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ADC161S626: interface with differential inputs

cay
Prodigy 60 points
Part Number: ADC161S626
Other Parts Discussed in Thread: LMP91000

Hello,

I`ll use ADC161s626 to read output of LMP91000. The thing is differential measurement will be used, therefore C1 and C2 pins of LMP91000 will be used. The question is, how can we interface this C1 and C2 pins with ADC? Is there a need for buffer circuits before connecting to ADC inputs because people say there must be a buffer when using SAR ADCs?. 

Thanks.

  • 0
    TI__Genius 16890 points
    Hi Cay,

    The output of the LMP91000 is a single ended output available at the VOUT pin. The C1 and C2 pins are for adding an external gain resistor for the transimpedance amplifier. The way to connect it to the ADC161S626 is shown in the evaluation board schematic. Download the document snau121a.pdf to see the schematic.

    Mike
  • 0 in reply to Michael Stout
    Prodigy 60 points

    Hi Michael,

    According to the datasheet of LMP91000 and first answer on this post (e2e.ti.com/.../1104118, differential ADC can be connected to the C1 and C2 pins. But on the evaluation board schematic, only single-ended measurement is shown. I just wonder about differential measurement. It is okay for C2 pin since it is output of an op-amp but should I connect a buffer after C1 pin to interface with ADC161s626?

    thank you for your reply,
    Cay.

  • 0 in reply to cay
    TI__Genius 16890 points

    Hi Cay,

    I am not very familiar with the LMP91000 (another group supports it) and so I am not sure what the internal circuit is connected to C1.  If you post to the precision amplifier forum they may be able to answer that question. 

    You could try connecting it as you mention and see if it is giving you accurate numbers for the current through the feedback resistor.  Another option would be to connect one of the current sense devices that TI makes (see this page:  ) to to the pins and then connect that output to the ADC. 

    Mike