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DRV8320: Gate Drive Fault

K.Hamamoto
Guru 12155 points
Part Number: DRV8320

Hi

I have some question about GDF (Gate Driver Fault ) condition.

1. The condition what the GDF flag is operated is the below condition,

    Addr 0x02 [b8] DIS_GDF = 0b    and   "If the VGS voltage has not reached the correct threshold at the end of the tDRIVE period,"

    There are only 2 conditions what the GDF flag (nFault) become active(= pulled logic low). Is that correct?

2.This function is for the follwoing purpose.

- To check whether the setting of tDrive and iDrive(P/N) is appropriate.
- To check the short of the each gate line.

  Is my understanding correct?

3. What kind of case that is disabled the GDF function?

  If GDF is disabled,what is there any risk?

Best Regards,

Koji Hamamot

  • 0
    TI__Expert 8985 points
    Hi Hamamoto-san,

    Yes, only two possible reasons the GDF triggers are found in section 8.3.6.5.

    Turning off the GDF is a not a recommended proposition. This will mean that the GHx and GLx pins are not monitored such that if the voltage on the external MOSFET gate does not increase or decrease after the tDRIVE time OR no gate driver fault may be encountered if the selected IDRIVE setting is not sufficient to turn on the external MOSFET within the tDRIVE period.

    Read this section for more information:

    8.3.6.5 Gate Driver Fault (GDF)

    The GHx and GLx pins are monitored such that if the voltage on the external MOSFET gate does not increase or
    decrease after the tDRIVE time, a gate driver fault is detected. This fault may be encountered if the GHx or GLx
    pins are shorted to the PGND, SHx, or VM pins. Additionally, a gate driver fault may be encountered if the
    selected IDRIVE setting is not sufficient to turn on the external MOSFET within the tDRIVE period. After a gate drive
    fault is detected, all external MOSFETs are disabled and the nFAULT pin driven low. In addition, the FAULT,
    GDF, and corresponding VGS bits are latched high in the SPI registers. Normal operation starts again (gate
    driver operation and the nFAULT pin is released) when the gate driver fault condition clears and a clear faults
    command is issued either through the CLR_FLT bit or an ENABLE reset pulse (tRST). On SPI devices, setting the
    DIS_GDF bit high disables this protection feature.
    Gate driver faults can indicate that the selected IDRIVE or tDRIVE settings are too low to slew the external MOSFET
    in the desired time. Increasing either the IDRIVE or tDRIVE setting can resolve gate driver faults in these cases.
    Alternatively, if a gate-to-source short occurs on the external MOSFET, a gate driver fault is reported because of
    the MOSFET gate not turning on.
  • 0 in reply to Hector Hernandez Luque
    Guru 12155 points
    Hi Hector-san,

    I read the section 8.3.6.5.
    The condition is
    * MUST condition; Addr 0x02 DIS_GDF = 0b

    (1) GHx or GLx is shorted to PGND or SHx or VM pin.
    (2) "The GHx and GLx pins are monitored such that if the voltage on the external MOSFET gate does not increase or decrease after the tDRIVE time, a gate driver fault is detected."

    And for GDF we can increase the IDRIVE and tDRIVE setting. Most of the reason what is caused is the setting is too low.

    On the other hand, the background we are asking the above question is GDF is indicated on customer's board. Now they are investigating the reason. And It is occured even if the iDRIVE and tDRIVE is setting as maximum.

    Also our customer would like to disable the GDF function dut to the above reason.
    If this function should not be disabled as you mentioned above,why this function is implemented to be able to enable and disable?
    And could you tell me the case of that the function can be dsiabled? (What is the risk no GDF function?)

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Expert 8985 points

    On the other hand, the background we are asking the above question is GDF is indicated on the customer's board. Now they are investigating the reason. And It occurs even if the iDRIVE and tDRIVE are set as the maximum.

    Can they verify if, when the fault is triggered, the GLx or GHx pins are shorted?

    or 

    Can they verify after the tDrive time passes if the MOSFET's gate voltage does not increase or decrease?

    If this function should not be disabled as you mentioned above, why this function is implemented to be able to enable and disable? 

    We typically always have a disable for protection features just in case of an unforeseen requirement. 

    And could you tell me the case of that the function can be disabled? (What is the risk no GDF function?)

    One scenario to disable GDF is if they need a really long switching time past the max TDRIVE.