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DRV8412: DRV8432 - Bootstrap Capacitor Voltage

Fahri Türedi
Prodigy 40 points
Part Number: DRV8412

Tool/software:

Hi,

We are using DRV8432DKD PWM Motor Driver IC for a Brushed DC Motor control application. We configured the driver in Paralel Full Bridge Mode of operation. For that we've designed our schematic as given in Figure 9 of the datasheet.

The problem is for some of the drivers the reading between the BST_X-GND_X and OUT_X-GND_X pins of the device are not as expected for some of those pins.

For example, for some devices the readings are as follows:

Driver 1:

OUT_A-GND_A = 27.9V, BST_A-GND_A = 27.3V

OUT_B-GND_B = 27.9V, BST_B-GND_B = 27.3V

OUT_C-GND_C = 0.7V, BST_C-GND_C = 11.4V

OUT_D-GND_D= 0.7V, BST_D-GND_D = 11.4V

Driver 2:

OUT_A-GND_A = 0.7V, BST_A-GND_A = 11.4V

OUT_B-GND_B = 0.7V, BST_B-GND_B = 11.4V

OUT_C-GND_C = 27.9V, BST_C-GND_C = 27.2V

OUT_D-GND_D= 27.9V, BST_D-GND_D = 27.2V

Our PVDD_X-GND_X voltage is 28V. GVDD_X-GND_X voltage is 12V.

And during those measurements, no motor was connected to the OUT_X pins of the driver and LOW (0) signals were applied to the all PWM_X pins.

What could be the reason for those 27.9V and 27.2V readings?

  • 0
    TI__Mastermind 32765 points

    Hi Fahri,

    Fahri Türedi said:
    We are using DRV8432DKD PWM Motor Driver IC for a Brushed DC Motor control application. We configured the driver in Paralel Full Bridge Mode of operation. For that we've designed our schematic as given in Figure 9 of the datasheet.

    Did you you mean the below schematic in the datasheet?

    Fahri Türedi said:

    And during those measurements, no motor was connected to the OUT_X pins of the driver and LOW (0) signals were applied to the all PWM_X pins.

    What could be the reason for those 27.9V and 27.2V readings?

    Could you please measure the voltages across the bootstrap capacitors only? They should not measure higher than GVDD_x, in your system this would be 12 V or less.

    You said "LOW (0) signals were applied to the all PWM_X pins". This would mean all LSFETs were conducting. In this case all the OUT_x to GND_x should be close to 0 V. I'm not sure how you measured close to PVDD_x of 28 V in some instances with no load connected, while all PWM_x pins were LOW. Could you please get scope captures for us? Thank you.

    Regards, Murugavel 

  • 0 in reply to Murugavel4637
    Prodigy 40 points

    Hi Murugavel,

    Yes I mean the Figure 7-8 that you posted. Our datasheet was an older version.

    The measured bootstrap capacitor voltages are as follows:

    Driver 1:

    BST_A - OUT_A = -0.670V

    BST_B - OUT_B = -0.671V

    BST_C- OUT_C = 10.78V

    BST_D - OUT_D = 10.77V

    Driver 2:

    BST_A - OUT_A = 10.80V

    BST_B - OUT_B = 10.80V

    BST_C- OUT_C = -0.667V

    BST_D - OUT_D = -0.661V

    I am reading no driver fault as well.

  • 0 in reply to Fahri Türedi
    TI__Mastermind 32765 points

    Hi Murugavel,

    Thanks for the additional details. I assume you measured this immediately after power up and with no OUT_A,B,C, D pins correct? Did you verify both the PWM_A and PWM_B to be at low impedance GND potential? I assume you had PWM_C and PWM_D connected to GND directly.

    Fahri Türedi said:
    The problem is for some of the drivers the reading between the BST_X-GND_X and OUT_X-GND_X pins of the device are not as expected for some of those pins.

    How many devices show these issues and out of how many? Have you verified for ESD related damages during handling and assembly of the PCBA? Do these devices function normally when you connect load and drive PWM_A and PWM_B PWM inputs? What is the value of ROC_ADJ resistor? 

    Regards, Murugavel