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INA350: Output Characteristics While In Shutdown

Part Number: INA350
Other Parts Discussed in Thread: INA322

I am considering tying the outputs of two INA350 devices together and enabling (only) one of them while the other one is held in Shutdown.

For the INA322, there is a comment in the datasheet (Page-11 "SHUTDOWN MODE") that "Once in 'sleep mode' the amplifier has high output impedance, making the INA322 suitable for multiplexing".

But the INA350 datasheet doesn't really define what happens to the INA350 output when it's put into shutdown mode.

For my application, it would be OK if the INA350 still presented some load at its output while in shutdown, it doesn't need to be Hi-Z, but it's just not clear exactly what actually does happen to the output while in Shutdown.

Can you please elaborate?

Thanks,

Matt

  • Hey Matt, 

    Welcome to e2e!

    I did not see any documentation on the output while in shutdown of the INA350.
    I'll go into lab tomorrow and test what the output does while in shutdown. 

    All the best,
    Carolina

  • Thanks Carolina.

    I’m hoping that the output is such that connecting the outputs of two INA350s together and enabling one or the other will work.

    I look forward to hearing your findings.

    Thanks for your support on this Carolina.

  • Hey Matt, 

    The output in shutdown mode is VREF

    This ppt attached has the measurements I took in lab: SD_INA350.pptx

    The structure is shown below in the INA350's block diagram: 

    RG is not "open" during shutdown, therefore there will be a high resistance path (about 430k) from REF to OUT through all those resistors. In other words, OUT (unloaded) in shutdown will be same as REF.

    To answer the initial question, 

    I am considering tying the outputs of two INA350 devices together and enabling (only) one of them while the other one is held in Shutdown.

    For the INA322, there is a comment in the datasheet (Page-11 "SHUTDOWN MODE") that "Once in 'sleep mode' the amplifier has high output impedance, making the INA322 suitable for multiplexing".

    The INA350 output is not high impedance when in shutdown and therefore is not suitable for multiplexing in the way that the INA322 is. 

    All the best,
    Caro

  • Hi Caro,

    If I understand your findings correctly, I can connect the outputs of two INA350s together and enable them one at a time while the other is in shutdown mode.

    If it is the case that when in shutdown, the INA350's output is left connected to REF through about 430K via it's internal resistors (and is not clamped to REF or anything else or driven in any way) then the enabled INA350 would have no problem driving it's own output while connected to the output of the other INA350 that's in shutdown mode.

    The output of the enabled INA350 would just see a load at it's output of the 430K to the other Op Amp's REF voltage.

    For example if REF on both INA350s were connected to GND, then the enabled INA350 would drive it's output with no problem, it would just see a load of 430K to GND at it's output from the INA350 that's in shutdown.

    Do you agree with this assessment?

    Thanks,

    Matt

  • Hey Matt, 

    Yep that's it. I got so focused on the not high impedance that I forgot about the additional statement below. 

    For my application, it would be OK if the INA350 still presented some load at its output while in shutdown, it doesn't need to be Hi-Z,

    I would like to highlight that the load is slightly lower if using the gain of 10 or 20 (ABS): 

    All the best,
    Carolina 

  • Thanks for your support on this Carolina!

    Matt