SI9122A_08 VISHAY [Vishay Siliconix], SI9122A_08 Datasheet - Page 9

• Manufacturer Part Number: SI9122A_08
• Description: 500-kHz Half-Bridge DC/DC Controller with Integrated Secondary Synchronous Rectification Drivers
• Manufacturer: VISHAY [Vishay Siliconix]

DETAILED OPERATION
Start-Up
When V
begins to charge up the V
external V
internal DMOS device. When V
voltage of 8.8 V a soft-start cycle of the switch mode supply
is initiated. The V
pre-regulator until V
between V
in V
operation. This situation is avoided by the hysteresis
between V
Document Number: 73492
S-80038-Rev. D, 14-Jan-08
C
L_CONT
V
CS2
CS1
INDET
R
V
CC
REF
OSC
EP
SS
INEXT
falling below V
CC
UVLO
REG
Oscillator
Feedforward
60 kΩ
8 V
capacitor is limited to typically 40 mA by the
Voltage
Current
Control
rises above 0 V, the internal pre-regulator
and V
and V
100 mV
Reference
Bandgap
CC
V
3.3 V
132 kΩ
CC
supply continues to be charged by the
CC
-
+
+
-
REG
OSC
UVLO
Gain
V
20 µA
REF
equals V
UVLO
Clock
, excessive load current will result
/2
Frequency
C
Foldback
Control
CC
and correct sizing of the V
Loop
L_CONT
and stopping switch mode
Blanking
capacitor. Current into the
Soft-Start
REG
CC
. During this period,
exceeds the UVLO
–
+
Figure 4. Detailed Si9122A Block Diagram
PWM
Generator
V
+
-
+
-
550 mV
REF
SS Enable
V
V
UV
SD
GND
Clock
CC
V
SD
capacitor, bootstrap capacitor and the soft-start capacitor.
The value of the V
to be capable of maintaining switch mode operation until the
required V
(e.g via a power transformer winding and zener regulator).
Feedback from the output of the switch mode supply charges
V
isolating V
for the duration of switch mode operation. In the event of an
over voltage condition on V
turns on at 14.5 V to shunt excessive current to GND.
CC
V
V
CC
UV
Logic
Logic
Timer
BBM
V
above V
REG
V
UVLO
160 C Temp
9.1 V
Protection
V
IN
CC
CC
12 V
current can be supplied from the external circuit
from V
REG
OTP
V
UVLO
CC
and fully disconnects the pre-regulator,
IN
capacitor should therefore be chosen
. V
Pre-Regulator
High V oltage
+
-
+
-
Interface
CC
Si9122A
is then maintained above V
CC
, an internal voltage clamp
Vishay Siliconix
8.8 V
V
V
V
CC
CC
CC
9.1 V
High-Side
Synchronous
Synchronous
Primary
Si9122A
Driver
www.vishay.com
Low-Side
Driver
(High)
Driver
(Low)
Driver
BST
D
L
D
PGND
SR
SR
X
H
L
H
L
REG
9