The R1242 is 30V input voltage Synchronous type Step down CMOS DC/DC converter. It contains Nch high side Tr. (Typ. 100mΩ) to make a simple step down DC/DC to supply maximum 3A output current. In terms of Low side switch, to improve the efficiency, external FET can be set. The FET turns off when the R1242 is shut down.

The R1242 is composed with an oscillator, a PWM control circuit, a voltage reference unit, an error amplifier, a phase compensation circuit, a slope control circuit, a soft-start circuit, protection circuits, an internal regulator, a switch, and so on. A step-down DCDC converter can be composed with this IC, an inductor, resisters, an external MOSFET, capacitors. The R1242 operates with the current mode control type without the sense resistor and it realizes the fast transient response and high efficiency.

There are four types for the oscillator frequency. A/B version's frequency is adjustable in the range from 330kHz to 1000kHz, C/D version's frequency is fixed 330kHz, E/F version's one is fixed 500kHz, and G/H version's frequency is fixed 1000kHz. As a protection function, cycle by cycle current limit function limits maximum current into 4.5A . There are two types for short protection, A/C/E/G version has latch protection function with 5ms delay time and B/D/F/H version has foldback protection function with reducing oscillator frequency into 1/4 of the initial frequency