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LM83 ok to ground D-?

Alvin Jee
Prodigy 20 points
Other Parts Discussed in Thread: LM83

Hello!

I have an LM83 going to 3 different temp diodes in 3 different chips. One chip grounds the TDN pin in the silicon. Will this affect the readings from the other 2 chips where the TDN are not grounded? The app note shows all 3 TDN signals being tied together to the D- pin of the LM83, though.

Thanks!

  • 0
    TI__Expert 4905 points

    Hi Alvin,

    Sorry to say that all of the remote diode D- pins should be floating, that is not connected to ground for the LM83 to work properly. It relies on the fact that the D- pin of the LM83 will bias up all of the remote diode D- pins to some voltage level around a diode drop. Believe it or not this was done on purpose because by biasing up the base of the remote diode transistor you isolate the emmiter base junction that is used for the remote diode from substrate noise issues.When you ground the D- the part does not work very well. We do not test it in this mode so if it works you are taking a risk, I would not recommend it for a production worthy solution as it is not in the datasheet . If this is a lab experiment then maybe you could get away with it working. You would also need to measure the error for each LM83 you use as it would not probably be within spec and not consistent.

    Since all three three remote diodes are sequentially monitored all of their D- pins can be connected together (that is if they are all floating).

    Take care,

  • 0 in reply to Emmy Denton
    Prodigy 20 points

    Hmm.. that's unfortunate. Thanks for the detailed info!