STC4054 Datasheet, PDF (10/17 Pages) STMicroelectronics – 800mA Standalone linear Li-Ion Battery charger with thermal regulation

Application information
6
Application information
STC4054
The STC4054 uses an internal P-Channel MOSFET to work in constant current and
constant voltage method. It is able to provide up to 800mA with a final regulated output
voltage of 4.2V ± 1% in full temperature range. No blocking diode and sensing resistor are
required. It is also possible to use an USB port as power supply voltage.
6.1
Charge cycle
A charge cycle begins when the voltage at the V_CC pin rises above the UVLO threshold
level, the R_PROG program resistor of 1% is connected between the PROG pin to GND pin
and when a battery is connected to the charger output. If the battery voltage is below 2.9V,
the charger enters in Trickle Charge mode. In this condition, the device supplies 1/10 of the
programmed charge current to bring the battery voltage up to safe level otherwise the life of
a battery is reduced. If the BAT pin voltage is higher than 2.9V the charger enters in
Constant Current Mode. When the BAT pin voltage is close to the final float voltage (4.2V)
the device enters in Constant Voltage Mode and the charge current begins to decrease. The
charge cycle is terminated when the current drops to 1/10 of the programmed value.
6.2
V_CC Pin
Input Supply Voltage. This pin is used to supplie the device in the range from 4.25V to 6.5V
voltage. A bypass capacitor of 1µF is recommended for use. When V_CC value drops of
30mV of the BAT pin voltage, the device enters in Shutdown Mode, dropping I_BAT to less
than 2µA.
6.3
CHRG pin
This is a flag open drain. It indicates three different status of the output. When the charge is
in progress this pin is pulled low instead at the end of the charge cycle, a weak pull down of
approximately 20µA is connected to the CHRG pin, indicating a present supply power; if the
flag is forced high impedance an under voltage condition is detected.
6.4
PROG pin
Charge Current Program, Charge Current Monitor and Shutdown Pin. The charge current is
programmed by connecting a 1% resistor, R_PROG, to ground. When the device is charging in
constant current, the value of voltage on this pin is 1.0V. In other conditions, the voltage on
this pin can be used to measure the charge current using the following formula:
I_BAT = (V_PROG/R_PROG)*1000
The PROG pin is used to shut down the device, disconnecting the program resistor from
ground a 1µA current flows to pull the PROG pin high. If the value of this Pin is 1.21V
(shutdown threshold voltage), the device enters Shutdown mode and the input supply
current drops to 25µA. Driving this pin to voltage beyond 2.4V a current of 35µA flows into
the device from PROG pin.
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