
ADP3203
REV. PrD
–
11
–
PRELIMINARY TECHNICAL DATA
near the MOSFETs will help. Even just small airflow
can help tremendously. Paralleled MOSFETs to achieve
a given resistance will help spread the heat.
6. An external "antiparallel" schottky diode (across the
bottom MOSFET) may help efficiency a small amount
(< ~1 %) depending on its forward voltage drop com-
pared to the MOSFET's body diode at a given current; a
MOSFET with a built in antiparallel schottky is more
effective. For an external schottky, it should be placed
next to the bottom MOSFET or it may not be effective
at all.
7. The VCC bypass capacitor should be close to the VCC
pin and connected on either a very short trace to the
GND pin or to the GND plane.
Output Filter
Output Inductor and Capacitors, Current Sense Resistor
8. Locate the current sense resistors very near to the output
voltage plane.
9. The load-side heads of two sense resistors should join as
closely as possible for accurate current signal measure-
ment of each phase.
10.PCB trace resistances from the current sense resistors to
the regulation point should be minimized, known
(calculated or measured), and compensated for as part
of the design if it is significant. (Remote sensing is not
sufficient for relieving this requirement!) A square
section of 1-ounce copper trace has a resistance of
~500 m
and this adds to the specified DC output
resistance of the power converter. The output capaci-
tors should similarly be close to the regulation point and
well tied into power planes as impedance here will add
to the "AC output resistance" (i.e., the ESR) that is
implicitly specified as well.
11.Whenever high currents must be routed between PCB
layers, vias should be used liberally to create parallel
current paths so that the resistance and inductance is
minimized and the via current rating is not exceeded.
Control Circuitry
ADP3203, Control Components
12.If the ADP3203 cannot be placed as previously recom-
mended, at the least care should be taken to keep the
device and surrounding components away from radia-
tion sources (e.g., from power inductors) and capacitive
coupling from noisy power nodes.
13.Noise immunity can be improved by the use of a
devoted signal ground plane for the power controller
and its surrounding components. Space for a ground
plane might readily be available on a signal plane of the
PCB since it is often unused in the vicinity of the power
controller.
14.If critical signal lines (i.e., signals from the current sense
resistor leading back to the ADP3203) must cross
through power circuitry, it is best if a signal ground
plane can be interposed between those signal lines and
the traces of the power circuitry. This serves as a shield
to minimize noise injection into the signals.
15.Absolutely avoid crossing any signal lines over the
switching power path loop, described previously.
16.Accurate voltage positioning depends on accurate
current sensing, so the control signals which monitor the
voltage differentially across the current sense resistor
should be kelvin connected. Please refer to ADI Evalua-
tion Board of the ADP3203 and its documentation for
control signal connection with sense resistors.
17.The RC filter used for the current sense signal should be
located near the control components as this serves the
dual purpose of filtering out the effect of the current
sense resistors' parasitic inductance and noise picked up
along the routing of the signal. The former purpose is
achieved by having the time constant of the RC filters
approximately matched to that of the sense resistors and
is important for maintaining the accuracy of the current
signal.
TABLE 1. VID CODE
VID2
VID1
VID4
VID3
VID0
VOUT
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
1.750
1.700
1.650
1.600
1.550
1.500
1.450
1.400
1.350
1.300
1.250
1.200
1.150
1.100
1.050
1.00
0.975
0.950
0.925
0.900
0.875
0.850
0.825
0.800
0.775
0.750
0.725
0.700
0.675
0.650
0.625
0.600