SI9122 Datasheet, PDF (2/17 Pages) Vishay Siliconix – 500-kHz Half-Bridge DC-DC Converter With Integrated Secondary Synchronous Rectification Drivers

Si9122
Vishay Siliconix
TECHNICAL DESCRIPTION
Si9122 is a voltage mode controller for the half-bridge
topology. With 100-V depletion mode MOSFET capability, the
Si9122 is capable of powering directly from the high voltage
bus to V_CC through an external PNP pass transistor, or may be
powered through an external regulator directly through the
V_CC pin. With PWM control, Si9122 provides peak efficiency
throughout the entire line and load range. In order to simplify
the traditional secondary synchronous rectification, Si9122
provides intelligent gate drive signals to control the secondary
MOSFETs. With independent gate drive signals from the
controller, transformer design is no longer limited by the gate
to a source rating of the MOSFETs. Si9122 provides constant
V_GS voltage, independent of line voltage to minimize the gate
charge loss as well as conduction loss. A break-before-make
function is included to prevent shoot through current or
transformer shorting. Adjustable Break-Before-Make time is
incorporated into the IC and is programmable by an external
resistor value.
Si9122 is packaged in TSSOP-20 and MLP65-20 packages.
In TSSOP-20 packaging, both standard and lead (Pb)-free
options are available. The MLP65-20 package is
lead (Pb)-free. In order to satisfy the stringent ambient
temperature requirements, Si9122 is rated to handle the
industrial temperature range of –40 to 85_C. When a situation
arises which results in a rapid increase in primary (or
secondary current) such as output shorted or start-up with a
large output capacitor, control of the PWM generator is handed
over to the the current loop. Monitoring of the load current is
by means of a sense resistor on the primary low-side switch.
DETAILED BLOCK DIAGRAM
V_IN
V_CC
R_OSC
REG_COMP
V_INDET
V_REF
EP
SS
CS2
CS1
Pre-Regulator
V_REF
9.1 V
+
V_UVLO
−
8.8 V
132 kW
60 kW
−
Error Amplifier
+
20 mA
VREF
2
I_SS
8V
+ ^VUV
−
+ ^VSD
−
550 mV
+
−
PWM
Comparator
High-Side
Primary
Driver
Int
V_FF
Ramp
OSC
Low-Side
Driver
Driver
Control
and
Timing
OTP
+
−
Peak DET
Over Current Protection
GND
Duty Cycle
Control
C_{L_CONT}
BBM
Si9122
V_CC
V_CC
SYNC
Driver High
V_CC
SYNC
Driver Low
BST
D_H
L_X
D_L
PGND
SR_H
SR_L
www.vishay.com
2
Figure 2.
Document Number: 71815
S-41944—Rev. F, 18-Oct-04