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TPS92518HV: What happens if your load opens when the TPS92158HV is running?

Brian McKee
Intellectual 405 points
Part Number: TPS92518HV
Other Parts Discussed in Thread: LM3409HV, TPS92518

I just open circuited my TPS92518HV eval board while it was running and let the smoke out of the TPS92518HV.

In my application it is imperative that the output be allowed to be on and open.

I haven't found anything in the spec about this. Is it possible I messed up the registers and caused this to happen?

I changed a few components on that channel:

1. Inductor to 490 uH.

2. Rsense = 0.2 Ohm

3. Removed the two 1uF output caps.

In the software, I changed the rsense value to 0.2. I had slid the max off time to 255. I had changed the off time, but it was somewhere in the middle. I don't remember the exact value. As far as I know that was the only changes I made.

The circuit was stable and running when I removed the connection. There was an arc at the load and then a flash and snap from the controller on the eval board.

Flames shot out from the upper right corner of the part.

I'm used to the LM3409HV which does not take issue with sudden changes of conductivity.

Three questions:

1. Can I have a replacement part?

2. How do I prevent this from happening in my future design so I can use the chip in my application?

3. Can #2 be implemented on the eval board?

Thanks in advance

  • 0
    Intellectual 405 points

    I'm attaching a picture. I believe that the part stuffed on the board is not the HV variant. Can someone confirm?

  • 0 in reply to Brian McKee
    TI__Mastermind 28655 points
    Hello Brian,

    1) You can request samples on TI's website, it looks like up to five for free.

    2) The TPS92518 can get damaged if you open the LED string. The EVM does not have the protection stated below from the datasheet. When the inductor opens the current has to continue to flow. If it's not clamped the voltage will go higher than Vin and can damage the TPS92518.

    From the datasheet:
    8.3.3.1 Output Ringing and TPS92518 Protection
    During shunt dimming, ringing may occur at the channel output due to PCB and device parasitic capacitances
    and inductances. This should be checked as part of the design process. If the ringing approaches the absolute
    maximum of any pin, a clamping diode must be added to the design. Connect the diode anode to the output at
    VLEDx and the cathode to the input voltage. This protection must also be used if the LED load is ever to be
    connected or removed while the output is enabled.

    3) Yes, by adding two diodes for both channels feeding back to Vin.

    Regards,