FMS6141CSX datasheet(8/11 Pages) ONSEMI

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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 w hen

calculating overall pow er dissipation. Care must be taken

not to exceed the maximum die junction temperature. The

follow ing

example

can

used

calculate the

FMS6141’s pow er dissipation and internal temperature

rise.

TJ = TA + PCHANNEL ΘJA

w here PCHANNEL = VCC • ICH + (VO

2/R

VO = 2VIN + 0.280V

ICH = ICC + (VO/RL)

VIN = RMS value of input signal

ICC = 7mA

VS = 5V

RL = 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.

FMS6141CSX Datasheet(PDF) 8 Page - ON Semiconductor

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