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DRV8701: nFault during driving div. motors

Franz Giesen
Prodigy 130 points
Part Number: DRV8701

We would like to use the DRV8701 chip. The circuit is supposed to control different UNKNOWN motors in the area of model toys. The motor types range from brushed motors to bell-shaped armature motors. Depending on the motor type, the error output nFault is set at low current (approximately 200mA) and the chip reaches the intended waiting time of a few ms. The wiring diagram corresponds to the appendix. The chip is controlled by an STM 3.3V CPU via the two channels In1 and In2.
Can TI support help us?
Motor sheet V1M4.pdfMotor sheet V1M4.pdf

  • 0
    TI__Guru** 114905 points
    Hi Franz,

    Can you confirm the AVDD and DVDD capacitors used? The schematic shows 22uF and 100uF, respectively. The datasheet recommends 1uF.

    Also, how much bulk capacitance is on VCC#10?
    To find the cause of the fault, it is recommended to start from the fault signal and work backwards in time using Table 7 of the datasheet.
  • 0 in reply to Rick Duncan
    Prodigy 130 points
    Hello Rick Duncan,
    we have two capacitors on the line DVdd each 100uF - we need them. This capacitor is no problem without driving a motor. Some motors work but most doesn't. On the line AVdd is 22uF. This pass is without load at the moment. Later we have about 10 - 20 mA. The load on DVdd ist about 10mA.
    Best regards
    Franz Giesen
  • 0 in reply to Franz Giesen
    TI__Guru** 114905 points

    Hi Franz,

    May I ask why you need such large capacitors?

    What problems did you see when using 1uF capacitors on AVDD and DVDD?

    The device was designed to operate with 1uF capacitors on AVDD and DVDD, and for the load specified in the datasheet.

  • 0 in reply to Rick Duncan
    Prodigy 130 points

    Ladies and gentlemen,
    we use the DRV8701P in a prototype design. After some experience with this chip we would like to ask you to answer the following questions: The capacitor listed on page 28 with "bulk" is indicated with min. 10uF. Is there a way to calculate the capacitance of this capacitor? Does the size of the capacity depend on the motor current? The manual does not provide any facts at this point!
    Another problem arises from the fact that we have to regulate the speed of a connected DC motor in both directions of travel. The aim is to keep the rotational speed of the engine constant over its entire working range. An external potentiometer gives a voltage to a CPU and the motor connected to the DRV chip must reach a speed proportional to the voltage. We adapt the PWM in each case. For this purpose, we measure the generator voltage of the motor in a gap (no PWM present; IN1=IN2=0) of approx. 0.5 to 1.0ms and transmit it to the motor controller. When the motor is at standstill, a constant voltage of approx. 0.7V is applied between contacts SH1 and SH2! We cannot distinguish this voltage from the generator voltage! The controller erroneously suspects that the motor is rotating. Is there a proposal from TI on how the problem can be solved?
    We look forward to hearing from you.
    With kind regards
    F. Giesen