Data Sheet

ADPL42005

analog.com

Rev. 0

15 of 26

THEORY OF OPERATION

The ADPL42005 is a low quiescent current, low-dropout linear regulator that operates from 4V to 20V and provides

up to 500mA of output current. Drawing a low 1mA of quiescent current (typical) at full load makes the ADPL42005

ideal for battery-operated portable equipment. Typical shutdown current consumption is 40μA at room

temperature.

Optimized for use with small 1µF ceramic capacitors, the ADPL42005 provides excellent transient performance.

Figure 39. Fixed Output Voltage Internal Block Diagram

Figure 40. Adjustable Output Voltage Internal Block Diagram

Internally, the ADPL42005 consists of a reference, an error amplifier, and a PMOS pass transistor. Output current is

delivered through 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.

The ADPL42005 is available in six fixed output voltage options, ranging from 1.5V to 5.0V and in an adjustable version

with an output voltage that can be set to between 1.22V and 19V by an external voltage divider. The output voltage

can be set according to the following Equation 3:

VOUT = 1 . 22V (1 +

R1

R2

)

(3)

SHUTDOWN

VIN

GND

EN/

UVLO

VOUT

REFERENCE

VREG

PGOOD

PG

SENSE

SHORT-CIRCUIT,

THERMAL

PROTECT

10µA

SHUTDOWN

VIN

GND

EN/

UVLO

VOUT

1.22V

REFERENCE

VREG

PGOOD

PG

ADJ

SHORT-CIRCUIT,

THERMAL

PROTECT

10µA