AP1501A

150Khz, 5A PWM Buck DC/DC Converter

Anachip Corp.

www.anachip.com.tw

Rev.0.4 Feb 19, 2004

7/11

Typical Application Circuit

12

3

5

4

12V

DC Input

Capacitor

FB

SD

D1

Schottky Diode

Vin

Gnd

Output

AP1501A

-33

Co

Capacitor

Inductor

L1

3.3V/5A

Output Load

Function Description

Pin Functions

This is the positive input supply for the IC switching

regulator. A suitable input bypass capacitor must be

present at this pin to minimize voltage transients

and to supply the switching currents needed by the

regulator.

Ground

Circuit ground.

Output

Internal switch. The voltage at this pin switches

minimize coupling to sensitive circuitry, the PC

board copper area connected to this pin should be

kept a minimum.

Feedback

Senses the regulated output voltage to complete

the feedback loop.

ON /OFF

Allows the switching regulator circuit to be

shutdown using logic level signals thus dropping

the total input supply current to approximately

150uA. Pulling this pin below a threshold voltage of

approximately 1.3V turns the regulator on, and

pulling this pin above 1.3V (up to a maximum of

25V) shuts the regulator down. If this shutdown

feature is not needed, the ON /OFF pin can be

wired to the ground pin or it can be left open, in

either case the regulator will be in the ON condition.

Thermal Considerations

The AP1501A is available in two packages, a 5-pin

TO-220 and a 5-pin surface mount TO-263.

The TO-220 package needs a heat sink under most

conditions. The size of the heatsink depends on the

input voltage, the output voltage, the load current

and the ambient temperature. The AP1501A

junction

temperature

rises

above

ambient

temperature for a 5A load and different input and

output voltages. The data for these curves was

taken with the AP1501A (TO-220 package)

operating as a buck switching regulator in an

ambient temperature of 25

temperature rise numbers are all approximate and

there are many factors that can affect these

temperatures. Higher ambient temperatures require

more heat sinking.

The TO-263 surface mount package tab is

designed to be soldered to the copper on a printed

circuit board. The copper and the board are the

heat sink for this package and the other heat

producing components, such as the catch diode

and inductor. The PC board copper area that the

package is soldered to should be at least 0.8 in

and ideally should have 2 or more square inches of

2 oz. Additional copper area improves the thermal

characteristics, but with copper areas greater than

approximately 6 in

heat dissipation are realized. If further thermal

improvements are needed, double sided, multilayer

PC board with large copper areas and/or airflow are

recommended.