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ACF2101 offset input range in com pin

Khai Lee
Prodigy 180 points
Other Parts Discussed in Thread: ACF2101

Hi,

one of my customer wants to apply offset voltage 0 to 5V to com pin in ACF2101

what is the input range of positive input of op amp?

Also, do we have any application note for layout guide?

Thanks and Regards,

Khai Lee 

  • 0
    TI__Guru* 93105 points

    Hi Khai,

    Well, I haven't seen an offset applied to the ACF2101 com pin before, and don't know if it can be done without creating a biasing problem for the internal FET switches. The internal integrators use JFET input operational amplifiers. Amplifiers of their era and design usually had a common-mode input voltage range that extended up to about 4 to 5 V of the power supply rails. I suspect that is the case for the ACF2101 amplifiers and they will behave okay. 

    The voltage on the FET switch terminals will be different when a common-mode voltage is applied. It then becomes a matter of whether, or not, the voltages on the FET terminals are of the correct polarity and level for the FET to turn on and off correctly. The FET switch control circuitry uses TLL levels, but that is with the common-mode voltage at 0 V. I suggest setting up a couple of devices up on the bench and try them under the expected conditions and see if the device operates as needed.

    Probably the best resource regarding ACF2101 board layout is the obsolete EVM guide. It includes discussion about the board layout and provides best practices. I found the EVM document on a web site outside of TI:

    http://pdf.datasheetcatalog.com/datasheet/BurrBrown/mXxsvxx.pdf

    I hope this helps.

    Regards, Thomas

    PA - Linear Applications Engineering