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IR3622MPBF

HIGH FREQUENCY 2-PHASE, SINGLE OR DUAL OUTPUT SYNCHRONOUS STEP DOWN CONTROLLER WITH OUTPUT TRACKING AND SEQUENCING

International Rectifier 

Circuit Description

THEORY OF OPERATION

Introduction

The IR3622 is a versatile device for high

performance buck converters. It consists of two

synchronous buck controllers which can be

operated either in two independent outputs mode

or in current share single output mode for high

current applications.

The timing of the IC is provided by an internal

oscillator circuit which generates two 180o-out-of-

phase clock signals that can be externally

programmed up to 600kHz per phase.

Under-Voltage Lockout

The under-voltage lockout circuit monitors four

signals (Vcc, VcH1, VcH2 and Enable). This

ensures the correct operation of the converter

during power up and power down sequence. The

driver outputs remain in the off state whenever

one of these signals drop below set thresholds.

Normal operation resumes once these signals

rise above the set values. Figure 3 shows a

typical start up sequence.

IR3622MPbF

Programmable Enable Input

The enable features another level of flexibility for

start up. The Enable has precise threshold which

is internally monitored by under-voltage lockout

circuit.

It’s threshold can be externally programmed to

desired level by using two external resistors, so

the converter doesn’t start up until the input

voltage is sufficiently high (see figure 3).

11V

7.2V

12V

12V

Vbus

Vcc

Vout3

Seq

Enable

SS

7.2V

Enable OK (IC's POR)

3V

Fig. 3: Normal Start up, Enable threshold is externally set to 11V

Seq pin is pulled to Vout3 prior to start up

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