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19-1772; Rev 2; 5/02
Low-Cost, Multichemistry BatteryCharger Building Block
General Description Features
o Input Current Limiting o 0.5% Output Voltage Accuracy Using Internal Reference (0C to +85C) o Programmable Battery Charge Current >4A o Analog Inputs Control Charge Current and Charge Voltage o Monitor Outputs for: Current Drawn from AC Input Source Charging Current AC Adapter Present o Up to 18.2V (max) Battery Voltage o 8V to 28V Input Voltage o >95% Efficiency o 99.99% (max) Duty Cycle for Low-Dropout Operation o Charges Any Battery Chemistry: Li+, NiCd, NiMH, Lead Acid, etc.
MAX1772
The MAX1772 is a highly-integrated, multichemistry battery-charger control IC that simplifies the construction of accurate and efficient chargers. The MAX1772 uses analog inputs to control charge current and voltage and can be programmed by the host or hardwired. High efficiency is achieved by a buck topology with synchronous rectification. Maximum current drawn from the AC adapter is programmable to avoid overloading the AC adapter when supplying the load and the battery charger simultaneously. This enables the user to reduce the cost of the AC adapter. The MAX1772 provides outputs that can be used to monitor the current drawn from the AC adapter, battery-charging current, and the presence of an AC adapter. The MAX1772 can charge two to four lithium-ion (Li+) series cells, easily providing 4A. When charging, the MAX1772 automatically transitions from regulating current to regulating voltage. It is available in a space-saving 28-pin QSOP package.
Applications
Notebook and Subnotebook Computers Personal Digital Assistants Hand-Held Terminals
Pin Configuration
TOP VIEW
DCIN 1 LDO 2 CLS 3 REF 4 CCS 5 CCI 6 CCV 7 GND 8 GND 9 ICHG 10 ACIN 11 ACOK 12 REFIN 13 ICTL 14 28 IINP 27 CSSP 26 CSSN 25 BST
Ordering Information
PART MAX1772EEI TEMP RANGE -40C to +85C PIN-PACKAGE 28 QSOP
MAX1772
24 DHI 23 LX 22 DLOV 21 DLO 20 PGND 19 CSIP 18 CSIN 17 BATT 16 CELLS 15 VCTL
QSOP ________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
ABSOLUTE MAXIMUM RATINGS
DCIN, CSSP, CSSN to GND ...................................-0.3V to +30V BST to GND ............................................................-0.3V to +36V BST to LX..................................................................-0.3V to +6V DHI to LX ....................................................-0.3V to (BST + 0.3V) LX to GND .................................................................-6V to +30V BATT, CSIP, CSIN to GND........................................-0.3V to 20V CSIP to CSIN or CSSP to CSSN or PGND to GND .............................................-0.3V to +0.3V CCI, CCS, CCV, DLO, ICHG, IINP, ACIN, REF to GND ..............................-0.3V to (VLDO + 0.3V) DLOV, VCTL, ICTL, REFIN, CELLS, CLS, LDO, ACOK to GND ....................................-0.3V to +6V DLOV to LDO.........................................................-0.3V to +0.3V DLO to PGND ..........................................-0.3V to (DLOV + 0.3V) LDO Short-Circuit Current ..................................................50mA Continuous Power Dissipation (TA = +70C) 28-Pin QSOP (derate 10.8mW/C above +70C).........860mW Operating Temperature Range MAX1772EEI ....................................................-40C to +85C Junction Temperature ........................................................150C Storage Temperature Range .............................-60C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDCIN = VCSSP = VCSSN = 18V, VBATT = VCSIP = VCSIN = 12V, VREFIN = 3.0V, VVCTL = VICTL = 0.75 REFIN, CELLS = 2.0V, ACIN = 0, CLS = REF, VBST - VLX = 4.5V, GND = PGND = 0, CLDO = 1F, LDO = DLOV, CREF = 1F; pins CCI, CCS, and CCV are compensated per Figure 1a; TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER SYMBOL CONDITIONS MIN 8 DCIN falling DCIN rising IDCIN 8.0V < VDCIN < 28V 8.0V < VDCIN < 28V, no load 0 < ILDO < 10mA VDCIN = 8.0V 0 < IREF < 500A REF falling 3.20 4.072 5.25 7.0 7.4 7.5 2.7 5.40 34 4.00 4.096 3.1 7.85 6.0 5.55 100 5.15 4.120 3.9 TYP MAX 28 UNITS V V mA V mV V V V
SUPPLY AND LDO REGULATOR VDCIN DCIN Input Voltage Range DCIN Undervoltage Lockout Trip Point DCIN Quiescent Current LDO Output Voltage LDO Load Regulation LDO Undervoltage Lockout Trip Point REF Output Voltage REF Undervoltage Lockout Trip Point TRIP POINTS BATT POWER_FAIL Threshold BATT POWER_FAIL Threshold Hysteresis ACIN Threshold ACIN Threshold Hysteresis ACIN Input Bias Current CLS Input Range CLS Input Bias Current SWITCHING REGULATOR Minimum Off-Time Maximum On-Time Oscillator Frequency fOSC (Note 1) VBATT =16.8V VCLS = 2.0V ACIN rising 0.5% of REF VACIN = 2.048V VCSSP falling
50 100 2.007 10 -1 1.6 -1 1.00 5
100 200 2.048 20
150 300 2.089 30 +1 REF +1
mV mV V mV A V A s ms kHz
1.25 10
1.50 15 400
2
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Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VCSSP = VCSSN = 18V, VBATT = VCSIP = VCSIN = 12V, VREFIN = 3.0V, VVCTL = VICTL = 0.75 REFIN, CELLS = 2.0V, ACIN = 0, CLS = REF, VBST - VLX = 4.5V, GND = PGND = 0, CLDO = 1F, LDO = DLOV, CREF = 1F; pins CCI, CCS, and CCV are compensated per Figure 1a; TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DLOV Supply Current BST Supply Current LX Input Bias Current LX Input Quiescent Current DHI Maximum Duty Cycle DHI On-Resistance High DHI On-Resistance Low DLO On-Resistance High DLO On-Resistance Low BATT Input Current CSIP/CSIN Input Current CSSP/CSSN Input Current BATT/CSIP/CSIN Input Voltage Range CSIP to CSIN Full-Scale Current-Sense Voltage CSSP to CSSN Full-Scale Current-Sense Voltage ERROR AMPLIFIERS GMV Amplifier Transconductance GMI Amplifier Transconductance GMS Amplifier Transconductance CCI/CCS/CCV Clamp Voltage CURRENT AND VOLTAGE SETTING Charging-Current Accuracy ICTL, VCTL, REFIN Input Bias Current ICTL Power-Down Mode Threshold Voltage ICTL = REFIN (see Equation 2) ICTL = REFIN/32 (see Equation 2) VVCTL = VICTL = VREFIN = 3V VDCIN = 0, VVCTL = VICTL = VREFIN = 5V -8 -55 -1 -1 REFIN /100 REFIN /55 +8 +55 +1 +1 REFIN /33 % A V VCTL = REFIN, VBATT = 16.8V, CELLS = LDO ICTL = REFIN, VCSIP - VCSIN = 150.4mV VCLS = 2.048V, VCSSP - VCSSN = 102.4mV 0.25V < VCCV/S/I < 2.0V 0.0625 0.5 0.5 150 0.1250 1 1 300 0.250 2 2 600 S S S mV VBATT = 12V IBATT VBST - VLX = 4.5V, IDHI = +100mA VBST - VLX = 4.5V, IDHI = -100mA VDLOV = 4.5V, IDLO = +100mA VDLOV = 4.5V, IDLO = -100mA VBATT = 19V, VDCIN = 0 VBATT = 2V to 19V, VDCIN > VBATT + 0.3V VDCIN = 0 VCSIP = VCSIN = 12V VDCIN = 0 VCSSP = VCSSN = VDCIN > 8.0V 0 189 189 204 204 0.1 200 1 SYMBOL IDLOV IBST DLO low DHI high VDCIN = 28V, VBATT = VLX = 20V VDCIN = 0, VBATT = VLX = 20V 99.0 CONDITIONS MIN TYP 5 6 150 0.3 99.9 4 1 4 1 7 2 7 2 5 500 5 800 0.3 800 19 219 219 MAX 10 15 500 1.0 UNITS A A A A % A A A V mV mV
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Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VCSSP = VCSSN = 18V, VBATT = VCSIP = VCSIN = 12V, VREFIN = 3.0V, VVCTL = VICTL = 0.75 REFIN, CELLS = 2.0V, ACIN = 0, CLS = REF, VBST - VLX = 4.5V, GND = PGND = 0, CLDO = 1F, LDO = DLOV, CREF = 1F; pins CCI, CCS, and CCV are compensated per Figure 1a; TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER SYMBOL CONDITIONS VVCTL = VREFIN (2, 3, or 4 cells) (see Equation 1) VVCTL = VREFIN/20 (2, 3, or 4 cells) (see Equation 1) MIN -0.5 -0.5 2.0 1.20 VICHG to (VCSIP - VCSIN); VCSIP VCSIN = 0.185V; VICHG = 0, 3.0V VCSIP - VCSIN = 0.185V VCSIP - VCSIN = 0.05V VIINP to (VCSSP - VCSSN); VCSSP VCSSN = 0.185V; VIINP = 0, 3.0V (Note 2) VCSSP - VCSSN = 0.185V VCSSP - VCSSN = 0.05V (Note 2) 0.95 -5 -10 0.85 -15 -20 -10 -10 8.0 1.00 1.00 TYP MAX +0.5 % +0.5 3.6 1.92 1.05 +5 +10 1.15 +15 +20 +10 +10 28 V V S % S % % V UNITS
Battery-Regulation Voltage Accuracy
REFIN Range REFIN Undervoltage Lockout ICHG Transconductance ICHG Accuracy IINP Transconductance IINP Current Accuracy CSSP - CSSN Accuracy CSSP + CSSN Input Voltage Range LOGIC LEVELS CELLS Input Low Voltage CELLS Input Middle Voltage CELLS Input High Voltage CELLS Input Bias Current ACOK Sink Current ACOK Leakage Current CELLS = 0 or VLDO VACOK = 0.4V VACOK = 5.5V
VCSSP - VCSSN = 0.08V, VCLS = 1.6V VCSSP - VCSSN = 0.2V, CLS = REF
0.2 0.4 VLDO - 0.25 -10 1 -1 +1 VLDO - 0.5 VLDO +10
V V V A mA A
4
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Low-Cost, Multichemistry BatteryCharger Building Block
ELECTRICAL CHARACTERISTICS
(VDCIN = VCSSP = VCSSN = 18V, VBATT = VCSIP = VCSIN = 12V, VREFIN = 3.0V, VVCTL = VICTL = 0.75 REFIN, CELLS = 2.0V, ACIN = 0, CLS = REF, VBST - VLX = 4.5V, GND = PGND = 0, CLDO = 1F, LDO = DLOV, CREF = 1F; pins CCI, CCS, and CCV are compensated per Figure 1a; TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER SUPPLY AND LDO REGULATOR DCIN Input Voltage Range DCIN Undervoltage Lockout Trip Point DCIN Quiescent Current LDO Output Voltage TRIP POINTS BATT POWER_FAIL Threshold BATT POWER_FAIL Threshold Hysteresis ACIN Threshold ACIN Threshold Hysteresis ACIN Input Bias Current CLS Input Range CLS Input Bias Current SWITCHING REGULATOR Minimum Off-Time Maximum On-Time Oscillator Frequency DHI Maximum Duty Cycle BATT Input Current CSIP/CSIN Input Current CSSP/CSSN Input Current BATT/CSIP/CSIN Input Voltage Range CSIP to CSIN Full-Scale Current-Sense Voltage CSSP to CSSN Full-Scale Current-Sense Voltage CURRENT AND VOLTAGE SETTING Charging Current Accuracy ICTL, VCTL, REFIN Input Bias Current ICTL = REFIN (see Equation 2) ICTL = REFIN/32 (see Equation 2) VVCTL = VICTL = VREFIN = 3V VDCIN = 0, VVCTL = VICTL = VREFIN = 5V -8 -55 -1 -1 +8 +55 +1 +1 % A VBATT = 12V IBATT VBATT = 19V, VDCIN = 0 VBATT = 2V to 19V, VDCIN > VBATT + 0.3V VDCIN = 0 VCSIP = VCSIN = 12V VDCIN = 0 VCSSP = VCSSN = VDCIN > 8.0V 0 189 189 fOSC (Note 1) 99 5 500 5 800 0.3 800 19 219 219 VBATT = 16.8V 1 5 1.5 15 400 s ms kHz % A A A V mV mV VCLS = 2.0V ACIN rising 0.5% of REF VACIN = 2.048V VCSSP falling 50 100 2.007 10 -1 1.6 -1 150 300 2.089 30 +1 REF +1 mV mV V mV A V A IDCIN VDCIN DCIN falling DCIN rising 8.0V < VDCIN < 28V 8.0V < VDCIN < 28V, no load 5.25 8.0 7 7.85 6 5.65 28.0 V V mA V SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1772
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Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VCSSP = VCSSN = 18V, VBATT = VCSIP = VCSIN = 12V, VREFIN = 3.0V, VVCTL = VICTL = 0.75 REFIN, CELLS = 2.0V, ACIN = 0, CLS = REF, VBST - VLX = 4.5V, GND = PGND = 0, CLDO = 1F, LDO = DLOV, CREF = 1F; pins CCI, CCS, and CCV are compensated per Figure 1a; TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER ICTL Power-Down Mode Threshold Voltage VVCTL = VREFIN (2, 3, or 4 cells) (see Equation 1) VVCTL = VREFIN/20 (2, 3, or 4 cells) (see Equation 1) SYMBOL CONDITIONS MIN REFIN /100 -1 -1 2.0 VCSIP - VCSIN = 0.185V VCSIP - VCSIN = 0.05V VCSSP - VCSSN = 0.185V VCSSP - VCSSN = 0.05V (Note 2) -5 -10 -15 -20 -10 -10 8 TYP MAX REFIN /33 +1 % +1 3.6 1.92 +5 +10 +15 +20 +10 +10 28 V V % % % V UNITS V
Battery Regulation Voltage Accuracy
REFIN Range REFIN Undervoltage Lockout ICHG Accuracy IINP Current Accuracy CSSP - CSSN Accuracy CSSP + CSSN Input Voltage Range LOGIC LEVELS CELLS Input Low Voltage CELLS Input Middle Voltage CELLS Input High Voltage CELLS Input Bias Current ACOK Sink Current ACOK Leakage Current CELLS = 0 or VLDO VACOK = 0.4V VACOK = 5.5V
VCSSP - VCSSN = 0.08V, VCLS = 1.6V VCSSP - VCSSN = 0.2V, CLS = REF
0.2 0.4 VLDO - 0.25 -10 1 -1 +1 VLDO - 0.5 VLDO +10
V V V A mA A
Note 1: Guaranteed by design. Not production tested. Note 2: Tested under DC conditions. See text for more detail.
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Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
Typical Operating Characteristics
(Circuit of Figure 1a, VDCIN = 20V, TA = +25C, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE (BATTERY REMOVAL AND REINSERTION)
MAX1772 toc01
LOAD-TRANSIENT RESPONSE (STEP-IN LOAD CURRENT)
MAX1772 toc02
VBATT 20V/div IBATT 2A/div CCV CCI CCI 500mV/div CCV 500mV/div 1ms/div BATTERY PRESENT ICTL = 0.957V VCTL = 3.3V
CCI CCS
CCS 500mV/div CCI 500mV/div VBATT 20V/div ILOAD 2A/div
1ms/div ICTL = 3.30V CHARGING CURRENT = 2.0A VBATT = 16V LOAD STEP = 0 TO 3A ISOURCE LIMIT = 5A
LINE-TRANSIENT RESPONSE
MAX1772 toc03
LDO LOAD REGULATION
DCIN 10V/div LDO ERROR (%) 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 VCTL = 0 ICTL = 3.3V DCIN = 20.0V LDO = 5.40V
MAX1772 toc04
0.4
VBATT (AC-COUPLED) 100mV/div
2ms/div VBATT = 16V DCIN = 18.5V TO 27.5V ILOAD = 150mA
0
1
2
3
4
5
6
7
8
9
10
LDO CURRENT (mA)
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Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
Typical Operating Characteristics (continued)
(Circuit of Figure 1a, VDCIN = 20V, TA = +25C, unless otherwise noted.)
LDO LINE REGULATION
MAX1772 toc05
REF VOLTAGE LOAD REGULATION
MAX1772 toc06
REF VOLTAGE ERROR vs. TEMPERATURE
0.4 0.3 REF VOLTAGE ERROR (%) 0.2 0.1 0 -0.1 -0.2 -0.3 ICTL = 0 VCTL = 0 NO LOAD REF = 4.096V
MAX1772 toc07
1.0 0.8 0.6 0.4 LDO ERROR (%) LDO = 5.40V
0.20 0.15 0.10 REF ERROR (%) 0.05 0 -0.05 -0.10 -0.15 -0.20 VCTL = 0 ICTL = 3.3V CELL = 4 REF = 4.096V
0.5
0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 8 12 16 20 24 28 DCIN (V)
-0.4 -0.5 0 50 100 150 200 250 300 350 400 450 500 REF CURRENT (A) -40 -15 10 35 60 85 TEMPERATURE (C)
EFFICIENCY vs. BATTERY CURRENT (VOLTAGE CONTROL LOOP)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.1 1 10 100 1000 10,000 BATT CURRENT (mA) VCTL = 0 ICTL = 3.3V REFIN = 3.3V CELL = 4 CELL = 3 CELL = 2
MAX1772 toc08
EFFICIENCY vs. BATTERY CURRENT (CURRENT CONTROL LOOP)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VCTL = 0 ICTL = 3.3V REFIN = 3.3V 100 1000 BATT CURRENT (mA) 10,000 CELL = 3 CELL = 4 CELL = 2
MAX1772 toc09
100
100
8
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Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
Typical Operating Characteristics (continued)
(Circuit of Figure 1a, VDCIN = 20V, TA = +25C, unless otherwise noted.)
OUTPUT V/I CHARACTERISTICS
MAX1772 toc10
BATT VOLTAGE ERROR vs. VCTL
0.18 BATT VOLTAGE ERROR (%) 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0 CELL = 4 REFIN = 3.3V NO LOAD
MAX1772 toc11
0.050 0.045 BATT VOLTAGE ERROR (%) 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0 0 CELL = 2 CELL = 3 VCTL = 0 ICTL = 3.3V CELL = 4
0.20
500 1000 1500 2000 2500 3000 3500 4000 BATT CURRENT (mA)
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 VCTL/REFIN (%)
CURRENT SETTING ERROR vs. ICTL
MAX1772 toc12
ICHG ERROR vs. BATT LOAD CURRENT
3.5 3.0 ICHG ERROR (%) VCTL = 0 ICTL = 3.3V CELL = 4
MAX1772 toc13
5
REFIN = 3.3V
4.0
CURRENT SETTING ERROR (%)
4
3
2.5 2.0 1.5 1.0
2
1 BATT > 2V 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 ICTL/REFIN (%)
0.5 0 0 500 1000 1500 2000 2500 3000 3500 4000 BATT LOAD CURRENT (mA)
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Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
Pin Description
PIN 1 2 3 4 5 6 7 8, 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 NAME DCIN LDO CLS REF CCS CCI CCV GND ICHG ACIN ACOK REFIN ICTL VCTL CELLS BATT CSIN CSIP PGND DLO DLOV LX DHI BST CSSN CSSP IINP Charging Voltage Input Device Power Supply. Output of the 5.4V linear regulator supplied from DCIN. Bypass with a 1F capacitor. Source Current-Limit Input. Voltage input for setting the current limit of the input source. 4.096V Voltage Reference. Bypass with 1F to GND. Input Current Regulation Loop Compensation Point. Use 0.01F to GND. Output Current Regulation Loop Compensation Point. Connect 0.01F to GND. Voltage Regulation Loop Compensation Point. Connect 1k in series with 0.1F to GND. Analog Ground ICHG is a scaled-down replica of the battery output current being sensed. It is used to monitor the charging current and indicates when the chip changes from voltage mode to current mode. The transconductance of (CSIP - CSIN) to ICHG is 1S. Connect ICHG pin to GND if it is unused. AC Detect Input. Detects when the AC adapter voltage is available for charging. AC Detect Output. Open-drain output is high when ACIN is less than REF/2. Reference Input. Allows the ICTL and VCTL pins to have ratiometric ranges for increased DAC accuracy. Input for Setting Maximum Output Current. Range is REFIN/32 to REFIN. The device shuts down if this pin is forced below REFIN/55 (typ). Input for Setting Maximum Output Voltage. Range is 0 to REFIN. Trilevel Input for Setting Number of Cells. GND = 2 cells, LDO/2 = 3 cells, LDO = 4 cells. Battery Voltage Input Output Current-Sense Negative Input Output Current-Sense Positive Input. Connect a current-sense resistor from CSIP to CSIN. Power Ground Low-Side Power MOSFET Driver Output. Connect to low-side NMOS gate. Low-Side Driver Supply Power Connection for the High-Side Power MOSFET Driver. Connect to source of high-side NMOS. High-Side Power MOSFET Driver Output. Connect to high-side NMOS gate. Power Connection for the High-Side Power MOSFET Driver. Connect a 0.1F capacitor from LX to BST. Input Current-Sense for Charger (negative input) Input Current-Sense for Charger (positive input). Connect a current-sense resistor from CSSP to CSSN. IINP is a scaled-down replica of the input current being sensed. It is used to monitor the total system current. The transconductance of (CSSP - CSSN) to IINP is 1mS. Connect IINP pin to GND if it is unused. FUNCTION
10
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Low-Cost, Multichemistry BatteryCharger Building Block
Detailed Description
The MAX1772 includes all of the functions necessary to charge Li+, NiMH, and NiCd batteries. A high-efficiency synchronous-rectified step-down DC-DC converter controls charging voltage and current. It also includes input source-current limiting and analog inputs for setting the charge current and charge voltage. The DC-DC converter uses external N-channel MOSFETs as the buck switch and synchronous rectifier to convert the input voltage to the required charging current and voltage. The typical application circuit shown in Figure 1a uses a microcontroller (C) to allow control of charging current or voltage, while Figure 1b shows a typical application with charging voltage and current fixed to specific values for the application. The voltage at ICTL and the value of RS2 set the charging current. The DCDC converter generates the control signals for the external MOSFETs to regulate the voltage and the current set by the VCTL, ICTL, and CELLS inputs. The MAX1772 features a voltage-regulation loop (CCV) and two current-regulation loops (CCI and CCS). The CCV voltage-regulation loop monitors BATT to ensure that its voltage never exceeds the voltage set by VCTL. The CCI battery current-regulation loop monitors current delivered to BATT to ensure that it never exceeds the current limit set by ICTL. A third loop (CCS) takes control and reduces the battery-charging current when the sum of the system load and the battery-charging current exceeds the charging source current limit set by CLS. cations. Individual compensation of the voltage regulation and current-regulation loops allow for optimal compensation.
MAX1772
Setting the Charging-Current Limit
The ICTL input sets the maximum charging current. The current is set by current-sense resistor RS2, connected between CSIP and CSIN. The nominal differential voltage between CSIP and CSIN is 204mV; thus, for a 0.05 sense resistor, the maximum charging current is 4A. Battery-charging current is programmed with ICTL using the equation: ICHG = VREF V 1 x ICTL x RS2 VREFIN 20
(2)
The input range for ICTL is REFIN/32 to REFIN ( 3.3V). The device shuts down if ICTL is forced below REFIN/55 (typical). The current at ICHG is a scaleddown replica of the battery output current being sensed across CSIP and CSIN. When choosing the current-sense resistor, note that the voltage drop across this resistor causes further power loss, reducing efficiency. However, adjusting ICTL to reduce the voltage across the current-sense resistor may degrade accuracy due to the input offset of the current-sense amplifier. The charging current-error amplifier (GMI) is compensated at CCI. A 0.01F capacitor at CCI provides suitable performance for most applications.
Setting the Battery Regulation Voltage
The MAX1772 uses a high-accuracy voltage regulator for charging voltage. The VCTL input adjusts the battery output voltage. VCTL is allowed to vary from 0 to REFIN ( 3.3V). The per-cell battery termination voltage is a function of the battery chemistry and construction; thus, consult the battery manufacturer to determine this voltage. The battery voltage is calculated by the equation: V V VBATT = CELLS x VREF + REF x VCTL 10 VREFIN
Setting the Input Current Limit
The total input current (from a wall cube or other DC source) is a function of the system supply current and the battery-charging current. The input current regulator limits the source current by reducing the charging current when the input current exceeds the set input current limit. System current will normally fluctuate as portions of the system are powered up or put to sleep. Without input current regulation, the input source must be able to supply the maximum system current and the maximum charger input current. By using the input current limiter, the current capability of the AC wall adapter may be lowered, reducing system cost. The MAX1772 limits the current drawn by the charger when the load current becomes high. The device limits the charging current, so the AC adapter voltage is not loaded down. An internal amplifier compares the voltage between CSSP and CSSN to the voltage at CLS. VCLS can be set by a resistor-divider between REF and GND. Connect CLS to REF for maximum input current limiting.
(1)
CELLS is the programming input for selecting cell count. Table 1 shows how CELLS is connected to charge 2, 3, or 4 cells. Use a voltage-divider from LDO to set the desired voltage at CELLS. The internal error amplifier (GMV) maintains voltage regulation (Figure 2). The voltage error amplifier is compensated at CCV. The component values shown in Figure 1 provide suitable performance for most appli-
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11
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
VIN 8VDC TO 28VDC
D1
RS1 0.04 C1 22F
TO EXTERNAL LOAD C2 22F
R14 4.7 C6 O.47F C7 O.47F
R15 4.7
R6 59.0k
D4 CSSP R7 19.6k C5 1F DCIN CSSN CELLS LDO C13 1F D3 R13 33
D/A OUTPUT D/A OUTPUT VCC R8 1M DIGITAL INPUT A/D INPUT
VCTL ICTL REFIN ACIN ACOK ICHG
BST DLOV C15 0.1F DHI LX DLO N2 C16 1.0F N1
MAX1772
PGND A/D INPUT C14 0.1F HOST R9 15.4k C20 0.1F R10 12.4k R5 1k C11 0.1F CSIN CCI CCS C9 0.01F AVDD/REF R20, R21, R22 10k C12 1F C10 0.01F REF CLS BATT GND C3 22F IINP CSIP CCV C18 0.1F R11 1
D2 L1 22H
RS2 0.05 C19 0.1F R12 1
BATT+ C4 22F
SMART BATTERY SCL SDA TEMP BATT-
SCL SDA A/D INPUT GND
PGND
GND
Figure 1a. C-Controlled Typical Application Circuit 12 ______________________________________________________________________________________
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
VIN 8VDC TO 28VDC
D1
RS1 0.04 C1 22F
TO EXTERNAL LOAD C2 22F
R14 4.7 C6 O.47F C7 O.47F
R15 4.7
3.30V D4 3.30V R6 59.0k R19 29.4k R7 19.6k C5 1F CSSP DCIN CSSN CELLS LDO C13 1F D3 R22 10k R20 10k REFIN VCTL ICTL R8 1M ACIN ACOK ICHG BST DLOV C15 0.1F DHI LX DLO N2 C16 1.0F N1 R13 33 910 1.5k
R21 10k
MAX1772
PGND IINP C14 0.1F R9 15.4k C20 0.1F R10 12.4k R5 1k C11 0.1F CSIN CCI CCS C9 0.01F C10 0.01F REF CLS BATT GND C3 22F CSIP CCV C18 0.1F R11 1
D2 L1 22H
RS2 0.05 C19 0.1F R12 1
BATT+ C4 22F BATTERY BATT-
C12 1F
Figure 1b. Stand-Alone Typical Application Circuit ______________________________________________________________________________________ 13
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
DCIN LDO 5.4V LINEAR REGULATOR 4.096V REFERENCE REF
MAX1772
GND GND ICTL ACIN SRDY ACOK REF/2 LOGIC BLOCK 1/55 REFIN
CCS CLS
IINP
GMS CSSP CSSN LEVEL SHIFTER ICHG
CSIP CSIN
LEVEL SHIFTER LEVEL SHIFTER GMI 204mV X ----REFIN DRIVER
BST DHI LX
ICTL CCI BATT
LVC R1
DC-DC CONVERTER
CELLS CCV
CELL SELECT LOGIC
GMV DRIVER
DLOV DLO PGND
VCTL
409mV X ----REFIN
VOS
Figure 2. Functional Diagram 14 ______________________________________________________________________________________
Low-Cost, Multichemistry BatteryCharger Building Block
Table 1. Cell-Count Programming Table
CELL VCELLS < 0.20V 0.40V < VCELLS < VLDO-0.5V VLDO - 0.25V < VCELLS < VLDO CELL COUNT 2 3 4
Use IINP to monitor the system input current being sensed across CSSP and CSSN. The output voltage range is 0 to 3V. The voltage of IINP is proportional to the output current by the equation: VIINP = ISOURCE x RS1 x GIINP x R10
MAX1772
(6)
The input source current is the sum of the device current, the charger input current, and the load current. The device current is minimal (6mA) in comparison to the charge and load currents. The actual source current required is determined as follows:
ISOURCE = ILOAD + (ICHARGE x VBATT ) / (VIN x )
where ISOURCE is the DC current being supplied by the AC adapter power, GIINP is the transconductance of IINP (1mS typ), and R10 is the resistor connected between IINP and ground. In the typical application circuit, duty cycle affects the accuracy of V IINP (Figure 3). AC load current also affects accuracy (Figure 4). Connect IINP pin to ground if it is not used.
[
]
(3)
where is the efficiency of the DC-DC converter (85% to 95% typ). V CLS determines the reference voltage of the GMS error amplifier. Sense resistor RS1 sets the maximum allowable source current. Calculate the maximum current as follows: ISOURCE_MAX = VCLS / (20 x RS1)
LDO Regulator
LDO provides a 5.4V supply derived from DCIN and can deliver up to 15mA of current. The MOSFET drivers are powered by DLOV and BST, which must be connected to LDO as shown in Figure 1. LDO also supplies the 4.096V reference (REF) and most of the control circuitry. Bypass LDO with a 1F capacitor.
(4)
DC-to-DC Converter
The MAX1772 employs a buck regulator with a bootstrapped NMOS high-side switch and a low-side NMOS synchronous rectifier. DC-DC Controller The control scheme is a constant off-time variable frequency, cycle-by-cycle current mode. The off-time is constant for a given BATT voltage. It varies with VBATT operation; a maximum on-time of 10ms allows the controller to achieve >99% duty cycle with continuous conduction. Figure 5 shows the controller functional diagram. MOSFET Drivers The low-side driver output DLO swings from 0 to DLOV. DLOV is usually connected through a filter to LDO. The high-side driver output DHI is bootstrapped off LX and swings from V LX to V BST. When the low-side driver turns on, BST rises to one diode voltage below DLOV. Filter DLOV with a resistor-capacitor (RC) circuit whose cutoff frequency is about 50kHz. The configuration in Figure 1 introduces a cutoff frequency of around 48kHz: f = 1/2RC = 1 / (2 33 0.1F) = 48kHz (7)
Once the input current limit is reached, the charging current is tapered back until the input current is below the desired threshold. When choosing the current-sense resistor, note that the voltage drop across this resistor causes further power loss, reducing efficiency.
AC Adapter Detection
Connect the AC adapter voltage through a resistive divider to ACIN to detect when AC power is available, as shown in Figure 1. ACOK is an open-drain output and is high when ACIN is less than REF/2.
Current Measurement
Use ICHG to monitor the battery-charging current being sensed across CSIP and CSIN. The output voltage range is 0 to 3V. The voltage of ICHG is proportional to the output current by the equation: VICHG = ICHG x RS2 x GICHG x R9
(5)
where ICHG is the battery-charging current, GICHG is the transconductance of ICHG (1mS typ), and R9 is the resistor connected between ICHG and ground. Connect ICHG pin to ground if it is not used.
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15
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
30 VDCIN = 16V VBATT = 8.2 VDCIN = 16V VBATT = 12.3 IINP ACCURACY (%) 0 -1
MAX1772
AC ADAPTER
RS1
AC LOAD 2A 1A FREQUENCY
20 IINP ACCURACY (%)
-2 FREQ = 50kHz -3 -4 -5 FREQ = 125kHz FREQ = 250kHz
10 VDCIN = 18V VBATT = 16.4 0
-10 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 IRS1 (A)
-6 0 10 20 30 40 50 60 70 80 DUTY CYCLE (%)
Figure 3. IINP Accuracy vs. VDCIN/VBATT
Figure 4. IINP Accuracy vs. AC Load Duty Cycle
Dropout Operation
The MAX1772 has 99.99% duty-cycle capability with a 10ms maximum on-time and 1s off-time. This allows the charger to achieve dropout performance limited only by resistive losses in the DC-DC converter components (D1, N1, RS1, RS2) (Figure 1). The actual dropout voltage is limited to 100mV between CSSP and CSIN by the power-fail comparator.
MOSFETs and Schottky Diodes
Schottky diode D1 provides power to the load when the AC adapter is inserted. This diode must be able to deliver the maximum current as set by RS1. The N-channel MOSFETs (N1, N2) are the switching devices for the buck controller. High-side switch N1 should have a current rating of at least 8A and have an on-resistance (RDS(ON)) of 50m or less. The driver for N1 is powered by BST; its current should be less than 10mA. Select a MOSFET with a low total gate charge (QGATE) and determine the required drive current by IGATE = QGATE f (where f is the DC-DC converter's 400kHz maximum switching frequency). The low-side switch (N2) should also have a current rating of at least 8A, have an RDS(ON) of 100m or less, and a total gate charge less than 10nC. N2 is used to provide the starting charge to the BST capacitor (C15). During normal operation, the current is carried by Schottky diode D2. Choose a Schottky diode capable of carrying the maximum charging current. D3 is a signal-level diode, such as the 1N4148. This diode provides the supply current to the high-side MOSFET driver.
Compensation
Each of the three regulation loops--the input current limit, the charging current limit, and charging voltage limit--can be compensated separately using the CCS, CCI, and CCV pins, respectively. The charge-current-loop error-amp output is brought out at CCI. Likewise, the source current error-amp output is brought out at CCS; 0.01F capacitors to ground at CCI and CCS compensate the current loops in most charger designs. Raising the value of these capacitors reduces the bandwidth of these loops. The voltage-regulating-loop error-amp output is brought out at CCV. Compensate this loop by connecting a series RC network from CCV to GND. Recommended values are 1k and 0.1F. The zero set by the series RC increases midfrequency gain to provide phase compensation. The pole at CCV is set by the capacitor and the voltage error-amp output impedance at low frequencies to integrate the DC error.
Inductor Selection
Inductor L1 provides power to the battery while it is being charged. It must have a saturation current of at least 4A plus 1/2 of the current ripple (IL): ISAT = 4A + (1/2) IL (8)
Component Selection
Table 2 lists the recommended components and refers to the circuit of Figure 1. The following sections describe how to select these components.
16
______________________________________________________________________________________
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
10ms S BST IMAX 4.0V R Q CSSP CSS CSSN BST R CCMP CHG Q DHI DHI LX CBST RS1 DCIN LDO
RESET
MAX1772
IMIN 0.25V
S
Q DLO 1s DLO L1
ZCMP 0.1V CSI
CSIP RS2 CSIN LVC GMS BATT COUT GMI BATTERY
GMV SETV CONTROL SETI CLS CELLS CELL SELECT LOGIC
CCS
CCI
CCV
Figure 5. DC-to-DC Converter Functional Diagram ______________________________________________________________________________________ 17
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
The controller determines the constant off-time period, which is dependent on BATT voltage. This makes the ripple current independent of input and battery voltage, and it should be kept to less than 1A. Calculate IL with the following equation: IL = 21Vs L(H) (9) Use the following step-by-step guide: 1) Place the high power connections first, with their grounds adjacent: * Minimize the current-sense resistor trace lengths, and ensure accurate current sensing with Kelvin connections. * Minimize ground trace lengths in the high current paths. * Minimize other trace lengths in the high current paths. * Use >5mm wide traces. * Connect C1 and C2 to high-side MOSFET (10mm max length). * LX node (MOSFETs, rectifier cathode, inductor (15mm max length)). Ideally, surface-mount power components are flush against one another with their ground terminals almost touching. These high-current grounds are then connected to each other with a wide, filled zone of top-layer copper, so they do not go through vias. The resulting top-layer subground plane is connected to the normal inner-layer ground plane at the output ground terminals, which ensures that the IC's analog ground is sensing at the supply's output terminals without interference from IR drops and ground noise. Other high current paths should also be minimized, but focusing primarily on short ground and current-sense connections eliminates about 90% of all PC board layout problems. 2) Place the IC and signal components. Keep the main switching node (LX node) away from sensitive analog components (current-sense traces and REF capacitor). Important: the IC must be no further than 10mm from the current-sense resistors. Keep the gate drive traces (DHI, DLO, and BST) shorter than 20mm, and route them away from the current-sense lines and REF. Place ceramic bypass capacitors close to the IC. The bulk capacitors can be placed further away. Place the current-sense input filter capacitors under the part, connected directly to the GND pin. 3) Use a single-point star ground placed directly below the part. Connect the input ground trace, power ground (subground plane), and normal ground to this node.
Higher inductor values decrease the ripple current. Smaller inductor values require high saturation current capabilities and degrade efficiency. Typically, a 22H inductor is ideal for all operating conditions.
Current-Sense Input Filtering
In normal circuit operation with typical components, the current-sense signals can have high-frequency transients that exceed 0.5V due to large current changes and parasitic component inductance. To achieve proper battery and input current compliance, the currentsense input signals should be filtered to remove large common-mode transients. The input current-limit sensing circuitry is the most sensitive case due to large current steps in the input filter capacitors (C6, C7) in Figure 1. Use 0.47F ceramic capacitors from CSSP and CSSN to ground. Smaller 0.1F ceramic capacitors (C18, C19) can be used on the CSIP and CSIN inputs to ground since the current into the battery is continuous. Place these capacitors next to the single-point ground directly under the MAX1772.
Layout and Bypassing
Bypass DCIN with a 1F to ground (Figure 1). D4 protects the MAX1772 when the DC power source input is reversed. A signal diode for D4 is adequate because DCIN only powers the LDO and the internal reference. Bypass LDO, BST, DLOV, and other pins as shown in Figure 1. Good PC board layout is required to achieve specified noise, efficiency, and stable performance. The PC board layout artist must be given explicit instructions--preferably, a pencil sketch showing the placement of the power switching components and high current routing. Refer to the PC board layout in the MAX1772 evaluation kit for examples. A ground plane is essential for optimum performance. In most applications, the circuit will be located on a multilayer board, and full use of the four or more copper layers is recommended. Use the top layer for high current connections, the bottom layer for quiet connections (REF, CCV, CCI, CCS, DCIN, and GND), and the inner layers for an uninterrupted ground plane.
18
______________________________________________________________________________________
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
Table 2. Component List
DESIGNATION C1, C2, C3, C4 DESCRIPTION 22F, 35V low-ESR tantalum capacitors AVX TPSE226M035R0300 or Sprague 593D226X0035E2W 1F, 50V ceramic capacitor (1210) Murata GRM42-2X7R105K050 0.47F, 25V ceramic capacitors (1210) Murata GRM42-2X7R474K050 0.01F ceramic capacitors (0805) 1F, 10V ceramic capacitors (0805) Taiyo Yuden LMK212BJ105MG 0.1F, 50V ceramic capacitors (0805) Taiyo Yuden UMK212BJ104MG or Murata GRM40-034X7R104M050 Schottky diode (DPAK) STM-Microelectronics STPS8L30B or ON Semiconductor MBRD630CT or Toshiba U5FWK2C42 30V, 3A Schottky diode Nihon EC31QS03L 100mA Schottky diodes (SOT23) Central Semiconductor CMPSH-3 or Hitachi HRB0103A 22H power inductor Sumida CDRH127-220 RS2 R5 R6 R7 R8 R9 R10 R11, R12 R13 R14, R15 R19 R20, R21, R22 DESIGNATION N1 DESCRIPTION N-channel MOSFET International Rectifier IRF7805 or Fairchild FDS6680 N-channel MOSFET Fairchild FDS6612A 0.04 1%, 1W resistor Dale WSL-2512-R040-F or IRC LR2512-01-R040-F 0.05 1%, 1W resistor Dale WSL-2512-R050-F or IRC LR2512-01-R050-F 1k 5% resistor (0805) 59.0k 1% resistor (0805) 19.6k 1% resistor (0805) 1M 5% resistor (0805) 15.4k 1% resistor (0805) 12.4k 1% resistor (0805) 1 5% resistors (0805) 33 5% resistor (1206) 4.7 5% resistors (1206) 29.4k 1% resistor (0805) 10k 1% resistors (0805)
C5 C6, C7 C9, C10 C12, C13 C11, C14, C15, C16, C18, C19, C20
N2
RS1
D1
D2
D3, D4
L1
Chip Information
TRANSISTOR COUNT: 2733 PROCESS: S12
______________________________________________________________________________________
19
Low-Cost, Multichemistry BatteryCharger Building Block MAX1772
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
QSOP.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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