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UC3886 Output range of voltage error amplifier

Siyu He
Expert 1040 points

Hi all,

I am trying to test the current loop of uc3886 and left voltage loop open. Based on the application note u-156, the voltage error amplifier output range is from buffer voltage-0.7 to buffer voltage+1, however, I tried to connect both command pin and buffer pin  to the ground and set sense pin high, the comp pin is about 1V. After this, I also tried to connect 0.35V via VREF to the comp, the voltage on the comp pin is still around 1V. For my current loop test, the comp should be 0.35 to verify the current loop.

My question is that is it possible to get comp voltage lower than 1V?  Also, from the electrical charateristic chart, the output range is from 1.9 to 4.1, which conflicts with my measurement.

He, Siyu

  • 0
    TI__Guru**** 191445 points

    Just FYI UC3886 is an old part.  Not sure if it is fully supported any longer.  Let me see what I can find out.  Datasheet says you can drive COMP to 0.7 V below COMMAND.  I suppose COMMAND would hat be set to 1 V to allow you to drive COMP to 0.3 V.

  • 0 in reply to JohnTucker
    Expert 1040 points

    Hi John,

    Thanks for your comment. As you mentioned, I tried to connect COMMAND below 1V and connect Vsense to COMP to set the voltage error amplifier as a voltage follower, however, the output was still around 1V.

    He, Siyu