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ISO1211: SUB Pin Connection

PY (Pengyu) Song
Expert 5860 points
Part Number: ISO1211


Hi team,

Understand from datasheet that SUB pin should be floating and not to connect to FGND or any other signal. Can you please share what is the reason of floating the SUB pin? 

Since it is chip substrate, it would be already at ground level but with relatively not so low impedance - why it still can't be connected to FGND? For improved noise immunity? Or for surge protection etc? 

  • +1
    TI__Expert 8030 points

    Hi PY,

    Thanks for reaching out. 

    Connecting the SUB pin to FGND bypasses the internal reverse polarity protection. The customer can do this if they do not need reverse polarity protection. When there is no reverse polarity protection, the signal should only operate between 0 and 60 V. Operating outside of this range when there is no reverse polarity protection can damage the device. 

    If the customer needs reverse polarity protection, then we do not recommend for them to connect the SUB pin to FGND. 

    Regards,

    Kenneth