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CM port of ADS900 for 1.5V bias

Lingli Liu
Prodigy 210 points
Other Parts Discussed in Thread: ADS900, THS4509

Hi,

I want to use the CM port of ADS900 (1.5V) to bias 3 single-supply amplifiers at the same time. Is there any problem with that?

Thank you very much for your kind reply!

Lingli

 


  • 0
    TI__Mastermind 29220 points

    Hi,

    That should be fine, as long as you don't load down the signal too much.  As shown in figure 7 of the ADS900 data sheet, the CM signal is generated simply from a 2-resistor voltage divider from REFT and REFB, and the buffers driving REFT and REFB have a suggested limit of 1mA loading.  If you try to load down the CM signal too much then you will see some movement of the CM signal. 

    If the amplifier has a common mode input pin (such as the THS4509 has) then these usually present a very light load on the CM pin.  The THS4509 for example pulls only about 40uA typical from the CM pin, so three of these loads should not be an issue.

    Regards,

    Richard P.

  • 0 in reply to Richard Prentice
    Prodigy 210 points

    Hi, Richard,

    Thank you very much for your detailed explanation! That is really helpful for our electronic board testing. 

    Lingli