MAX8510/MAX8511/MAX8512
Ultra-Low-Noise, High PSRR,
Low-Dropout, 120mA Linear Regulators
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Detailed Description
The MAX8510/MAX8511/MAX8512 are ultra-low-noise,
low-dropout, low-quiescent current linear regulators
designed for space-restricted applications. The parts
are available with preset output voltages ranging from
1.5V to 4.5V in 100mV increments. These devices can
supply loads up to 120mA. As shown in the
Functional
Diagram
, the MAX8510/MAX8511 consist of an innova-
tive bandgap core and noise bypass circuit, error
amplifier, P-channel pass transistor, and internal feed-
back voltage-divider. The MAX8512 allows for
adjustable output with an external feedback network.
The 1.225V bandgap reference is connected to the
error amplifier’s inverting input. The error amplifier com-
pares this 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 low. This allows more current to pass to
the output and increases the output voltage. If the feed-
back voltage is too high, the pass transistor gate is
pulled high, allowing less current to pass to the output.
The output voltage is fed back through an internal resis-
tor voltage-divider connected to the OUT pin.
An external bypass capacitor connected to BP
(MAX8510) reduces noise at the output. Additional
blocks include a current limiter, thermal sensor, and
shutdown logic.
Internal P-Channel Pass Transistor
The MAX8510/MAX8511/MAX8512 feature a 1Ω (typ)
P-channel MOSFET pass transistor. This provides seve-
ral advantages over similar designs using a PNP pass
transistor, including longer battery life. The P-channel
MOSFET requires no base drive, which considerably
reduces quiescent current. PNP-based regulators waste
considerable current in dropout when the pass transis-
tor saturates. They also use high base-drive current
under heavy loads. The MAX8510/MAX8511/MAX8512
do not suffer from these problems and consume only
40µA of quiescent current in light load and 220µA in
dropout (see the
Typical Operating Characteristics
).
Output Voltage Selection
The MAX8510/MAX8511 are supplied with factory-set
output voltages from 1.5V to 4.5V, in 100mV increments
(see
Ordering Information
). The MAX8512 features a
user-adjustable output through an external feedback
network (see the
Typical Operating Circuits
).
To set the output of the MAX8512, use the following
equation:
where R2 is chosen to be less than 240kΩ and V
REF
=
1.225V. Use 1% or better resistors.
