Ultra-Low-Noise, High PSRR, Low-Dropout,

120mA Linear Regulators in SC70

6

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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 several

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

transistor saturates. They also use high base-drive cur-

rent under heavy loads. The MAX8510/MAX8511/

MAX8512 do not suffer from these problems and con-

sume 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:

1.225V. Use 1% or better resistors.

Shutdown

The MAX8510/MAX8511/MAX8512 feature a low-power

shutdown mode that reduces quiescent current less

than 1µA. Driving SHDN low disables the voltage refer-

ence, error amplifier, gate-drive circuitry, and pass

transistor (see the Functional Diagram), and the device

output enters a high-impedance state. Connect SHDN

to IN for normal operation.

Current Limit

The MAX8510/MAX8511/MAX8512 include a current

limiter, which monitors and controls the pass transis-

tor’s gate voltage, limiting the output current to 200mA.

RR X

V

V

OUT

REF

12

1

=













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Pin Description

PIN

MAX8510

MAX8511

MAX8512

NAME

FUNCTION

111

IN

Unregulated Input Supply

222

GND

Ground

333

SHDN

Shutdown. Pull low to disable the regulator.

4—

—

BP

Noise Bypass for Low-Noise Operation. Connect a 10nF capacitor from

BP to OUT. It is short to OUT in shutdown mode.

—4

—N.C.

Not Internally Connected

——

4FB

Adjustable Output Feedback Point

555

OUT

Regulated Output Voltage. Bypass with a capacitor to GND. See the

Capacitor Selection and Regulator Stability section for more details.