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DRV8843 3.3V Regulator Problem

Jake Vander Ploeg
Other Parts Discussed in Thread: DRV8843

Hi I am currently trying to use the DRV8843 to drive two DC motors that can consume up to about .5 A when fully loaded. I am essentially using the same logic as the diagram on page 2 of the datasheet, and I have nReset and nSleep tied to +5V, and Decay left floating. I'm not using the current sense pins and have tied those to ground. After an hour or so of testing my application, the chip no longer seemed to work. I checked a few of the pins and the 3.3V regulator output was no longer giving 3.3, and instead just stuck at ground. I was having it directly drive the VREF pins, however after soldering a new chip on I disconnected it completely, instead using a simple voltage divider for the VREF pins. Any suggestions as to why this would happen? 

  • 0
    TI__Mastermind 26065 points

    Hi,

    Could you give more info about the application conditions? like motor resistor and VM voltage. 

    If you don't use current sense resistor, while your motor resistor is small, the peak current may get too big and reach the OCP(see Page11 of datasheet), and then nfault outputs and the parts remains in the OCP state untill power cycled.

    It is recommended that the current sense resistor be used in the application, you can set the current level at 2x of your normal running current 0.5A according to the setting equation, which not affect your normal running but also limit the start or stall current to the level below the OCP threshold.

    Beside, you can check and make sure the TSD and UVLO not assert when the issue happens.

    BTW, is this issue a one time happening or can be reproduced every time?

    Thanks.

    Wilson

    Motor Application Team

     

  • 0 in reply to Wilson Zuo

    Hi Wilson,

    Thanks for the response. I don't have easy access to the motors since this is a robotics application and they are buried in the chassis, however when I run one motor at 15V from a power supply it consumes about 500 mA when it is just turning the wheel in the air, and about 1.5~2 A when I forcibly try to stall the motor, which shouldn't be happening in the application. I had VM at 15V during the application, with a regulated 5V input into the logic supply. I realize I forgot to mention that after the chip is no longer driving the outputs, and the 3.3V regulator is no longer giving an appropriate output, nothing seems to be able to fix the chip. I have power cycled and the same behavior persists. I also have soldered on new chips to try to figure it out, but once the chip's 3.3V regulator goes it seems like the chip is fried. The nFault pin wasn't driven low either after power cycling. I unfortunately ran out of chips over the weekend to keep testing (I ran into this problem with the 3 chips I had), so I had to move on with a simple H-Bridge (the L298N), however I should have more arriving soon so I can try to repeat exactly what happens. I will add current sense resistors as well to ensure current regulation, just in case the motors stalling  cause a spike in current higher than I can see and killing the chips. Is there anything else that might be causing this behavior? Thanks again for the help.

    - Jake

  • 0 in reply to Jake Vander Ploeg
    TI__Guru 55605 points

    Jake,

    Have you soldered down the PowerPAD to your PCB?  Do you have proper decoupling (0.1uF close to each VMx pin....also a bulk 100uF capacitor)?  Can you share a schematic?

    A good reference for you with layout and schematic can be found online under the EVM folder. 

     

  • 0 in reply to Ryan Kehr

    Hi Ryan,

    I did solder down the PowerPAD as well as having 0.1uF decoupling caps next to the power pins. I did not have a bulk 100uF capacitor, though I do have an extra 10uF and 1uF capacitors next to the regulator which is physically right next to the DRV chip. The schematic is here:

     6758.motor_board.pdf

    The other sheet in this schematic is completely unrelated to the motor drive circuit, so I have left it out. Basically, I have a simple 10 pin header that brings in the enables, PWM signals, and direction bits from a microprocessor, and that goes through an opto-isolater and inverter, then to the DRV.

    Thanks for the help.

     

    - Jake

  • 0 in reply to Jake Vander Ploeg
    TI__Mastermind 26065 points

    Hi Jake

    It is strongly recommended that you put extra 100uF near by VM and GND directly. This is important for almost motor drivers. Especially when you do not have current regulation resistor, the peak current could cause obvious ripple on VM pin. All the driver functions will work correctly as long as the VM is stable and within the operation range.

    You can have test again with the 100uF cap manually add to you current board. Make sure add the cap near by the driver side other than the power side.

    Thanks.

    Wilson