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UC2827-1: UC2827-1

rj
Prodigy 10 points
Part Number: UC2827-1

Hello Team

I was testing UC2827-1 for a new design and noticed high frequency oscillation across Rt pin .  Rt= 7.5k, Ct = 680pF fs = 152kHz and oscillation across Rt resistor - 424mV/12.8MHz. Also , there was some jitter present at saw tooth. Is it normal to have a MHz oscillation across Rt resistor  for this controller ?

R. J.

  • 0
    TI__Guru 51835 points

    Hi,

    Can you provide the waveform to show the jitter - usually there should not be jitter since the saw-tooth just capacitor charging - so should not have jitter - so need to see the waveform to decide what it is?

  • 0 in reply to Hong Huang
    Prodigy 10 points

    Hello Hong

    A small jitter was present with 50ns/div using isolated scope, but is much steadier with line powered scope with ground.  Just want to confirm that i don't have to filter the high frequency oscillation at Rt pin. 

    Two wave forms are attached.

    Ch1- Ct Waveform

    Ch2- Rt waveform

    Thanks

    Rj

  • 0 in reply to rj
    TI__Guru 51835 points

    Hi, 

    The second waveform yellow trace does not show same jitter as the first. I suspect the first yellow waveform jitter due to your oscilloscope instead of the waveform reality. Otherwise the second waveform should show similar jitter as well. It looks the jitter due to your oscilloscope either setup or some other noise. 

    If it is a digital oscilloscope, then the scope resolution may need to be adjusted..

  • 0 in reply to Hong Huang
    Prodigy 10 points

    Hello

     So, the Rt waveform with MHz oscillation is normal for this chip?  I agree that saw tooth ramp jitter might be a function of scope resolution.

  • +1 in reply to rj
    TI__Guru 51835 points

    Hi,

    Yes, you can ignore the RT pin waveform - the key waveform is CT which to be used to generate the pulses and to adjust pulse width.