• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 313 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LMR50410-Q1: Failure when 28V is applied directly

G Ploeg
Prodigy 10 points
Part Number: LMR50410-Q1
Other Parts Discussed in Thread: TPS560430-Q1, TPS560430

Hello,

We have made a design with the LMR50410YQDBVRQ1 to create a 5V voltage rail.
So we tested is mainly using a lab bench power supply and never connected / disconnected it via the banana-plugs but only via the power supply itself(On/off button).

Now the test results looked very promising so we decided to implement it in out prototype. But when we connected 28V to the system without the lab bench power supply and connected it directly to 28V.
The VIN pin was straight away destroyed. Any voltage <28V is not destroying the device.
So let me further explain: the lab bench power supply uses an internal soft start circuit to regulate the output to the entered value. But in our use case the voltage comes directly from an 24V battery and the system does not have a soft start on board. I took two scope pictures from the input voltage when we connected it. There is a little contact bounce but I do not think that this is the problem. The values are all within the absolute maximum ratings.

So I tried some tests with a pull-up resistor on the EN pin to the VIN pin etc. but nothing worked.
That's why we decided to go with the pin-to-pin compatible TPS560430-Q1 and for now it looks like the problem has been resolved.
But it doesn't feel right not knowing what the problem is. And that an almost the same IC works.

What could cause this type of behavior?
Maybe a latch up of the IC?

I hope there is someone that can clarify this problem.

  • 0
    TI__Mastermind 35210 points

    Hello,

    This failure looks very similar to EOS on HS FET of the device due to BVDS violation.

    Looking at scope capture, it does read ~33V, approaching absmax of 38V.

    Was this measured right at the pin?

    When power the board, are you using long wires? This can tend to cause a large ring on VIN. If not carefully measured at input cap of the device, you may not capture the full amplitude of the ring.

    MY suspicion is that you are getting a large ring on Vin.

    If your final solution involves power the device this way, we will need to consider a damping network on Vin, as the same issue would remain.

  • 0 in reply to Marshall_Beck
    Prodigy 10 points

    I did some extra measurements and it looks like you are right. There is a small chance that the BVDS is violated for a short amount of time, and that maby the TPS560430 it a bit less sensitive to this. 
    I have to figure out a way to eliminate this ringing because we are going to power it with a longer cable that I used for the test.