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THS3491: Single, negative, power supply use.

Part Number: THS3491
Other Parts Discussed in Thread: TINA-TI

Can I us the THS3491 with just a -15V power supply for -VS? and +VS connected to GND?

If so, what would be the correct voltage to turn on the part at the PD pin, I am using the RGT package. This setup seems to simulate OK in TINA, just want to be sure.


Dave Roberts

  • Hello Dave,

    I am looking into the capability of the THS34941 to be supplied off a negative rail with positive rail grounded.



  • Here was a start on a thorough discussion of this shutdown feature - this might help you some, not sure all of this is in the model, but this silicon operation focused. 

    THS3491 Disable operation discussion updated Dec6_2016.docx

  • Hello Dave,

    I am working through some simulations and discussing with my team regarding your use case for the THS3491.  



  • Hello David,

    Thank you for your patience this week.  I will answer your question in two parts:

    1) Yes, you can operate the THS3491 on Vs+ = GND and Vs- = -15V.

    2) The REF pin creates a range that the PD pin operates within.  If Vs+ is set to GND, due to the range of the REF pin present in the datasheet, the REF pin must be set <= -5V.  This is to say the maximum voltage at the REF pin is -5V.  Using -6V is also possible, but NOT using -4V.  Do not float the REF pin, and do not set it to GND.  By using a single rail negative supply, you will need a separate -5V (or less) for the REF pin.  This setting maintains compliance with the REF pin range of Vs- <= REF <= (Vs+ - 5). 

    While the THS3491 can be driven by a single supply and keep REF @ GND, this is only true for using Vs+ as the positive supply.  The REF pin can be set to Vs-, which is GND in the case present in the docx Word file.  However, the need to set REF = -5V (or lower) is also demonstrated by the upper limit of the (Vs+-5V) REF range.

    Now for the PD_bar pin: another negative supply voltage will be needed to disable/enable the THS3491. Normally the PD_bar pin could be set between 0V and 1.3V for a large positive single supply.  However, as the REF pin is shifted  from GND to -5V, so must the PD_bar pin range shift.  The new range for PD_bar should be:

    - Guaranteed Off Above -5.8V (the minimum value before the amplifier turns on)

    - Guaranteed On Below - 7.5V (the maximum value before the amplifier turns off)

    These values are based on the 0.8V and 1.5V values and shifted by the REF offset.  REF is typically GND, but is now REF = -5V (or lower) in your application.  

    The TINA-TI schematic simulation does work without changing your PD_bar values to accommodate the negative single supply.  However, the model & implementation of the circuitry were not designed to test this use case; I would be weary of following those simulated results without first considering the datasheet recommendations and valid operating ranges.



  • Thank you for your help on this.


    Dave R