ADP150

Rev. A | Page 11 of 20

THEORY OF OPERATION

The ADP150 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 150 mA of output current. Drawing a low 220 µA

of quiescent current (typical) at full load makes the ADP150 ideal

for battery-operated portable equipment. Shutdown current

consumption is typically 200 nA.

Using new innovative design techniques, the ADP150 provides

superior noise performance for noise sensitive analog and

RF applications without the need for a noise bypass capacitor.

The ADP150 is also optimized for use with small 1 µF ceramic

capacitors.

VOLTAGE

REFERENCE

SHORT CIRCUIT,

UVLO, AND

THERMAL

PROTECT

SHUTDOWN

R1

R2

VOUT

VIN

GND

EN

Figure 26. Internal Block Diagram

Internally, the ADP150 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 that 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.

The ADP150 is available in 14 output voltage options, ranging

from 1.8 V to 3.3 V. The ADP150 uses the EN pin to enable and

disable the VOUT pin under normal operating conditions. When

EN is high, VOUT turns on, and when EN is low, VOUT turns

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