STC4054 Datasheet, PDF (12/17 Pages) STMicroelectronics – 800mA Standalone linear Li-Ion Battery charger with thermal regulation

Application information
STC4054
6.11
Thermal regulation
An internal thermal feedback loop reduces the output current if the die temperature attempts
to rise above a present value of approximately 120°C. This feature protects the device from
excessive temperature and allows the user to push the limits of the power handling
capability of a given circuit board without risk of damaging the device.
6.12
Power dissipation
It is very important to use a good thermal PC board layout to maximize the available output
current. The thermal path for the heat generated by the 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. The footprint copper pads should be as wide 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 in improving
the overall thermal performance of the device. Other heat sources on the board, not related
to the device, must also be considered when designing a PC board layout because they will
affect overall temperature rise and the maximum output current.
6.13
Stability considerations
The STC4054 contains two control loops: constant voltage and 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 series inductance
to require a bypass capacitor of at least 1µF from BAT to GND. Furthermore, a 4.7µF
capacitor with a 0.2Ω to 1Ω series resistor from BAT to GND is required to keep ripple
voltage low when the battery is disconnected.
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