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TPSI3050-Q1: Question about waveform of VDRV.

David Kim2
Expert 2275 points
Part Number: TPSI3050-Q1

Hi

When turnoff becomes slow (12V=>0V_about 270ms), VDRV repeats on/off.

-Condition-

Switching product: IGBT

Two wire mode

Waveform : Ch1(yellow): VDRV , Ch2(blue): EN

=>Zoom

When the EN voltage is 5~6 V, the VDRV is turned on/off.

Is there any way to improve it?

Thanks

  • 0
    TI__Expert 3575 points

    Hi David Kim2, 

    Thank you very much for reaching out with this question. What capacitance values do you currently have in VDDP?

    Sincerely, 

    Francisco Lauzurique 

  • 0 in reply to Francisco Lauzurique
    Expert 2275 points

    Hi Francisco

    VDDP is 220nF.

    Thanks

  • 0 in reply to David Kim2
    TI__Expert 3575 points

    Hi David Kim2, 

    Thank you very much for the answer. My initial thought was that VDDP had a large capacitor, but based in your feedback this is not the case. 

    The main concern here is that when EN is switching from 12V to 0V, due to a slow ramp, the device is between VIH(6.0V) and VIL(2.0V) for a long time. If we can reduce this ramp time this behavior should not occur. 

    I am trying to better understand why is EN ramp down this slow and what can be done to change this ramp down timing. Is there a large capacitor in EN that gets disconnected and discharged slowly?

    Sincerely, 

    Francisco Lauzurique

      

  • 0 in reply to Francisco Lauzurique
    Expert 2275 points

    Hi Francisco

    Thank you for the answer. 

    The customer said that  there is a large capacitor in EN.

    When the EN voltage is between 5 and 6 V, it is necessary to improve repeating ON/OFF.

    Is it correct to repeat ON/OFF when the EN voltage is between 5 and 6V?

    Is there a way to improve this?

    Thanks

  • 0 in reply to David Kim2
    TI__Expert 3575 points

    Hi David Kim2, 

    Thank you very much for the extra information. I am aligning internally with the team to provide a more complete feedback. I will have a final answer to this challenge before the end of the day tomorrow. Thank you very much for your understanding. 

    Sincerely, 

    Francisco Lauzurique 

  • 0 in reply to Francisco Lauzurique
    TI__Expert 3575 points

    Hi David Kim2, 

    Thank you very much for your patience. I was able to replicate the concern on a bench and find a possible solution. I will begin by explaining the reason for this behavior. 

    While the capacitor discharges between 6V to 2V, the slow ramp down is affecting the operation of the device. The device attempts to turn ON because the logic low (2V) is not present.  

    Solution. Decrease the discharge time of the capacitor to less than 1.9ms to improve this behavior. This can be accomplished by reducing the size of the capacitor.  

    Questions: Why is there such a large capacitor in EN? According to my calculation the worse case could be about 180uf capacitor. Is this a test that the customer is running? What is the purpose for this test? 

    Let us know if this answered your questions. 

    Sincerely, 

    Francisco Lauzurique 

  • +1 in reply to Francisco Lauzurique
    TI__Expert 3575 points

    Hi David Kim2, 

    Let us know if the previous answer helped.

    Sincerely, 

    Francisco Lauzurique