FEATURES

• 92 primary/secondary duty cycle

• 135 °C over temperature protection

• Compatible with ETSI 300 132-2

• 28 V to 75 V input voltage range

• Integrated ± 1 A half bridge primary drivers

• Secondary synchronous rectifier control signals with

programmable deadtime delay

• Voltage mode control

• Voltage feedforward compensation

• High voltage pre-regulator operates during start-up

• Current sensing on low-side primary device

• Frequency foldback eliminates constant current tail

• Advanced maximum current control during start-up and

shorted load

• Low input voltage detection

• Programmable soft-start function

APPLICATIONS

• Network cards

• Power supply modules

• Distributed power systems

• Intermediate bus converter

• Brick converter

DESCRIPTION

Si9122E is a half-bridge controller IC ideally suited to fixed

telecom applications where high efficiency is required at low

output voltages (e.g. < 3.3 V). Designed to operate within the

fixed telecom voltage range of 36 V to 75 V, the IC is capable

of controlling and driving both the low and high-side switching

devices of a half bridge circuit and also controlling the

switching devices on the secondary side of the bridge. Due

to the very low on-resistance of the secondary MOSFETs, a

significant increase in conversion efficiency can be achieved

as compared with conventional Schottky diodes. Control of

the secondary devices is by means of a pulse transformer

and a pair of inverters. Such a system has efficiencies well in

excess of 90 even for low output voltages.

On-chip control of the dead time delays between the primary

and secondary synchronous signals keep efficiencies high

and prevent shorting of the power transformer. An external

resistor sets the oscillator frequency from 200 kHz to

500 kHz.

Si9122E has advanced current monitoring and control

circuitry which allow the user to set the maximum current in

the primary circuit. Such a feature acts as protection against

output shorting and also provides constant current into large

capacitive loads during start-up or when paralleling power

supplies. Current sensing is by means of a sense resistor on

the low-side primary device.