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Original question:

LM5170EVM-BIDIR: I received a broken EVM board

LM5170EVM-BIDIR: EvKit dead on arrival

Michael Bayern1
Prodigy 30 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170

Hi,

I ordered the EvKit a few weeks back and just got to hooking it up. After setting up the jumpers for my mode (buck only, using the onboard voltage loop) and applying 48v, nothing happened. It appears the UVLO line is being held low by shorted pins on the onboard supply regulators U3, U4, and U5. After lifting the EN pin on the LDOs, I can get the UVLO net up to 3.3v using an external supply (but of course the internal 10v supply is off). It seems U5 also has a short in the UVLO pin (but not the enable pin), when the pin is soldered in place I can measure 3.3v across R53. 

I'd really rather have the onboard 10v supply for my bench testing, so I'd like to confirm that those 3 parts are the issue and get replacements if possible... though I'm not sure if I'll be able to replace U5 with its thermal pad on the massive power planes and no thermal relief. 

  • 0
    TI__Guru 68675 points

    Hi Michael,

    Thank you for considering the LM5170.  Please install 100k at R4, and close J1 jumper to 48V side, which will enable the onboard UVLO function.  If you still see problem in powering-up, please show me a photo picture of your board so I can check if there is any jumper misplacement.

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 30 points

    Hi,

    I previously installed R4, however with R4 and J1 set as you described the UVLO still measured 0v. The only way for the UVLO line to measure anything other than 0v was to lift the pins on the three ICs previously mentioned.

    I've attached a picture of the current jumper setup. My only goal with this setup is to see the 10v Aux rail function.

  • 0 in reply to Michael Bayern1
    Prodigy 30 points

    As an update,

    I've replaced U3/U4/U5 and was able to get the 10v, 5v and 3.3v rails to power up. I further replaced the LM5170 and now have intermittent output. It looks like it's hiccuping, 3ms on and 3ms off, but I don't see a fault output from the chip and none of the CH1En, CH2En, UVLO, DIR pins are floating or otherwise changing state. The average output voltage is 19v. I think there may be a problem with the onboard voltage loop not regulating properly that's triggering the overvoltage lockout on the LV port. I'll continue to investigate further.

    Edit: After bypassing the built in voltage loop the output is stable up to 12v. Above 12v it begins to hiccup again, since my application requires a 28v output I'll continue to troubleshoot, but since that's outside the scope of the EvKit I think my issues here are resolved. Shame the voltage loop isn't working properly, it would've made my initial testing much easier. 

    Edit 2: Yup, 22v ovp by default according to the user guide. Swapped the resistor on ovpb for a 33k and I'm good up to ~36v out.