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UCC27624DGNEVM: UCC27624DGNEVM

tinglei hong
Prodigy 10 points
Part Number: UCC27624DGNEVM
Other Parts Discussed in Thread: UCC27624, UCC27524

1)Electrical performance test at room temperature ；The circuit topology is three-phase Vienna ；The driving scheme is digital isolator + non-isolated driver IC

2)when the power supply voltage of the driving IC is basically stable at 15V, even if the input signal voltage of the input IC is greater than 2V, the output voltage drops and remains at a low level for a short time;

3)why do the output voltage drops and even remains at a low level for a short time? It seems UCC27624 is better than UCC27524, the outB is better than outA of UCC27624,why?

UCC27524UCC27624

  • 0
    TI__Expert 5715 points

    Hi Tinglei,

    From your schematic, I see the resistance in the RC filter is 0. Try adding some resistance, which may help with noise filtering and that spike on the input causing the momentary turn off in the output.

    In the meantime, can you also provide waveforms of the input signal probed at the pin with a short ground connection to the driver's ground (pin and barrel technique)? If the output signal isn't probed at the pin, please do the same for that as well. Also, please provide the current waveform for the input and output signals.

    Thanks,

    Rubas

  • 0 in reply to Rubas Khalid
    Prodigy 10 points

    Hi Rubas:

    1)the resistor has been changed from 100Ω to 50Ω、20Ω and 5Ω,the input signal of the IC will be better , but the output signal of the IC has the same problem;

    2)the input signal is from the point of IC, not the point before the RC filter，it is my wrong;

    3)the current waveform my be difficuty to test

     

  • 0 in reply to tinglei hong
    TI__Expert 5715 points

    Hi Tinglei,

    Can you double check if your VCC is stable? If your input signal gets better but the output stays problematic, there's probably an issue with VCC. I would recommend placing your VCC capacitors as close as possible to the driver. Likewise, the RC filter should be as close as possible to the driver. Can you share the layout of the board, so I can double check?

    Thanks,

    Rubas

  • 0 in reply to Rubas Khalid
    Prodigy 10 points

    Hi Rubas:

    1)The Vcc is stable ;very sorry I couldn't upload the figure;

    2)The layout is as fellow;

    3)you can see the picture below, when the direction of current is as same as I1, the output signal is OK; if the  direction of current is as same as I2,the output voltage drops and remains at a low level for a short time;

    4)In addition, both the IC input and output signals are measured with voltage differential probes；

    Current direction

  • 0 in reply to tinglei hong
    TI__Expert 5715 points

    Hi Tinglei,

    Thanks for following up. I'm a little confused on what your new schematic is showing? Are the OUT pins in the schematic in the original post driving the gates of the MOSFETs in this new schematic? In a low-side setup, the source should be tied to ground, while in this schematic it looks like its being tied together. Below is a typical low-side application:

    Please let me know where the outputs of the gate drive is connected to, and please share the entire layout and schematic.

    Thanks,

    Rubas

  • 0 in reply to Rubas Khalid
    Prodigy 10 points

    HI Rubas:

    1)The circuit topology is three-phase Vienna; you see the picture below, i think you will got it.

  • +1 in reply to tinglei hong
    Prodigy 10 points

    HI Rubas:

    2)The driver sch:

  • 0 in reply to tinglei hong
    TI__Expert 5715 points

    Hi Tinglei,

    Thanks for providing the topology. Let us go back to the beginning and review the input signal. Our drivers should not cause any drop in input prior to entering the device, but as with any chips, there are parasitics that could yield the signal to drop internally. I see how the input voltage drops to around 2V, which may drop even lower internally to trigger the output to switch low.

    We can first start by attempting to smooth out that input signal such that there are no drops. The input signal for the driver is coming out of the isolator, so you could start there. I also notice that the gate beads and resistors are in the same ground loop as the driver, so experiment with those values, and it could help smoothen out the input signal as well. 

    Since the input pins of the driver are tied together, we recommend that you tie the outputs together as well. Try that and see if that yields a better output.

    Best,

    Rubas