MD3221N 데이터 시트보기 (PDF) - Shindengen
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MD3221N Datasheet PDF : 26 Pages
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6 Cautions for Pattern Design
Substrate pattern design has a major effect on DC-DC converter characteristics. As the MD3221N switches
a large current very rapidly, a large inductance component in the pattern will provide a source of noise. It is
therefore very important to ensure that the primary circuit pattern is as thick and short as possible.
◆Primary Circuit Pattern Design
● Wiring Pattern Illustration
Vi
VDD
VCC
VOUT
MD3221N
GND
P.GND2
+VO
The choke coil and output condenser are
connected next. As this pattern carries a
continuous current, voltage drop rather than
noise is the important consideration. A long
pattern in this case will result in a voltage drop due
to pattern DC resistance, and reduced
efficiency.
The MD3221N is designed to radiate heat
through the substrate pattern. In particular, both
the VDD and VOUT pins are allocated each to four
pins, and connected directly to the internal lead
frame. All of these pins may therefore be used to
ensure a large pattern area and thus provide
for effective radiation of heat.
◆Control Circuit Pattern Design
In the main circuit, the pattern between the input
condenser and VDD, and between P.GND2 and the
input condenser, are subject to the greatest
variations in current. Particular attention should
therefore be given to ensure that these patterns
are as thick and as short as possible. The use of
through-holes in these patterns is to be avoided.
Voltage drop due to the DC resistance of
through-holes may result in a change in the
over-current detection point in some cases.
The SBD pattern is connected next. Connect
the anode to P.GND2, and the cathode to VOUT.
A long pattern in this case will not only result in
considerable noise, but will also cause a drop in
efficiency.
The control circuit pattern must be designed to
ensure that it is not subject to noise, electric
fields, and magnetic field from the choke coil.
The GND pin is the control IC GND. Connect this
pin close to the input condenser. The VCC pin is the
control circuit input pin. Always connect a
condenser (C7) across the VCC and GND pins to
eliminate noise.
The Vref pin provides the reference voltage for the
internal logic circuit of the IC. Noise at this pin may
result in a malfunction. Always connect a
condenser (C8) to this pattern to eliminate noise.
The P.GND1 pin is the low side driver GND and is
connected to the P.GND2 pin. Ensure that these pins
are connected close to the -ve pin of the input
condenser.
16
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