LM98555

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SNAS290D – DECEMBER 2005 – REVISED APRIL 2013

Several other techniques will also help maintain signal quality, and minimize timing differences between critical

signals. Vias should not be used for critical timing signals. These can add impedance discontinuities that will

affect the waveform quality. Traces should have gradual bends and avoid sharp changes in direction that can

also introduce impedance discontinuities.

SELECTIVE DRIVER ENABLING

With the Enable pins, the user has the capability to enable only the drivers that are required for the application,

thus eliminating unnecessary outputs switching. The following table shows the details.

EN1

EN0

Driver-set State

0

0

P1Aout(1:0) and P2Aout(1:0) are enabled; all others disabled.

0

1

P1Aout(3:0) and P2Aout(3:0) are enabled; all others disabled.

1

0

P1Aout(5:0) and P2Aout(5:0) are enabled; all others disabled.

1

1

All P1Aout and P2Aout drivers are enabled.

Note: The disabled drivers' outputs are in TRI-STATE.

POWER SUPPLY SEQUENCING

POWER AND GROUND - PLANES VERSUS BUSES

The best performance will be achieved by using planes rather than traces for power and ground. Planes provide

lower electrical and thermal impedance. Ground bounce and ringing are reduced, electromagnetic emissions are

minimized and the best thermal performance will be realized.

A single common ground plane should be used for all power and signal domains.

Another circuit board layer can be used to provide power to the various circuitry. Different power buses can be

provided by isolated planes within this layer of the circuit board.

EMI MANAGEMENT

Good EMI control will be achieved by addressing the following items:

•

Provide proper source termination of output signals

•

Limit length of output traces

•

Ensure adequate power supply decoupling

•

Provide power and ground planes as much as possible

•

Provide common ground plane for all signals, especially between LM98555 outputs and load CCD

•

Enable and use the minimum number of outputs needed

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