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DRV8302: GVDD is at 0V

Adam Hendrych
Prodigy 10 points
Part Number: DRV8302

Tool/software:

Hi,

I've recently ordered a batch of BLDC drivers that I have designed around DRV8302. It is a third iteration of the same design (it has some minor changes in layout). So I have 2 fully working prototypes in the workshop. My problem is that the new drivers have their GVDD pin at 0V all the time, which results in nFault pin going low and no output being produced.

Only major thing that is different in the new driver is the current sense (both SP and SN 1/2). I removed the low-side current sensing setup and replaced it with inline one. Is this is a problem? Is the DRV8302 dependent on the low-side sensing setup presence?

I also tried to reduce distance between the large GND pad of the chip and source pins of the low side mosfets with wires, but I had no luck with that. DVDD and PVDD voltages are at expected levels. Specifically:

DVDD = 3.45V

PVDD1 = 20.0V (powered from 20V power supply)

But GVDD and AVDD are both at 0V.

This is my schematic and layout:

Schematic

Does anyone know what could be the cause? 

  • 0
    TI__Genius 14995 points

    Hi Adam,

    Not sure what the cause of this issue could be but can you tell me the voltage rating of C3 and C4?

    The way you are using SPx and SNx for in-line current sense isn't something I've seen before. 

    This is how SPx and SNx pins are used. If you're wanting to use in-line current sense I believe the integrated CSAs do not support this, you would have to use external ones like this:

    https://www.ti.com/product/INA240

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 10 points

    Hi yara, the C3 is rated up to 16V and C4 is rated up to 50V. I used the same capacitors in all my previous designs without any probelms (the GVDD was always around 11.4V so the 16V cap handled it just fine).

    I am also concerned about the missing low side current sense. The datasheet is not very clear about this, since only thing it states is this:

    It includes "inline current measurement", but does not state wheter or not does the IC need the sense resistors placed as shown in the picture you sent. Is it mandatory to connect the resistors between SN_X and SP_X like shown? Does the IC internally work with this somehow?

  • 0 in reply to Adam Hendrych
    TI__Genius 14995 points

    Hi Adam,

    In that same section 7.3.2 it mentions how SPx should connect to resistor ground

    I understand how the use of 'in-line' here can cause confusion but heres another example the datasheet provides for how SPx and SNx should be used:

    Also 16V for the GVDD cap rating might be fine but I would also consider replacing it with one that is 2x the value of GVDD to account for potential capacitor derating.

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 10 points

    Hi Yara,

    I will look deeper into this. Perhaps I will try to cut SN_X and SP_X traces on the working drivers and see if it will lead to the same problem (and then accept the suggested answer).

    Even though I fully admit my mistake with this I still think that the datasheet (or the resources in general) for this IC is/are not very specific about what the the circuitry around it does (the "inline" word is particularly confusing).

    I also have a small followup question about the sensing. What are these yellow marked components supposed to do in the circuit?Aren't they redundant when the current sensing is handled by the SN and SP pins? The typical application circuit says you should connect the X_SENSE pins to the MCU. So what are they reporting (also quite unclear from the sheet)?

  • 0 in reply to Adam Hendrych
    TI__Genius 14995 points

    Hi Adam,

    These circuits are dependent on your commutation method, for example they could be use for voltage sense when doing sensorless trapezoidal commutation to detect the 0 crossings.

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 10 points

    Hi Yara,

    So I tried to "rewire" the board to use the low side sensing, but still, no success. The GVDD is still at 0V. It seems like this batch of chips is defective somehow. When I cut the traces on the old pcb (SN_X and SP_X traces) it still works. It seems that those inputs don't have to be connected at all. 

    It is most likely just a broken IC, but still... Can this be caused by the layout only? Meaning that all the connections + schematic are done correctly, but the part placement on the actual PCB is "incorrect"?

  • 0 in reply to Adam Hendrych
    TI__Genius 14995 points

    Hi Adam,

    Theres a good chance your devices are damaged, especially since SPx and SNx were used "in-line" that would expose them to SHx voltage which I believe they're not rated for.

    Regards,

    Yara