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LMH6518: Split supply +/-2.5V

Emmanouil Tsachalidis
Intellectual 850 points
Part Number: LMH6518
Other Parts Discussed in Thread: OPA859, THS4541

Hi,

I am trying to find ways to interface a stage of two (pos & neg side) OPA859 used as buffers, with their CMV centered at GND, to a LMH6518 which requires a CM range of 1-4V.

Since OPA859 is not a rail-to-rail opamp, it won't work with the max OPA859 swing of about 3Vpp.

It could be done with a THS4541 (or another FDA) used as a CMV shifter but i do not want that because it would degrade noise performance since i am using 4-OPA859 in parallel (instead of one) to lower its' noise.

So one option, if applicable, would be to use LMH6518 under a split supply topology. Is that doable? Will the digital circuitry inside LMH6518 still be functional with a +3.3V supply rail?

I am not worrying about the output of the LMH6518 having a CMV ranging around GND since a FDA will be used to drive the ADC instead.

So is it possible to run LMH6518 with a split supply of +/-2.5V?

Thanks in advance

Manos Tsachalidis

  • 0
    TI__Genius 16725 points

    Hi Manos,

    I don't see how the LMH6518 would work with +/- 2.5 V. Especially since there is no negative supply pin for you to be able to provide the negative supply to the device. An FDA seems like the most likely option to shift your Vcm to what you need.

    Thanks!
    -Karan

  • 0 in reply to Karan Kotadia
    Guru 48185 points
    the ground could act like the negative supply for most devices, but here you would also need to level shift the control logic to reference off of -2.5V
  • 0 in reply to Michael Steffes
    Intellectual 850 points

    Thank you Michael. I was able to directly interface OPA859 stages with LMH6518 by setting their supply rails to +4V & -1V. (LMH6518 was supplied with a single 5V).

    The CMV of OPA859s outputs was set to 1.5V which is still within the LMH6518 valid range (1-4V) and their output swing was able to reach the expected max level.

    I therefore do not need the intermediate FDA stage.

    Thanks

    Regards

    Manos Tsachalidis