ADM7172

Data Sheet

THEORY OF OPERATION

The ADM7172 is a low quiescent current, low dropout linear

regulator that operates from 2.3 V to 6.5 V and provides up to

2 A of load current. Drawing a low 4.8 mA of quiescent current

(typical) at full load makes the ADM7172 ideal for portable

equipment. Typical shutdown current consumption is 0.25 μA

at room temperature.

Optimized for use with small 4.7 µF ceramic capacitors, the

ADM7172 provides excellent transient performance.

VOUT

SENSE

SS

GND

CURRENT-LIMIT,

THERMAL

PROTECT

SOFT START

REFERENCE

SHUTDOWN

EN

VIN

Figure 56. Internal Block Diagram

Internally, the ADM7172 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. When 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.

When 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.

The ADM7172 is available in 17 fixed output voltage options,

ranging from 1.2 V to 5 V. The ADM7172 architecture allows

any fixed output voltage to be set to a higher voltage with an

external voltage divider. For example, a fixed 5 V output ADM7172

can be set to a 6 V output according to the following equation:

VOUT

SENSE

VIN

ADM7172

GND

VIN

VOUT

SS

1nF

4.7µF

4.7µF

EN

OFF

ON

R1

2kΩ

R2

10kΩ

Figure 57. Typical Adjustable Output Voltage Application Schematic

Use a value of less than 200 kΩ for R2 to minimize errors in the

output voltage caused by the SENSE pin input current. For

example, when R1 and R2 each equal 200 kΩ and the default

output voltage is 1.2 V, the adjusted output voltage is 2.4 V. The

output voltage error introduced by the SENSE pin input current

is 0.1 mV or 0.004%, assuming a typical SENSE pin input bias

current of 1 nA at 25°C.

The ADM7172 uses the EN pin to enable and disable the VOUT

tie EN to VIN (Pin 7 or Pin 8).

Rev. C | Page 16 of 23