ST L6924D User Manual

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

VFQFPN16

■Programmable charge current up to 1 A

■Programmable pre-charge current

■Programmable end-of-charge current

■Programmable pre-charge voltage threshold

■Programmable charge timer

■Programmable output voltage at 4.1 V and 4.2 V, 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 (3 x 3 mm)

Applications

■PDAs

■Handheld devices

■Cellular phones

■Digital cameras

■Standalone chargers

■USB-powered chargers

Table 1.	Device summary
	Order code	Package	Packaging
	L6924D	VFQFPN16	Tube
	L6924D013TR		Tape and reel
September 2010		Doc ID 11908 Rev 9	1/38
			www.st.com

Contents	L6924D

Contents

1	Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 3
2	Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . .		. 4
	2.1	Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
3	Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
	3.1	Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6
	3.2	Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6
4	Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
	4.1	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7
5	Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		9
6	Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		10
	6.1	Linear mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
	6.2	Quasi-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
7	Applications information: charging process . . . . . . . . . . . . . . . . . . . .		16
	7.1	Charging process flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	7.2	Pre-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	7.3	Pre-charge voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	7.4	Fast charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	18
	7.5	End-of-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
	7.6	Recharge flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
	7.7	Recharge threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
	7.8	Maximum charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
	7.9	Termination modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
8	Application information: monitoring and protection . . . . . . . . . . . . . .		23
	8.1	NTC thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23
	8.2	Battery absence detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	27
	8.3	Status pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	27

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L6924D			Contents
	8.4	Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . . 28
9	Additional applications information . . . . . . . . . . . . . . . . . . . . . . .		. . . . 30

9.1 Selecting the input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.2 Selecting the output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.3 Layout guidelines and demonstration board description . . . . . . . . . . . . . 30

10	Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	34
	10.1 USB battery charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	34
11	Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	35
12	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	37

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Description	L6924D

1 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 integrates all of the power elements (the power MOSFET, reverse blocking diode and the sense resistor) in a small VFQFPN16 (3 x 3 mm) 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 quasipulse 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 2.5 V to 12 V. 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 Pins description and connection diagrams

Figure 3. Pins connection (top view)

IPRE	IPRG VPRE	IEND
VIN		VREF
VINSNS		V	OUT
ST2		VOSNS
ST1		VOPRG
TPRG	GND SD	TH

2.1Pin description

	Table 2.		Pin functions
	Pin	I/O	Name			Pin description
	1	I	VIN	Input pin of the power stage.
	2	I	VINSNS	Supply voltage pin of the signal circuitry.
				The operating input voltage ranges from 2.5 V to 12 V and the start-up threshold is 4 V.
	3-4	O	ST2-ST1	Open-collector status pins.
				Maximum charging time program pin.
	5	I	TPRG	It must be connected with a capacitor to GND to fix the maximum charging time, see
				Chapter 7.8: Maximum charging time on page 20
	6	-	GND	Ground pin.
	7	I	SD	Shutdown pin.
				When connected to GND enables the device; when floating disables the device.
				Temperature monitor pin.
	8	I	TH	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 23.
	9	I	VOPRG	Output voltage selection pin.
				V	= 4.1 V if left floating. V	= 4.2 V if connected to GND.
				OUT	OUT
	10	I	VOSNS	Output voltage sense pin.
				It senses the battery voltage to control the voltage regulation loop.
	11	O	VOUT	Output pin. (connected to the battery)

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Pins description and connection diagrams				L6924D
Table 2.		Pin functions
12	O	VREF	External reference voltage pin.(reference voltage is 1.8 V±2%)
			Charge termination pin.
			A resistor connected from this pin to GND fixes the charge termination current threshold
13	I/O	IEND	IENDTH: if I < IENDTH, the charger behaves according to the VPRE status (see Chapter 7.5:
			End-of-charge current on page 19). 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.
14	I	VPRE	If the pin is floating, VPRETH = 2.8 V. If the voltage on VPRE pin is lower than 0.8 V, VPRETH =
			2.8 V and the charge is not automatically terminated when I < IENDTH.
			If the voltage on VPRE goes lower than 0.5 V (edge sensitive), the maximum charging time is
			reset.
			Charge current program pin.
15	I	IPRG	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.
16	I	IPRE	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 17.

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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.

3.1Absolute maximum ratings

	Table 3.	Absolute maximum ratings
	Symbol		Parameter	Value	Unit
		VIN	Input voltage	–0.3 to 16	V
	VINSNS, SD		Input voltage	–0.3 to VIN	V
	VOUT, VOSNS		Output voltage	–0.3 to 5	V
	ST1, ST2		Output voltage	–0.3 to 6	V
			Output current	30	mA
	VREF, TH, IEND, IPRG,			–0.3 to 4	V
	VPRE, IPRE, VOPRG,
	TPRG, GND
	ST1 and TH pins		Maximum withstanding voltage range test condition:	±1.5	kV
			CDFAEC-Q100-002 (Normal “human body model”
	Other pins			±2	kV
			acceptance criteria performance)

3.2Thermal data

Table 4.	Thermal data
Symbol		Parameter	Value	Unit
R		Thermal resistance junction to ambient (1)	75	°C/W
thJA
TSTG		Storage temperature range	–55 to 150	°C
TJ		Junction temperature range	–40 to 125	°C
PTOT		Power dissipation at T= 70 °C	TBD	W

1. Device mounted on demonstration board

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Electrical specifications	L6924D

4 Electrical specifications

4.1Electrical characteristics

TJ = 25 °C, VIN = 5 V, unless otherwise specified.

Table 5.		Electrical characteristics
Symbol		Parameter	Test condition		Min	Typ	Max	Unit
V	(1)	Operating input voltage			2.5		12	V
	IN	Start up threshold					4.1	V
I	(1)	Supply current	Charging mode (RPRG = 24kΩ)			1.8	2.5	mA
IN			Shutdown mode (RPRG = 24kΩ)			60	80	µA
			Shutdown mode (RPRG = 24kΩ)				500	nA
ISINK		Current flowing from VOUT	Stand by mode (R	= 24kΩ)
			PRG				500	nA
			(VIN = 2.5V < VBATTERY)
	(1)		VOPRG at VIN		4.06	4.1	4.14	V
VOUT		Battery regulated voltage	VOPRG at GND		4.16	4.2	4.24	V
ICHG		Charge current	RPRG = 24kΩ		450	490	525	mA
			RPRG = 12kΩ		905	975	1045	mA
IPRECH		Pre-Charge current	IPRE floating		41	49	56	mA
		[default value = 10% ICHG]	RPRG = 24kΩ
IPRECH		Pre-Charge current	RPRE = 62kΩ to GND;		57	67	78	mA
			RPRG = 24kΩ
IPRECH		Pre-Charge current	RPRE = 39kΩ to VREF;		29.5	35	40.1	mA
			RPRG = 24kΩ
VPRETH		Pre-Charge voltage threshold	VPRE = VPRETHDefault = Floating		2.7	2.8	2.9	V
		[default]
VPRETH		Pre-Charge voltage threshold	RVPRE = 13kΩ; RPRG = 12kΩ		2.87	3.03	3.19	V
		Pre-Charge voltage threshold
VPRETH		[default]. Charge termination			2.7	2.8	2.9	V
		disabled
IENDTH		Termination current	REND = 3K3		12	16	20	mA
	(2)	Maximum charging time	CTPRG = 10nF			3		hours
TMAXCH			R[IPRG] = 24kΩ
TMAXCH		Maximum charging time accuracy	CTPRG = 5.6nF			10%
(2)			RPRG = 24kΩ
SDTH		Shutdown threshold high					2	V
		Shutdown threshold low			0.4			V
ST1,2		Output status sink current	Status on			10		mA
RDS(on)		Power MOSFET resistance	RDS(on)@ICHG = 500mA			280	380	mΩ

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L6924D			Electrical specifications
Table 5.	Electrical characteristics (continued)
Symbol	Parameter	Test condition	Min	Typ	Max	Unit
TH	NTC pin hot threshold voltage		10.625	12.5	14.375	%VREF
	NTC pin cold threshold voltage		45	50	55	%VREF

1.TJ from –40°C to 125°C.

2.Guaranteed by design.

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Block diagram	L6924D

5 Block diagram

Figure 4. Block diagram

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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 2.5 V) 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’s one (Chapter 7.4 on page 18). 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.

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 reaches the selected output voltage, the device starts to reduce the current, until the charge termination is done.

The full flexibility is provided by:

●Programmable pre-charging current and voltage thresholds (IPRETH and VPRETH) (Chapter 7.2 on page 17, Chapter 7.3 on page 17).

●Programmable fast-charging current (ICHG) (Chapter 7.4 on page 18).

●Programmable end of charge current threshold (IENDTH) (Chapter 7.5 on page 19).

●Programmable end of charge timer (TMAXCH) (Chapter 7.8 on page 20).

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 120°C, the thermal control loop starts working, and reduces the charging current, in order to keep the IC junction temperature at 120°C.

●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 µC 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 0.8 V, when I < IENDTH, the end of charge is notified by the status pin, but the charging process is not disabled. The charge process ends when the maximum charging time expires.

●If the voltage at VPRE pin false under 0.5 V 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 shows the real charging profile of a Li-Ion battery, with a fast charge current of 450 mA (RPRG = 26 kΩ),

Figure 5. Li-Ion charging profile

Charging profile

	0.500							4.500
	0.450							4.000
	0.400							3.500
	0.350						Ichg	3.000
	0.300						Vbatt
Ichg (A)								2.500	Vbatt (V)
	0.250
	0.200							2.000
	0.150							1.500
	0.100							1.000
	0.050							0.500
	0.000							0.000
	0	200	400	600	800	1000		1200

Charging time (sec)

6.1Linear 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 pre-charge phase takes place. The battery is pre-charged with a low current IPRE

(Chapter 7.2 on page 17).

When the battery voltage goes higher than VPRETH, the battery is charged with the fast charge current ICHG, set through an external resistor (Chapter 7.4 on page 18).

Finally, when the battery voltage is close to the regulated output voltage VOPRGTH (4.1 V or 4.2 V), the voltage regulation phase takes place and the charging current is reduced. The

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