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DRV8304: Charge Pump Undervoltage

Stuart Coats
Prodigy 40 points

Part Number: DRV8304

I am designing a driver for a BLDC motor as a senior project. I am using a DRV8304 to drive 6 N-channel MOSFETS arranged in a three phase inverter. I am currently having issues with a fault condition that I am unable to clear properly. Having read the "Fault Action and Response" table in the datasheet provided by TI several times, I believe I have isolated the problem to be a Charge Pump undervoltage error. I have gone through the datasheet and am fairly confident that the passive components connected to the charge pump are correct. Additionally, I have checked all of the pins on the IC for shorts and have not been able to find anything that does not seem normal. Any advice on how to fix this error would be greatly appreciated. I have attached copies of my schematic and board deisgns.bldcDriverV1.1brd.pdfbldcDriverV1.1.pdf

  • 0
    TI__Guru 66550 points

    Stuart,

    Thanks for posting on the MD forum!

    Have you checked the VCP pin voltage right at the pin of the DRV to see if it is as expected? Do you see any dips in the waveform there?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 40 points

    Adam,

    I have tested the VCP pin voltage, however not directly at the pin of the DRV. I have tested it on the VCP side of the capacitor with a multimeter and I am getting a reading of around 11.5V (Context: my VM voltage is 12V). I have not yet tried to hook up an oscilloscope to try and analyze the waveform, however the 11.5V reading seems to be constant, at least at the multimeter's relatively low sampling rate.


    Thank you for helping me out!

    Stuart

  • 0 in reply to Stuart Coats
    TI__Guru 66550 points

    Stuart,

    I have often seen an acceptable voltage on a multimeter when in actuallity the voltage at that node is dipping below the undervoltage tripping point. Please check this node with a scope and do so as close to the DRV as possible. Please provide the plot if possible.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 40 points

    Adam,

    I hooked up my oscilloscope to the board as close to the pin as I was able and have attached a picture of the resulting waveform. I sampled the data at 100 MHz (as fast as my scope will allow) if that provides additional information.

    Stuart

  • 0 in reply to Stuart Coats
    TI__Guru 66550 points

    Stuart,

    Was this check done with the board switching? I want to make sure the charge pump works under normal operating conditions and load.

    Can you explain how you arrived at the assumption that the fault you are seeing is caused by chargepump undervoltage?

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 40 points

    Adam,

    The new waveform of the charge pump voltage (attached) was taken with the board switching (or trying to) the N-channel FETs. 

    I arrived at the fault being the chargepump undervoltage based on the fault condition table in the DRV8304 datasheet. There are only two fault conditions that cannot be cleared by performing a power on reset, i.e. pulling the enable pin low for a short period. One of which is a VM undervoltage condition where the VM is below a certain threshold ~6V. My VM voltage remains constant at 12V and I have added a bypass capacitor to help filter out power supply voltage drops/spikes. Additionally, the Vcp voltage is reading under 12V. The datasheet says that the voltage reading should be 10V higher than VM.


    Thanks,

    Stuart

  • 0 in reply to Stuart Coats
    TI__Guru 66550 points

    Stuart,

    Please send me an email at adamsidelsky(at)ti(dot)com.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    TI__Guru 66550 points

    Update for the forum,

    We suspect that the device may be damaged due to IDRIVE being too high or excessive oscillations/overshoot/undershoot on the phase/gate. Stuart will be populating a second board to try this as well as swapping the original IC on the first board.

    Regards,

    -Adam