Datasheet

Data Sheet ADP172
Rev. D | Page 11 of 20
THEORY OF OPERATION
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.
SHORT CIRCUIT,
UVLO AND
THERMAL
PROTECT
0.5V REFERENCE
SHUTDOWN
VIN VOUT
R1
R2
GND
EN
ADP172
06111-022
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.