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ADP1752-1.5-EVALZ

0.8 A, Low VIN, Low Dropout Linear Regulator

Analog Devices 

Data Sheet

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.

ADP1752

VIN

UVLO

REVERSE POLARITY

PROTECTION

VOUT

GND

PG

EN

SHORT-CIRCUIT

AND THERMAL

PROTECTION

PG

DETECT

0.5V

REF

SHUTDOWN

SENSE

R1

R2

0.9µA

SS

VIN

GND

Figure 24. ADP1752 Internal Block Diagram

ADP1753

UVLO

REVERSE POLARITY

PROTECTION

VOUT

SHORT-CIRCUIT

AND THERMAL

PROTECTION

PG

0.5V

REF

PG

DETECT

EN

SHUTDOWN

ADJ

0.9µA

SS

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.

ADP1752/ADP1753

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:

tSS = VREF × (CSS/ISS)

(1)

where:

tSS is the soft start period.

VREF is the 0.5 V reference voltage.

CSS is the soft start capacitance from SS to GND.

ISS is the current sourced from SS (0.9 µA).

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

start capacitor is discharged to GND through an internal 100 Ω

resistor.

2.50

2.25

EN

2.00

1.75

1nF

1.50

1.25

4.7nF

1.00

10nF

0.75

0.50

0.25

0

0

2

4

6

8

10

TIME (ms)

Figure 26. VOUT Ramp-Up with External Soft Start Capacitor

Rev. E | Page 11 of 20

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