MAX1589
Detailed Description
The MAX1589 is a low-dropout, low-quiescent-current,
high-accuracy linear regulator designed primarily for
battery-powered applications. The device supplies
loads up to 500mA and is available with preset output
voltages from +0.75V to +3.0V. As illustrated in Figure 1,
the MAX1589 contains a reference, an error amplifier, a
P-channel pass transistor, an internal feedback voltage-
divider, and a power-good comparator.
The error amplifier compares the reference with the
feedback voltage and amplifies the difference. If the
feedback voltage is lower than the reference voltage,
the pass-transistor gate is pulled lower, allowing more
current to pass to the output and increasing 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.
Internal P-Channel Pass Transistor
The MAX1589 features a 0.33Ω (R
DS(ON)
) 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 regulators also waste considerable current in
dropout when the pass transistor saturates and use
high base-drive currents under large loads. The
MAX1589 does not suffer from these problems and
consumes only 90µA (typ) of quiescent current under
heavy loads, as well as in dropout.
Shutdown
Pull SHDN low to enter shutdown. During shutdown, the
output is disconnected from the input, an internal 1.5kΩ
resistor pulls OUT to GND, RESET is actively pulled
low, and supply current drops below 1µA.
RREESSEETT
Output
The MAX1589’s microprocessor (µP) supervisory cir-
cuitry asserts a guaranteed logic-low reset during
power-up, power-down, and brownout conditions down
to +1V. RESET asserts when V
OUT
is below the reset
threshold and remains asserted for at least 70ms (t
RP
)
after V
OUT
rises above the reset threshold.
Current Limit
The MAX1589 monitors and controls the pass transis-
tor’s gate voltage, limiting the output current to 850mA
(typ). If the output current exceeds I
LIM
, the MAX1589
output voltage drops.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX1589. When the junction temperature
exceeds +165°C, a thermal sensor turns off the pass
Low-Input-Voltage, 500mA LDO Regulator
with
RREESSEETT
in SOT and TDFN
6 _______________________________________________________________________________________
PART
SOT23 TDFN
NAME FUNCTION
16IN
Regulator Input. Supply voltage can range from +1.62V to +3.6V. Bypass IN with at least a
1µF ceramic capacitor to GND (see the Capacitor Selection and Regulator Stability
section).
2 — GND
Ground. GND also functions as a heatsink. Solder GND to a large pad or circuit-board
ground plane to maximize SOT23 power dissipation.
— 4 GND Ground
35SHDN
Active-Low Shutdown Input. A logic low reduces supply current to below 1µA. Connect to
IN or logic high for normal operation.
43RESET
Active-Low, Open-Drain Reset Output. RESET rises 100ms after the output has achieved
regulation. RESET falls immediately if V
OUT
drops below 82.5% of its nominal voltage, or if
the MAX1589 is shut down.
5 2 I.C. Internally Connected. Leave floating or connect to GND.
6 1 OUT
Regulator Output. Sources up to 500mA. Bypass with a 4.7µF low-ESR ceramic capacitor
to GND.
—
Exposed
Pad
EP
Ground. EP also functions as a heatsink. Solder EP to a large pad or circuit-board ground
plane to maximize TDFN power dissipation.
