ST L6924U User Manual

L6924U

USB compatible battery charger system with integrated power switch for Li-Ion/Li-Polymer

Features

■Fully integrated solution, with power MOSFET, reverse blocking diode, sense resistor, and thermal protection

■Charges single-cell Li-Ion batteries from selectable AC adapter or USB input

■Programmable charge current up to 1 A in AC adapter mode

■ Programmable charging current in USB mode	VFQFPN16
for both high power and low power inputs

■4.2 V output voltage with ± 1 % accuracy

■Linear or quasi-pulse operating mode

■Closed loop thermal control

■Programmable end-of-charge current

■Programmable charge timer

■(NTC) or (PTC) thermistor interface for battery temperature monitoring and protection

■Status outputs to drive LEDs or to interface with a host processor

■Small VFQFPN 16-leads package (3 x 3 mm)

Applications

■PDAs, GPS and MP3 players

■USB powered devices

■Cellular phones

■Digital still cameras

■Standalone chargers

■Wireless appliances

Table 1.	Device summary
	Order codes	Package	Packaging
	L6924U013	VFQFPN16	Tube
	L6924U013TR		Tape and reel
September 2010		Doc ID 14716 Rev 2	1/37
			www.st.com

Contents	L6924U

Contents

1	Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 3
2	Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4
	2.1	Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
3	Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
4	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	Pre-charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	7.2	AC or USB mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	7.3	Fast charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	7.4	End-of-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
	7.5	Recharge flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
	7.6	Recharge threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20
	7.7	Maximum charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	20

8	Application information: monitoring and protection . . . . . . . . . . . . . .		22
	8.1	NTC thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
	8.2	Battery absence detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
	8.3	Status pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	27
	8.4	Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	27

9	Additional applications information . . . . . . . . . . . . . . . . . . . . . . . . . . .		28
	9.1	Selecting the input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28
	9.2	Selecting the output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28

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L6924U	Contents

9.3 Layout guidelines and demonstration board . . . . . . . . . . . . . . . . . . . . . . . 28

10 Application idea: dual input management with AC priority . . . . . . . . 31

11 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

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Description	L6924U

1 Description

The L6924U is a fully monolithic battery charger that safely charges single-cell LiIon/Polymer battery from either an USB power source or an AC adapter. In USB mode, the L6924U supports both low power and high power mode. Alternatively the device can charge from an AC wall adapter. The ideal solution for space-limited portable products integrates the power MOSFET, reverse blocking diode, sense resistor and thermal protection into a compact VFQFPN16 package. When an external voltage regulated adapter or USB port is used, the L6924U 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 2.5 V to 12 V and it allows the user to program many parameters, such as fast-charge current, end-of-charge current threshold, and charge timer. The L6924U 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 L6924U also provides other features like gas gauge function, check for battery presence, and monitors and protects the battery from unsafe thermal conditions.

Figure 1. Minimum size application board

Figure 2. Basic application schematic

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L6924U	Pin description

2 Pin description

Figure 3. Pin connection (top view)

2.1Pin description

Table 2.	Pin functions
Pin	I/O	Name	Pin description
1	I	VIN	Input pin of the power stage.
			Supply voltage pin of the signal circuitry.
2	I	VINSNS	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 7.7: Maximum charging time on
			page 21.
6	-	GND	Ground pin.
			Shutdown pin.
7	I	SD	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
8	I	TH	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.

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Pin description				L6924U
	Table 2.	Pin functions (continued)
	Pin	I/O	Name	Pin description
				Switches between high power USB (IUSB up to 500 mA) and low
	9	I	ISEL	power USB (IUSB/5) in USB mode. A low level sets the L6924U in
				low power mode and a high level sets the L6924U in high power
				mode. When the AC mode is selected, the ISEL pin must be
				connected to ground or left floating.
	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)
	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 sets the charge
	13	I/O	IEND	termination current threshold IENDTH: if ICHG < IENDTH, the charge
				process ends. The voltage across the resistor is proportional to the
				current delivered to the battery (gas gauge function).
				Selects pin AC adapter or USB port input modes. A high level sets
	14	I	MODE	the L6924U in USB mode while a low level sets the L6924U in the
				AC adapter mode. When the AC adapter input is selected, the ISEL
				pin status does not affect the current set.
				Charge current program pin in USB mode: a resistor connected
	15	I	IUSB	from this pin to ground sets the fast charge current value (IUSB up to
				500 mA) with an accuracy of 7 %. The USB high power/low power
				mode is selected with the ISEL pin.
				Charge current program pin in AC mode: a resistor connected from
	16	I	IAC	this pin to GND sets the fast charge current value (IAC up to 1 A)
				with an accuracy of 7 %.

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L6924U	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.

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
ISEL, MODE		Input voltage	-0.3 to 6	V
ST1, ST2		Output voltage	-0.3 to VIN	V
		Output current	30	mA
VREF, TH, IEND,
IAC, IUSB, TPRG,			-0.3 to 4	V
GND
		Maximum withstanding voltage range test condition:
All pins		CDFAEC-Q100-002- “human body model”	± 2	kV
		acceptance criteria: “normal performance’

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	0.67	W

1. Device mounted on demonstration board

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Electrical characteristics	L6924U

4 Electrical characteristics

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

	Table 5.		Electrical characteristics
	Symbol		Parameter	Test condition	Min.	Typ.	Max.	Unit
		(1)	Operating input voltage		2.5		12	V
		VIN	Start up threshold				4.1	V
		(1)		Charging mode (RPRG = 24 kΩ)		1.8	2.5	mA
		IIN	Supply current	Shutdown mode (RPRG = 24 kΩ)		60	80	µA
				Shutdown mode (RPRG = 24 kΩ)			500	nA
		ISINK	Current flowing from VOUT	Stand by mode (RPRG = 24 kΩ)			500	nA
				(VIN = 2.5 V < VBATTERY)
		(1)	Battery regulated voltage		4.16	4.2	4.24	V
	VOUT
		IAC	Charge current with AC	MODE at GND, RPRG = 24 kΩ	450	490	525	mA
			adapter input	MODE at GND, RPRG = 12 kΩ	905	975	1045	mA
				MODE at HIGH, ISEL at HIGH,	450	490	525
			Charge current with USB	RPRG-USB = 24 kΩ
		IUSB						mA
			input	MODE at HIGH, ISEL at LOW,	86	96	105
				RPRG-USB = 2 4 kΩ
		IPRE_AC	Pre-charge current with AC	MODE at GND,	41	49	56	mA
			input	RAC = 24 kΩ
			Pre-charge current with USB	MODE at HIGH, ISEL at HIGH	41	49	56	mA
			input (high power mode)	RUSB = 24 kΩ
	IPRE_USB
			Pre-charge current with USB	MODE at HIGH, ISEL at LOW	7.6	9.6	11.4	mA
			input (low power mode)	RUSB = 24 kΩ
		VPRETH	Pre-charge voltage threshold		2.9	3.0	3.1	V
		IENDTH	Termination current	REND = 3.3 kΩ	12	16	20	mA
	T	(2)	Maximum charging time	CTPRG = 10 nF		3		hours
		MAXCH		R[IPRG] = 24 kΩ
		(2)	Maximum charging time	CTPRG = 5.6n F		10		%
	TMAXCH		accuracy	RPRG = 24 kΩ
		SDTH	Shutdown threshold high				2	V
			Shutdown threshold low		0.4			V
		ST1,2	Output status sink current	Status on		10		mA
	MODETH		MODE threshold high				1.3	V
			MODE threshold low		0.4			V
		ISELTH	ISEL threshold high				1.3	V
			ISEL threshold low		0.4			V

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L6924U			Electrical characteristics
Table 5.	Electrical characteristics (continued)
Symbol	Parameter	Test condition	Min.	Typ.	Max.	Unit
RDS(on)	Power MOSFET resistance	Charge current = 500 mA		280	380	mΩ
	(3)
	NTC pin hot threshold		10	12.5	15	%VREF
TH	voltage
	NTC pin cold threshold		40	50	60	%VREF
	voltage

1.TJ from -40 °C to 125 °C

2.Guaranteed by design

3.Device working in quasi pulse mode

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Block diagram	L6924U

5 Block diagram

Figure 4. Block diagram

				Logic	Logic
				I FAULT	I DETECT
VIN
						VOUT
				POWER MOS
VINS	Logic	UVLO	BODY	Gas Gauge		IEND
				VDD
SD			CONTROL
		Logic		Mos		VOSNS
				Driver
	ANALOG	VDD	Logic
	PRE.					VREF
		VBG	Charge		4.2V
		BG		CA-VA-TA
	Logic		Control
				REG
ISEL				THERMAL
				CONTROL
MODE					VREF
IAC					VPRE
IUSB				LOGIC	VDD
	VREF
					NTC/PTC	TH
					MANAG.
				OSC	VDD
	TPRG	ST2	ST1	GND

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L6924U	Operation description

6 Operation description

The L6924U 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 or USB port.

However, thanks to its very low minimum input voltage (down to 2.5 V) the L6924U can also work as a quasi-pulse charger when powered from a current limited adapter. To work in this condition, it is enough to set the device’s charging current higher than the adapter’s one (Chapter 6.2: Quasi-pulse mode on page 14). 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 power source. However, the advantage of the quasi-pulse approach is that the power dissipated inside the portable equipment is dramatically reduced.

The L6924U 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 (internally set to 10 % of the fastcharge current).

●Fast-charge constant current: in this phase the device charges the battery with the maximum current (IAC for AC adapter mode, IUSB for USB mode).

●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 fast-charging current (IAC or IUSB) (Chapter 7.3 on page 18).

●Programmable end of charge current threshold (IENDTH) (Chapter 7.4 on page 20).

●Programmable end of charge timer (TMAXCH) (Chapter 7.7 on page 21).

If a PTC or NTC resistor is used, the device can monitor the battery temperature in order to protect the battery from operating under 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 microcontroller ADC.

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 on page 12 shows the real charging profile of a Li-Ion battery, with a fast charge current of 450 mA (R1 or R2 = 26 kΩ).

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Operation description	L6924U

Figure 5. Li-Ion charging profile

0.500							4.500
0.450							4.000
0.400							3.500
0.350						Ichg	3.000	Vbatt (V)
0.300						Vbatt
Ichg(A)							2.500
0.250
							2.000
0.200
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 L6924U. If the battery voltage is lower than the default pre-charge voltage (VPRETH), the pre-charge phase takes place. The battery is pre-charged with a low current, internally

set to 10 % of the fast charge current.

When the battery voltage goes higher than VPRETH, the battery is charged with the fast charge current (IUSB or IAC according to the selection of the MODE pin).

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

ends when the charging current reaches the programmed value (IENDTH) or when the charging timer expires.

Figure 6 shows the different phases.

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