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UCC28950: About the Burst mode.

Guru 10385 points
Part Number: UCC28950

Hi team.

I 'd like to know about the order of pulses in the Burst mode.

The bellow figure's pulse sometimes occurs in my measurement.

I think that the correct order is B and D to A and C.

(*According to http://www.tij.co.jp/jp/lit/an/slua787/slua787.pdf)

Why is C leading and only C ?

Could you tell me the mechanism?

Sincerely.

Kengo.

  • Hi team.

    I'd like to receive your advice ASAP.

    I'm waiting for your nice advice.

    Sincerely.

    Kengo.

  • Hello Kengo-san

    Apologies for the delay, I was travelling on business for the last few days with no chance to look into e2e.

    I have checked again and the signal order shown in Figure 1 of the datasheet is correct, that is B and D to A and C so I don't know what might be causing the pattern you see. It would be interesting to see the OUTA, OUTB,OUTC and OUTD signals on the same screen.

    I am sure you have already done so but please can you re-check the waveforms at the OUTx pins of the IC. If you look at the gates of the MOSFETs then it is possible that one of the MOSFET driver outputs is not functioning - for example if one of the driver ICs went into UVLO. Or if the drivers come out of UVLO at slightly different times. Looking at the OUTx pins will help eliminate the drivers as the source of the problem.

    It sometimes happens that the first OUTD pulse in a burst is shorter than normal, but the sequence of the OUTx pulses does not change. This behaviour is noted in the caption to Figure 1.

    It is also possible that noise injected into the IC can upset the switching pattern - for example, you should avoid running the OUTx lines under the IC body, please check the PCB layout for this.

    Regards

    Colin

  • Hi Colin-san.

    Thank you for your kind reply.

    My customer take a waveform that is bellow att.

    What do you think about this waveform?

    Sincerely.

    Kengo.

  • Hello Kengo-san

    I checked the OUTx signals at the beginning of a burst on my EVM just now - please let me know if the image below is not visible -

    Yel: OUTA, Red: OUTB, Blu: OUTC, Grn: OUTD.

    If you compare the pulse pattern with the one the customer got you can see that the OUTA, OUTB relationship is the same but it is almost as if the OUTC and OUTD signals got reversed in the customer image. The obvious explanation is that the customer has mis-identified the OUTC, OUTD signals but other than that I cannot think of any reason.

    My EVM is running at approx 100kHz, please let me know the frequency that the customer controller is running at - the horizontal scale is not clear.

    Regards

    Colin

  • Hi Colin-san.

    I got a schematic from my customer.

    Can I talk with you in private message.

    If OK, could you tell me your e-mail address.

    Sincerely.
    Kengo.

  • Hello Kengo-san

    My email address is colingillmor@ti.com 

    Regards
    Colin