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LMH3401 - is the input common mode range guaranteed to include VS-?

Per Magnusson
Intellectual 500 points
Other Parts Discussed in Thread: LMH3401

I would like to use the LMH3401 in a single supply (5V) application where the input signal will swing around 0V. In the electrical characteristics section, page 6, it says:

Input common-mode range low: typ VS- - 0.7 V, max VS- + 0.2 V

This seems to indicate that 0V common mode might not always work well for all LMH3401. But on page 22 it says:

"The input common-mode range extends from the negative rail to approximately 1 V above the mid-supply voltage when powered with a 5-V supply."

So, can I trust that I will not severely degrade distortion performance if I use the amplifier with a common mode input level of VS-?

  • 0
    TI__Genius 13935 points

    Hello Per,

    We can not guarantee this condition.  The typical conditions include room temperature and a 5V supply.   Testing and simulation has shown that under some conditions the input needs to be slightly above the negative supply.  Also, distortion performance is specified at the mid supply condition, distortion performance with respect to input common mode is shown in the curves section of the datasheet and it does indeed degrade with low voltages. 

    With a ground refrenced signal you have a couple of options.  One option is to use pull up resistors on the amplifier inputs pins to shift the signal up from the negative rail.  Another option is to use a split supply to allow the input signal to be within the optimal input common mode range. 

    Would either of these options work for you? 

    Regards,

    Loren

     

  • 0 in reply to Loren Siebert 1
    Intellectual 500 points

    Thanks for your reply Loren.

    Then I will probably have to resort to using split supplies, although the negative one will be less than a volt below ground. I was hopeful for a while that I could avoid the negative supply when I found the passage in the datasheet that reads "The input common-mode range extends from the negative rail to approximately 1 V above the mid-supply voltage when powered with a 5-V supply."

    Regards

    Per

  • 0 in reply to Per Magnusson
    TI__Genius 13935 points

    Hello Per,

    Split supplies is a good option.  When signals are ground referenced they will swing below ground. 

    I know it is misleading, but the input "common mode range" needs to leave room for signal swing.  It would be more accurate to call it the input signal range.  The common mode range is defined for zero input swing, so for increasing signal swing the common mode range will shrink accordingly.

    Regards,

    Loren