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TDC1000: Vcon function issue

harry jang
Prodigy 50 points
Part Number: TDC1000

Tool/software:

hi, our customer want know "Vcom"  function..

Ti data sheet describe that "should not be loaded with more than 20 μA.".

If this pin loaded over 20uA, what happen TDC1000.

please help!

  • 0
    TI__Mastermind 43580 points

    Hello Harry,

    VCOM is the common mode voltage bias output.  This is used as reference voltage for the LNA, PGA, and comparators.  This can be seen in the block diagram in section 8.2.

    See section 8.4.6.4 of the datasheet.  It is recommended to use 10nF for the VCOM capacitor for proper settling time.  If a larger value is used, it may take multiple TOF cycles to reach a final value. 

    Can you provide some details on what the customer is expecting to load this pin with?  In general, I would not recommend loading this pin with additional current as this could make the regulated voltage unstable which is used for reference in the device causing inaccuracies.  

  • 0 in reply to Eddie LaCost
    Prodigy 50 points

    Thanks for your comment, May I know this pin loading capability? I want know max loading current. Thanks

  • 0 in reply to harry jang
    TI__Mastermind 43580 points

    Harry,

    The datasheet does not recommend loading more than 20uA.  Additional loading on the VCOM pin will have an impact on measurement accuracy and stability.  In the EVM, we even use a buffer, shown below, to prevent additional loading while measuring VCOM on a scope.  

    Can you provide some more details on what they are trying to accomplish?  Are they trying to power some other device from this pin?