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DRV8353: No high-side drive signals

Tim Harper
Prodigy 20 points
Part Number: DRV8353

Tool/software:

I am using a DRV8353S in a BLDC design at 24VDC.  

The very same driver design was used in a previous board with very good results, but in a new board with a changed microcontroller, we are now only seeing low-side gate drive but no high-side.  

VCP is stable around 35V, so the charge pump is working fine.  We are running in 3-PWM mode.  The INHx signals are all correct and operating from the micro as expected.  

The switching frequency for the PWM inputs is 8kHz. Nothing very fast at all.   

SPI signals look good in and out. No errors are being reported over the SPI and the _nFault pin is sitting high, so nothing internal is erring and pulling it low.  

The INLx pins are all at high logic level (3.3V).  

So, why would my GLx signals all be operating correctly (around 11V amplitude, complementing the signals at the INHx pins), but my GHx pins are not doing anything?  

Are we possibly missing something in the initialization register?   

Somewhere along the way the high-side outputs are just not being activated.  

Ideas? 

Thanks!

  • 0
    TI__Mastermind 23506 points

    Hey Tim,

    Would you be able to send a waveform of INHx, GHX, SHX and VM, when you switch your inHx signals?

    Best,
    Akshay

  • 0 in reply to Akshay Rajeev Menon
    Prodigy 20 points

    Hello Akshay, sure thing..

    Here's a picture of the signals you requested.  Sorry, the network security around here has prevented me from tying this old scope onto the network or using an insecure thumb drive to grab the screenshot directly.   So, iphone to the rescue.  Sorry if it's difficult to read.  

    You can see that the INHA signal was good and so was VM.  But there's just not a reaction at GHA or SHA.  The GLA (not shown) works just fine and complements INHA.  

    Thanks,

    Tim

  • +1 in reply to Tim Harper
    TI__Mastermind 23506 points

    Hey Tim,

    Would you be able to read back the register setting to confirm if you are actually in 3x mode? It is possible you might be in 6x mode. So when both GLX and GHX are commanded high the shoot through protection of the device will highz the outputs.

    Please then send a waveform of INHx, GHx, INLx, GLx.

    Best,

    Akshay

  • 0 in reply to Akshay Rajeev Menon
    Prodigy 20 points

    Hello Akshay, you are on exactly the same wavelength as we are.  Yesterday afternoon our software engineer found a mistake in the SPI initialization that was doing exactly as you say...putting us into 6x mode.  The SCK was set as active high instead of active low, and when he fixed this bit, the DRV8353 was properly initialized in 3x mode.  It is ALIVE!  All gate signals are working as expected, so now we can continue our work in setting up everything else. 

    I appreciate your time and your quick response on this!  There are some great experts out here! 

    Kind regards,

    Tim