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LM7705: Stackable?

Jeffrey Wright
Expert 2855 points
Part Number: LM7705
Other Parts Discussed in Thread: LPV821, , LM27761, TPS60400

Hello;

I'm considering using this device to supply an LPV821 precision amplifier to implement a bi-directional, low-side current sense. The requirement is that the amplifier will generate +/- 200mV. However, the TI group supporting this amp. points out that I should not drive the output to within 100mV of Vss, and so that means -230mV + 100mV = -130mV .

So, I was thinking that if I could stack 2 of the 7705's, would that work, producing -460mV? Or have I gone round the bend ;-D

Thanks!

7705x2.pdf

  • 0
    TI__Guru*** 142710 points

    Hi Jeffrey,

    I think this could work but you should order 2x LM7705 EVMs to make sure.

    What positive voltage will you power the amplifier with?  Using the same +3.3V will exceed its 3.6V rating with -460mV.

    We also have TPS60400 family, in case you have a +1.8V rail or LM27761 to get as low as -1.5V.

  • 0 in reply to Chris Glaser
    Expert 2855 points

    Thanks Chris;

    I had earlier checked the 27761 but its Iq is too high. My client's TI FAE Antonio Fadhel suggested the 7705, and think it will be fine. My simulations at least say so, but I wanted to cover all my bases. And yes, I see now that  the LPV821's recommended  max Vdd would be violated, and so I'm going to stick with the single reference for now.

    Thanks for your help!