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.