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THS4521 output error

Kwan
Intellectual 510 points
Other Parts Discussed in Thread: THS4521, TINA-TI

Hi,

I connect a very simple circuit on breadboard as follows just to verify
whether the opamp works well. Opamp is THS4521SHKQ

Input voltage is DC 2V and AC 10mV.

I also did a simulation in TINA, output should be as following:

However, when i did actual measurement on the IC on the PCBA, using oscciloscope, i see below result:

VF1 is a DC voltage around 3.27V.

VF2 is a DC voltage around 570mV.

Pls help to advise if anything wrong with the design if not, then would have to send the IC in for FA.

This is another circuit design also does not seem to have amplification:

Thanks.

  • 0
    TI__Mastermind 22825 points

    Hi Kwan,

    With the large gain that you have (1M / 10k = 100 V/V), the input (VG1) DC voltage of 2.0V must match Vocm (2.0V) precisely, or you will get an output offset voltage (as you seem to be observing on the bench). I have a feeling that's what you are dealing with here.

    Also, you are setting the THS4521 input to 2.0V, where datasheet states 1.9V is the maximum allowed, and I recommend you reduce it in your design to allow for power supply variation, safety margin, etc.

    In TINA-TI is easy to set Vocm and VG DC voltage to exactly 2.0V, but on the bench you may have to do some "fine-tuning" to make sure you do not have any offset.

    Here is an example of the large output offset you will experience with only 0.1V difference between VG1 DC and Vocm (I've set VG1 DC to 1.9V instead of 2.0V):

    Here is my TINA-TI file for the image above:

    /cfs-file/__key/communityserver-discussions-components-files/14/1122.THS4521DC-offset-E2E-Hooman-12_5F00_16_5F00_14.TSC

    Regards,

    Hooman

  • 0 in reply to Hooman Hashemi
    Intellectual 510 points
    Hi Hooman,

    Thanks, i'll look into your proposal and i realise the input connection is mixed up. After rectify the connection, the amplifier works.

    Thanks.