200mA & 250mA SmartLDOs
TM
POWER MANAGEMENT
Description
The SC1531(A) is designed to maintain a glitch-free 3.3V
output when at least one of two inputs, 5V (VIN) and
3.3V (VAUX), is present.
SC1531(A)
Features
Glitch-free transition between input sources
Internal logic selects input source
Gate drive for external PMOS bypass switch
5V detection with hysteresis
1% regulated output voltage accuracy
200mA load current capability
(250mA for SC1531A)
Remote sense
SO-8 package
u
u
u
u
Whenever VIN exceeds a predetermined threshold value,
u
the internal 3.3V linear regulator is enabled, and DR is
u
pulled high.
u
When VIN falls below a lower threshold value, DR is pulled
u
low and the internal linear regulator is turned off. DR has
been designed to drive the gate of an external low
threshold P-channel MOSFET, which can be used to
connect the 3.3V supply directly to the regulator output.
This ensures an uninterrupted 3.3V output even if VIN
falls out of specification. A typical R
DS(ON)
of 400mW is
recommended (320mW for SC1531A).
When both supplies are simultaneously available, the
drive pin (DR) will be pulled High, turning off the external
PMOS switch.
The internal 5V detector has its upper threshold (for VIN
rising) set to 4.18V (typical) while the lower threshold (for
VIN falling) is at 4.05V (typical) giving a hysteresis of
approximately 130mV.
The SENSE pin, which is connected to the load, connects
internally to the inverting input of the LDO error
amplifier. It enables tight regulation of the load voltage
(while the 5V supply is present) despite variations in load
current.
The SC1531(A) is available in the popular SO-8 surface
mount package.
Applications
u
u
u
u
u
Desktop Computers
Network Interface Cards (NICs)
PCMCIA/PCI Interface Cards
Cardbus
TM
Technology
Power supplies with multiple input sources
Typical Application Circuit
Notes for Typical Application Circuit:
(1) External switch (Q1): use Motorola MGSF1P02ELT1
or equivalent (PMOS, typical Gate Threshold Voltage =
1V, typical R
DS(ON)
= 0.4W at V
GS
= 2.5V) for SC1531. Use
Vishay Si2301DS or equivalent for SC1531A.
(2) Connection of VAUX (pin 3) is optional.
Q1
U1
5V
3.3V
1
2
3
4
C1
0.1uF
C2
4.7uF
C3
0.1uF
VIN
DR
NC
VO
VAUX SENSE
GND
NC
SC1531
8
7
6
5
C4
4.7uF
C5
0.1uF
3.3V OUT
Revision 1, December 2000
1
www.semtech.com
SEMTECH [ SEMTECH CORPORATION ]
