Datasheet

500mA, Low-Dropout,
Ripple-Rejecting LDO in µMAX
6 _______________________________________________________________________________________
MAX1857
Pin Description
PIN
NAME
FUNCTION
1, 2 IN
Regulator Input. Supply voltage can range from +2.5V to +5.5V. Bypass with a 1µF capacitor or greater to
GND (see Capacitor Selection and Regulator Stability). Connect both input pins together externally.
3
RST
Open-Drain, Active-Low Reset Output. RST remains low while the output voltage (V
OUT
) is below the reset
threshold and for at least 4ms after V
OUT
rises above the reset threshold. Connect a 100kΩ pullup resistor
to OUT.
4 SHDN
Active-Low Shutdown Input. A logic low reduces supply current to 0.1µA. In shutdown, the RST output is
low and OUT is pulled low through an internal 5kΩ resistor. Connect to IN for normal operation.
5 GND Ground
6 SET
Voltage-Setting Input. Connect to GND for preset output. Connect a resistive voltage-divider from OUT to
set the output voltage between 1.25V and 5.0V.
7, 8 OUT
Regulator Output. Sources up to 500mA. Bypass with a 3.3µF low-ESR capacitor to GND. Use a 4.7µF
capacitor for output voltages below 2V. Connect both output pins together.
100mV
SHDN
IN
IN
RST
ON
OFF
C
IN
1µF
V
IN
= +2.5V TO +5.5V
OUT
OUT
V
OUT
= 1.25V TO 5.0V
C
OUT
3.3µF
THERMAL
SENSOR
SET
MOSFET
DRIVER WITH
I
LIM
DELAY
TIMER
SHUTDOWN
LOGIC
V
REF
1.25V
ERROR
AMPLIFIER
GND
R1
R2
R
RST
100kΩ
LOGIC SUPPLY
VOLTAGE (V
OUT
)
86% V
REF
TO
µC
5kΩ
MAX1857
Figure 1. Functional Diagram