SI9122E Datasheet, PDF (1/20 Pages) Vishay Siliconix – 500-kHz Half-Bridge DC/DC Controller with Integrated Secondary Synchronous Rectification Drivers

Si9122E
Vishay Siliconix
500-kHz Half-Bridge DC/DC Controller
with Integrated Secondary Synchronous Rectification Drivers
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.
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
RoHS
COMPLIANT
• 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
FUNCTIONAL BLOCK DIAGRAM AND PIN CONFIGURATION
36 V to 75 V
V_INDET
Si9122E
C_{L_CONT}
BST
DH
LX
DL
CS2
CS1
SR_H
SR_L
EP
Figure 1.
Synchronous
Rectifiers
1 V to 12 V Typ.
+
V_OUT
-
Error
V_CC
Amplifier
+
-
V_REF
Opto Isolator
Document Number: 73866
S-80112-Rev. D, 21-Jan-08
www.vishay.com
1