SI9122 Datasheet, PDF (1/17 Pages) Vishay Siliconix – 500-kHz Half-Bridge DC-DC Converter With Integrated Secondary Synchronous Rectification Drivers

Si9122
Vishay Siliconix
500-kHz Half-Bridge DC-DC Converter
With Integrated Secondary Synchronous Rectification Drivers
FEATURES
D 12-V to 72-V Input Voltage Range
D Compatible with ETSI 300 132-2
D Integrated Half Bridge Primary Drivers
(1-A Drive Capability)
D Secondary Synchronous Signals With Programmable
Deadtime Delay
D Voltage Mode Control
D Voltage Feedforward Compensation
D High Voltage Pre-Regulator Operates During Start-Up
D Current Sensing On Low-Side Primary Device
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 33−72 V and withstand 100 V,
100 ms transients, 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
D Frequency Foldback Eliminates Constant Current Tail
D Advanced Maximum Current Control During Start-Up and
Shorted Load
D Low Input Voltage Detection
D Programmable Soft-Start Function
D Over Temperature Protection
APPLICATIONS
D Network Cards
D Power Supply Modules
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 600 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.
FUNCTIONAL BLOCK DIAGRAM
V_IN
D₁
C_BOOST
+
−
C_VIN1
V_CC
CV_CC
EP
Voltage
Information
CS2
CS1
Current
Sense
BST
L_X
Pre-Reg
Voltage
Control
Primary
Drivers
PWM
t
Current
Control
Timer
BBM
Secondary
Drivers
D_H
(High)
D_L
(Low)
R_S
SRH
R_BBM
Si9122
Half-Bridge
Synchronous
SRL
Controller
Document Number: 71815
S-41944—Rev. F, 18-Oct-04
Figure 1.
Power
Transformer
Pulse
Transformer
Opto
Error
Amp
To
V_CC
V_OUT
C_LOAD
R_LOAD
1.215 V
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