MAX1725/MAX1726
12V, Ultra-Low I
Q
, Low-Dropout
Linear Regulators
6
Maxim Integrated
Shutdown
To enter shutdown, drive the SHDN pin below 0.5V.
When the MAX1725/MAX1726 are shut down, the output
pass transistor shuts off, the output falls to ground, and
supply current drops from 2µA to 0.7µA. Connect SHDN
to IN for normal operation. If reverse-battery protection
is needed, drive SHDN through a 100kΩ resistor.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX1725/MAX1726. When the junction tem-
perature exceeds T
J
= +150°C, the thermal sensor
signals the shutdown logic, turning off the pass transistor
and allowing the IC to cool. The thermal sensor turns
the pass transistor on again after the IC’s junction tem-
perature cools by 15°C, resulting in a pulsed output
during continuous thermal-overload conditions.
Thermal-overload protection is designed to protect the
devices in the event of fault conditions. For continuous
operation, do not exceed the absolute maximum junction
temperature rating of T
J
= +150°C.
Foldback Current Limiting
The MAX1725/MAX1726 also include a foldback current
limiter. When the output is shorted to ground, the output
PMOS drive is limited so that the output current does
not exceed 40mA (typ). The output can be shorted to
ground indefinitely without damaging the part.
Reverse-Battery Protection
The MAX1725/MAX1726 have a unique protection
scheme that limits the reverse supply current to less
than 10µA when V
IN
is forced below ground. The cir-
cuitry monitors the polarity of the input, disconnecting
the internal circuitry and parasitic diodes when the battery
is reversed. This feature prevents the device, battery,
and load from overheating and electrical stress. For
reverse-battery protection, drive SHDN through a
100kΩ resistor.
Applications Information
Capacitor Selection and
Regulator Stability
For general purposes, use a 1µF capacitor on the
MAX1725/MAX1726 input and output. Larger input
capacitor values and lower ESR provide better supply-
noise rejection and transient response. A higher-value
input capacitor (10µF) may be necessary if large, fast
transients are anticipated and the device is located sev-
eral inches from the power source. For stable operation
over the full temperature range, use a minimum of 1µF
on the output.
Output-Voltage Selection
For fixed 1.8V, 2.5V, 3.3V, or 5V output voltages, use
the MAX1726.
The MAX1725 features an adjustable output voltage
from 1.5V to 5V, using two external resistors connected
as a voltage-divider to FB (Figure 1). The MAX1725 is
optimized for operation with R2 = 1.2MΩ. The output
voltage is set by the following equation:
where typically V
FB
= 1.245V. To simplify resistor selec-
tion:
Choose R2 = 1.2MΩ for best accuracy.
Power-Supply Rejection and Operation
from Sources Other than Batteries
The MAX1725/MAX1726 are designed to deliver low
dropout voltages and low quiescent currents in battery-
powered systems. Power-supply rejection is 60dB at low
frequencies and rolls off above 100Hz. At high frequen-
cies, the output capacitor is the major contributor to the
rejection of power-supply noise (see the Power-Supply
Rejection Ratio vs. Frequency graph in the
Typical
Operating Characteristics
).
When operating from sources other than batteries,
improve supply-noise rejection and transient response
by increasing the value of the input and output capaci-
tors, and by using passive filtering techniques (see the
Supply and Load Transient Response graph in the
Typical Operating Characteristics
).
