LDO Regulator Application Note

Various protection circuits are built into Ricoh regulators.

The Inrush Current Limit Circuit

Inrush Current Limit Circuit has a function that limits the output current for a fixed period of time to reduce the inrush current at the start-up and prevents the fluctuation of the input voltage.

The volume of inrush current will affected by the capacitance of the output capacitor.
The time of the inrush current become longer when the output capacitor is large. A sufficient effect of inrush current limitation might not be achieved when the output capacitor is large.

If you need to limit the inrush current completely in case of using the large output capacitor, Ricoh recommends the product equipped with an Adjustable Inrush Current Limit Time Function.
The inrush current limit circuit of the R1190x Series and RP132x Series has a DELAY pin and it is possible to adjust the time of the inrush current limitation by connecting a capacitor to the DELAY pin.

Imaginary graph

Products with Inrush Current Limit Circuit
  • *1) Inrush Current Limit Time can be adjusted by external capacitor.
  • *2) The RP115x prevents the inrush current by the constant current limit circuit during the starting up operation.

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