ST L6924U User Manual
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
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)
L6924U
VFQFPN16
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
L6924U013TR Tape and reel
September 2010 Doc ID 14716 Rev 2 1/37
Tube
www.st.com
37
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
Doc ID 14716 Rev 2 3/37
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)
2.1 Pin description
Table 2. Pin functions
Pin I/O Name Pin description
1IV
2IV
3 - 4 O ST
5IT
6 - GND Ground pin.
7ISD
8ITH
Input pin of the power stage.
IN
Supply voltage pin of the signal circuitry.
INSNS
2
PRG
The operating input voltage ranges from 2.5 V to 12 V, and the
start-up threshold is 4 V.
-ST1Open-collector status pins.
Maximum charging time program pin.
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.
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.
Doc ID 14716 Rev 2 5/37
Pin description L6924U
Table 2. Pin functions (continued)
Pin I/O Name Pin description
9 I ISEL
10 I V
11 O V
12 O V
13 I/O I
OSNS
OUT
REF
END
14 I MODE
15 I I
16 I I
USB
AC
Switches between high power USB (I
power USB (I
) in USB mode. A low level sets the L6924U in
USB/5
up to 500 mA) and low
USB
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.
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 1.8 V ± 2 %)
Charge termination pin.
A resistor connected from this pin to GND sets the charge
termination current threshold I
ENDTH
: if I
CHG
< I
ENDTH
, 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
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
from this pin to ground sets the fast charge current value (I
USB
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
this pin to GND sets the fast charge current value (IAC up to 1 A)
with an accuracy of 7 %.
6/37 Doc ID 14716 Rev 2
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
V
V
V
IN
, SD Input voltage -0.3 to V
INSNS
, V
OUT
OSNS
Input voltage -0.3 to 16 V
IN
Output voltage -0.3 to 5 V
ISEL, MODE Input voltage -0.3 to 6 V
ST1, ST2 Output voltage -0.3 to V
IN
Output current 30 mA
V
REF
IAC, I
, TH, I
USB, TPRG
END
,
,
-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
thJA
T
STG
T
J
P
TOT
1. Device mounted on demonstration board
Thermal resistance junction to ambient
Storage temperature range - 55 to 150 °C
Junction temperature range - 40 to 125 °C
Power dissipation at T = 70 °C 0.67 W
(1)
75 °C/W
V
V
Doc ID 14716 Rev 2 7/37
Electrical characteristics L6924U
4 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)
VIN
Start up threshold 4.1 V
IIN
I
SINK
V
OUT
I
AC
I
USB
I
PRE_AC
I
PRE_USB
V
PRETH
I
ENDTH
T
MAXCH
T
MAXCH
(1)
Supply current
Charging mode (R
Shutdown mode (R
Shutdown mode (R
Current flowing from V
OUT
Stand by mode (R
(VIN = 2.5 V < V
(1)
Battery regulated voltage 4.16 4.2 4.24 V
Charge current with AC
adapter input
MODE at GND, R
MODE at GND, R
MODE at HIGH, ISEL at HIGH,
Charge current with USB
input
Pre-charge current with AC
input
Pre-charge current with USB
input (high power mode)
Pre-charge current with USB
input (low power mode)
R
PRG-USB
MODE at HIGH, ISEL at LOW,
R
PRG-USB
MODE at GND,
R
AC
MODE at HIGH, ISEL at HIGH
R
USB
MODE at HIGH, ISEL at LOW
R
USB
= 24 kΩ
= 2 4 kΩ
= 24 kΩ
= 24 kΩ
= 24 kΩ
Pre-charge voltage threshold 2.9 3.0 3.1 V
Termination current R
(2)
Maximum charging time
Maximum charging time
(2)
accuracy
= 3.3 kΩ 12 16 20 mA
END
C
= 10 nF
TPRG
R[I
] = 24 kΩ
PRG
C
= 5.6n F
TPRG
= 24 kΩ
R
PRG
= 24 kΩ)1.82.5mA
PRG
= 24 kΩ)6080µA
PRG
= 24 kΩ)500nA
PRG
= 24 kΩ)
PRG
BATTERY
)
= 24 kΩ 450 490 525 mA
PRG
= 12 kΩ 905 975 1045 mA
PRG
500 nA
450 490 525
86 96 105
41 49 56 mA
41 49 56 mA
7.6 9.6 11.4 mA
3 hours
10 %
Shutdown threshold high 2 V
SD
TH
Shutdown threshold low 0.4 V
mA
ST1,2 Output status sink current Status on 10 mA
MODE threshold high 1.3 V
MODE
TH
MODE threshold low 0.4 V
ISEL threshold high 1.3 V
ISEL
TH
ISEL threshold low 0.4 V
8/37 Doc ID 14716 Rev 2
L6924U Electrical characteristics
Table 5. Electrical characteristics (continued)
Symbol Parameter Test condition Min. Typ. Max. Unit
R
DS(on)
Power MOSFET resistance
(3)
Charge current = 500 mA 280 380 mΩ
NTC pin hot threshold
voltage
TH
NTC pin cold threshold
voltage
1. TJ from -40 °C to 125 °C
2. Guaranteed by design
3. Device working in quasi pulse mode
10 12.5 15 %V
40 50 60 %V
REF
REF
Doc ID 14716 Rev 2 9/37
Block diagram L6924U
5 Block diagram
Figure 4. Block diagram
VINS
ISEL
MODE
IAC
IUSB
Logic
VIN
Logic
SD
ANALOG
PRE.
Logic
UVLO
Logic
BG
VDD
VBG
BODY
CONTROL
Logic
Charge
Control
POWER MOS
VDD
Mos
Driver
THERMAL
CONTROL
I FAULT I DETECT
Gas Gauge
CA-VA-TA
REG
VREF
VPRE
LOGIC
VREF
OSC
ST2TPRG
ST1
GND
VDD
VDD
NTC/PTC
MANAG.
Logic
VOUT
IEND
VOSNS
VREF
4.2V
TH
10/37 Doc ID 14716 Rev 2
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 (I
● Constant voltage: when the battery voltage reaches the selected output voltage, the
device starts to reduce the current, until the charge termination is done.
for AC adapter mode, I
AC
for USB mode).
USB
The full flexibility is provided by:
● Programmable fast-charging current (I
● Programmable end of charge current threshold (I
● Programmable end of charge timer (T
or I
AC
MAXCH
) (Chapter 7.3 on page 18).
USB
) (Chapter 7.4 on page 20).
ENDTH
) (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 I
and GND gives information about the
END
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 V
OUT
. If V
doesn’t detect the
OSNS
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 (R
or R2 = 26 kΩ).
1
Doc ID 14716 Rev 2 11/37
Operation description L6924U
Figure 5. Li-Ion charging profile
0.500
4.500
0.450
0.400
0.350
0.300
Ichg (A)
0.250
0.200
0.150
0.100
0.050
0.000
0 200 400 600 800 1000 1200
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).
Charging time (sec )
Ichg
Vbatt
4.000
3.500
3.000
2.500
2.000
1.500
1.000
0.500
0.000
Vbatt (V)
V
is the output voltage of the upstream AC-DC adapter that is, in turn, the input voltage
ADP
of the L6924U. If the battery voltage is lower than the default pre-charge voltage (V
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 V
charge current (I
or IAC according to the selection of the MODE pin).
USB
PRETH
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 (I
charging timer expires.
Figure 6 shows the different phases.
12/37 Doc ID 14716 Rev 2
PRETH
, the battery is charged with the fast
) or when the
ENDTH
),
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