The RP904 series are CMOS-based PWM/PFM step-down DC/DC Converters with synchronous rectifier, low supply current and through mode.
DC/DC converter of the RP904X consists of an oscillator, a PWM/PFM control circuit, a reference voltage unit, an error amplifier, a soft-start circuit, protection circuits, a protection against miss operation under low voltage (UVLO), PWM-DC to DC converter or bypass switch alternative circuit, a chip enable circuit, and a driver transistor. A high efficiency step-down DC/DC converter can be easily composed of this IC with only a few kinds of external components, or an inductor and capacitors.
The output voltage of the DC/DC converter has two kinds of output voltage, and alternative with the VSEL pin.
The RP904 series are PWM/PFM step-down DC/DC converter, thus, when the load current is small, the operation can be switching into the PFM operation from PWM control if the user chooses the VFM mode. As protection circuits, the current limit circuit which limits peak current of Lx at each clock cycle, and the latch type protection circuit which works if the term of the over-current condition keeps on a certain time in PWM mode.
Latch-type protection circuit works to latch an internal driver with keeping it disable. To release the protection, after disable 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 than UVLO.
The RP904 has also a bypass switch between VDD and VOUT.