Data Sheet

ADM7150

THEORY OF OPERATION

The ADM7150 is an ultralow noise, high power supply rejection

ratio (PSRR) linear regulator targeting radio frequency (RF)

applications. The input voltage range is 4.5 V to 16 V, and it can

deliver up to 800 mA of output current. Typical shutdown current

consumption is 0.1 µA at room temperature.

Optimized for use with 10 µF ceramic capacitors, the ADM7150

provides excellent transient performance.

VREG

GND

VOUT

VIN

EN

REF

REF_SENSE

REFERENCE

SHUTDOWN

ACTIVE

RIPPLE

FILTER

SHORT CIRCUIT,

THERMAL

PROTECT

OTA

E/A

BYP

Figure 51. Simplified Internal Block Diagram

Internally, the ADM7150 consists of a reference, an error amplifier,

and a P-channel MOSFET 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.

By heavily filtering the reference voltage, the ADM7150 is able

to achieve 1.7 nV/√Hz output typical from 10 kHz to 1 MHz.

Because the error amplifier is always in unity gain, the output

noise is independent of the output voltage.

To maintain very high PSRR over a wide frequency range, the

ADM7150 architecture uses an internal active ripple filter. This

stage isolates the low output noise LDO from noise on VIN.

The result is that the PSRR of the ADM7150 is significantly

higher over a wider frequency range than any single stage LDO.

The ADM7150 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, EN can be tied to VIN.

VREG

VIN

REF_SENSE

REF

OUT

BYP

GND

EN

18V

6V

6V

6V

6V

6V

6V

6V

6V

18V

18V

Figure 52. Simplified ESD Protection Block Diagram

The ESD protection devices are shown in the block diagram as

Zener diodes (see Figure 52).

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