LDO Regulator Application Note
Various protection circuits are built into Ricoh regulators.
The Inrush Current Preventing Circuit
At the start-up of a regulator, a large current flows until the output capacitor is charged up to the set output voltage if the regulator does not have an inrush current protection circuit or soft-start circuit. When the inrush current is large, the input voltage of a regulator may be unstable. If there is a large input voltage drop, the operation of another connected device may be affected.
Ricoh provides two kinds of Inrush Current Protection Circuits, and both have different features.
|Control Method||Start up Time|
|Inrush Current Limit Circuit||Limiting with constant current.||When COUT is small, it is possible to start up quickly compared with a constant slope circuit.|
|Constant Slope Circuit||Limiting with constant time, so-called Soft Start Function.||Start-up time is fixed in the IC and start-up time does not change by the capacitance of COUT.|
RP115x have build-in both the inrush current protection circuit and the constant slope circuit, and switches the circuits according to the capacitance of COUT. Please refer to a datasheet for details.