Application information

STC4054

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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 0.2

Ω to 1Ω series resistor from BAT to GND is required to keep ripple

voltage low when the battery is disconnected.