FMS6144AMTC14X datasheet(12/15 Pages) ONSEMI

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FMS6144A • Rev. 1.0.2

Layout Considerations

General layout and supply bypassing play a major role

high-frequency

performance

and

thermal

characteristics. Fairchild offers a four-layer board with

full power and ground planes 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 best results,

follow the steps and recommended routing rules below.

Recommended Routing / Layout Rules

 Do not run analog and digital signals in parallel.

 Use separate analog and digital power planes to

supply power.

 Traces should run on top of the ground plane at all

times.

 No trace should run over ground/power splits.

 Avoid routing at 90-degree angles.

 Minimize clock and video data trace length

differences.

 Include 10μF and 0.1μF ceramic power supply

bypass capacitors.

 Place the 0.1μF capacitor within 2.54mm (0.1in)

of the device power pin.

 Place the 10μF capacitor within 19.05mm (0.75in)

of the device power pin.

 For multi-layer boards, use a large ground plane to

help dissipate heat.

 For two-layer boards, use a ground plane that

extends beyond the device body at least 12.7mm

(0.5in) on all sides. Include a metal paddle under

the device on the top layer.

 Minimize all trace lengths to reduce series

inductance.

Output Considerations

The outputs are DC offset from the input by 150mV

therefore VOUT = 2 • VIN DC + 150mV. This offset is

required for optimal performance from the output driver

and is held at the minimum value to decrease the

standing DC current into the load. Since the FMS6144A

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 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 the device pin to the series termination resistor

should be no greater than 2.54mm (0.1in).

Figure 22.

Termination Resistor Placement

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 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

 Understand the system power requirements and

environmental conditions.

 Maximize thermal performance of the PCB.

 Consider using 70μm of copper for high-power

designs.

 Make the PCB as thin as possible by reducing FR4

thickness.

 Use vias in power pad to tie adjacent layers

together.

 Remember that baseline temperature is a function

of board area, not copper thickness.

 Modeling techniques provide a first-order

approximation.

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