AP1512/A

50KHz, 2A/3A PWM Buck DC/DC Converter

Anachip Corp.

www.anachip.com.tw

Rev.1.1 Oct. 14, 2005

8/12

Typical Application Circuit (Continued)

B. Vin=10V~60V, Vout=3.3V, Iout=0.7A~2A, Iout below 0.7A DCM

L1

33uH

12

Vin

C2

3.3u

D1

SR360

ON/OFF

C1

220uF/100V

Vout

AP1512/A

1

5

2

4

3

Vin

SD

OUTPUT

FB

GND

3.3u

C3

1500uF/16V

C7

Function Description

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

40V) shuts the regulator down. If this shutdown

feature is not needed, the SD 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 AP1512/A 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 AP1512/A

junction

temperature

rises

above

ambient

temperature for a 2A load and different input and

output voltages. The data for these curves was

taken with the AP1512/A (TO-220 package)

operating as a buck

switching regulator in an ambient temperature of

25

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 0.4 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.