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LMR51610: Backfeeding sensitivity when driving some inductive load.

Noel Le Moult
Prodigy 50 points

Part Number: LMR51610

Tool/software:

Hello,

I'm using the LMR51610 buck converter to generate a +12V power rail from a +48V input source. I'm powering a fan, a water pump, and some LEDs with a high-side driver connected to the +12V rail. When I use the water pump, I get power feedback, which the converter seems to accept without issue. The semiconductor temperature rises by +15°C when used with 600mA output, which seems correct to me.

Could this cause a reliability issue? Is it recommended to add a diode at the converter output to limit feedback? Do you have any other suggestions?

The diode necessarily causes a voltage drop and energy dissipation, I would like to avoid it if it is not necessary and if the converter can completely operate with this power return.

Here is my current schematic :

Here is a capture of the 12V rail at the converter output when the pump is running. We can clearly see a feedback that is limited to +15V by a TVS in parallel with the output, and then the power rail return to +12V.

Here is a test with a diode at the converter output, the feedback is no longer present and the behavior corresponds more to rapid switch with or without load caused by the pump motor.

Regards,

Noel

  • 0
    TI__Guru* 79815 points

    Hi Noel,

    Thank you for designing with our product.  I don't seen an issue for the LMR51610 in such applications. The only thing you need to pay attention to is, during the output voltage jumping high, the input voltage is always higher than the output.  If Vout jumps to 15V but Vin is >15V, the IC should be safe.  Otherwise, the high side FET body diode can conduct uncontrollably (as shown in the green path), which may damage the IC.  If you cannot exclude such an condition, insert a blocking diode in the input line to block it, and this would  have lower power dissipation than having the diode on the output line. 

    Best Regards,

    Youhao