Overcurrent Protection Circuit
The overcurrent protection circuit functions when an overcurrent flows through the current detection resistor during the step-up operation and the voltage at the ISENSE pin rises over the set voltage value. When the overcurrent protection function works, the transistor drive pin SWO comes to the VSS level and the switching transistor is turned off. Since the overcurrent protection circuit links to the soft start circuit, it drops the voltage at the SSCAP pin to the VSS level during overcurrent detection. When the overcurrent detection is released, the voltage at the SSCAP pin rises slowly and the soft start operation starts.
Power lost at the current detection resistor becomes a factor of lower efficiency. When the overcurrent protection circuit is not necessary, short-circuit the ISENSE pin to the VSS pin. The ISENSE pin cannot be used in an open state.
Operation of Series Regulator
S1F71200 has a built-in series regulator control circuit. When driving the PNP transistor as an external part, S1F71200 reduces voltage supplied to the VDD2 pin and constitutes a series regulator. The VDD2 pin is generally connected to the VSW pin of step-up output.
This series regulator operates monitoring voltage at the VO pin of step-up/step-down output. It controls the drive current (base current of the PNP transistor) at the EXO pin to stabilize voltage at the VO pin.
Power Off Function
S1F71200 can control circuit operations according to external signal control. When the POFFX pin is set to the VSS level, all circuits stop and their powers are turned off. The current consumption at the power off state is less than 1μA. When the power is off, the SWO pin is set to the VDD level, the EXO pin is set to the VDD2 level and respective external transistors are turned.
The voltage at the SSCAP pin comes to the VSS level, and the soft start circuit controls the step-up operation output voltage is controlled with the soft start circuit after the power off state is released. The soft start circuit controls step-up operations after power off release. When being set to the VDD level, the POFFX pin operates in general. The POFFX pin cannot be used in an open state. When the power off function is not used, connect the POFFX pin to the VDD1 pin.
