R1221N Series

The R1221N series are PWM step-down DC/DC converter controllers embedded with a voltage detector, with low supply current by CMOS process.

Each step-down DC/DC converter in these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable circuit, and resistors for voltage detection. A low ripple, high efficiency step-down DC/DC converter can be composed of this IC with only four external components, or a power-transistor, an inductor, a diode and a capacitor. The output voltage of DC/DC converter can be supervised by the built-in voltage detector.

With a PWM/VFM alternative circuit, when the load current is small, the operation turns into the VFM oscillator from PWM oscillator automatically, therefore the efficiency at small load current is improved. And the PWM/VFM alternative circuit is an option, in terms of C version and D version, the circuit is not included.

If the term of maximum duty cycle keeps on a certain time, the embedded protection circuit works. There are two types of protection function. One is latch-type protection circuit, and it works to latch an external Power MOS with keeping it disable. To release the condition of protection, after disable this IC with a chip enable circuit, enable it again, or restart this IC with power-on. The other is Reset-type protection circuit, and it works to restart the operation with soft-start and repeat this operation until maximum duty cycle condition is released. Either of these protection circuits can be designated by users’ request.