FAC1507 datasheet(11/15 Pages) FS

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3A 150KHZ PWM Buck DC/DC Converter

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

80uA. 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 FAC1507 is available in TO252-5L package.

The TO252 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 FAC1507 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 FAC1507 (TO252

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 TO252 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

FAC1507

(TO252

package)

junction

temperature rise above ambient temperature with

a 3A 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 3A 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.

FAC1507

2019. 03. 27

11/15

Revision No : 1

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