LDO Regulator Application Note

Various protection circuits are built into Ricoh regulators.

The Constant Slope Circuit

RP110x25xB/D Inrush Current Characteristics

Some products have a Constant Slope Circuit which prevents the overshoot of the output voltage.
The constant slope is a kind of soft-start circuit which allows the output voltage to start up gradually. The capacitor to create the start-up slope is built-in the IC that doesn't require any external components. The start-up time and start-up slope angle are fixed inside the IC.
If the capacitance of the external output capacitor is above a certain capacitance, the output current limit circuit minimizes the incoming current of the output capacitor at the start-up. As a result, the start-up time becomes longer and the start-up slope angle becomes less steep.

See "Inrush Current Characteristics Example of RP110x25xB/D" on the right, if the output capacitor is less than 4.7µF, the Constant Slope Circuit operates during start-up, likewise, if the output capacitor is over 10µF, the output current limit circuit operates during the start-up. The boundary point of using these two circuits is inversely proportional to the output voltage. If the output voltage is higher, the output current limit circuit operates even if the output capacitor capacitance is small. The boundary points varies with each products.

Products with Constant Slope Circuit

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