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LM5176: I am having issues with component failure attempting to generate 50 v

Part Number: LM5176

I am having issues with generating 50V from 4-24V input. 

I changed the feedback resistors to a higher value but the same ratio. and 48v was there for a while, and then the component failed again. 

I am debugging a design that was handed down to me.

The initial differences I see are that the FB resistors were smaller in value (same ratio) and I changed this to match the simulator. 

Also we are using CDS19534 components instead of the simulator recommended parts,  and finally I see that we are not sampling the current but rather have .02 ohms to ground, but the drop across the resistor is not fed to the chip. 

Finally the person before me did not have Bias tied to .1uF cap, but it is now. 

It seems to me the part is having an over voltage failure.. but without knowing.. it's a guess. 

  • Hello Bad,

    Would you please share your design? Which transistors have been recommended?

  • Hi Brigitte, sorry for very slow response.  The design was initially for 24V output and someone tried to change just the FB resistors to accommodate 50V..digging deeper I discovered all sorts of problems with the BOM, so we are in the process of fixing this based on the 5176 Designer/simulator BOM and have hope that this will fix the issue. The big find was the bias pin not being handled properly for the 50V output. Stay tuned, as if we still have issues once the BOM and pin 24 bias is fixed.. I may need another set of eyes. 

    Regards, 

    Brad

     

  • Hello Brad,

    Ok, then I will close this thread at the moment. For further discussions, just post again here or start another thread if this one is already locked.

  • So, I went through my design and per the web bench details, I replicated the components as specified, and was able to get 50V out of the regulator for about 1 minute.. then it died. I could not even get the scope probes hooked up before it was gone. 

    The failure was the LM5176 again. as replacing it  allows for the same startup followed by failure. 

    I can't even tell if this is a voltage or current failure mechanism.

    If there is something that can be done to protect the circuit and allow for debug... any guidance would be helpful. 

    Regards, 
    Brad

    The design is here: 

    https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=0ACCF03E310940C7

  • Hello Brad,

    In general the first step I would do to check your design with the quickstart calculator of LM5176. You shared the Webench design, but I would prefer to see your design instead of the result of Webench.

    You mentioned in your first post above that the current from the sense resistor is not going back to LM5176, if this is the case, this would be an area to check in detail.

  • Hello Brad,

    I expect that you have been able to solve the issue and will close this thread now. If this is not the case, please post more information below or if the thread is locked, please create a new thread.