FMS6364A Datasheet, PDF (10/12 Pages) Fairchild Semiconductor – Low-Cost Four-Channel Standard Definition (SD) & High (HD) Definition Video Filter Driver

Layout Considerations
General layout and supply bypassing play a major role
in high-frequency performance and thermal
characteristics. Fairchild offers a demonstration board to
guide layout and aid device evaluation. The demo board
is a four-layer board with full power and ground planes.
Following this layout configuration provides optimum
performance and thermal characteristics for the device.
For the best results, follow the steps and recommended
routing rules listed below.
Recommended Routing/Layout Rules
ƒ Do not run analog and digital signals in parallel.
ƒ Use separate analog and digital power planes to
supply power.
ƒ Do not run traces on top of the ground plane.
ƒ Run no traces over ground/power splits.
ƒ Avoid routing at 90-degree angles.
ƒ Minimize clock and video data trace length
differences.
ƒ Include 0.01μF and 0.1μF ceramic power supply
bypass capacitors.
ƒ Place the 0.1μF capacitor within 0.1 inches of the
device power pin.
ƒ Place the 0.01μF capacitor within 0.75 inches of the
device power pin.
ƒ For multi-layer boards, use a large ground plane to
help dissipate heat.
ƒ For two-layer boards, use a ground plane that
extends beyond the device body at least 0.5 inches
on all sides. Include a metal paddle under the
device on the top layer.
ƒ Minimize all trace lengths to reduce series
inductance.
ƒ Place a 75Ω series resistor within 0.5 inches of the
output pin to isolate the output driver from board
parasitics.
Output Considerations
The FMS6364A outputs are DC offset from the input by
150mV; therefore VOUT = 2 • VIN DC+150mV. This offset
is required to obtain optimal performance from the
output driver and is held at the minimum value to
decrease the standing DC current into the load. Since
the FMS6364A has a 2x (6dB) gain, the output is
typically connected via a 75Ω-series back-matching
resistor followed by the 75Ω video cable. Because of the
inherent divide by two of this configuration, the blanking
level at the load of the video signal is always less than
1V. When AC coupling the output, ensure that the
coupling capacitor of choice passes the lowest
frequency content in the video signal and that line time
distortion (video tilt) is kept as low as possible. The
selection of the coupling capacitor is a function of the
subsequent circuit input impedance and the leakage
current of the input being driven. To obtain the highest
quality output video signal, the series termination
resistor must be placed as close to the device output pin
as possible. This greatly reduces the parasitic
capacitance and inductance effect on the output driver.
The distance from device pin to the series termination
resistor should be no greater than 0.5 inches.
0.5”
Figure 19. Recommended Resistor Placement
Thermal Considerations
Since the interior of systems such as set-top boxes,
TVs, and DVD players are at +70ºC; consideration must
be given to providing an adequate heat sink for the
device package for maximum heat dissipation. When
designing a system board, determine how much power
each device dissipates. Ensure that devices of high
power are not placed in the same location, such as
directly above (top plane) or below (bottom plane), each
other on the PCB.
PCB Thermal Layout Considerations
ƒ Understand the system power requirements and
environmental conditions.
ƒ Maximize thermal performance of the PCB.
ƒ Consider using 70μm of copper for high-power
designs.
ƒ Make the PCB as thin as possible by reducing FR4
thickness.
ƒ Use vias in the power pad to tie adjacent layers
together.
ƒ Remember that baseline temperature is a function
of board area, not copper thickness.
ƒ Consider modeling techniques a first-order
approximation.
© 2010 Fairchild Semiconductor Corporation
FMS6364A • Rev. 3.0.1
10
www.fairchildsemi.com