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DRV8303: Current consumption when EN_GATE is LOW

nvs_12
Prodigy 90 points
Part Number: DRV8303

We're seeing in some circuits with the DRV8303 that even that the EN_GATE is LOW the current consumption of the DRV8303 is higher than the value indicated by the datasheet.

We're unable to measure directly on each pin of the DRV8303, but we calculated the sum of current consumption on pins PVDD, SH_A, SH_B and SH_C pins. We're observing 2 patterns, in some DRV8303 we're obtaining a current around 4mA, in fact we observe that the total impedance is around 3kOhm. In other cases we are observing current consumption up to 12mA corresponding to an impedance of 570 ohm

Since there's no mention on the impedance of SH_A, SH_B and SH_C on the datasheet, could you give us an estimated impedance or current consumption on those pins where the EN_GATE is LOW?

  • 0
    TI__Guru 61380 points
    Nvs,

    With EN_GATE low, the output stage is in high impedance, there should be no voltage present on SHx. Why are you seeing voltage and therefore leakage there?

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 90 points

    Hello Adam

    When we're testing the motor controller in the test jig we connected 3 resistors of 2.2 ohm in star configuration to each phase, then in the middle of the star we connect another resistor of 2.2K to the high voltage bus. In order to check that the low side power mosfets on each phase are not short circuited, before connecting PVDD to the high voltage bus we measure the voltages in the middle of the star, and at the PVDD. For measuring the voltages we have 20.6k equivalent resistor to gnd on each phase and in PVDD, on the middle of the star we have an equivalent resistor of 41.2k.

    There's a path through the high side mosfet's diodes from the phases to PVDD, depending on the current flowing through the PVDD pin and SH_x pins, the voltage on PVDD could be calculated. According to the datasheet with the EN_GATE in Low, the current through PVDD pin should be around 40uA. And we're not sure how much should be the current flowing through SH_x pins or how big is their impedance.

    Assuming PVDD is consuming 40uA, we've calculated 2 different cases, one where the impedance is around 1.2k on each SH_x pin and other one the impedance is much lower, around 170 ohms. In both cases the device seems to be operating well, however we would like to know what should be the correct value and why do we have those 2 different cases.

  • 0 in reply to nvs_12
    Prodigy 90 points
    Sorry, the calculated impedance on the SHx pins for the 2 cases we've seen are 10.8k and 1.7k
  • 0 in reply to nvs_12
    TI__Guru 61380 points
    NVS,

    We do not provide this info, no voltage should be forced into SHx.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 90 points
    Hi Adam,

    That doesn't make any sense, the SHx pins are in fact the same connection as the motor phases, if a motor is rotating powered by an external source (like for example in a vehicle that it's going downhill) the Back EMF of the motor will "force" some voltages at the SHx pins.
  • 0 in reply to nvs_12
    TI__Guru 61380 points
    NVS,

    Yes in a backdrive condition this can happen. Let me check with design.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 90 points

    Hello Adam

    Do you have any news about this?

    Regards

    Nicolas

  • 0 in reply to nvs_12
    TI__Guru 61380 points
    NVS,

    We know there may be leakage on the SHx node depending on several factors. We cannot guarantee a specific impedance on the output node as factors such as the FET body diode conduction can change this.

    Regards,

    -Adam