ADP121 Analog Devices, ADP121 Datasheet - Page 11

• Manufacturer Part Number: ADP121
• Description: 150 mA, Low Quiescent Current, CMOS Linear Regulator in 5-Lead TSOT or 4-Ball WLCSP
• Manufacturer: Analog Devices

Data Sheet
THEORY OF OPERATION
The ADP121 is a low quiescent current, low dropout linear
regulator that operates from 2.3 V to 5.5 V and provides up
to 150 mA of output current. Drawing a low 30 μA quiescent
current (typical) at full load makes the ADP121 ideal for battery-
operated portable equipment. Shutdown current consumption
is typically 100 nA.
Optimized for use with small 1 µF ceramic capacitors,
the ADP121 provides excellent transient performance.
GND
VIN
EN
SHUTDOWN
Figure 27. Internal Block Diagram
SHORT CIRCUIT,
UVLO, AND
THERMAL
PROTECT
0.8V REFERENCE
R1
R2
VOUT
Rev. E | Page 11 of 20
Internally, the ADP121 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 con-
trolled 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 flow 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 flow and decreasing the output voltage.
The ADP121 is available in output voltages ranging from 1.2 V to
3.3 V. The ADP121 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.
ADP121