Rainbow Electronics MAX7473 - Manual (Page 16)

MAX7472/MAX7473
Power-Supply Bypassing and
Layout Considerations
The MAX7472/MAX7473 operate from a single +5V
analog supply and +3.3V digital supply. Bypass each
AV
DD to AGND with a 0.1µF capacitor with an addition-
al 1µF capacitor in parallel for low-frequency decou-
pling. Determine the proper power-supply bypassing
necessary by taking into account the desired distur-
bance level tolerable on the output, the power-supply
rejection of the MAX7472/MAX7473, and the amplitude
and frequency of the disturbance signals present in the
vicinity of the MAX7472/MAX7473. Use an extensive
ground plane to ensure optimum performance. The
three AV
DD
inputs (pins 18, 20, and 22) that supply the
individual channels can be connected together and
bypassed as one provided the components are close
to the pins. Bypass DV
DD to DGND with a 0.1µF capac-
itor. Connect all ground pins to a low-impedance
ground plane as close to the device as possible.
Place the input termination resistors as close to the
device as possible. Alternatively, the terminations can
be placed further from the device if the PC board
traces are designed to be a controlled impedance of
75Ω. Minimize parasitic capacitance as much as possi-
ble to avoid performance degradation in the upper fre-
quency range possible with the MAX7472/MAX7473.
Refer to the MAX7472/MAX7473 evaluation kit for a
proven PC board layout.
Exposed Pad and Heat Dissipation
The MAX7472/MAX7473 TQFN package provides an
exposed pad on the bottom side of the package. This
pad is electrically connected to AGND and must be
soldered to the ground plane for proper thermal con-
ductivity. Do not route any PC board traces under the
package.
The MAX7472/MAX7473 typically dissipate 900mW of
power; therefore, pay attention to heat dispersion. Use
at least a two-layer board with a good ground plane. To
maximize heat dispersion, place copper directly under
the MAX7472/MAX7473 package to match the outline
of the plastic encapsulated area. Repeat the same with
the bottom ground plane layer and place as many vias
as possible connecting the top and bottom layers to
thermally connect to the ground plane.
Maxim has evaluated a four-layer board using FR-4
material and 1oz copper with equal areas of metal on
the top and bottom side coincident with the plastic
encapsulated areas of the package. The two middle
layers are used as power and ground planes. The
board has 21, 15-mil, plated-through via holes between
top, bottom, and ground plane layers. Thermocouple
measurements confirm device temperatures to be safe-
ly within maximum limits.
HDTV Anti-Aliasing Filters with Triple-Input Mux
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