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What is wrong in my design?

Arjuna Weerasinghe
Prodigy 50 points
Other Parts Discussed in Thread: INA286

untitled.brd PCB in eagle brd format.

untitled.sch  Schematic in eagle sch format

It is not working.

How should I connect control pins for testing? (OTW, FAULT, PWMA, Reset_AB, PWMB, Reset_CD)

Here are some images of actual circuit board

  • 0
    TI__Guru** 114905 points
    Hi Arjuna,

    Can you clarify?
    What is the device doing?
    What voltage are you powering the device?
    How much current is the device drawing?
    What is the VREG voltage?
    What is the FAULT and OTW pin voltages?
    Are you able to toggle the outputs?

    Any additional steps that you have tried will help.
  • 0 in reply to Rick Duncan
    Prodigy 50 points
    This is for a current controlled dc motor application. Here DRV8432 IC is in a bridge mode for driving a single motor. Motor Current is measured using two shunt resistors and INA286 current amplifier ICs. INA286 ICs are powered through a 7805 Voltage regulator IC. Motor voltage is 30V but I applied about 18V for testing. A 7812 voltage regulator IC has been employed to step down PVDD voltage to GVDD voltage (+12V). 2 indicator LEDs are used at the output to detect the direction.

    1. I was unable to toggle an output
    2. IC temperature goes very high without any load
    3. VREG=0
    4. FAULT=0V
    5.OTW=0
  • 0 in reply to Arjuna Weerasinghe
    TI__Guru** 114905 points

    Hi Arjuna,

    Please note that VREG = 0 when power is applied is abnormal. Also high temperature without any load is unexpected, although the device requires a heat sink.

    Look for the reason VREG is at 0V. This could be a short or something else. If you can monitor the board current during power up this may help provide a clue. If you have a second board assembled, use it for comparison.

    Another resource for comparison is the DRV8432EVM. This can be used to compare signals, or compare the schematic (LINK).

    The device will not work until VREG is approximately 3.3V.

  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hello Rick,

    Thank you for your advice.

    I'll assemble another board and check whether I can achieve better results. I have uploaded CAD design of my PCB. I would be pleased if I you can check and see whether my component placements are acceptable. Actually I did not use SMD capacitors which might affect results. I feel like my routing is not good enough.  

    Is it necessary to have two power supplies for PVDD and GVDD?

    I stepped down PVDD voltage for GVDD supply by means of a 7812 regulator IC. 

  • 0 in reply to Arjuna Weerasinghe
    TI__Guru** 114905 points
    Hi Arjuna,

    It is not necessary to have two supplies as long as the main can supply the current for both. Stepping down PVDD to make GVDD is a common practice.

    I did not see anything in the schematic that stands out. I suggest you ramp board power up slowly and watch for higher than expected current. That may provide a clue. Also take a look at VDD and GVDD. VDD is used to create VREG.

    Set the PWM_A and PWM_B inputs to a logic low, and RESET_AB and RESET_CD to a logic high when powering up.

    Using SMD caps may help, but there is a more pressing problem. First you have to get the device to power up properly with no PWM inputs.
  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hi Duncan,

    Thanks a lot for your instructions which worked well and being supportive regarding this matter.   Now I have properly powered up my Motor Driver. Now VREG is about 3.3V. At previous attempts I have given voltages to RESET and PWM inputs which are higher than absolute maximums.  :( 

    Now >>>

    PWM_A and PWM_B are connected to 0V level.

    RESET_AB and RESET_CD are connected to 3.3V level.

    then, how should I apply PWM input signals? Should I use OPTO couplers to isolate voltage levels?

    What are the combinations of logic levels of PWM_A , PWM_B , RESET_AB, RESET_CD   to change motor rotational direction, breaking etc....??? 

  • 0 in reply to Arjuna Weerasinghe
    TI__Guru** 114905 points
    Hi Arjuna,

    Glad to hear the device is powered up properly. Now you can proceed to control the outputs and eventually controlling the motor.

    There is no need to use optocouplers as long as the control inputs remain within the absolute max and min values. Using optocouplers can help if the ground is noisy.

    To drive the motor, you will need to keep RESET_AB and RESET_CD as a logic high. Then depending on the direction and speed, you will use PWM_A and PWM_B to control the outputs. To begin, it is recommended to try controlling the outputs with no motor connected. This will allow you to verify the outputs are toggling as desired.
  • 0 in reply to Rick Duncan
    Prodigy 50 points

    Hi Rick, 

    I debugged my motor driver design properly. :)

    Thank you so much for your support. Now it is up and running as expected.

    Issue was with the control signal input voltage level. 

    Good Day!

  • 0 in reply to Arjuna Weerasinghe
    TI__Guru** 114905 points

    Hi Arjuna,

    I am glad to hear your design is up and running.

    Thank you for following up with the issue. This will help others.