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Número de pieza | L6924U | |
Descripción | USB compatible battery charger system | |
Fabricantes | STMicroelectronics | |
Logotipo | ||
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No Preview Available ! 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
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
VFQFPN16
Table 1. Device summary
Order codes
L6924U013
L6924U013TR
September 2010
Package
VFQFPN16
Doc ID 14716 Rev 2
Packaging
Tube
Tape and reel
1/37
www.st.com
37
1 page L6924U
2 Pin description
Figure 3. Pin connection (top view)
Pin description
2.1
Pin description
Table 2.
Pin
1
2
3-4
5
6
7
8
Pin functions
I/O Name
Pin description
I VIN Input pin of the power stage.
Supply voltage pin of the signal circuitry.
I VINSNS The operating input voltage ranges from 2.5 V to 12 V, and the
start-up threshold is 4 V.
O ST2-ST1 Open-collector status pins.
Maximum charging time program pin.
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.
- GND Ground pin.
Shutdown pin.
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
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.
Doc ID 14716 Rev 2
5/37
5 Page L6924U
6 Operation description
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 fast-
charge 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).
Doc ID 14716 Rev 2
11/37
11 Page |
Páginas | Total 37 Páginas | |
PDF Descargar | [ Datasheet L6924U.PDF ] |
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