Data Sheet

ADPL42002

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Rev. 1

13 of 22

THEORY OF OPERATION

The ADPL42002 is a low quiescent current, LDO linear regulator that operates from 2.7V to 20V and provides up to

200mA of output current. Drawing a low 240μA of quiescent current (typical) at full load makes the ADPL42002 ideal

for portable equipment. Typical shutdown current consumption is less than 3µA at room temperature.

Optimized for use with small 2.2µF ceramic capacitors, the ADPL42002 provides excellent transient performance.

Internally, the ADPL42002 consists of a reference, an error amplifier, 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 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 ADPL42002 is available in four fixed output voltage options, ranging from 1.2V to 5.0V. The ADPL42002

architecture allows any fixed output voltage to be set to a higher voltage with an external voltage divider. For

example, a fixed 5V output can be set to a 6V output according to the following equation:

VOUT = 5V (1 + R1/R2) (3)

where R1 and R2 are the resistors in the output voltage divider shown in Figure 26.

To set the output voltage of the adjustable ADPL42002, replace 5V in Equation 3 with 1.2V.

Figure 26. Typical Adjustable Output Voltage Application Schematic

It is recommended that the R2 value be less than 200kΩ to minimize errors in the output voltage caused by the

SENSE/ADJ pin input current. For example, when R1 and R2 each equal 200kΩ and the default output voltage is 1.2V,

the adjusted output voltage is 2.4V. The output voltage error introduced by the SENSE/ADJ pin input current is 1mV

or 0.04%, assuming a typical SENSE/ADJ pin input current of 10nA at 25°C.

The ADPL42002 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.

VOUT

SENSE/ADJ

VIN

ADPL42002

GND

SS

CSS

1nF

CIN

2.2µF

COUT

2.2µF

EN

OFF

ON

VIN = 7V

VOUT = 6V

R1

2kΩ

R2

10kΩ