• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 47 subscribers
  • Views 224 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS4551: Single-end input

Hank Wang
Prodigy 50 points
Part Number: THS4551

Hi

Here is my schematic. I used THS4551 as a single-end input. 

However, FDA_MADC_INP is 1.094V and FDA_MADC_INN is 0V without any input signal.

Should FDA_MADC_INP and FDA_MADC_INN  be 1.65V ? 

Here are power supply voltage.

MADC_FDA_VOCM = 1.65V

MADC_FDA_VSP = 3 V

MADC_FDA_VSN = -2 V

Thanks

BR,

Hank

  • 0
    Prodigy 50 points

    Updated : MADC_FDA_VSP = 3.4V

  • 0 in reply to Hank Wang
    TI__Genius 11020 points

    Hi Hank,

    The reason you are seeing different results than expected at the FDA_MADC_INP is due to a high impedance being seen at MUX_MADC_OUTPUT. The FDA will force an output common-mode voltage of 1.65V, however it will shift the outputs of the FDA to account for the feedback network impedance imbalance to also create a virtual short at its inputs. If you were to ground the left pad of R207 you will see a voltage divider from R4 to R1 of half since they are equal from the 1.65V at the output. The reason you see FDA_MADC_INN as zero is because that node is directly grounded.

    Best Regards,

    Ignacio