R1234D SERIES

PWM/VFM Step-Down DC/DC CONVERTER with Synchronous Rectifier

NO.EA-137-070221

1

OUTLINE

The R1234D Series are CMOS-based PWM step-down DC/DC Converters with synchronous rectifier, low

supply current.

Each of these ICs consists of an oscillator, a PWM 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/VFM

alternative circuit, a chip enable circuit, and a driver transistor. A low ripple, 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. (As for R1234D001C/D types, divider resistors are also necessary.) In terms of Output Voltage, it is

fixed internally in the R1234Dxx1A/B types. While in the R1234D001C/D types, Output Voltage is adjustable with

external divider resistors.

PWM/VFM alternative circuit is active with Mode Pin of the R1234D Series. Thus, when the load current is

small, the operation can be switching into the VFM operation from PWM operation by the logic of MODE pin and

the efficiency at small load current can be improved. As protection circuits, Current Limit circuit which limits peak

current of Lx at each clock cycle, and Latch type protection circuit which works if the term of Over-current

condition keeps on a certain time in PWM mode exist. Latch-type protection circuit works to latch an internal

driver 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 or make the supply voltage at UVLO detector threshold level or

lower than UVLO.

FEATURES

• Supply Current ..................................................Typ. 230µA (R1234Dxx1A/C)

Typ. 250

µA (R1234Dxx1B/D)

• Standby Current ................................................Typ. 0µA

• Input Voltage Range ........................................ 2.4V to 5.5V (ABSOLUTE MAXIMUM : 6.5V)

• Output Voltage Range.......................................2.2V to 3.3V (R1234Dxx1A/B)

• Output Voltage Accuracy...................................±2.0% (R1234DxxA/B)

• Oscillator Frequency .........................................Typ. 500kHz (R1234Dxx1A/C)

Typ. 800kHz (R1234Dxx1B/D)

• Control mode switch .........................................MODE pin=”L”: PWN

MODE pin

=”H”: VFM

• Efficiency...........................................................Typ. 90%

• Package ............................................................SON-8

• Built-in Soft-start Function.................................Typ. 1.5ms

• Latch-type Protection Function .........................Typ. 1.5ms

• Built-in Current Limit Circuit

APPLICATIONS

• Power source for portable equipment.