -- R/W --
* Register value is automatically saved to EEPROM during ACTIVE mode operation and recalled from EEPROM on power up.
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DS2780 Standalone Fuel Gauge IC
Table 3. PARAMETER EEPROM MEMORY BLOCK 1
ADDRESS (HEX) 60 61 62 63 64 65 66 67 68 69 6A 6B 6C 6D 6E 6F DESCRIPTION CONTROL - Control Register AB - Accumulation Bias AC - Aging Capacity MSB AC - Aging Capacity LSB VCHG - Charge Voltage IMIN - Minimum Charge Current VAE - Active Empty Voltage IAE - Active Empty Current Active Empty 40 RSNSP - Sense Resistor Prime Full 40 MSB Full 40 LSB Full 3040 Slope Full 2030 Slope Full 1020 Slope Full 0010 Slope ADDRESS (HEX) 70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 7E 7F DESCRIPTION AE 3040 Slope AE 2030 Slope AE 1020 Slope AE 0010 Slope SE 3040 Slope SE 2030 Slope SE 1020 Slope SE 0010 Slope RSGAIN - Sense Resistor Gain MSB RSGAIN - Sense Resistor Gain LSB RSTC - Sense Resistor Temp. Coeff. FRSGAIN - Factory Gain MSB FRSGAIN - Factory Gain LSB Reserved Reserved Reserved
1-WIRE BUS SYSTEM
The 1-Wire bus is a system that has a single bus master and one or more slaves. A multidrop bus is a 1-Wire bus with multiple slaves. A single-drop bus has only one slave device. In all instances, the DS2780 is a slave device. The bus master is typically a microprocessor in the host system. The discussion of this bus system consists of four topics: 64-bit net address, hardware configuration, transaction sequence, and 1-Wire signaling.
64-BIT NET ADDRESS
Each DS2780 has a unique, factory-programmed 1-Wire net address that is 64 bits in length. The first eight bits are the 1-Wire family code (32h for DS2780). The next 48 bits are a unique serial number. The last eight bits are a cyclic redundancy check (CRC) of the first 56 bits (see Figure 18). The 64-bit net address and the 1-Wire I/O circuitry built into the device enable the DS2780 to communicate through the 1-Wire protocol detailed in the 1-Wire Bus System section of this data sheet.
Figure 18. 1-Wire Net Address Format
8-BIT CRC MSb 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE (32h) LSb
CRC GENERATION
The DS2780 has an 8-bit CRC stored in the most significant byte of its 1-Wire net address. To ensure error-free transmission of the address, the host system can compute a CRC value from the first 56 bits of the address and compare it to the CRC from the DS2780. The host system is responsible for verifying the CRC value and taking action as a result. The DS2780 does not compare CRC values and does not prevent a command sequence from proceeding as a result of a CRC mismatch. Proper use of the CRC can result in a communication channel with a very high level of integrity. The CRC can be generated by the host using a circuit consisting of a shift register and XOR gates as shown in Figure 19, or it can be generated in software. Additional information about the Dallas 1-Wire CRC is available in 22 of 31
DS2780 Standalone Fuel Gauge IC Application Note 27, Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor Touch Memory Products. (This application note can be found on the Maxim/Dallas Semiconductor website at www.maxim-ic.com.) In the circuit in Figure 19, the shift register bits are initialized to 0. Then, starting with the least significant bit of the family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial number is entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC value.
Figure 19. 1-Wire CRC Generation Block Diagram
INPUT MSb XOR XOR LSb XOR
HARDWARE CONFIGURATION
Because the 1-Wire bus has only a single line, it is important that each device on the bus be able to drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must connect to the bus with open-drain or tri-state output drivers. The DS2780 uses an open-drain output driver as part of the bidirectional interface circuitry shown in Figure 20. If a bidirectional pin is not available on the bus master, separate output and input pins can be connected together. The 1-Wire bus must have a pullup resistor at the bus-master end of the bus. For short line lengths, the value of this resistor should be approximately 5k. The idle state for the 1-Wire bus is high. If, for any reason, a bus transaction must be suspended, the bus must be left in the idle state to properly resume the transaction later. If the bus is left low for more than 120s (16s for overdrive speed), slave devices on the bus begin to interpret the low period as a reset pulse, effectively terminating the transaction. The DS2780 can operate in two communication speed modes, standard and overdrive. The speed mode is determined by the input logic level of the OVD pin; a logic 0 selects standard speed and a logic 1 selects overdrive speed. The OVD pin must be at a stable logic level of 0 or 1 before initializing a transaction with a reset pulse. All 1-Wire devices on a multinode bus must operate at the same communication speed for proper operation. 1-Wire timing for both standard and overdrive speeds are listed in the Electrical Characteristics: 1-Wire Interface tables.
Figure 20. 1-Wire Bus Interface Circuitry
BUS MASTER Vpullup (2.0V to 5.5V) 4.7k Rx 0.2A (typ) RX = RECEIVE TX = TRANSMIT 100 MOSFET DS2780 1-WIRE PORT
RX TX
Tx
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DS2780 Standalone Fuel Gauge IC
TRANSACTION SEQUENCE
The protocol for accessing the DS2780 through the 1-Wire port is as follows: Initialization Net Address Command Function Command Transaction/Data
The sections that follow describe each of these steps in detail. All transactions of the 1-Wire bus begin with an initialization sequence consisting of a reset pulse transmitted by the bus master followed by a presence pulse simultaneously transmitted by the DS2780 and any other slaves on the bus. The presence pulse tells the bus master that one or more devices are on the bus and ready to operate. For more details, see the 1-Wire Signaling section.
NET ADDRESS COMMANDS
Once the bus master has detected the presence of one or more slaves, it can issue one of the net address commands described in the following paragraphs. The name of each ROM command is followed by the 8-bit opcode for that command in square brackets. Figure 21 presents a transaction flowchart of the net address commands. Read Net Address [33h or 39h]. This command allows the bus master to read the DS2780's 1-Wire net address. This command can only be used if there is a single slave on the bus. If more than one slave is present, a data collision occurs when all slaves try to transmit at the same time (open drain produces a wired-AND result). The RNAOP bit in the status register selects the opcode for this command, with RNAOP = 0 indicating 33h, and RNAOP = 1 indicating 39h. Match Net Address [55h]. This command allows the bus master to specifically address one DS2780 on the 1-Wire bus. Only the addressed DS2780 responds to any subsequent function command. All other slave devices ignore the function command and wait for a reset pulse. This command can be used with one or more slave devices on the bus. Skip Net Address [CCh]. This command saves time when there is only one DS2780 on the bus by allowing the bus master to issue a function command without specifying the address of the slave. If more than one slave device is present on the bus, a subsequent function command can cause a data collision when all slaves transmit data at the same time. Search Net Address [F0h]. This command allows the bus master to use a process of elimination to identify the 1Wire net addresses of all slave devices on the bus. The search process involves the repetition of a simple threestep routine: read a bit, read the complement of the bit, then write the desired value of that bit. The bus master performs this simple three-step routine on each bit location of the net address. After one complete pass through all 64 bits, the bus master knows the address of one device. The remaining devices can then be identified on (R) additional iterations of the process. See Chapter 5 of the Book of DS19xx iButton Standards for a comprehensive discussion of a net address search, including an actual example. (This publication can be found on the Maxim/Dallas Semiconductor website at www.maxim-ic.com.) Resume [A5h]. This command increases data throughput in multidrop environments where the DS2780 needs to be accessed several times. Resume is similar to the Skip Net Address command in that the 64-bit net address does not have to be transmitted each time the DS2780 is accessed. After successfully executing a Match Net Address command or Search Net Address command, an internal flag is set in the DS2780. When the flag is set, the DS2780 can be repeatedly accessed through the Resume command function. Accessing another device on the bus clears the flag, thus preventing two or more devices from simultaneously responding to the Resume command function.
iButton is a registered trademark of Maxim Integrated Products, Inc.
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DS2780 Standalone Fuel Gauge IC
FUNCTION COMMANDS
After successfully completing one of the net address commands, the bus master can access the features of the DS2780 with any of the function commands described in the following paragraphs. The name of each function is followed by the 8-bit opcode for that command in square brackets. The function commands are summarized in Table 4. Read Data [69h, XX]. This command reads data from the DS2780 starting at memory address XX. The LSb of the data in address XX is available to be read immediately after the MSb of the address has been entered. Because the address is automatically incremented after the MSb of each byte is received, the LSb of the data at address XX + 1 is available to be read immediately after the MSb of the data at address XX. If the bus master continues to read beyond address FFh, data is read starting at memory address 00 and the address is automatically incremented until a reset pulse occurs. Addresses labeled "Reserved" in the memory map contain undefined data values. The read data command can be terminated by the bus master with a reset pulse at any bit boundary. Reads from EEPROM block addresses return the data in the shadow RAM. A Recall Data command is required to transfer data from the EEPROM to the shadow. See the Memory section for more details. Write Data [6Ch, XX]. This command writes data to the DS2780 starting at memory address XX. The LSb of the data to be stored at address XX can be written immediately after the MSb of address has been entered. Because the address is automatically incremented after the MSb of each byte is written, the LSb to be stored at address XX + 1 can be written immediately after the MSb to be stored at address XX. If the bus master continues to write beyond address FFh, the data starting at address 00 is overwritten. Writes to read-only addresses, reserved addresses and locked EEPROM blocks are ignored. Incomplete bytes are not written. Writes to unlocked EEPROM block addresses modify the shadow RAM. A Copy Data command is required to transfer data from the shadow to the EEPROM. See the Memory section for more details. Copy Data [48h, XX]. This command copies the contents of the EEPROM shadow RAM to EEPROM cells for the EEPROM block containing address XX. Copy data commands that address locked blocks are ignored. While the copy data command is executing, the EEC bit in the EEPROM register is set to 1 and writes to EEPROM addresses are ignored. Reads and writes to non-EEPROM addresses can still occur while the copy is in progress. The copy data command takes tEEC time to execute, starting on the next falling edge after the address is transmitted. Recall Data [B8h, XX]. This command recalls the contents of the EEPROM cells to the EEPROM shadow memory for the EEPROM block containing address XX. Lock [6Ah, XX]. This command locks (write-protects) the block of EEPROM containing memory address XX. The LOCK bit in the EEPROM register must be set to 1 before the lock command is executed. To help prevent unintentional locks, one must issue the lock command immediately after setting the LOCK bit (EEPROM register, address 1Fh, bit 06) to a 1. If the LOCK bit is 0 or if setting the lock bit to 1 does not immediately precede the lock command, the lock command has no effect. The lock command is permanent; a locked block can never be written again.
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DS2780 Standalone Fuel Gauge IC
Table 4. Function Commands
COMMAND PROTOCOL 69h, XX 6Ch, XX BUS STATE AFTER COMMAND PROTOCOL Master Rx Master Tx
COMMAND
DESCRIPTION Reads data from memory starting at address XX Writes data to memory starting at address XX Copies shadow RAM data to EEPROM block containing address XX Recalls EEPROM block containing address XX to RAM Permanently locks the block of EEPROM containing address XX
BUS DATA Up to 256 bytes of data Up to 256 bytes of data None
Read Data Write Data
Copy Data
48h, XX
Master Reset
Recall Data
B8h, XX
Master Reset
None
Lock
6Ah, XX
Master Reset
None
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DS2780 Standalone Fuel Gauge IC
Figure 21. Net Address Command Flow Chart
MASTER TX RESET PULSE
DS2780 Tx PRESENCE PULSE MASTER Tx NET ADDRESS COMMAND
33h / 39h READ
NO
55h MATCH
NO
F0h SEARCH
NO
CCh SKIP
NO
A5h RESUME
NO
YES DS2780 Tx FAMILY CODE 1 BYTE
YES MASTER TX BIT 0
YES DS2780 Tx BIT 0 DS2780 Tx BIT 0 MASTER Tx BIT 0
YES
YES RESUME FLAG SET ? NO
CLEAR RESUME
DS2780 Tx SERIAL NUMBER 6 BYTES BIT 0 MATCH ? DS2780 Tx CRC 1 BYTE NO NO BIT 0 MATCH ?
YES MASTER TX FUNCTION COMMAND MASTER TX FUNCTION COMMAND
YES MASTER TX BIT 1
YES DS2780 Tx BIT 1 DS2780 Tx BIT 1 MASTER Tx BIT 1
CLEAR RESUME
BIT 1 MATCH ?
NO
NO
BIT 1 MATCH ?
YES
YES
MASTER TX FUNCTION COMMAND
MASTER TX BIT 63
DS2780 Tx BIT 63 DS2780 Tx BIT 63 MASTER Tx BIT 63
SET RESUME FLAG
YES
BIT 63 MATCH ?
NO
CLEAR RESUME
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DS2780 Standalone Fuel Gauge IC
1-WIRE SIGNALING
The 1-Wire bus requires strict signaling protocols to ensure data integrity. The four protocols used by the DS2780 are as follows: the initialization sequence (reset pulse followed by presence pulse), write 0, write 1, and read data. All of these types of signaling except the presence pulse are initiated by the bus master. The initialization sequence required to begin any communication with the DS2780 is shown in Figure 22. A presence pulse following a reset pulse indicates that the DS2780 is ready to accept a net address command. The bus master transmits (Tx) a reset pulse for tRSTL. The bus master then releases the line and goes into receive mode (Rx). The 1-Wire bus line is then pulled high by the pullup resistor. After detecting the rising edge on the DQ pin, the DS2780 waits for tPDH and then transmits the presence pulse for tPDL.
Figure 22. 1-Wire Initialization Sequence
tRSTL tPDH tPDL tRSTH
DQ
PACK + PACKLINE TYPE LEGEND: BUS MASTER ACTIVE LOW BOTH BUS MASTER AND DS2780 ACTIVE LOW DS2780 ACTIVE LOW RESISTOR PULLUP
WRITE-TIME SLOTS
A write-time slot is initiated when the bus master pulls the 1-Wire bus from a logic-high (inactive) level to a logic-low level. There are two types of write-time slots: write 1 and write 0. All write-time slots must be tSLOT in duration with a 1s minimum recovery time, tREC, between cycles. The DS2780 samples the 1-Wire bus line between 15s and 60s (between 2s and 6s for overdrive speed) after the line falls. If the line is high when sampled, a write 1 occurs. If the line is low when sampled, a write 0 occurs (see Figure 23). For the bus master to generate a write 1 time slot, the bus line must be pulled low and then released, allowing the line to be pulled high within 15s (2s for overdrive speed) after the start of the write-time slot. For the host to generate a write 0 time slot, the bus line must be pulled low and held low for the duration of the write-time slot.
READ-TIME SLOTS
A read-time slot is initiated when the bus master pulls the 1-Wire bus line from a logic-high level to a logic-low level. The bus master must keep the bus line low for at least 1s and then release it to allow the DS2780 to present valid data. The bus master can then sample the data tRDV from the start of the read-time slot. By the end of the read-time slot, the DS2780 releases the bus line and allows it to be pulled high by the external pullup resistor. All read-time slots must be tSLOT in duration with a 1s minimum recovery time, tREC, between cycles. See Figure 23 for more information.
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DS2780 Standalone Fuel Gauge IC
Figure 23. 1-Wire Write- And Read-Time Slots
WRITE 0 SLOT tSLOT tLOW0 VPULLUP tREC
WRITE 1 SLOT tSLOT tLOW1
GND
DS2780 Sample Window TYP MAX 30s DS2780 Sample Window TYP MAX 30s
Mode Standard Overdrive
15s
MIN
>1s 15s
MIN
15s
15s
2s
1s
3s
2s
1s
3s
READ 0 SLOT tSLOT tREC VPULLUP
READ 1 SLOT tSLOT
GND
>1s
Master Sample Window
Master Sample Window
tRDV
tRDV
LINE TYPE LEGEND: Bus master active low Both bus master and DS2780 active low DS2780 active low Resistor pullup
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DS2780 Standalone Fuel Gauge IC
PACKAGE INFORMATION
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. DOCUMENT NO. PACKAGE TYPE PACKAGE CODE 8 TSSOP 10 TDFN H8-2 T1034+1 21-0175 21-0268
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DS2780 Standalone Fuel Gauge IC
REVISION HISTORY
REVISION DATE DESCRIPTION Changed the VDD maximum operating range in the Electrical Characteristics table to 4.5V. Multicell schematic regulator changed to MAX1616 and set to 4.5V. Added "VIN pin is limited to VDD voltage" text in the Voltage Measurement section. PAGES CHANGED 2-4 6 7
051209
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Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
(c) 2009 Maxim Integrated Products
31 Inc. The The Maxim logo is a registered trademark of Maxim Integrated Products, of 31 Dallas logo is a registered trademark of Dallas Semiconductor Corporation.

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