Data Sheet

ADP151

THEORY OF OPERATION

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Rev. J | 11 of 23

The ADP151 is an ultralow noise, low quiescent current, LDO 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 operating supply

current (typical) at full load makes the ADP151 ideal for battery

operated, portable equipment. Shutdown current consumption is

typically 0.2 µA.

Using a proprietary architecture, 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.

Figure 27. Internal Block Diagram

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 pulls 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 pulls 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, and when EN is low, VOUT turns off. For automatic

startup, tie EN to VIN.