Data Sheet

ADP151

Rev. E | 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.

Shutdown 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

R1

R2

VOUT

VIN

GND

EN

Figure 27. 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.