SC1532 Datasheet, PDF (1/9 Pages) Semtech Corporation – 400mA SmartLDOTM with Internal Pass MOSFET

400mA SmartLDO^TM with Internal Pass
MOSFET
SC1532
January 3, 2000
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DESCRIPTION
Intended for applications such as Power Managed PCI,
the SC1532 is designed to maintain a glitch-free 3.3V
output when at least one of two inputs, 5V (VIN1) and
3.3V (VIN2), is present.
The SC1532 combines a 5V to 3.3V linear regulator
with an integral 3.3V bypass switch, along with logic
and detection circuitry to control which supply provides
the power for the output.
Whenever VIN1 exceeds a predetermined threshold
value, the internal 3.3V PMOS linear regulator is en-
abled, and the internal pass NMOS is turned off.
When VIN1 falls below a lower threshold value, the
NMOS pass device is turned on and the PMOS linear
regulator is turned off. This ensures an uninterrupted
3.3V output even if VIN1 falls out of specification.
When both supplies are simultaneously available, the
PMOS linear regulator will be turned on, and the
NMOS pass will be turned off, thus preferentially sup-
plying the output from the 5V supply.
FEATURES
• Glitch-free transition between input sources
• Internal logic selects input source
• 5V detector with hysteresis
• 1% regulated output voltage accuracy
• 400mA load current capability
APPLICATIONS
• Desktop Computers
• Network Interface Cards (NICs)
• PCMCIA/PCI Interface Cards
• Peripheral Cards
ORDERING INFORMATION
Part Number⁽¹⁾
Package
SC1532CS
SO-8
Note:
(1) Add suffix ‘TR’ for tape and reel packaging.
The internal 5V detector has its upper threshold (for
VIN1 rising) set to 4.18V (typical) while the lower
threshold (for VIN falling) is at 4.1V (typical) giving a
hysteresis of approximately 80mV.
The SC1532 is available in the popular SO-8 surface
mount package.
TYPICAL APPLICATION CIRCUIT
3.3VAUX IN
5V IN
3.3V OUT
C1
4.7uF
C2
4.7uF
C3
4.7uF
U1
1
8
2
3
4
VIN2 GND
VIN1 GND
VO GND
7
6
5
CP GND
SC1532
C4
1nF
NOTES:
(1) Ceramic capacitors are recommended - see Applications Information for further details.
(2) Output capacitor C3 needs to be 1.0uF or greater for stability. Additional capacitance (tantalum or ceramic) will
improve overall performance.
© 2000 SEMTECH CORP.
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