ADP151 Analog Devices, ADP151 Datasheet - Page 11

• Manufacturer Part Number: ADP151
• Description: Ultra Low Noise, 200 mA CMOS Linear Regulator
• Manufacturer: Analog Devices

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.
GND
VIN
EN
R
EN
SHUTDOWN
Figure 27. Internal Block Diagram
SHORT-CIRCUIT,
UVLO, AND
THERMAL
PROTECT
REFERENCE
R1
R2
VOUT
Rev. D | Page 11 of 24
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.
ADP151