SI9122 Vishay Siliconix, SI9122 Datasheet - Page 8

• Manufacturer Part Number: SI9122
• Description: 500-kHz Half-Bridge DC-DC Converter With Integrated Secondary Synchronous Rectification Drivers
• Manufacturer: Vishay Siliconix

Si9122
Vishay Siliconix
DETAILED OPERATION
Start-Up
When V
to charge up the Vcc capacitor. Current into the external V
capacitor is limited to typically 40 mA by the internal DMOS
device. When Vcc exceeds the UVLO voltage of 8.8 V a
soft-start cycle of the switch mode supply is initiated. The V
supply continues to be charged by the pre-regulator until V
equals Vreg. During this period, between V
excessive load current will result in V
and stopping switch mode operation. This situation is avoided
by the hysteresis between V
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8
C
L_CONT
V
CS2
CS1
INDET
R
V
OSC
REF
EP
SS
INEXT
Oscillator
Feedforward
60 kW
8 V
rises above 0 V, the internal pre-regulator begins
Voltage
Current
Control
100 mV
Reference
Bandgap
V
3.3 V
132 kW
CC
−
+
+
−
OSC
V
Gain
20 mA
REF
Clock
REG
Frequency
/2
C
Foldback
Control
Loop
L_CONT
and V
Blanking
Soft-Start
CC
UVLO
falling below V
−
+
and correct sizing
PWM
Generator
UVLO
V
+
−
+
−
550 mV
Figure 4.
REF
and V
SS Enable
V
V
UV
SD
GND
UVLO
Clock
REG
Detailed Functional Block
CC
CC
CC
,
V
SD
of the V
capacitor. The value of the V
chosen to be capable of maintaining switch mode operation
until the V
a power transformer winding and zener regulator). Feedback
from the output of the switch mode supply charges V
V
from V
of switch mode operation. In the event of an over voltage
condition on V
to shunt excessive current to GND.
REG
V
V
CC
UV
Timer
Logic
Logic
BBM
V
9.1 V
V
and fully disconnects the pre-regulator, isolating V
IN
REG
UVLO
. V
160_C Temp
CC
Protection
V
CC
IN
CC
capacitor, bootstrap capacitor and the soft-start
can be supplied from the external circuit (e.g via
CC
is then maintained above V
OTP
V
, an internal voltage clamp turns on at 14.5 V
UVLO
Pre-Regulator
High Voltage
Interface
+
−
+
−
CC
Si9122
capacitor should therefore be
8.6 V
V
V
V
S-41944—Rev. F, 18-Oct-04
CC
CC
CC
Document Number: 71815
REG
9.1 V
High-Side
Synchronous
Synchronous
Primary
Driver
for the duration
Low-Side
Driver
(High)
Driver
(Low)
Driver
CC
BST
D
L
D
PGND
SR
SR
above
X
H
L
H
L
CC