Datasheet

6.6 Programming charge current
R
PROG
resistor sets the charge current value. The battery charge current is 1000 times the PROG pin current
value. The program resistor and the charge current are calculated according to the following equation:
R
PROG
= 1000 ×
V
PROG
I
BAT
(2)
The charge current out of BAT pin can be monitored by PROG pin voltage as per below equation:
I
BAT
=
V
PROG
R
PROG
× 1000 (3)
6.7 BAT pin
The charge current output pin provides the battery with charge current and regulates the final float voltage to 4.2
V. An internal resistor is a feedback loop, which compares V
O
with the reference.
6.8 Charge termination
A charge cycle is terminated when the final float voltage is reached while the charge current falls 1/10
th
ofthe
programmed value. The charge is over when PROG pin voltage falls below 100 mV for a time longer than t
TERM
(~1 ms). The charge current is latched off, the device is in standby mode and the input supply current drops to
200 µA.
6.9 Soft-start
When a charge cycle starts, an internal soft-start circuit minimizes the inrush current. At starting phase, the
charge current ramps from zero to full scale in 100 µs.
6.10 Thermal regulation
An internal thermal feedback loop reduces the output current if the die temperature rises above a present value of
approximately 120 °C. This feature protects the device from the excessive temperature and allows the user to
push the limits of the power handling the capability of a given circuit board without damaging the device.
6.11 Power dissipation
A good thermal PC board layout should be used to maximize the available output current. The thermal path for
the heat generated by IC is from the die to the copper lead frame through the package leads and exposed pad to
the PC board copper.
The PC board copper is the heat sink. Footprint copper pads should be as wider as possible and expand out to
larger copper areas to spread and dissipate the heat to the surrounding ambient. Feed-through vias to inner or
backside copper layers are also useful to improve the overall thermal performance of the device. Other heat
sources on the board, not related to the device, have to be considered when a PC board layout is designed
because they affect the overall temperature rise and the maximum output current.
6.12
Stability considerations
The STBC08 contains two control loops: the constant voltage and the constant current. The constant voltage loop
is stable without any compensation when a battery is connected with low impedance leads. Excessive lead
length, however, may add enough parasitic series inductance to require 1 µF bypass capacitor from BAT to GND.
Furthermore, a 4.7 µF capacitor with a series resistor (0.2 Ω to 1 Ω) from BAT to GND is required to keep ripple
voltage low when the battery is disconnected.
STBC08
Programming charge current
DS4901 - Rev 4
page 11/20