TMUXHS4212: Interface forum

Prodigy 60 points

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Part Number: TMUXHS4212


We have a system where we have to connect a ZynQ ultrasclae EVK to 6 nos of Spartan 6 FPGA through asynchronous LVDS (Tx&Rx) running at 100 Mbps (50MHz),  DC coupling mode ( no ac caps or no DC bias). So we have a multi stage MUX/DEMUX setup using MAX9394. In this case, only one spartan FPGA is connected to ZynQ MPSoC EVK. All these 6 Spartan FPGA's are independently powered. So the one of the six FPGA, actively connected to ZynQ EVK is only powered. During that time , the inactive LVDS channels of MUX/DEMUX configuration using MAX9394 have Vcom=1.2V in their pins. We would like to prevent this voltage into the IO's of unpowered Spartan 6 FPGA's for its safety. 

So that we would like to use TMUXHS4212 MUX chipset in between MUX/DEMUX  setup and spartan 6 FPGA's to prevent the Vcm voltage during power off condition of the spartan FPGA. For the connection we use A-B or B-A ( TMUXHS4212 is bidirectional) channel to connect the MUX/DEMUX config to Spartan 6 FPGA's . The C channel of TMUXHS4212 is un connected. So our plan is to make A-B or B-A of TMUXHS4212 during normal working, and use A-C or C-A during unpowered condition of Spartan 6 FPGA. Since TMUXHS4212 is a passive differential switch; we expect, it can prevent the Vcm voltage into the IO's of unpowered spartan 6 FPGA.

This is our idea, can you comment/confirm whether this configuration of TMUXHS4212 is work for this application. If any other part other theTMUXHS4212 can be used for this, please let us know. 

Sample schematic and Block diagram attached.

regards,TI Query- preventing Vcom to FPGA while unpowered conditions.pdf

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