SI9177 Datasheet, PDF (6/8 Pages) Vishay Siliconix – 200-mA PSM Step Down Converter with Bypass Capability

Si9177
Vishay Siliconix
New Product
DETAIL OPERATIONAL DESCRIPTION (CONT’D)
An external Schottky diode is required for PSM mode
operation. The Schottky diode handles the freewheeling
inductor current after the p-channel MOSFET is turned off.
The current rating of the Schottky is based on the maximum
load current in PSM mode with the conduction time being the
greatest at maximum input voltage. Combined with the
maximum load current of 200 mA, the Schottky must be able
to conduct 200 mA continuously. Since the forward voltage
drop of the diode, V_F, determines the conduction losses, select
the diode with the lowest V_F to maximize the converter’s
efficiency. The diode should also be selected for fast switching
speed to improve efficiency. The diode must be connected
from the L_X pin to GND.
Over Temperature Protection
Si9177 includes an over temperature protection circuit to
prevent thermal runaway in the MOSFET switch. If the junction
temperature reaches 165_C, an internal soft-start capacitor is
discharged, shutting down the output stage. The converter
remains disabled until the junction temperature falls below
140_C, allowing the converter to resume operation.
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
Supply Current vs. Input Voltage
180
160
PSM Mode
140
120
100
80
BP Mode
60
2
3
4
5
6
7
Voltage (V)
100.00
95.00
Efficiency vs. Load Current
V_IN = 3.6 V
V_OUT = 3.0 V
90.00
85.00
V_OUT = 2.2 V
80.00
75.00
70.00
0
50
100
150
200
250
Current (mA)
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r_DS(on) vs. Input Voltage
240
220
200
85 _C
180
25 _C
160
140
- 25 _C
120
100
2
3
4
5
6
7
Voltage (V)
Switching Frequency vs. Load Current
500
450
V_OUT = 3.3 V
400
350
V_IN = 4.0 V
300
250
200
150
100
V_IN = 6.0 V
50
0
0
50
100
150
200
Current (mA)
Document Number: 70312
S-03663—Rev. B, 07-Apr-03