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DRV8323: DRV8323 shoot-through with small MOSFETs

Karsten Weiss
Prodigy 20 points
Part Number: DRV8323
Other Parts Discussed in Thread: CSD18541F5,

Hi,

we are using the DRV8323 to drive small MOSTETs type CSD18541F5 in 3x PWM mode to control a small 24V-BLDC motor (motor power 9W). See schematics below. If the PWM input is either low or high, current consumption of the circuit is okay (35mA including micro controller). But when toggling the PWM input, it seems that for a short period of time both high and low side MOSFET are on, as the current consumtion even with no motor connected (motor replaced by some LEDs to visualize the turning field) raises with the frequency of the PWM signal. We're using the default settings of the chip, except the Driver Control Register is set to 20h (PWM_MODE: 3x PWM enabled). The effect can be reduced by changing the dead time in OCP Control register from 100 to 400 ns, however there are still 300 mA flowing on 1 kHz PWM switching clock. The status doesn't show any error.

Do we need to change the configuration or is any addition external circuitry required with this small MOSFETs?

Thanks for any hint in advance

Karsten

  • 0
    TI__Guru 61310 points

    Karsten,

    Thanks for posting on the MD forum!

    The DRV8323 sets the IDRIVE to maximum by default which will attempt to drive your very small 1.6nC Qgd with 1A source and 2A sink. This is likely causing the partial shoot-through as the gates will ring and bounce with this large current and tiny gate capacitance.

    I would program IDRIVE to the lowest setting in registers 0x3 and 0x4 and try the test again. Likely if you check GH/GL/SH before and after the change you will see a drastic improvement.

    I also have an IDRIVE FAQ and App Note here: https://e2e.ti.com/support/motor-drivers/f/38/t/796378

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Prodigy 20 points

    Hi Adam,

    thanks for your quick and helpful reply. Reducing IDRIVE significantly reduced the ringing for my setup. However, the frequency-dependent current consumption still occurrs. It seems that the root of the issue is the ESD protection feature integrated on the CSD18541F5 MOSFETs that utilizes a quite large series resistor to the gate and thus large switching delay > 1000 ns which probably causes the shoot-through (honestly, I oversaw this when first reading the specs....). I think the only solution will be to select another MOSFET.

    Best regards

    Karsten

  • 0 in reply to Karsten Weiss
    TI__Guru 61310 points

    Karsten,

    Would you like me to forward your post to the FET team for some help with part selection?

    Regards,

    -Adam