Datasheet
6 Application information
The STBC08 uses an internal P-channel MOSFET to work in constant current and constant voltage method. It
provides up to 800 mA with a final regulated output voltage of 4.2 V ±1% in full temperature range. Neither
blocking diode nor sensing resistor are required. The USB port can be used as a power supply voltage.
6.1 Charge cycle
A charge cycle begins when the voltage at the V
CC
pin rises above UVLO threshold level, R
PROG
program
resistor of 1% is connected between PROG pin and GND pin and when a battery is connected to the charger
output. If the battery voltage is below 2.9 V, the charger enters trickle charge mode. In this condition, the device
supplies 1/10
th
of the programmed charge current to keep the battery voltage in a safe level otherwise the life of a
battery reduces. If BAT pin voltage is higher than 2.9 V the charger goes to constant current mode. When BAT pin
voltage is close to the final float voltage (4.2 V) the device goes to constant voltage mode and the charge current
begins decreasing. The charge cycle is over when the current drops 1/10
th
of the programmed value.
6.2
V
CC
pin
Input supply voltage is used to supply the device in the range from 4.25 V to 6.5 V voltage. A bypass capacitor of
1 µF is recommended. When V
CC
value drops below 30 mV of BAT pin voltage, the device goes to shutdown
mode, dropping I
BAT
less than 2 µA.
6.3 POWER ON pin
POWER ON pin is an open drain flag indicating V
CC
presence, V
UVLO
< V
CC
< 7.2 V and V
CC
> V
BAT
. While in
high impedance, it indicates that V
CC
< V
UVLO
, V
CC
> 7.2 V or V
CC
< V
BAT
. In high impedance status V
CC
does
not start the charge cycle.
6.4 CHRG pin
CHRG pin is an open drain flag indicating the status of the charge. When the pin is in low-state, the device
charges the battery. If the pin is in high impedance state the charge is over.
Table 5. Flag status values for CHRG pin
POWER ON CHRG Description
0 0
Pre-charge mode (trickle charge mode) or charge mode. V
CC
is higher than V
UVLO
and
R
PROG
is connected to PROG pin.
0
1
(1)
Standby mode (charge completed) or shutdown mode (R
PROG
not connected).
1
(1)
1
(1)
Supply is not sufficient.
1. Output pin in high impedance (external pull-up needed).
6.5 PROG pin
Charge current program, charge current monitor and shutdown pin. The charge current is programmed by
connecting a resistor of 1%, R
PROG
to ground. When the device charges in constant current, the voltage value of
this pin is 1.0 V. In other conditions, the voltage on this pin can measure the charge current thanks to the following
formula:
I
BAT
=
V
PROG
R
PROG
× 1000
(1)
PROG pin shuts down the device; disconnecting the program resistor from ground, the current of 1 µA flows to
pull PROG pin high.
If the value of this pin is 1.21 V (shutdown threshold voltage), the device enters shutdown mode and the input
supply current drops to 25 µA. Driving this pin to voltage beyond 2.4 V, a current of 35 µA flows to the device from
PROG pin.
STBC08
Application information
DS4901 - Rev 4
page 10/20