ADP151ACBZ-2.5-R7 datasheet(11/24 Pages) AD

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ADP151

Rev. 0 | Page 11 of 24

THEORY OF OPERATION

The ADP151 is an ultralow noise, low quiescent current, low

dropout linear regulator that operates from 2.2 V to 5.5 V and

can provide up to 200 mA of output current. Drawing a low

265 μA of quiescent current (typical) at full load makes the

ADP151 ideal for battery-operated portable equipment. Shut-

down current consumption is typically 200 nA.

Using new innovative design techniques, the ADP151 provides

superior noise performance for noise-sensitive analog and RF

applications without the need for a noise bypass capacitor. The

ADP151 is also optimized for use with small 1 µF ceramic

capacitors.

REFERENCE

SHORT CIRCUIT,

UVLO, AND

THERMAL

PROTECT

SHUTDOWN

REN

VOUT

VIN

GND

Figure 25. Internal Block Diagram

Internally, the ADP151 consists of a reference, an error

amplifier, a feedback voltage divider, and a PMOS pass

transistor. Output current is delivered via the PMOS pass

device, which is controlled by the error amplifier. The error

amplifier compares the reference voltage with the feedback

voltage from the output and amplifies the difference. If the

feedback voltage is lower than the reference voltage, the gate of

the PMOS device is pulled lower, allowing more current to pass

and increasing the output voltage. If the feedback voltage is

higher than the reference voltage, the gate of the PMOS device

is pulled higher, allowing less current to pass and decreasing the

output voltage.

An internal pull-down resistor on the EN input holds the input

low when the pin is left open.

The ADP151 is available in 16 output voltage options, ranging

from 1.1 V to 3.3 V. The ADP151 uses the EN pin to enable and

disable the VOUT pin under normal operating conditions.

When EN is high, VOUT turns on; when EN is low, VOUT

turns off. For automatic startup, EN can be tied to VIN.

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