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Low Iq "Floating" Type LDO

user3897445
Prodigy 120 points
Other Parts Discussed in Thread: LM317, SN6501, TPS7A4001

Hi,

I'm designing  a bi-directional high side current sense circuit that will sense current on 200VDC bus.

Circuit is simulated with a voltage source sharing the positive terminal with the 200VDC bus to power the op-amps. 

The component I'm missing to power the circuit is an LDO that is referenced to VIN (much like the almighty LM317), but with sub 100uA Iq.

Could not find a suitable LDO - Anyone used such a beast?

Thanks,

S.B.D

  • 0
    TI__Genius 10680 points

    Hello,

    The TPS7A4001 is rated to 100 V, unfortunately we don't have any 200 V LDOs.  A common solution for this problem is using an isolated DC/DC, such as the sn6501 + transformer.

    Let me know if this helps.

    Regards,

    Mike

  • 0 in reply to Michael Hartshorne
    Prodigy 120 points

    Hi Mike,

    Thanks for the reply.  

    Maybe this is the way to go... Use your suggested LDO along with a low knee current zener diode (I think around 50uA ones are out there) connected from LDO's GND pin to system ground, this will lift the LDO's ground pin to a valid voltage differential from VIN to GND pin.

    This solution may require to use an op-amp with a wider VIN - since output voltage will not be tightly regulated.

     

    S.B.D

  • 0 in reply to user3897445
    TI__Genius 10680 points
    Hello,

    Yes, this could be made to work. You would need to be sure the input and output cap. are referrenced to the LDO GND, and also be sure that any additional capacitor that is system ground-referenced on the output does not create a case where the VIN-VOUT difference is too high. If the system-referenced cap. is uncharged, and VIN is immediately forced with a high slew rate, then I would be concerned there is an excessively high voltage between VIN and VOUT or GND and VOUT.

    Let me know if this helps.

    Regards,
    Mike