• State TI Thinks Resolved
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 68 views
  • Users 0 members are here
Support feedback
Options
Options
Related

ADS127L21: ADS127L21: Use of Pin VCM

Roland Störi
Prodigy 10 points
Part Number: ADS127L21


When the VCM Buffer Output is disable, is the Driver Output Stage inactiv / High Impedance? 

 - There are no notes to prove this one, based on the datasheet

  • The idea is to drive the VCM output of the ADS127L21 with a external defined VCM Signal.
  • So we can define it as a function of VREF with better TK and better noise.
  • This will only work when we have the knowledge of the condition of the VCM driver when its Disabled!

Is it possible to get more information then we have in the datasheet?

  • 0
    TI__Mastermind 48240 points

    Hello Roland,

    Welcome to the TI E2E community.

    The VCM output, when disabled, is in a Hi-z state.  However, this voltage is only a buffered version of the internal VCM level, and providing an external voltage to this pin will not change the internal biasing of the ADC modulator.  In other words, the VCM pin cannot be used as a VCM input when the VCM buffer is disabled.

    However, you can use an external source to set the common mode voltage for the ADC inputs if you prefer; we include the VCM buffer as a convenience.  The ADS127L21 can operate with a wide range of common mode voltage, but the typical level is (AVDD1-AVSS)/2, which is also the common mode voltage that we characterized the operation of the ADC.

    Regards,
    Keith Nicholas
    Precision ADC Applications