Datasheet

LMH1980

SNLS263A –JULY 2007–REVISED MARCH 2013

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PCB LAYOUT CONSIDERATIONS

Please refer to the “LMH1980 Evaluation Board Instruction Manual” Application Note (AN-1618 [SNLA096]) for a

good PCB layout example, which adheres to the following suggestions for component placement and signal

routing.

LMH1980 IC Placement

The LMH1980 should be placed such that critical signal paths are short and direct to minimize PCB parasitics

from degrading the video input and logic output signals.

Ground Plane

A two-layer, FR-4 PCB is sufficient for this device. One of the PCB layers should be dedicated to a single, solid

ground plane that connects to the GND pin of the device and connects to other components, serving as the

common ground reference. It also helps to reduce trace inductances and minimize ground loops. Routing supply

and signal traces on another layer can help to maintain as much ground plane continuity as possible.

Power Supply Routing

The power supply pin should be connected using short traces with minimal inductance. When routing the supply

traces, try not to disrupt the solid ground plane.

For high frequency bypassing, place 0.1 µF and 0.01 µF SMD ceramic bypass capacitors with very short

connections to V

and GND pins. Place a 4.7 or 10 µF SMD tantalum bypass capacitor nearby the V

for low

frequency supply bypassing.

EXT

Resistor

The R

EXT

resistor should be a 10 kΩ 1% SMD precision resistor. Place R

EXT

as close as possible to the device

and connect to pin 1 and the ground plane using the shortest possible connections. All input and output signals

should be kept as far as possible from this pin to prevent unwanted signals from coupling into this bias reference

pin.

Video Input

The input signal path should be routed using short, direct traces between video source and input pin. Use a 75Ω

load termination on the board, if not on the cable. If applicable, the chroma filter components should be

connected using short traces and the filter capacitor should be connected to the ground plane. There should be a

sufficient return path from the LMH1980 back to the input source via the ground plane.

Output Routing

The output signal paths should be routed using short, direct traces to minimize parasitic effects that may degrade

these high-speed logic signals. The logic outputs do not have high output drive capability. Each output should

have a resistive load of about 10kΩ or more and capacitive load of about 10pF including parasitic capacitances

for optimal signal quality. Each output can be protected against brief short-circuit events using a small series

resistor, like 100Ω, to limit output current.

Product Folder Links: LMH1980