AP1501
150Khz, 3A PWM Buck DC/DC Converter
Typical Application Circuit
FB
12V
DC Input
Vin
1
5
4
AP1501
-33
3
SD
2
Output
L1
Inductor
3.3V/3A
Output Load
C
in
Capacitor
Gnd
D1
Schottky Diode
Co
Capacitor
Function Description
Pin Functions
+V
IN
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 (+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 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
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 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
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 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
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, multilayer
PC board with large copper areas and/or airflow are
recommended.
Anachip Corp.
www.anachip.com.tw
7/11
Rev.A7 Feb. 10, 2004
ANACHIP [ ANACHIP CORP ]
