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ucc27611: Driving UCC27611 with a square wave oscillator

Marc Worthington
Prodigy 40 points
Part Number: UCC27611
Other Parts Discussed in Thread: UCC27611, SN74LVC2G14

I am trying to drive the UCC27611 part with a square wave oscillator but it does not appear to be working.  I have attached a document with 4 plots that describe what I am getting.

FET driver and Osc interface.docx

Plot 1 is the output of the oscillator when it is not in the circuit, note that the oscillator appears to have some inherent frequency content superimposed on the square wave.  The oscillator is operating at ~4MHz, the superimposed frequency is about 20MHz.

Plot 2 is the output of the oscillator after I connect the output of the oscillator to the input of the UCC27611 part.  Note that the shape of the signal is very similar.

Plot 3 is the same as Plot 2 but with the addition of the output of the UCC27611 part past the OUTH and OUTL resistors (blue trace).  Note that the output appears to roughly follow the input and it is not a very nice looking square form.  I was surprised that the UCC27611 part was not sharpening up the output pulse.

Plot 4 now adds the output of the GaN FET (green trace).  I am wanting the FET to switch between 9V (when off) and 0V (when on).  Clearly this is not happening.

 

I am not sure how to proceed, perhaps I just need an oscillator that has a little cleaner output?

FYI, I also have an open question on the forum related to request for a Spice model of an inverting buffer (SN74LVC2G14), I thought I better mention this to avoid confusion.

 

Also, if you have a recommended Ti oscillator that would work better than the one I am using, I would appreciate knowing about it.  At this point, for proof of concept, any frequency from 1MHz to 100MHz would work.  It would also be helpful if the oscillator had a spice model.

 

Thanks for your help

Marc

  • 0
    TI__Genius 9790 points
    Thanks for your interest in TI here. I've contacted the appropriate product group. You should hear from them soon.
  • 0
    TI__Mastermind 23215 points

    Hello Marc,

    I am an applications engineer with the TI High Power Driver group and will work to resolve your concerns.

    I see a couple of concerns with the input signal to the driver from the oscillator. The 20MHz ringing that is present on the intended switching frequency has a ring amplitude that can exceed the high threshold when the input signal is low. This can cause the driver to trigger on the 20MHz ring peaks, at least the 1st ring.

    Also the driver has an input voltage limit of -0.3V on the input, and the negative ring looks like it can be as low as -2.6V. Negative voltage exceeding the device ratings can cause incorrect output behavior.

    Have you tried some measure to attenuated the 20MHz ring on the oscillator output? Some small filtering may attenuate the 20MHz enough and still provide the intended switching frequency.

    Regards

    Richard Herring

  • 0 in reply to Richard Herring
    Prodigy 40 points

    Richard,

    I attempted to use various sizes of capacitors in the hope that these might filter out some of the peaks, this did not seem to work.

    I started to investigate additional filtering but got lazy so I thought I would get some advice before attempting to build yet another circuit.  Do you have any recommendations for the type of filter I might want to use?

    Also, are you aware of a Ti oscillator that might produce the output I am looking for without having to build the filter circuity?

    Thanks,

    Marc