Basic Knowledge of Voltage Regulator（3/4）
Protection Function/Power Saving Function
Over current Protection and Heat Protection
Since linear regulators are power ICs, they normally have some kinds of protection functions. Commonly used protections are current limiter circuits and foldback circuits for overcurrent protection, and thermal shutdown circuits for heat protection.
Graph 12 shows the operational characteristics example of a constant current limiter and a foldback circuit. When output current is going to get higher than 240mA, the constant current limiter operates and the output voltage descends almost vertically in the graph. As the descent continues, the foldback circuit operates and reduces the output current. Eventually the output current is decreased to 60mA, so the heat loss can be reduced as low as about 240mW in the case input voltage is 4.0V.
[Graph 12] Current Limit and Foldback Operation (XC6504x181)
Some of recent CMOS linear regulators can automatically discharge the charge remained in load capacitors, synchronizing the regulators’ ON/OFF switch. This power management function is often used to improve the efficiency of the batteries in portable electronic devices. Since each block discharges the charge remained in capacitors at the moment of power off, the time to wait discharging is shortened and thus it is easy to program ON/OFF sequence of each block. Graph 13 shows an output voltage waveform of the high-speed discharge, XC6221B series when the CE pin is OFF. You can see the remained charge in a load capacitor is discharged in high speed when the CE pin voltage reaches to 0V.
[Graph 13] High Speed Discharge Waveform (XC6221 Series)
Without high speed discharge
With High speed discharge