• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 168 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC27531: Failure on turn on

Warren Muir
Intellectual 525 points
Part Number: UCC27531

Tool/software:

Hi Forum Members

Can anyone assist with why we have catastrophic failure of the UCC27531 on turn on - Q3 not switched on? Vcc is 16-24Vdc, so well within specification. When I lift the EN pin on the proto PCBs, the unit does not fail. Please see schematic below 

  • 0
    TI__Intellectual 810 points

    Hey Warren,

    Thanks for reaching out here! Would you please elaborate on the intended functionality of Q3? Is the goal to create an inverting input signal? 

    Also, please describe what you are doing when you "lift" the enable pin. Which unit no longer fails when you take this action, UCC27531 or Q3?

    Thank you,

    Grant

  • 0 in reply to Grant Wilson
    Intellectual 525 points

    Hey Grant, thanks for reverting.

    1. Q3 is to invert the logic since we are driving a P-channel FET

    2. We physically bent the pin on the device off the PCB pad. This was due to a hunch, since the datasheet shows a 5V8 reference on the EN pin, so we thought that Vcc on this pin might be causing the issue. After lifting the pin, the device functions as expected.

    3. Below are pics of the PCB and the failed devices - U1 and U2 are exactly the same circuit.

  • 0 in reply to Warren Muir
    TI__Intellectual 810 points

    Hey Warren,

    Will you please clarify what is not working when the enable pin is touching the PCB? Is the Gate Driver IC not outputting?

    For reference, we typically recommend a 10k resistor between VDD and EN. Also, if you don't wish to use enable you can leave the pin floating. Leaving the pin floating will enable output. 

    Best,

    Grant

  • 0 in reply to Grant Wilson
    Intellectual 525 points

    Hi Grant

    The UCC27531 fails catastrophically when the EN pin is connected to Vcc (or Vdd pin) - please refer to the picture showing U1 and U2 completely burnt. 

    I did not see any information recommending connecting EN to Vdd with a 10k. The absolute maximum ratings show that EN can sustain the same voltage as the IN pins, so I am not sure why the device fails catastrophically???

    Regards
    Warren 

  • 0 in reply to Warren Muir
    TI__Intellectual 810 points

    Hey Warren,

    Though it shouldn't lead to failure, it is worth noting the recommended max for EN and IN is 25V, so you are nearing this spec with the high end of VDD 24V.

    After adding a 10k resistor between VDD and EN do you see this same failure? Also, do you intend to use the EN function of this device, or could you leave this pin floating? 

    Thank you,

    Grant

  • 0 in reply to Grant Wilson
    TI__Intellectual 810 points

    Hey Warren,

    Wanted to follow up here. Refer to datasheet 9.3.2 Input Stage: 

    Essentially too much current is flowing to the input stage. Having a 150 Ohm resistor will limit the current flow.

    Best,

    Grant

  • 0 in reply to Grant Wilson
    Intellectual 525 points

    Hi Grant

    Thanks for both responses and apologies for the delayed response - I was playing golf yesterday!

    To answer both your responses

    1. We did first tests at 16V, and experienced the immediate failure of the UCC27531.
    2. We are not able to easily incorporate a 10k onto the current board, so have left the EN pin floating
    3. Based on tests performed so far, we will probably leave the EN pin floating as this functions satisfactorily. My issue was that the datasheet was ambiguous wrt the EN pin, and clearly this cannot sustain the maximum ratings quoted
    4. Noted on section 9.3.2 - we exceeded the suggested 15V by 1V on the EN pin and the device failed catastrophically. Maybe this should be more clearly highlighted in the datasheet

    Thanks for the assistance.