AP1506
150KHz, 3A PWM BUCK DC/DC CONVERTER
AP1506
Document number: DS31015 Rev. 7 - 2
7 of 14
www.diodes.com
June 2010
© Diodes Incorporated
Functional Description
Pin Functions
+V
IN
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 (+V
IN
– V
SAT
) and approximately – 0.5V, with a duty cycle
of approximately V
OUT
/ V
IN
. 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
25
o
C (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
2
,
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.
