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WEBENCH® Tools/LMR33640: Built-in Circuit Protections Preventing High Current Load.

Guillaume Arcand
Prodigy 20 points
Part Number: LMR33640

Tool/software: WEBENCH® Design Tools

Hi,

I've recently designed a switching power supply using the "WEBENCH Design Tools".

Vin = 7 - 9V,    Vout = 1,5V,    Iout = 4A

The only use for this power supply is to feed a glow plug(very low impedance: ~0,4ohm) for a set time using a remote control input.

The glow plug should sink approximatly 3,5A.

As soon as I enable the load (using a SPST relay), the power supply drops to approx. 0,2V.

I'm pretty sure the IC interprets the load as a short-circuit and enables its short-circuit protection.

Is there a safe way to bypass these protections?

Thanks

  • 0
    TI__Guru 50120 points

    Hi Guiillaume,

    Just wanted to confirm that the power supply is regulating just fine without the load.

    Only when the glow plug load is connected is there an issue with the power supply. 

    How are you testing your board? Are you using a stable input power supply that isn't current limited?

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    Prodigy 20 points

    Hi Jimmy,

    With minimum load, the IC is regulating just fine.

    My input power supply is from a 10VA transformer 115/230VAC (VPP10-1000).

    I feel kind of bad right now but I think you might have pointed out the real issue: I might require more than 10VA at the start.

    I've tried powering up my circuit with a much bigger/stable DC source and it seems like the power is ramping up.

    I'll take a closer look at the input power supply.

    Thanks,

    Guillaume

  • 0 in reply to Guillaume Arcand
    TI__Guru 50120 points

    Hi Guillaume,

    The input power supply sounds like the bottleneck here. Please make sure that the power supply can properly source the required current for your application during startup when there is a bit of inrush current. 

    I'll close this thread for now. If you have any device level questions on this part, please let me know by replying to this thread and it will reopen for further discussion.

    Regards,

    Jimmy