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LM5017: SW pin 10V higher than VIN (more than abs. max rating)

Prodigy 230 points

Replies: 2

Views: 85

Part Number: LM5017

Hello,

We are using the LM5017 flybuck isolated supply reference design in document SNVR323 http://www.ti.com/lit/df/snvr323/snvr323.pdf

VIN is 48V and I am seeing the SW pin go all the way up to ~58V - what could be causing this? Waveform of SW pin wrt GND:

Waveform of SW wrt VIN (gnd of scope probe connected to VIN) showing a max of 10.8V between VSW and VIN during ON period.

We have measured f_sw and T_on to be correct, but Vout is ~2V higher than what the feedback resistors are calculated to output. Rfdb1 and Rfdb2 are selected for a ~10.2V output but it generally reads ~12V.

I don't think we are overloading the output as the load current never exceeds ~40mA or so, and we have simulated the circuit and do not see this phenomenon. 

Oscilloscope and probe have been checked to be accurate as well.

I am wondering if this could be related to the failure where a hole burns in the VIN pin of the chip. Some previous posts here:

https://e2e.ti.com/support/power-management/f/196/t/782471

https://e2e.ti.com/support/power-management/f/196/t/273008

Thanks,

Vishaal

  • Hi,

    The part should be able to handle up to 100V so 58V should be ok. 

    In this case is the primary voltage reads at 12V when you load it? 

    I guess the bigger question would be that is your primary voltage regulates at 12V

    Thanks

    -Arief

  • In reply to Arief Hernadi:

    Hi Vishaal.

    Do you still see this issue? If not please close this thread.

    Best Regards,

    Ankit Gupta

    Application Engineer

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