FMS6364AMTC14X datasheet(11/13 Pages) ONSEMI

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FMS6364A • Rev. 3.0.5

Layout Considerations

General layout and supply bypassing play a major role

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

 Do not run analog and digital signals in parallel.

 Use separate analog and digital power planes to

supply power.

 Do not run traces on top of the ground plane.

 Run no traces over ground/power splits.

 Avoid routing at 90-degree angles.

 Minimize clock and video data trace length

differences.

 Include 0.01 μF and 0.1 μF ceramic power supply

bypass capacitors.

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

of the device power pin.

 Place the 0.01 μF capacitor within 19.05 mm

(0.75 in) 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 12.7 mm

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

the device on the top layer.

 Minimize all trace lengths to reduce series

inductance.

 Place a 75 Ω series resistor within 12.7 mm (0.5 in)

of the output pin to isolate the output driver from

board parasitics.

Output Considerations

The FMS6364A outputs are DC offset from the input by

150 mV; therefore VOUT = 2 • VIN DC+150 mV. 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 2 x (6 dB) gain, the output is

typically connected via a 75

Ω-series back-matching

resistor followed by the 75

Ω 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 1 V. 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

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 12.7 mm (0.5 in).

Routing Trace

≤ 12.7mm

75-Ohm Series

Termination Resistor

Lead

Pad

Pad for

Resistor

Lead

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

 Understand the system power requirements and

environmental conditions.

 Maximize thermal performance of the PCB.

 Consider using 70 μm of copper for high-power

designs.

 Make the PCB as thin as possible by reducing FR4

thickness.

 Use vias in the power pad to tie adjacent layers

together.

 Remember that baseline temperature is a function

of board area, not copper thickness.

 Consider modeling techniques a first-order

approximation.

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