ST L6924D User Manual

Battery charger system with integrated

Features

■ Fully integrated solution, with a power

MOSFET, reverse blocking diode, sense
resistor, and thermal protection

■ Ideal for coke and graphite anode single-cell L

I

packs

ON

■ Both linear and quasi-pulse operation

■ Closed loop thermal control

■ USB BUS-compatible

■ 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)

L6924D

power switch for Li-Ion/Li-Polymer

-

I

VFQFPN16

Applications

■ PDAs

■ Handheld devices

■ Cellular phones

■ Digital cameras

■ Standalone chargers

■ USB-powered chargers

Table 1. Device summary

Order code Package Packaging

L6924D

VFQFPN16

L6924D013TR Tape and reel

September 2010 Doc ID 11908 Rev 9 1/38

Tube

www.st.com

38

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

Doc ID 11908 Rev 9 3/38

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

4/38 Doc ID 11908 Rev 9

L6924D Pins description and connection diagrams

2 Pins description and connection diagrams

Figure 3. Pins connection (top view)

I

PRG

V

PRE

V

V

INSNS

IN

I

PRE

ST2

ST1

T

PRG

GND SD

2.1 Pin description

Table 2. Pin functions

Pin I/O Name Pin description

1I V

2IV

3-4 O ST

5IT

6 - GND Ground pin.

7I SD

8I TH

9IV

10 I V

11 O V

INSNS

OPRG

OSNS

Input pin of the power stage.

IN

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.

-ST1Open-collector status pins.

2

Maximum charging time program pin.
It must be connected with a capacitor to GND to fix the maximum charging time, see

PRG

Chapter 7.8: Maximum charging time on page 20

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 23.

Output voltage selection pin.
V

= 4.1 V if left floating. V

OUT

Output voltage sense pin.
It senses the battery voltage to control the voltage regulation loop.

Output pin. (connected to the battery)

OUT

= 4.2 V if connected to GND.

OUT

I

I

END

END

TH

V

REF

V

OUT

V

V

OSNS

OSNS

V

OPRG

Doc ID 11908 Rev 9 5/38

Pins description and connection diagrams L6924D

Table 2. Pin functions

12 O V

13 I/O I

14 I V

15 I I

16 I I

External reference voltage pin.(reference voltage is 1.8 V±2%)

REF

Charge termination pin.
A resistor connected from this pin to GND fixes the charge termination current threshold

END

I

ENDTH

: if I < I

, the charger behaves according to the V

ENDTH

status (see Chapter 7.5:

PRE

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

PRETH

.

= 2.8 V. If the voltage on V

PRETH

goes lower than 0.5 V (edge sensitive), the maximum charging time is

PRE

pin is lower than 0.8 V, V

PRE

ENDTH

.

V
If the pin is floating, V

PRE

2.8 V and the charge is not automatically terminated when I < I
If the voltage on V

reset.

Charge current program pin.
A resistor connected from this pin to GND, fixes the fast charge current value (I

PRG

accuracy of 7%.

Pre-charge current program pin.
If the pin is floating I

PRE

different value, the pin has to be connected to GND or V

is equal to 10% of I

PRETH

CHG

. If I

has to be programmed at a

PRETH

,

through a resistor see

REF

Chapter 7.2: Pre-charge current on page 17.

CHG

=

PRETH

), with an

6/38 Doc ID 11908 Rev 9

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.

3.1 Absolute maximum ratings

Table 3. Absolute maximum ratings

Symbol Parameter Value Unit

V

IN

, SD Input voltage –0.3 to V

V

INSNS

V

, V

OUT

OSNS

ST1, ST2

V

REF

V

PRE

, TH, I

, I

T

PRG

PRE

END

, V

, GND

, I

PRG

OPRG

ST1 and TH pins Maximum withstanding voltage range test condition:

Other pins ±2 kV

3.2 Thermal data

Table 4. Thermal data

Symbol Parameter Value Unit

R

thJA

T

STG

T

J

P

TOT

1. Device mounted on demonstration board

Input voltage –0.3 to 16 V

IN

Output voltage –0.3 to 5 V

Output voltage –0.3 to 6 V

Output current 30 mA

,

,

–0.3 to 4 V

±1.5 kV
CDFAEC-Q100-002 (Normal “human body model”
acceptance criteria performance)

Thermal resistance junction to ambient

(1)

75 °C/W

Storage temperature range –55 to 150 °C

Junction temperature range –40 to 125 °C

Power dissipation at T= 70 °C TBD W

V

Doc ID 11908 Rev 9 7/38

Electrical specifications L6924D

4 Electrical specifications

4.1 Electrical characteristics

TJ = 25 °C, V

Table 5. Electrical characteristics

= 5 V, unless otherwise specified.

IN

Symbol Parameter Test condition Min Typ Max Unit

Operating input voltage 2.5 12 V

(1)

V

IN

I

IN

I

SINK

V

OUT

I

CHG

I

PRECH

I

PRECH

I

PRECH

V

PRETH

V

PRETH

Start up threshold 4.1 V

(1)

Supply current

Current flowing from V

(1)

Battery regulated voltage

OUT

Charge current

Pre-Charge current
[default value = 10% I

CHG

Pre-Charge current

Pre-Charge current

Pre-Charge voltage threshold
[default]

Pre-Charge voltage threshold R

Charging mode (R

Shutdown mode (R

Shutdown mode (R

Stand by mode (R

= 2.5V < V

(V

IN

V

at V

OPRG

V

OPRG

R

PRG

R

PRG

I

PRE

]

R

PRG

R

PRE

R

PRG

R

PRE

R

PRG

V

PRE

VPRE

IN

at GND 4.16 4.2 4.24 V

= 24kΩ 450 490 525 mA

= 12kΩ 905 975 1045 mA

floating

= 24kΩ

= 62kΩ to GND;

= 24kΩ

= 39kΩ to V

= 24kΩ

= V

PRETHDefault

= 13kΩ; R

= 24kΩ)1.82.5mA

PRG

= 24kΩ)6080µA

PRG

= 24kΩ)500nA

PRG

= 24kΩ)

PRG

BATTERY

)

4.06 4.1 4.14 V

41 49 56 mA

57 67 78 mA

;

REF

29.5 35 40.1 mA

= Floating 2.7 2.8 2.9 V

= 12kΩ 2.87 3.03 3.19 V

PRG

500 nA

Pre-Charge voltage threshold

V

PRETH

[default]. Charge termination

2.7 2.8 2.9 V

disabled

I

ENDTH

T

MAXCH

T

MAXCH

(2)

Termination current R

(2)

Maximum charging time

Maximum charging time accuracy

= 3K3 12 16 20 mA

END

C

= 10nF

TPRG

R[I

C

TPRG

R

PRG

PRG

= 24kΩ

] = 24kΩ

= 5.6nF

3 hours

10%

Shutdown threshold high 2 V

SD

TH

Shutdown threshold low 0.4 V

ST1,2 Output status sink current Status on 10 mA

R

DS(on)

Power MOSFET resistance R

DS(on)@ICHG

= 500mA 280 380 mΩ

8/38 Doc ID 11908 Rev 9

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 %V

NTC pin cold threshold voltage 45 50 55 %V

1. TJ from –40°C to 125°C.

2. Guaranteed by design.

REF

REF

Doc ID 11908 Rev 9 9/38

Block diagram L6924D

5 Block diagram

Figure 4. Block diagram

10/38 Doc ID 11908 Rev 9

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 (I

PRETH

and V

PRETH

)

(Chapter 7.2 on page 17, Chapter 7.3 on page 17).

● Programmable fast-charging current (I

● Programmable end of charge current threshold (I

● Programmable end of charge timer (T

) (Chapter 7.4 on page 18).

CHG

) (Chapter 7.5 on page 19).

ENDTH

) (Chapter 7.8 on page 20).

MAXCH

If the full flexibility is not required and a smaller number of external components is preferred,
default values of I

● If a PTC or NTC resistor is used, the device can monitor the battery temperature in

PRETH

and V

are available leaving the respective pins floating.

PRETH

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 I

and GND gives information about

END

the actual charging current (working as a Gas Gauge), and it can be easily fed into a µC
ADC.

Doc ID 11908 Rev 9 11/38

Operation description L6924D

When the V

pin is not used to program the Pre-Charge voltage threshold, it has two

PRE

different functions:

● If the voltage across V

pin is lower than 0.8 V, when I < I

PRE

, the end of charge is

ENDTH

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 V

pin false under 0.5 V the timer is reset on the falling edge.

PRE

Battery disconnection control is provided thanks to the differentiated sensing and forcing
output pins. A small current is sunk and forced through V

OUT

. If V

doesn’t detect the

OSNS

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 (R

PRG

= 26 kΩ),

Figure 5. Li-Ion charging profile

Charging profile

Ich g

Vb a tt

4.500

4.000

3.500

3.000

2.500

2.000

1.500

1.000

0.500

0.000

0.500

0.450

0.400

0.350

0.300

0.250

Ichg (A )

0.200

0.150

0.100

0.050

0.000

0 200 400 600 800 1000 1200

Charging time (sec)

Vbatt (V)

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).

V

is the output voltage of the upstream AC-DC adapter that is, in turn, the input voltage

ADP

of the L6924D. If the battery voltage is lower than a set pre-charge voltage (V
pre-charge phase takes place. The battery is pre-charged with a low current I
(Chapter 7.2 on page 17).

When the battery voltage goes higher than V
charge current I

, set through an external resistor (Chapter 7.4 on page 18).

CHG

Finally, when the battery voltage is close to the regulated output voltage V

4.2 V), the voltage regulation phase takes place and the charging current is reduced. The

12/38 Doc ID 11908 Rev 9

PRETH

), the

PRETH

PRE

, the battery is charged with the fast

OPRGTH

(4.1 V or