AP1501-12K5 Просмотр технического описания (PDF) - Anachip Corporation

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AP1501-12K5

5A PWM Buck DC/DC Converter

Anachip Corporation 

150Khz, 3A PWM Buck DC/DC Converter

AP1501

„ Function Description

Pin Functions

+VIN

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

between (+VIN – VSAT) and approximately – 0.5V,

with a duty cycle of approximately VOUT / VIN. To

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 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 AP1501 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 AP1501 junction

temperature rises above ambient temperature for a

3A load and different input and output voltages.

The data for these curves was taken with the

AP1501 (TO-220 package) operating as a buck

switching regulator in an ambient temperature of

25oC (still air). These 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 0.4 in2,

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 in2, only small improvements 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.

The AP1501 (TO-263 package) junction

temperature rise above ambient temperature with a

2A load for various input and output voltages. This

data was taken with the circuit operating as a buck

switching regulator with all components mounted on

a PC board to simulate the junction temperature

under actual operating conditions. This curve can

be used for a quick check for the approximate

junction temperature for various conditions, but be

aware that there are many factors that can affect

the junction temperature. When load currents

higher than 2A are used, double sided or multilayer

PC boards with large copper areas and/or airflow

might be needed, especially for high ambient

temperatures and high output voltages.

For the best thermal performance, wide copper

traces and generous amounts of printed circuit

board copper should be used in the board layout.

(Once exception to this is the output (switch) pin,

which should not have large areas of copper.)

Large areas of copper provide the best transfer of

heat (lower thermal resistance) to the surrounding

air, and moving air lowers the thermal resistance

even further.

Anachip Corp.

www.anachip.com.tw

Rev.1.2 Aug. 23, 2005

8/12

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