I would like to get some clarification on the operation of the DS10CP154A 4x4 cross-point switch. In particular, I would like to know your recommendations on how to connect unused inputs.
According to Application Note AN-1194, the recommended approach for internally terminated lines is to generate a external bias voltage using a pullup and pulldown resistor of 8k and 5k respectively.
Could you confirm that this is indeed the best approach to handle unused inputs for this device. Thanks.
Please advise what you are wanting to protect from, is it preventing noise switching and additional power in the input, or is the part set up more for say a 4 channel buffer and the concern is over a channel that is enabled without an input applied? Understanding the use case better, might change the recommendation.
Since this is a 4x4, the unused channels are ignored by the switch settings.
If the part is used in SMBus mode, additional functionality is obtained and the smartPWRD mode can be used shutdown the unused IN and OUT stages.
If there is concern over a unused channel and it is enabled, the external failsafe pull up (plus to VCC) and pull down (minus to GND) can be used. Select resistors to set the desired VOS and VID. Typically a 1k up and down will work for most applications. They can be raised if too strong or too much bias current.
DPS APPS / SVA
Thanks for your response. I have additional information I would like to provide you to see if your recommendation will change one way or the other.
The concern with unused inputs on LVDS is that if they are floating near the threshold, then the part will be switching internally which 1) generates noise, and 2) burns extra power. Given your explanation, I would bias the unused input as John suggested so that it doesn't create issues, and I would not worry about the three other inputs that you are using since having these at the high impedance state is not the normal use case.
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