Datasheet

MAX1792
500mA Low-Dropout
Linear Regulator in µMAX
7
Maxim Integrated
Detailed Description
The MAX1792 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 MAX1792 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.
Additional blocks include an output current limiter, ther-
mal sensor, and shutdown logic.
Internal P-Channel Pass Transistor
The MAX1792 features a 0.25Ω P-channel MOSFET
pass transistor. Unlike similar designs using PNP pass
transistors, P-channel MOSFETs require no base drive,
which reduces quiescent current. PNP-based regula-
tors also waste considerable current in dropout when
the pass transistor saturates, and use high base-drive
currents under large loads.
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
100k
LOGIC SUPPLY
VOLTAGE (V
OUT
)
93% V
REF
TO
µC
5k
MAX1792
Figure 1. Functional Diagram