AP1533

PWM CONTROL 1.8A STEP-DOWN CONVERTER

AP1533 Rev. 1

7 of 8

JULY 2007

www.diodes.com

Test Circuit

A

FB

V

CC

V

SS

EN

open

open

FB

EN

+

-

OUTPUT

OUTPUT

A

FB

EN

+

-

+

-

V

OUTPUT

OCSET

OCSET

OCSET

Enable function test

Feedback function test

Operation function test

V

CC

V

CC

V

SS

V

SS

Function Description

PWM Control

The AP1533 is a DC/DC converter that employs pulse width

modulation (PWM) scheme. Its pulse width varies in the range of

0% to 99%, based on the output current loading. The output

ripple voltage caused by the PWM high frequency switching can

easily be reduced through an output filter. Therefore, this

converter provides a low ripple output supply over a broad range

of input voltage & output current loading

Under Voltage Lockout

The under voltage lockout circuit of the AP1533 assures that the

high-side MOSFET driver remains in the off state whenever the

supply voltage drops below 3.3V. Normal operation resumes

Current Limit Protection

at OCSET pin. When the PWM voltage is less than the voltage at

OCSET, an over-current condition is triggered.

The current limit threshold is given by the following equation:

R

I

R

I

OCSET

OCSET

DS(ON)

PEAK

×

=

×

2

I)

(

I

I

(MAX)

OUT

PEAK

Δ

+

>

where,

IN

OUT

S

OUT

IN

V

V

x

xL

F

V

V

I

−

=

Δ

resistance (115m

Ω typical); F

typical). Also, the inductor value will affect the ripple current

ΔI.

The above equation is recommended for input voltage range of

5V to 18V. For input voltage lower than 5V, higher than 18V or

ambient

temperature

over

100°C,

is

recommended.

4

0.8

3.9K

5

3.3

3.3K

12

5

3.3K

18

12

3.3K

23

12

4.7K

current output.