The RP901K is CMOS based PWM step-down DC/DC converter combined with a 600mA LDO and a voltage detector (VD), with low supply current.
Because ofDFN( PLP)2527-10 package, high density mounting on boards is possible.

Step-down DC/DC converter
This portion consists of an oscillator, a switching control circuit, a reference voltage unit, an error amplifier, a soft-start circuit, current protection circuits, UVLO circuit, switching transistors and so on.
Because of synchronous rectifier type, a low ripple and high efficiency DC/DC converter can be easily composed of this IC with an inductor and capacitors only.
Mode alternative circuit works automatically for improving the efficiency at light load.
As protection circuits, the current limit circuit which limits peak current of Lx at each clock cycle, and latch type protection circuit which works if term of the over-current keeps on a certain time exists. The latch-type protection circuit works to latch an internal driver with keeping it disable. (LDO and VD keep working.)
In order to release the condition of the protection, after disabling this IC with a chip enable circuit, enable it again, or restart this IC with power-on or make the supply voltage at UVLO detector threshold level or lower.
The output voltage is internally fixed with +/-2% tolerance.

LDO
This portion consists of a reference voltage unit, an error amplifier, a short current protection circuit and so on.
The output voltage is internally fixed with +/-1% tolerance

VD
The input voltage is monitored by VD with Nch open drain output.
Power-on reset delay time is also included and internally set typically at 50ms.