Data Sheet

ADP1752/ADP1753

Rev. E | Page 11 of 20

THEORY OF OPERATION

The ADP1752/ADP1753 are low dropout linear regulators that

use an advanced, proprietary architecture to provide high power

supply rejection ratio (PSRR) and excellent line and load transient

response with only a small 4.7 µF ceramic output capacitor.

Both devices operate from a 1.6 V to 3.6 V input rail and

provide up to 0.8 A of output current. Supply current in

shutdown mode is typically 2 µA.

UVLO

VOUT

VIN

SENSE

SS

SHORT-CIRCUIT

AND THERMAL

PROTECTION

R1

0.5V

REF

R2

SHUTDOWN

EN

PG

GND

ADP1752

REVERSE POLARITY

PROTECTION

PG

DETECT

0.9µA

Figure 24. ADP1752 Internal Block Diagram

UVLO

VOUT

VIN

ADJ

SS

SHORT-CIRCUIT

AND THERMAL

PROTECTION

0.5V

REF

SHUTDOWN

EN

PG

GND

ADP1753

REVERSE POLARITY

PROTECTION

PG

DETECT

0.9µA

Figure 25. ADP1753 Internal Block Diagram

Internally, the ADP1752/ADP1753 consist of a reference, an error

amplifier, a feedback voltage divider, and a PMOS pass transistor.

Output current is delivered via the PMOS pass transistor, 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 ADP1752 is available in seven fixed output voltage options

between 0.75 V and 2.5 V. The ADP1752 allows for connection

of an external soft start capacitor that controls the output voltage

ramp during startup. The ADP1753 is the adjustable version

with an output voltage that can be set to a value between 0.75 V

and 3.3 V by an external voltage divider. Both devices are con-

trolled by an enable pin (EN).

SOFT START FUNCTION (ADP1752/ADP1753)

For applications that require a controlled startup, the ADP1752/

ADP1753 provide a programmable soft start function. The

programmable soft start is useful for reducing inrush current

upon startup and for providing voltage sequencing. To implement

soft start, connect a small ceramic capacitor from SS to GND.

Upon startup, a 0.9 µA current source charges this capacitor.

The ADP1752/ADP1753 start-up output voltage is limited by

the voltage at SS, providing a smooth ramp-up to the nominal

output voltage. The soft start time is calculated as follows:

(1)

where:

When the ADP1752/ADP1753 are disabled (using EN), the soft

start capacitor is discharged to GND through an internal 100 Ω

resistor.

2.50

0

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

0

2

4

6

8

10

TIME (ms)

EN

1nF

4.7nF

10nF