The R1215D Series are CMOS-based PWM step-up DC/DC converter controllers with low supply current. Each of the R1215D Series consists of an oscillator, a PWM comparator circuit, a reference voltage unit, an error amplifier, a reference current unit, a protection circuit, and an under voltage lockout (UVLO) circuit. A low ripple, high efficiency step-up DC/DC converter can be composed of this IC with some external components, or an inductor, a diode, a power MOSFET, resisters, and capacitors. Maximum duty cycle and the soft start time are easily adjustable with external resistors and capacitors. As for the protection circuit, after the soft-starting time, if the maximum duty cycle is continued for a certain period, the R1215D Series latch the external driver with its off state, or the latch-type protection circuit works. The delay time for latch the state can be set with an external capacitor. To release the protection circuit, restart with power-on (Voltage supplier is equal or less than UVLO detector threshold level).