Data Sheet

ADP7156

Rev. A | Page 13 of 22

THEORY OF OPERATION

The ADP7156 is an ultralow noise, high PSRR linear regulator

targeting radio frequency (RF) applications. The input voltage

range is 2.3 V to 5.5 V, and it can deliver up to 1.2 A of load

current. Typical shutdown current consumption is 0.2 µA at

room temperature.

Optimized for use with 10 µF ceramic capacitors, the ADP7156

provides excellent transient performance.

VREG

GND (EPAD)

VOUT

VIN

EN

REF

REF_SENSE

VOUT_SENSE

REFERENCE

SHUTDOWN

CURRENT-LIMIT,

THERMAL

PROTECT

OTA

BYP

INTERNAL

REGULATOR

Figure 41. Simplified Internal Block Diagram

Internally, the ADP7156 consists of a reference, an error ampli-

fier, and a P-channel MOSFET pass transistor. The 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.

By heavily filtering the reference voltage, the ADP7156 can

achieve 1.7 nV/√Hz typical output noise spectral density from

10 kHz to 1 MHz. Because the error amplifier is always in unity

gain, the output noise is independent of the output voltage.

The ADP7156 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, tie EN to VIN.

4V

7V

4V

4V

4V

4V

4V

4V

4V

4V

7V

7V

4V

VIN

VREG

REF

REF_SENSE

BYP

VOUT

VOUT_SENSE

EN

GND (EPAD)

Figure 42. Simplified ESD Protection Block Diagram

The ESD protection devices are shown in the block diagram as

Zener diodes (see Figure 42).