SI9124 Datasheet, PDF (11/16 Pages) Vishay Siliconix – 500-kHz Push-Pull DC-DC Converter With Integrated Secondary Synchronous Rectification Control

New Product
Si9124
Vishay Siliconix
Hiccup Operation
Current limiting is achieved by monitoring the differential
voltage between CS1 and CS2 pins which are connected
across a primary sense resistor. Once the differential voltage
exceeds the 150-mV trigger point, Hiccup operation is started.
The soft-start voltage on the SS pin is pulled to ground and
switching stops until the SS pin charges up to 2 V_be whereupon
a duty cycle limited soft start is initiated. The upper and lower
switching points of the current limit have 50 mV of hysteresis.
VINEXT Voltage Monitor – VINDET
The Si9124 provides a means of sensing the voltage on
V_INEXT to control the operating mode and provides the
feed-forward control voltage to the PWM controller. This is
achieved by choosing an appropriate resistive tap between
V_INEXT and ground.
When the V_INDET voltage is greater than 720 mV but less than
V_REF and V_CC is greater than V_UVLO, all internal circuitry is
enabled, but switching is stopped.
V_INDET also provides the input to the voltage feed-forward
function by adjusting the amplitude of the PWM ramp to the
PWM comparator.
Shutdown Mode
If V_INDET pin is forced below 470 mV the device will enter
SHUTDOWN mode. This powers down all unnecessary
functions of the controller, ensures that the primary switches
are off and results in a low level current demand of 150 mA from
the V_INEXT or V_CC supplies.
TYPICAL CHARACTERISTICS
V_SS vs. Temperature, V_CC = 12 V
8.20
8.15
8.10
8.05
T_C = +1.25 mV/C
V_INDET u V_REF
8.00
7.95
7.90
- 50 - 25 0
25 50 75 100 125 150
Temperature (_C)
I_SS1 vs. V_CC vs. Temperature
25
V_CC = 13 V
23
V_CC = 12 V
21
19
V_CC = 10 V
17
15
- 50 - 25
0
25 50 75
Temperature (_C)
100 125
Document Number: 72099
S-03638—Rev. B, 20-Mar-03
V_REG vs. Temperature, V_IN = 48 V
10.0
9.5
9.0
V_INDET u V_REF
T_C = - 11 mV/C
8.5
8.0
7.5
- 50 - 25 0
25 50 75 100 125 150
Temperature (_C)
I_SS2 vs. V_CC vs. Temperature
140
130
120
V_CC = 13 V
V_CC = 12 V
110
100
V_CC = 10 V
90
80
- 50 - 25
0
25 50 75
Temperature (_C)
100 125
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