AP1506 datasheet(7/14 Pages) DIODES

7 / 14 page

AP1506

150KHz, 3A PWM BUCK DC/DC CONVERTER

AP1506

Document number: DS31015 Rev. 7 - 2

7 of 14

www.diodes.com

June 2010

Functional Description

Pin Functions

+VIN

This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be

presented 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 to a minimum.

Feedback (FB)

Senses the regulated output voltage to complete the feedback loop.

ON/OFF (SD)

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 18V) shuts the regulator down. If this shutdown

feature is not needed, the ON / OFF pin can be wired to the ground pin.

Thermal Considerations

The AP1506 is available in two packages: a 5-pin TO220 and a 5-pin surface mount TO263.

The TO220 package needs a heat sink under most conditions. The size of the heat sink depends on the input

voltage, the output voltage, the load current and the ambient temperature. The AP1506 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 AP1506 (TO220 package) operating as a buck-switching regulator in an ambient temperature of

oC (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 TO263 surface mount package tab was designed to be soldering 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

2, only small improvements in heat

dissipation are realized. If further thermal improvements are needed, double sided, multi-layer PC board with large

copper areas and/or airflow will be recommended.

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