FEATURES

• 12 V to 72 V input voltage range

• Integrated half-bridge primary drivers

(1 A drive capability)

• Secondary synchronous 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

• Over temperature protections

APPLICATIONS

• Network cards

• Power supply modules

DESCRIPTION

Si9122 is a dedicated half-bridge IC ideally suited to fixed

telecom applications where efficiency is required at low

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

fixed telecom voltage range of 33 to 72 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 the 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 accidental destruction of the

power transformer. An external resistor sets the switching

frequency from 200 kHz to 625 kHz.

Si9122 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.