Application information

STC4054

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6

Application information

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

required. It is also possible to use an USB port as power supply voltage.

6.1

Charge cycle

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

Input Supply Voltage. This pin is used to supplie the device in the range from 4.25V to 6.5V

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

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:

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.