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Original question:

THS4521 differential input, common-mode voltage

THS4524: Questions about the tolerated input common mode

Pascal MAURERE
Prodigy 10 points
Part Number: THS4524
Other Parts Discussed in Thread: INA149

Tool/software:

Hi,

I would have some questions about the tolerated input common mode of the THS4524.
When I read its datasheet, information about the tolerated input common mode appear in this table:
First question: I don't understand the terms "Common-mode input voltage low" and "Common-mode input voltage high". What do they mean?
Moreover, these electrical characteristics seem to be given for:
  • Particular conditions (cf. the extract below).
  • A specific test circuit (cf. the schematic below).
Second question: As my THS4524 instantiation does not match exactly with this test circuit (and these conditions), would it be possible to have the tolerated input common mode of the THS4524:
  • Directly on its Vin+ and Vin- pins (not through this test circuit).
  • And according to the Vs+/Vs- power-supplies values?
The information level that I would like to obtain, matches with the information provided in the INA149 datasheet (cf. the extracts below):
I thank you in advance for your help.
Best regards.
  • 0
    Guru 308100 points

    1. There are separate specifications for the lower limit and the upper limit of the range. The typical range is from −0.2 V to 3.7 V at 25 °C, and the guaranteed worst-case range is from 0 V to 3.5 V over all temperatures. (In other words, it requires a headroom of 1.5 V to the positive supply.)

    2. There is no test circuit for the common-mode range shown. (Figure 57 is for the common-mode rejection.) The input voltages are measured directly at the pins, and the 1.5 V offset should be constant.

  • 0 in reply to Clemens Ladisch
    Prodigy 10 points

    Hi,

    Just for my understanding, this headroom of 1.5V (on the input common mode) to the positive supply is required:

    • For the input common mode tolerance OR

    • In order to let a margin to the differential mode and to fulfill the admissible input voltage constraints (cf. the extract below) when common and differential modes are applied to the THS4524?

    Thanks in advance for your return.

    Best regards.

  • 0 in reply to Pascal MAURERE
    Guru 308100 points

    I do not understand what exactly you mean with "tolerance".

    When you stay inside the input voltage common-mode range, the device is guaranteed to work correctly.
    When you stay inside the absolute maximum ratings, the device is guaranteed to not get damaged.