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CCS/DRV8301: nFAULT pin asserted and fluctuating before activating PWMs

Steven Shenker
Intellectual 930 points
Part Number: DRV8301


Tool/software: Code Composer Studio

Hi,

I have built a dual motor board based on the F28069M Launchpad and two DRV8301s. I am using the buck converter of the first DRV8301 and have disabled the buck converter on the second DRV8301 (Other than EN_BUCK which is tied to GND all the other buck converter related pins on this DRV8301 are floating - RTCLK, COMP, VSENSE, PWRGD,SS_TR,PVDD2, BST_BK, PH). Also note that the circuit layout for the problematic DRV8301 is very similar to the first. 

The first DRV8301 is working fine and I am able to spin a motor. For the second DRV8301, after starting debugging in CCS and activating EN_GATE the nFAULT pin is asserted and looking at it with an oscilloscope the fault seems to pulse off for a fraction of a second every millisecond. Looking at the SPI status registers 1 and 2 all the status bits are 1(This could be garbage if there is an SPI issue). I had a look at the voltage of GVDD and it is around 11.1V (The same as the other working DRV8301). When starting PWM output however this GVDD drops to around 9V+- 0.2V, whereas the GVDD on the first DRV8301 is stable.

Looking at the GH and GL outputs shows a weak but tiny frequency output on all 3 phases on the second DRV8301.

Please note that for these tests I did not have a motor connected to either output. I also confirmed with my board manufacturer that the powerPAD GNDs are also soldered.

Could you please offer some direction as to other things that I can check in order to determine the cause of this issue?

Thanks in advance!

   

  • 0
    TI__Expert 4650 points
    Hi Steven,

    Thank you for the information.

    I would start by trying to debug the SPI issue (all 1's in the status register). Is VDD_SPI connected and power up correctly?

    Are you able to measure the timing of the nFAULT pin? Is the pulse-low length 64-us?
  • 0 in reply to Phil Beard
    Intellectual 930 points
    Hi Phil,

    Thank you for your quick reply. I need to confirm the SPI is actually working - I did check VDD_SPI with a scope and it is fine. I will try and read and write something to the DRV8301.

    Regarding the nFAULT pin timing, before activating the PWM, nFAULT is low(fault active) for about 5 ms, and high for about 0.6ms. There are also very short spikes occuring every 0.6 m.s while low.

    When activating the PWM, nFAULT is constantly low with short spikes occuring every 0.6 m.s.
  • 0 in reply to Steven Shenker
    Intellectual 930 points

    Ok so regarding the 0.6m.s pulses - I think this might be related to the charge pump pins - is this the same frequency?

    I can confirm that SPI is definitely not working on the second DRV8301, but is working fine on the first. I always receive a bunch of 1s when requesting information. Is there anything else I should check to get the SPI working? Do you know where the SPI gets its ground from?

    Thanks! 

  • 0 in reply to Steven Shenker
    TI__Expert 4650 points
    Hi Steven,

    The 0.6 ms would be to low for the charge pump, this could be a couple different fault conditions.

    I would double check AGND and the PowerPad (solder pad underneath device) and make sure these are correctly soldered. I would also check the SDO line and determine if it's correctly connected to our device.

    Have you checked the DVDD, AVDD, and GVDD regulator voltages when EN_GATE is high? Is DVDD up at 3.3V?
  • 0 in reply to Phil Beard
    Intellectual 930 points

    Hi Phil,

    I took your advice and decided to resolder the chip to check the powerPAD, after doing this problem was solved! Clearly my supplier didnt do a very good job of soldering this pad.

    Thanks again for your help!

  • 0 in reply to Steven Shenker
    TI__Expert 4650 points
    Not a problem, let us know if you need any other support.