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L6924D
Battery charger system with integrated power switch for Li-ION/Li-POLYMER
Features
Fully integrated solution, with a power MOSFET, reverse blocking diode, sense resistor, and thermal protection Ideal for coke and graphite anode single-cell LI-ION packs Both linear and quasi-pulse operation Closed loop thermal control USB BUS-compatible Programmable charge current up to 1A Programmable pre-charge current Programmable end-of-charge current Programmable pre-charge voltage threshold Programmable charge timer Programmable output voltage at 4.1V and 4.2V, with 1% output voltage accuracy (NTC) or (PTC) thermistor interface for battery temperature monitoring and protection Flexible charge process termination Status outputs to drive LEDs or to interface with a host processor Small VFQFPN 16-leads package (3mm x 3mm) VFQFPN16

Applications

PDAs Handheld devices Cellular phones Digital cameras Standalone chargers USB-Powered chargers
Table 1. Device summary
Order codes L6924D L6924D013TR Package VFQFPN16 VFQFPN16 Packaging Tube Tape & Reel
June 2007
Rev 7
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Contents
L6924D
Contents
1 2 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 3.2 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4
Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5 6
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 6.2 Linear mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Quasi-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7
Applications information: charging process . . . . . . . . . . . . . . . . . . . . . . 17
7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 Charging process flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Pre-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Pre-charge voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Fast charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 End-of-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Recharge flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Recharge threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Maximum charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Termination modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
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L6924D
Contents
8
Application information: monitoring and protection . . . . . . . . . . . . . . . . 24
8.1 8.2 8.3 8.4 NTC thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Battery absence detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Status pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9
Additional applications information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1 9.2 Selecting input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1.1 Selecting output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Layout guidelines and demoboard description . . . . . . . . . . . . . . . . . . . . . . . 30
10
Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
10.1 USB battery charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
11 12
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
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Device description
L6924D
1
Device description
The L6924D is a fully monolithic battery charger dedicated to single-cell Li-Ion/Polymer battery packs. It is the ideal solution for space-limited applications, like PDAs, handheld equipment, cellular phones, and digital cameras. It is designed with BCD6 technology and integrates all of the power elements (the Power MOSFET, reverse blocking diode and the sense resistor) in a small VFQFPN16 3mm x 3mm package. When an external voltage regulated wall adapter is used, the L6924D works in Linear Mode, and charges the battery in a Constant Current/ Constant Voltage(CC/CV) profile. Moreover, when a current-limited adapter is used, the device can operate in Quasi-Pulse Mode, dramatically reducing the power dissipation. Regardless of the charging approach, a closed loop thermal control avoids device overheating. The device has an operating input voltage ranging from 2.5V to 12V. The L6924D allows the user to program many parameters, such as pre-charge current, fast-charge current, pre-charge voltage threshold, end-of-charge current threshold, and charge timer. The L6924D offers two open collector outputs for diagnostic purposes, which can be used to either drive two external LEDs or communicate with a host microcontroller. Finally, the L6924D also provides very flexible control of the charge process termination and Gas Gauge capability, as well as other functions, such as checking for battery presence, and monitoring and protecting the battery from unsafe thermal conditions. Figure 1. Minimum application size
Figure 2.
Basis application schematic
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L6924D
Pins description and connection diagrams
2
Figure 3.
Pins description and connection diagrams
Pins connection (top view)
IPRE IPRG VPRE IEND
VIN V
INSNS
VREF VOUT VOSNS VOPRG
ST2 ST1
TPRG GND SD
TH
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Pins description and connection diagrams
L6924D
2.1
Table 2.
Pin 1 2 3-4 5 6 7
Pin description
Pin functions
I/O I I O I I Name VIN VINSNS Input pin of the power stage. Supply voltage pin of the signal circuitry. The operating input voltage range is from 2.5V and 12V, and the start-up threshold is 4V. Pin description
ST2-ST1 Open-collector status pins. TPRG GND SD Maximum charging time program pin. It must be connected with a capacitor to GND to fix the maximum charging time, see Chapter 7.8: Maximum charging time on page 22 Ground pin. Shutdown pin. When connected to GND enables the device; when floating disables the device. Temperature monitor pin. It must be connected to a resistor divider including an NTC or PTC resistor. The charge process is disabled if the battery temperature (sensed through the NTC or PTC) is out of the programmable temperature window see Chapter 8.1: NTC thermistor on page 25 . Output voltage selection pin. If is it floating, VOUT = 4.1V. If is it connected to GND, VOUT = 4.2V. Output voltage sense pin. It senses the battery voltage to control the voltage regulation loop. Output pin. (connected to the battery) External reference voltage pin.(reference voltage is 1.8V2%) Charge termination pin. A resistor connected from this pin to GND fixes the charge termination current threshold IENDTH: if I < IENDTH, the charger behaves according to the VPRE status (see Chapter 7.5: End-of-charge current on page 20). The voltage across the resistor is proportional to the current delivered to the battery (Gas Gauge function). Multifunction pin. A resistor connected to GND allows the user to adjust the pre-charge voltage threshold VPRETH.
8
I
TH
9 10 11 12
I I O O
VOPRG VOSNS VOUT VREF
13
I/O
IEND
14
I
VPRE
- If the pin is floating, VPRETH = 2.8V. If the voltage on VPRE pin is lower than 0.8V, VPRETH = 2.8V and the charge is not automatically terminated when I < IENDTH. - If the voltage on VPRE goes lower than 0.5V (edge sensitive), the maximum charging time is reset.
15
I
IPRG
Charge current program pin. A resistor connected from this pin to GND, fixes the fast charge current value (ICHG), with an accuracy of 7%. Pre-charge current program pin. If the pin is floating IPRETH is equal to 10% of ICHG. If IPRETH has to be programmed at a different value, the pin has to be connected to GND or VREF, through a resistor see Chapter 7.2: Pre-charge current on page 18.
16
I
IPRE
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L6924D
Maximum ratings
3
Maximum ratings
Stressing the device above the rating listed in the "Absolute Maximum Ratings" table may cause permanent damage to the device. These are stress ratings only and operation of the device at these or any other conditions above those indicated in the Operating sections of this specification is not implied. Exposure to Absolute Maximum Rating conditions for extended periods may affect device reliability. Refer also to the STMicroelectronics SURE Program and other relevant quality documents.
3.1
Absolute maximum ratings
Table 3. Absolute maximum ratings
Parameter Input voltage Input voltage Output voltage Output voltage ST1, ST2 Output current VREF, TH, IEND, IPRG, VPRE, IPRE, VOPRG, TPRG, GND ST1 and TH pins Other pins Maximum Withstanding Voltage Range Test Condition: CDFAEC-Q100-002 (Normal "Human Body Model" Acceptance Criteria Performance) 30 -0.3 to 4 1.5 2 mA V kV kV Value -0.3 to 16 -0.3 to VIN -0.3 to 5 -0.3 to 6 Unit V V V V Symbol VIN VINSNS, SD VOUT, VOSNS
3.2
Thermal data
Table 4. Thermal data
Parameter Thermal resistance junction to ambient (1) Storage temperature range Junction temperature range Power dissipation at T= 70C Value 75 -55 to 150 -40 to 125 TBD Unit C/W C C W Symbol RthJA TSTG TJ PTOT
1. Device mounted on Demo board
7/38
Electrical specifications
L6924D
4
4.1
Electrical specifications
Electrical characteristics
TJ = 25C, VIN = 5V, unless otherwise specified Table 5.
Symbol VIN(1)
Electrical characteristics
Parameter Operating input voltage Start up threshold Supply current Charging mode (RPRG = 24K) Shutdown mode (RPRG = 24K) Shutdown mode (RPRG = 24K) 1.8 60 Test condition Min 2.5 Typ Max 12 4.1 2.5 80 500 500 4.06 4.16 450 905 41 4.1 4.2 490 975 49 4.14 4.24 525 1045 56 Unit V V mA A nA nA V V mA mA mA
IIN(1)
ISINK
Current flowing from VOUT Stand by mode (RPRG = 24K) (VIN = 2.5V < VBATTERY)
VOUT(1)
VOPRG at VIN Battery regulated voltage VOPRG at GND Charge current RPRG = 24K RPRG = 12K Pre-Charge current IPRE floating [default value = 10% ICHG] RPRG = 24K Pre-Charge current RPRE = 62K to GND; RPRG = 24K RPRE = 39K to VREF; RPRG = 24K VPRE = VPRETHDefault = Floating RVPRE = 13K; RPRG = 12K
ICHG
IPRECH
IPRECH
57
67
78
mA
IPRECH VPRETH VPRETH
Pre-Charge current Pre-Charge voltage threshold [default] Pre-Charge voltage threshold Pre-Charge voltage threshold [default]. Charge termination disabled Termination current Maximum charging time
29.5
35
40.1
mA
2.7 2.87
2.8 3.03
2.9 3.19
V V
VPRETH
2.7
2.8
2.9
V
IENDTH TMAXCH
(2)
REND = 3K3 CTPRG = 10nF R[IPRG] = 24K
12
16 3
20
mA hours
8/38
L6924D Table 5.
Symbol TMAXCH
(2)
Electrical specifications Electrical characteristics (continued)
Parameter Maximum charging time accuracy Shutdown threshold high Shutdown threshold low Output status sink current Status on Power MOSFET resistance NTC pin hot threshold voltage TH NTC pin cold threshold voltage
1. TJ from -40C to 125C. 2. Guaranteed by design.
Test condition CTPRG = 5.6nF RPRG = 24K
Min
Typ 10%
Max
Unit
SDTH ST1,2 RDS(on)
2 0.4 10 280 10 40 12.5 50 380 15 60
V V mA m %VREF %VREF
RDS(on)@ICHG = 500mA
9/38
Block diagram
L6924D
5
Figure 4.
Block diagram
Block diagram
10/38
L6924D
Operation description
6
Operation description
The L6924D is a fully integrated battery charger that allows a very compact battery management system for space limited applications. It integrates in a small package, all the power elements: power MOSFET, reverse blocking diode and the sense resistor. It normally works as a linear charger when powered from an external voltage regulated adapter. However, thanks to its very low minimum input voltage (down to 2.5V) the L6924D can also work as a Quasi-Pulse charger when powered from a current limited adapter. To work in this condition, is enough to set the device's charging current higher than the adapter one (Chapter 7.4 on page 19). The advantage of the linear charging approach is that the device has a direct control of the charging current and so the designer needn't to rely on the upstream adapter. However, the advantage of the Quasi-Pulse approach is that the power dissipated inside the portable equipment is dramatically reduced. Regards the charging approach, the L6924D charges the battery in three phases:

Pre-Charge constant current: in this phase (active when the battery is deeply discharged) the battery is charged with a low current. Fast-Charge constant current: in this phase the device charges the battery with the maximum current. Constant Voltage: when the battery voltage is closed to the selected output voltage, the device starts to reduce the current, until the charge termination is done. Programmable pre-charging current and voltage thresholds (IPRETH and VPRETH) (Chapter 7.2 on page 18, Chapter 7.3 on page 19). Programmable fast-charging current (ICHG) (Chapter 7.4 on page 19). Programmable end of charge current threshold (IENDTH) (Chapter 7.5 on page 20). Programmable end of charge timer (TMAXCH) (Chapter 7.8 on page 22).
The full flexibility is provided by:

If the full flexibility is not required and a smaller number of external components is preferred, default values of IPRETH and VPRETH are available leaving the respective pins floating.

If a PTC or NTC resistor is used, the device can monitor the battery temperature in order to protect the battery from operating in unsafe thermal conditions. Beside the good thermal behavior guaranteed by low thermal resistance of the package, additional safety is provided by the built-in temperature control loop. The IC monitors continuously its junction temperature. When the temperature reaches approximately 120C, the thermal control loop starts working, and reduces the charging current, in order to keep the IC junction temperature at 120C. Two open collector outputs are available for diagnostic purpose (status pins ST1 and ST2). They can be also used to drive external LEDs or to interface with a microcontroller. The voltage across the resistor connected between IEND and GND gives information about the actual charging current (working as a Gas Gauge), and it can be easily fed into a C ADC.

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Operation description
L6924D
When the VPRE pin is not used to program the Pre-Charge voltage threshold, it has two different functions:
If the voltage across VPRE pin is lower than 0.8V, when I < IENDTH, the end of charge in notified by the status pin, but the charging process is not disabled. The charge process ends when the maximum charging time expires. If pin VPRE goes lower than 0.5V the timer is reset on the falling edge.
Battery disconnection control is provided thanks to the differentiated sensing and forcing output pins. A small current is sunk and forced through VOUT. If VOSNS doesn't detect the battery, the IC goes into a standby mode. Figure 5 shown the real charging profile of a Li-Ion battery, with a Fast Charge current of 450mA (RPRG = 26K), Figure 5. Li-Ion charging profile
C harging profile
0.50 0 0.45 0 0.40 0 0.35 0 0.30 0 Ichg (A) 0.25 0 2.00 0 0.20 0 0.15 0 0.10 0 0.05 0 0.00 0 0 2 00 400 60 0 Charging tim e (sec ) 8 00 10 00 1.50 0 1.00 0 0.50 0 0.00 0 1 200 Ichg Vb att Vbatt (V) 2.50 0 4.50 0 4.00 0 3.50 0 3.00 0
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L6924D
Operation description
6.1
Linear mode
When operating in Linear Mode, the device works in a way similar to a linear regulator with a constant current limit protection. It charges the battery in three phases:

Pre-charging current ("Pre-Charge" phase). Constant current ("Fast-Charge" phase). Constant voltage ("Voltage Regulation" phase).
VADP is the output voltage of the upstream AC-DC adapter that is, in turn, the input voltage of the L6924D. If the battery voltage is lower than a set pre-charge voltage (VPRETH), the precharge phase takes place. The battery is pre-charged with a low current IPRE (Chapter 7.2 on page 18). When the battery voltage goes higher than VPRETH, the battery is charged with the Fast Charge current ICHG, set with an external resistor (Chapter 7.4 on page 19). Finally, when the battery voltage is close to the regulated output voltage VOPRGTH (4.1V or 4.2V), the voltage regulation phase takes place and the charging current is reduced. The charging process usually is terminated when the charging current reaches a set value or when a charging timer expires (Chapter 7.9 on page 23). Figure 6 shows the different phases. Figure 6. Typical charge curves in linear mode
Pre-Charge Phase
V ADP V OPRGTH
Fast-Charge Phase Adapter Voltage
Voltage-Regulation Phase
End Charge
Battery Voltage
V PRETH
I CHG
Charge Current
I PRETH
Power dissipation
13/38
Operation description
L6924D
The worst case in power dissipation occurs when the device starts the Fast-Charge Phase. In fact, the battery voltage is at its minimum value. In this case, this is the maximum difference between the adapter voltage and battery voltage, and the charge current is at its maximum value. The power dissipated is given by the following formula:
PDIS = (VADP - VBAT ) x I CHG
Eq. 7-1
The higher the adapter voltage is, the higher the power dissipated. The maximum power dissipated depends on the thermal impedance of the device mounted on board.
6.2
Quasi-pulse mode
The Quasi-Pulse Mode can be used when the system can rely on the current limit of the upstream adapter to charge the battery. In this case, ICHG must be set higher than the current limit of the adapter. In this mode, the L6924D charges the battery with the same three phases as in Linear Mode, but the power dissipation is greatly reduced as shown in Figure 7. Figure 7. Typical charge curves in quasi pulse mode
Pre-Charge Phase
V ADP V O PRGTH
Fast-Charge Phase
Voltage Regulation Phase Adapter Voltage Battery Voltage
End Charge
V PRETH
Ilim x Rdson
I CHG I LIM
Charge Current
I PRETH
Power dissipation
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L6924D
Operation description The big difference is due to the fact that ICHG is higher than the current limit of the adapter. During the Fast-Charge Phase, the output voltage of the adapter drops and goes down to the battery voltage plus the voltage drop across the power MOSFET of the charger, as shown in the following equation:
VIN = VADP = VBAT + VMOS
Where VMOS is given by:
Eq. 7-2
V
MOS
= R DS ( ON ) x I LIM
Eq. 7-3
Where, ILIM = current limit of the wall adapter, and RDS(on) = resistance of the power MOSFET. The difference between the set charge current and the adapter limit should be high enough to minimize the RDS(on) value (and the power dissipation). This makes the control loop completely unbalanced and the power element is fully turned on. Figure 8 shows the RDS(on) values for different output voltage and charging currents for an adapter current limit of 500mA. Figure 8. rDS(on) curves vs charging current and output voltage
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Operation description
L6924D
Neglecting the voltage drop across the charger (VMOS) when the device operates in this condition, its input voltage is equal to the battery one, and so a very low operating input voltage (down to 2.5V) is required. The power dissipated by the device during this phase is:
PCH = RDS ( on ) x I LIM
2
Eq: 7-4
When the battery voltage approaches the final value, the charger gets back the control of the current, reducing it. Due to this, the upstream adapter exits the current limit condition and its output goes up to the regulated voltage VADP. This is the worst case in power dissipation:
PDIS = (VADP - VBAT ) x I LIM Eq: 7-5
In conclusion, the advantage of the linear charging approach is that the designer has the direct control of the charge current, and consequently the application can be very simple. The drawback is the high power dissipation. The advantage of the Quasi-Pulse charging method is that the power dissipated is dramatically reduced. The drawback is that a dedicated upstream adapter is required.
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L6924D
Applications information: charging process
7
7.1
Applications information: charging process
Charging process flow chart
Figure 9. Charging process flow chart
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Applications information: charging process
L6924D
7.2
Pre-charge current
The L6924D allows pre-charging the battery with a low current when the battery voltage is lower than a specified threshold (VPRETH). The Pre-charge current has a default value equal to 10% of the fast-charge current (see Chapter 7.2: Pre-charge current on page 18). However it can be adjusted by connecting a resistor from the IPRE pin to GND or VREF Figure 10. When the resistor is connected from IPRE pin and GND, the current is higher than the default value. The RPRE value is given by:
RPRE =
VBG I PRECH VBG Eq: 8-1 - K PRE RPRG
Figure 10. IPRE pin connection
IPRE
L6924D
When RPRE is connected to VREF, the current is lower than the default value. VREF is the external reference equal to 1.8V, VBG is the internal reference equal to 1.23V and KPRE is a constant equal to 950.Figure 11 The relationship is shown in the equation 8.2:
RPRE =
VREF - VBG VBG I PRECH - RPRG KPRE
Eq: 8-2
Figure 11. IPRE pin connection
VREF
IPRE
L6924D
18/38
L6924D
Applications information: charging process
7.3
Pre-charge voltage
If the VPRE pin is floating, a default value of VPRETH is set, equal to 2.8V (VPRETHDefault). Otherwise, the device offers the possibility to program this value, with a resistor connected between the VPRE pin and GND Figure 12. In this case, the RVPRE is given by the equation 8.3:
VPRETH RVPRE = RPRG x V PRETHDefault
Figure 12. VPRE pin connection
Eq: 8-3
VPRE L6924D RPRE
Where RVPRE is the resistor between VPRE and GND, and RPRG is the resistor used to set the charge current (see Section 7.4: Fast charge current), and VPRETH is the selected threshold. A safety timer is also present. If the battery voltage doesn't rise over VPRETH, before this time is expired, a fault is given (see Section 7.8: Maximum charging time). If at the beginning of the charge process, the battery voltage is higher than the VPRETH, the Pre-Charge phase is skipped.
7.4
Fast charge current
When the battery voltage reaches the Pre-charge voltage threshold (VPRETH), the L6924D starts the Fast-charge Phase. In this phase, the device charges the battery with a constant current, ICHG, programmable by an external resistor that sets the charge current with an accuracy of 7% Figure 13. The formula used to select the RPRG as follows:
KPRG Eq: 8-4 RPRG = VBG x I CHG
Figure 13. IPRG pin connection
Where KPRG is a constant, equal to 9500. During this phase, the battery voltage increases until it reaches the programmed output voltage. A safety timer is also present. If this time expires, a fault is given (Section 7.8: Maximum charging time).
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Applications information: charging process
L6924D
7.5
End-of-charge current
When the charge voltage approaches the selected value (4.1V or 4.2V), the Voltage Regulation phase takes place. The charge current starts to decrease until it goes lower than a programmable end value, IENDTH, depending on an external resistor connected between the IEND pin and GND Figure 14. The formula that describes this relation as follows:
KEND REND = VMIN x I ENDTH
Figure 14. IEND pin connection
Eq: 8-5
Where KEND is 1050; and VMIN is 50mV. Typically, this current level is used to terminate the charge process. However, it is also possible to disable the charge termination process based on this current level (Chapter 7.9 on page 23). This pin is also used to monitor the charge current, because the current injected in REND is proportional to ICHG. The voltage across REND can be used by a microcontroller to check the charge status like a gas gauge.
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L6924D
Applications information: charging process
7.6
Recharge flow chart
Figure 15. Recharge flow chart
FROM CHARGING PROCESS FLOW CHART
FAULT
IND FAULT
END of CHARGE
DETECT LOW = a ISINK is sunk for a TDET from the battery DETECT HIGH = a IINJ is injected for a TDET in the battery DETECT LOW FAULT = a ISINK is sunk for a TDET from the battery DETECT HIGH FAULT = a IINJ is injected for a TDET in the battery VABS = VOPRG - 50mV VRCH = VOPRG - 150mV TDET = 100ms (Typ.) ISINK = IINJ = 1mA (Typ.)
VBAT > VRCH
YES
VBAT > VRCH
YES
NO
NO
Detect High Fault
Detect Low
VBAT < VABS
YES
VBAT > VPRETH NO
YES
FAST CHARGE
NO
Detect Low Fault
Detect High
RETURN TO CHARGING PROCESS FLOW CHART
YES
VBAT > VPRETH
VBAT > VRCH NO
YES
PRE CHARGE
NO
BATTERY ABSENT
BATTERY ABSENT
GO TO BATTERY ABSENT FLOW CHART
7.7
Recharge threshold
When, from an End-of-Charge condition, the battery voltage goes lower than the recharging threshold (VRCH), the device goes back in charging state. The value of the recharge threshold is VOPRG-150mV.
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Applications information: charging process
L6924D
7.8
Maximum charging time
To avoid the charging of a dead battery for a long time, the L6924D has the possibility can be set a maximum charging time starting from the beginning of the Fast-Charge Phase. This timer can be set with a capacitor, connected between the TPRG pin and GND. The CTPRG is the external capacitor (in nF) and is given by the following formula:
C TPRG
T MAXCH V BG x R PRG KT = V REF
x 10 9
Eq: 8-6
Note:
The maximum recommended CTPRG value must be less than 50 nF. Figure 16. TPRG pin connection
TPRG L6924D CTPRG
Where, VREF = 1.8V, KT = 279 x 105, VBG = 1.23V, and TMAXCH is the charging time given in seconds. If the battery does not reach the End-of-Charge condition before the time expires, a fault is issued. Also during the Pre-Charge Phase there is a safety timer, given by:
1 TMAXPRECH = x TMAXCH Eq: 8-7 8
If this timer expires and the battery voltage is still lower than VPRETH, a fault signal is generated, and the charge process is terminated.
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L6924D
Applications information: charging process
7.9
Termination modes
Figure 17. Charge termination flow chart
As shown in Figure 17, it is possible to set an end of charge current IENDTH connecting a resistor between the IEND pin and GND. When the charge current goes down to this value, after de-glitch time, the status pins notify that the charge process is complete. This de-glitch time expressed as:
TDEGLITCH =
TMAXCH 220
Eq: 8-9
However, the termination of the charger process depends on the status of the VPRE pin:
If the voltage at the VPRE pin is higher than 0.8V, the charger process is actually terminated when the charge current reaches IENDTH. If the voltage at VPRE pin goes lower than 0.8V, the charge process does not terminate, and the charge current can go lower than IENDTH. The status pins notify the End-of-Charge as a fault condition, but the device continues the charge. When the TMAXCH is elapsed, the charge process ends, and a fault condition is issued. If the voltage on VPRE pin is lower than 0.8V during the Pre-charge Phase, the device sets the VPRETHDefault automatically. If the voltage at the VPRE pin goes lower than 0.5V (edge sensitive), the timer is reset, both in Pre-Charge and in Fast-Charge Phase.
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Application information: monitoring and protection
L6924D
8
Application information: monitoring and protection
The L6924D uses a VFQFPN 3mm x 3mm 16-pin package with an exposed pad that allows the user to have a compact application and good thermal behavior at the same time. The L6924D has a low thermal resistance because of the exposed pad (approximately 75C/W, depending on the board characteristics). Moreover, a built-in thermal protection feature prevents the L6924D from having thermal issues typically present in a linear charger. Thermal Control is implemented with a thermal loop that reduces the charge current automatically when the junction temperature reaches approximately 120C. This avoids further temperature rise and keeps the junction temperature constant. This simplifies the thermal design of the application as well as protects the device against over-temperature damage. The figure above shows how the thermal loop acts (with the dotted lines), when the junction temperature reaches 120C..
Figure 18. Power dissipation both linear and quasi pulse mode with thermal loop
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L6924D
Application information: monitoring and protection
8.1
NTC thermistor
The device allows designers to monitor the battery temperature by measuring the voltage across an NTC or PTC resistor. Li-Ion batteries have a narrow range of operating temperature, usually from 0C to 50C. This window is programmable by an external divider which is comprised of an NTC thermistor connected to GND and a resistor connected to VREF. When the voltage on the TH pin exceeds the minimum or maximum voltage threshold (internal window comparator), the device stops the charge process, and indicates a fault condition through the status pin.
When the voltage (and thus, the temperature), returns to the window range, the device re-starts the charging process. Moreover, there is a hysteresis for both the upper and lower thresholds, as shown in Figure 20 Figure 19. Battery temperature control flow chart
Note:
TBAT = OK when the Battery temperature between 0C and 50C
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Application information: monitoring and protection
L6924D
Figure 20. Voltage window with hysteresis On TH
VMINTH VMINTH_HYS
900mV 780mV Voltage Variation on TH pin
Charge disable Charge enable
VMAXTH_HYS VMAXTH
248mV
225mV
Figure 21. Pin connection
VREF
TH
L6924D
NTC
When the TH pin voltage rises and exceeds the VMINTH = 50% of VREF (900mV typ), the L6924D stops the charge, and indicates a fault by the status pins. The device re-starts to charge the battery, only when the voltage at the TH pin goes under VMINTH_HYS = 780mV (typ). For what concerns the high temperature limit, when the TH pin voltage falls under the VMAXTH = 12.5% of VREF (225mV Typ.), the L6924D stops the charge until the TH pin voltage rises at the VMAXTH_HYS = 248mV (Typ.). When the battery is at the low temperature limit, the TH pin voltage is 900mV. The correct resistance ratio to set the low temperature limit at 0C can be found with the following formula:
VMINTH = VREF x
RNTC 0C RUP + RNTC 0C
Eq: 9-1
Where RUP is the pull-up resistor, VREF is equal to 1.8V, and RNTC0C is the value of the NTC at 0C. Since at the low temperature limit VMINTH = 900mV:
0.9 = 1.8 x
It follows that:
RNTC 0C RUP + RNTC 0C
Eq: 9-2
RNTC 0C = RUP Eq: 9-3
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L6924D
Application information: monitoring and protection Similarly, when the battery is at the high temperature limit, the TH pin voltage is 225mV. The correct resistance ratio to set the high temperature limit at 50C can be found with the following formula:
VMAXTH = VREF x
RNTC 50C RUP + RNTC 50C
Eq: 9-4
Where RNTC50C is the value of the NTC at 50C. Considering VMAXTH = 225mV it follows that:
0.225 = 1.8 x
Consequently:
RNTC 50C RUP + RNTC 50C
Eq: 9-5
RNTC 50C =
RUP 7
Eq: 9-6
Based on equations 9-3 and 9-6, it derives that:
RNTC 0C =7 RNTC 50C
Eq: 9-7
The temperature hysteresis can be estimated by the formula:
THYS =
VTH - VTH _ HYS VTH x NTCT
Eq: 9-8
Where VTH is the pin voltage threshold on the rising edge, VTH_HYS is the pin voltage threshold on the falling edge, and NTCT (- %/C) is the negative temperature coefficient of the NTC at temperature (T) expressed in % resistance change per C. For NTCT values, see the characteristics of the NTC manufacturers (e.g. the 2322615 series by VISHAY). At the low temperature, the hysteresis is approximately:
THYS 0C =
900mV - 780mV 900mV x NTC 0C
Eq: 9-9
Obviously at the high temperature hysteresis is:
THYS 50C =
225mV - 248mV 225mV x NTC 50C
Eq: 9-10
Considering typical values for NTC0C and NTC50C, the hysteresis is:
THYS 0C =
And:
900mV - 780mV 2.5o C 900mV x 0.051
Eq: 9-11
THYS 50C =
225mV - 248mV -2.5o C 225mV x 0.039
Eq: 9-12
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Application information: monitoring and protection
L6924D
If a PTC connected to GND is used, the selection is the same as above, the only difference is when the battery temperature increases, the voltage on the TH pin increases, and vice versa. For applications that do not need a monitor of the battery temperature, the NTC can be replaced with a simple resistor whose value is one half of the pull-up resistor RUP. In this case, the voltage at the TH pin is always inside the voltage window, and the charge is always enabled.
8.2
Battery absence detection
This feature provides a battery absent detection scheme to detect the removal or the insertion of the battery. If the battery is removed, the charge current falls below the IENDTH. At the end of de-glitch time, a detection current IDETECT, equal to 1mA, is sunk from the output for a time of TDETECT. The device checks the voltage at the output. If it is below the VPRETH, a current equal to IDETECT is injected in the output capacitor for a TDETECT, and it is checked to see if the voltage on the output goes higher than VABS (the value is VOPRGTH-50mV). If the battery voltage changes from VPRETH to VABS and vice versa in a TDETECT time, it means that no battery is connected to the charger. The TDETECT is expressed by::
TDETECT =
TMAXCH 54x 103
Eq: 9-13
Figure 22. Battery absent detection flow chart
BATTERY ABSENT
DETECT LOW ABSENT = a ISINK is sunk for a TDET from the battery DETECT HIGH ABSENT = a IINJ is injected for a TDET in the battery TDET = 100ms (Typ.) ISINK = IINJ = 1mA (Typ.)
Detect Low Absent
VBAT > VPRETH
YES
FAST CHARGE
NO
Detect High Absent
YES
VBAT > VRCH
NO
PRE CHARGE
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L6924D
Application information: monitoring and protection
8.3
Status pins
To indicate various charger status conditions, there are two open-collector output pins, ST1 and ST2. These status pins can be used either to drive status LEDs, connected with an external power source, by a resistor, or to communicate to a host processor. These pins must never be connected to the VIN when it overcomes their absolute value (6V). Figure 23. ST1 and ST2 connection with LEDs Or C
Table 6.
Status LEDs Indications
Description When the device is in Pre-Charge or fastCharge status When the charging current goes lower than the IENDTH When the input voltage goes under VBAT50mV When the voltage on the TH pin is out of the programmable window, in accordance with the NTC or PTC thermistor When the battery pack is removed When TMAXCH or TMAXPRECH is expired ST1 ON OFF OFF ST2 OFF ON OFF
Charge condition Charge in progress Charge done Stand By mode
Bad battery temperature Battery absent Over time
ON ON ON
ON ON ON
8.4
Shutdown
The L6924D has a shutdown pin; when the pin is connected to GND, the device is operating. When the pin is left floating, the device enters in shutdown mode, the consumption from the input is dramatically reduced to 60A (typ.). In this condition, VREF is turned OFF.
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Additional applications information
L6924D
9
9.1
Additional applications information
Selecting input capacitor
In most applications, a 1F ceramic capacitor, placed close to the VIN and VINSN pins can be used to filter the high frequency noise.
9.1.1
Selecting output capacitor
Typically, 1F ceramic capacitor placed close to the VOUT and VOUTSN pin is enough to keep voltage control loop stable. This ensures proper operation of battery absent detection in removable battery pack applications.
9.2
Layout guidelines and demoboard description
The thermal loop keeps the device at a constant temperature of approximately 120C which in turn, reduces ICHG. However, in order to maximize the current capability, it is important to ensure a good thermal path. Therefore, the exposed pad must be properly soldered to the board and connected to the other layer through thermal vias. The recommended copper thickness of the layers is 70m or more. The exposed pad must be electrically connected to GND. Figure 24 shows the thermal image of the board with the power dissipation of 1W. In this instance, the temperature of the case is 89C, but the junction temperature of the device is given by the following formula:
TJ = RTHJ - A x PDISS + TAMB
Eq: 10-1
Where the RTH J-A of the device mounted on board is 75C/W, the power dissipated is 1W, and the ambient temperature is 25C. In this case the junction temperature is:
TJ = 75 x1 + 25 = 100o C Eq: 10-2
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L6924D
Additional applications information
Figure 24. Thermal image of the demo board
The VOSNS pin can be used as a remote sense; so, it should be connected as closely as possible to the battery. The demo board layout and schematic are shown in Figure 25 and Figure 26. Figure 25. Demoboard layout, top side
Figure 26. Demoboard layout, bottom side
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Additional applications information Figure 27. Demoboard schematic
R3 R9
L6924D
C4 CHARGER C1 VINSNS R1 R2 C2 LD1 LD2 J2 ST2 ST1 J1 SHDN GND VOPRG J3 J4 IPRE R6 R10 VPRE J5 R5 R4 TPRG VIN VREF TH NTC VOUT VOSNS IEND BATTERY
L6924D
IPRG
C3
C
Vref R7 R8
Table 7.
Name R1 R2 R3 R4 R5 R6
Demo board components description
Value 1K 1K 1K 3K3 24K N.M. Description Pull up resistor. To be used when the ST1 is connected with a LED. Pull up resistor. To be used when the ST1 is connected with a LED. Pull up resistor. Connected between VREF and TH pin. End of Charge current resistor. Used to set the termination current and, as a "Gas Gauge" when measuring the voltage across on it. Fast-charge current resistor. Used to set the charging current. VPRETH resistor. Used to set programmable pre-charge voltage threshold. If not mounted, the VPRETHDefault, equal to 2.8V, is set. IPRETH resistor. Used to set the programmable pre-charge current threshold below the default one. If not mounted, the IPRETHDefault is set. IPRETH resistor. Used to set the programmable pre-charge current threshold above the default one. If not mounted, the IPRETHDefault is set. If a NTC is not used, a half value of R3 must be mounted to keep the TH voltage in the correct window. It has the same function of R6. Moreover, if it is replaced with a short-circuit, when J5 is closed, the timer is reset (falling edge). Input capacitor. TMAX capacitor. Used to set the maximum charging time. Output capacitor. VREF filter capacitor. ST1 LED.
R7
N.M.
R8 R9 R10 C1 C2 C3 C4 LD1
68K 470R N.M. 1uF 10nF 4.7uF 1nF GREEN
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L6924D Table 7.
Name LD2 J1 J2 J3 J4 J5
Additional applications information Demo board components description (continued)
Value RED ST2 LED. ST1 jumper. Using to select the LED or the external C. ST2 jumper. Using to select the LED or the external C. SD jumper. If open, the device is in SD mode; when closed, the device starts to work. VOPRG jumper. If closed, the 4.2V output voltage is set; if open, the 4.1V is set. VPRE jumper. If closed with R10 in short-circuit with GND, reset the timer. Description
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Application ideas
L6924D
10
10.1
Application ideas
USB battery charger
With a voltage range between 4.75V and 5.25V, and a maximum current up to 500mA, the USB power bus is an ideal source for charging a single-cell Li-Ion battery. Since it is not possible to rely on the USB current limit to charge the battery, a linear approach must be adopted. Therefore, it is only necessary to set the ICHG with a maximum value lower than 500mA, and the device will charge the battery in Linear mode. Figure 28 shows an example of USB charger application schematic. Figure 28. USB charger application
C4 R1
VBUS GND C1
VIN
VREF
TH VOUT VOSNS IEND C3
BATTERY PACK
VINSNS D- D+ TPRG C2
L6924D
ST1
IPRG R2 R3
SYSTEM AND USB CONTROLLER
VPRE
ST2 SD GND V IPRE OPRG
R4
R5
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L6924D
Package mechanical data
11
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK(R) packages. These packages have a Lead-free second level interconnect . The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com.
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Package mechanical data Table 8. VFQFPN16 (3mm x 3mm) mechanical data
Dimensions mm. Dim. Min. A A1 A2 A3 b D D2 E E2 e L ddd 0.180 2.875 0.250 2.875 0.250 0.450 0.300 0.800 Typ. 0.900 0.020 0.650 0.250 0.230 3.000 0.700 3.000 0.700 0.500 0.400 0.300 3.125 1.250 3.125 1.250 0.550 0.500 0.080 0.007 0.113 0.009 0.113 0.009 0.017 0.011 Max. 1.000 0.050 1.000 Min. 0.031 Typ. 0.035 0.001 0.025 0.010 0.010 0.120 0.027 0.118 0.027 0.019 0.015 inch
L6924D
Max. 0.039 0.002 0.039
0.012 0.123 0.050 0.123 0.049 0.021 0.019 0.003
Figure 29. Package dimensions
E
A K A1
E2
e D b K r D2
A3
L
This drawing is not to scale
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L6924D
Revision history
12
Revision history
Table 9.
Date 16-Dec-2005 20-Dec-2005 10-Jan-2006 14-Feb-2006 03-Jul-2006 07-Sep-2006 29-Jun-2007
Revision history
Revision 1 2 3 4 5 6 7 First draft Package dimensions updated Few updates Part number updated Updates to formula in page 22, updated block diagram Figure 4. Added Note: on page 22, updated value CTPRG page 8 Updated capacitor values C2, C3 in Table 7 on page 32 Changes
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L6924D
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