AP1516 Ver la hoja de datos (PDF) - Anachip Corporation
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AP1516 Datasheet PDF : 10 Pages
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150KHz, 3A PWM Buck DC/DC Converter + 1A Ultra Low
Drop Regulator
AP1516
Function Description (Continued)
Since the minimum load current requirement of the
channel 2 is 10mA, R1 is typically selected to be a
121Ω resistor so that it automatically satisfies this
condition. Notice that since the IFB2 is typically in
the range of 50uA it only adds a small error to the
output voltage and should be considered when very
precise output voltage setting is required.
Load Regulation
Since the channel 2 has separate pins for the
output (VOUT2) and the sense (VSENSE2), it is ideal for
providing true remote sensing of the output voltage
at the load. This means that the voltage drops due
to parasitic resistance such as PCB traces between
the regulator and the load are compensated for
using remote sensing. Figure following shows a
typical application of the channel 2 with remote
sensing.
Thermal Considerations
The SOP-16 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 AP1516
junction temperature rises above ambient
temperature for a 3A load and different input and
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.
Vin3
Vin3
Vout2
Channel 2-ADJ
Vsense2
Vin2
Vin2 FB2
R1
RL
R2
Stability
The channel 2 requires the use of an output
capacitor as part of the frequency compensation in
order to make the regulator stable. Typical designs
for the microprocessor applications use standard
electrolytic capacitors with typical ESR in the range
of 50 to 100mΩ and an output capacitance of
100uF to 1000uF. Fortunately as the capacitance
increases, the ESR decreases resulting in a fixed
RC time constant. The channel 2 takes advantage
of the phenomena in making the overall regulator
loop stable.
For most applications a minimum of 100uF
aluminum electrolytic capacitor insures both
stability and good transient response.
Package thermal resistance and junction
temperature rise numbers are all approximate, and
there are many factors that will affect these
numbers. Some of these factors include board
size, shape, thickness, position, location, and even
board temperature. Other factors are, trace width,
total printed circuit copper area, copper thickness,
single or double-sided, multi-layer board and the
amount of solder on the board.
The effectiveness of the PC board to dissipate heat
also depends on the size, quantity and spacing of
other components on the board, as well as whether
the surrounding air is still or moving. Furthermore,
some of these components such as the catch diode
will add heat to the PC board and the heat can vary
as the input voltage changes. For the inductor,
depending on the physical size, type of core
material and the DC resistance, it could either act
as a heat sink taking heat away from the board, or
it could add heat to the board.
Anachip Corp.
www.anachip.com.tw
Rev.1.1 May 23, 2005
9/10
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