AP3503

Document number: DS41526 Rev. 2 - 2

2 of 10

www.diodes.com

October 2018

© Diodes Incorporated

AP3503

Typical Applications Circuit

C3

3.3nF

C12

10

μF/25V

C22

22

μF/25V

D1

Optional

L 10

μH

R4

100k

R2

10k

R1

26.1k

R3

13k

C6

Optional

C4

10nF

C5

0.1

μF

3

5

1

6

7

8

2

4

BS

IN

SW

GND

FB

COMP

EN

SS

C21

22

μF/25V

C11

10

μF/25V

Input Voltage=12V

Output Voltage=3.3V

Pin Descriptions

Pin Number

Pin Name

Function

1

BS

Bootstrap pin. A bootstrap capacitor is connected between the BS pin and SW pin. The voltage

across the bootstrap capacitor drives the internal high-side power MOSFET

2

IN

Supply power input pin. A capacitor should be connected between the IN pin and GND pin to keep the

input voltage constant

3

SW

Power switch output pin. This pin is connected to the inductor and bootstrap capacitor

4

GND

Ground pin

5

FB

Feedback pin. This pin is connected to an external resistor divider to program the system output

voltage. When the FB pin voltage exceeds 1.1V, the over voltage protection is triggered. When the FB

pin voltage is below 0.3V, the oscillator frequency is lowered to realize short circuit protection

6

COMP

Compensation pin. This pin is the output of the transconductance error amplifier and the input to the

current comparator. It is used to compensate the control loop. Connect a series RC network from this

pin to GND. In some cases, an additional capacitor from this pin to GND pin is required

7

EN

Control input pin. EN is a digital input that turns the regulator on or off. Drive EN high/low to turn on/off

the regulator. Pull up with 100k

Ω resistor for automatic startup

8

SS

Soft-start control input pin. SS controls the soft-start period. Connect a capacitor from SS to GND to

set the soft-start period. A 0.1

μF capacitor sets the soft-start period to 15ms. To disable the soft-start

feature, leave SS unconnected

EP

Exposed pad. It should be connected to GND in PCB layout