FMS6141 — Low-Cost, Single-Channel 4
th
-Order Standard Definition Video Filter Driver
www.onsemi.com
8
Layout Considerations
General layout and supply bypassing play a major role in
high-frequency performance and thermal characteristics.
ON Semiconductor offers a demonstration board for the
FMS6141 to guide layout and aid device evaluation. The
demo board is a four-layer board w ith full pow er and
ground planes. Follow ing 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
Do not run analog and digital signals in parallel.
Use separate analog and digital pow er planes to supply
pow er.
Traces should run on top of the ground plane at all
times.
No trace should run over ground/pow er splits.
Avoid routing at 90-degree angles.
Minimize clock and video data trace length differences.
Include 10 µF and 0.1 µF ceramic pow er supply bypass
capacitors.
Place the 0.1 µF capacitor w ithin 0.1 inches of the
device pow er pin.
Place the 10 µF capacitor w ithin 0.75 inches of the
device pow er pin.
For multilayer boards, use a large ground plane to help
dissipate heat.
For tw o-layer boards, use a ground plane that extends
beyond the device body by at least 0.5 inches on all
sides. Include a metal paddle under the device on the
top layer.
Minimize all trace lengths to reduce series inductance.
Thermal Considerations
Since the interior of most 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 pow er
each device dissipates. Ensure that devices of high
pow er are not placed in the same location, such as
directly above (top plane) and below (bottom plane) each
other on the PCB.
PCB Thermal Layout Considerations
Understand the system pow er requirements and
environmental conditions.
Maximize thermal performance of the PCB.
Consider using 70 µm of copper for high-pow er
designs.
Make the PCB as thin as possible by reducing FR4
thickness.
Use vias in pow er pad to tie adjacent layers together.
Remember that baseline temperature is a function of
board area, not copper thickness.
Modeling techniques can provide a first-order
approximation.
Power Dissipation
Consider the FMS6141’s output drive configuration when
calculating overall pow er dissipation. Care must be taken
not to exceed the maximum die junction temperature. The
follow ing example can be used to calculate the
FMS6141’s pow er dissipation and internal temperature
rise.
T
J
= T
A
+ P
CHANNEL
Θ
JA
w here P
CHANNEL =
V
CC
• I
CH
+ (V
O
2
/R
L
)
V
O
= 2V
IN
+ 0.280V
I
CH
= I
CC
+ (V
O
/R
L
)
V
IN
= RMS value of input signal
I
CC
= 7mA
V
S
= 5V
R
L
= channel load resistance
The FMS6141 is specified to operate w ith output currents
typically less than 50 mA, w hich is more than sufficient
for a dual (75 Ω) video load. The internal amplifiers of the
FMS6141 are current limited to a maximum of 100 mA and
can w ithstand a brief-duration short-circuit condition, but
this capability is not guaranteed.
