SI91860 Datasheet, PDF (7/8 Pages) Vishay Siliconix – 400-mA Smart Regulator for Network Interface Card

BLOCK DIAGRAMS AND TYPICAL APPLICATION CIRCUIT
Si91860
1
5 V_SB
4.7 µF
2
5 V_{IN 4.7 µF}
5 V_SB
Regulator
Driver
3
4
3.3 V_AUX
4.7 µF
5 V_IN
Regulator
Driver
Logic
Control
5, 6
7, 8
Si91860
Vishay Siliconix
3.3 V_OUT
2.2 µF
DETAIL DESCRIPTION
During normal operation, the 5-V_IN input powers the fixed
3.3-V output (3.3 V_OUT) through an internal linear regulator.
When 5 V_IN falls below 4.07 V, the 3.3-V output is powered
through the linear regulator from 5 V_SB. If both 5 V_IN and 5 V_SB
are below 4.07 V, then the output (3.3 V_OUT) is powered from
3.3-V_AUX input. The power drawn sequence is from 5 V_IN, then
5 V_SB and lastly 3.3 V_AUX. If both 5 V_IN and 5 V_SB are above
4.30 V, then 5 V_IN will power the output. The device prevents
reverse current from flowing from the output to any unbiased
or low voltage input.
Linear Regulator Mode
The output is regulated at 3.3 V when either one of the 5-V_IN
or 5-V_SB pins is more than 4.30 V. The 5 V_IN takes precedence
when both the 5-V_IN and 5-V_SB pins are more than valid
threshold voltage (i.e. > 4.30 V). The linear regulator will
regulate the output until both the 5-V_IN and 5-V_SB pins fall
below 4.07 V.
Document Number: 71340
S-40704—Rev. B, 19-Apr-04
Bypass Mode
When both the 5-V_IN and 5-V_SB pins fall below 4.07 V, the
output is powered by 3.3 V_AUX through a 0.2-W internal switch.
Thermal and Over−current Protection
Thermal protection limits total power dissipation in the device.
It safeguards the device in the event of fault conditions. When
the junction temperature exceeds 165_C, the device turns off.
The device turns back on once its junction temperature cools
down by approximately 20_C. The device has overcurrent
protection (typically at 900 mA) when it operates in linear
regulator mode. A continuous short at output pin (3.3 V_OUT)
will result in a pulsed output as the thermal protection circuitry
cycles the device on and off. For continuous operation, do not
exceed the junction rating of 150_C. In bypass mode, the
device is not current limited.
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