Data Sheet

ADP172

THEORY OF OPERATION

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Rev. F | 11 of 17

The ADP172 is a low quiescent current, low-dropout linear regulator

that operates from 1.6 V to 3.6 V and can provide up to 300 mA of

output current. Drawing a low 170 µA of quiescent current (typical)

at full load makes the ADP172 ideal for battery-operated portable

equipment. Shutdown current consumption is typically 100 nA.

Optimized for use with small 1 µF ceramic capacitors, the ADP172

provides excellent transient performance.

Figure 23. ADP172 Internal Block Diagram

Internally, the ADP172 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.

The ADP172 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.