Datasheet

MAX1818
500mA Low-Dropout
Linear Regulator in SOT23
_______________________________________________________________________________________ 5
SHUTDOWN WAVEFORM
MAX1818 toc12
POK
SHUTDOWN
VOLTAGE
V
OUT
0
0
2V/div
0
200μs/div
1.00
1.01
1.02
1.03
1.04
1.05
1.06
1.07
1.08
1.09
1.10
1.11
2.5 3.0 3.5 4.0 4.5 5.0 5.5
SHORT-CIRCUIT CURRENT LIMIT
vs. SUPPLY VOLTAGE
MAX1818 toc13
SUPPLY VOLTAGE (V)
SHORT-CIRCUIT CURRENT LIMIT (A)
V
OUT(NOM)
= +2V
Detailed Description
The MAX1818 is a low-dropout, low-quiescent-current
linear regulator designed primarily for battery-powered
applications. The device supplies loads up to 500mA
and is available with preset output voltages. As illustrat-
ed in Figure 1, the MAX1818 consists of a 1.25V refer-
ence, error amplifier, P-channel pass transistor, and
internal feedback voltage-divider.
The 1.25V reference is connected to the error amplifier,
which compares this reference with the feedback volt-
age and amplifies the difference. If the feedback volt-
age is lower than the reference voltage, the
pass-transistor gate is pulled lower, which allows more
current to pass to the output and increases the output
voltage. If the feedback voltage is too high, the pass-
transistor gate is pulled up, allowing less current to
pass to the output.
The output voltage is fed back through either an inter-
nal resistive divider connected to OUT or an external
resistor network connected to SET. The Dual Mode
comparator examines V
SET
and selects the feedback
path. If V
SET
is below 50mV, the internal feedback path
is used and the output is regulated to the factory-preset
voltage.
Pin Description
PIN NAME FUNCTION
1IN
Regulator Input. Supply voltage can range from 2.5V to 5.5V. Bypass with a 1μF capacitor to GND (see
Capacitor Selection and Regulator Stability).
2 POK
Open-Drain POK Output. POK remains low while the output voltage (V
OUT
) is below the POK threshold.
Connect a 100kΩ pull-up resistor from POK to OUT to obtain an output voltage.
3 SHDN
Active-Low Shutdown Input. A logic low reduces supply current below 15μA. In shutdown, the POK output is
low, and OUT is high impedance. Connect to IN for normal operation.
4 GND Ground
5 SET
Voltage-Setting Input. Connect to GND for preset output. Connect to a resistive voltage-divider between
OUT and GND to set the output voltage between 1.25V and 5.0V.
6 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.
Typical Operating Characteristics (continued)
(V
IN
= (V
OUT
+ 500mV) or +2.5V, whichever is greater; SHDN = IN, C
IN
= 1µF, C
OUT
= 3.3µF, T
A
= +25°C, unless otherwise noted.)