• State TI Thinks Resolved
  • Locked Locked
  • Replies 11 replies
  • Answers 1 answer
  • Subscribers 29 subscribers
  • Views 287 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8306 크랙: The current value is high and the motor is hot.

on off
Prodigy 20 points
Part Number: DRV8306
Other Parts Discussed in Thread: CSD88584Q5DC, CSD87333Q3D
I used a translator. Please excuse me.
Hi.
I am inquiring about the DRV8306 motor driver.
I attached the data sheet and circuit diagram of the BLDC motor that I am using.

When operating the motor, the current value rises from the maximum duty ratio to 3A, and the motor is severely heated.

1. When the PWM frequency is 100 kHz, there is no difference in speed or current value from 50% duty ratio or higher.
2. If the PWM frequency is raised to 200 kHz, there is a difference in speed and current value, but the motor is severely heated.
    The current goes up to 3A when the duty ratio is 90%.
3. R sense(R64) shunt resistor was connected 0.075 ohms according to the formula below because the current value was too high when 0.007 ohms was connected the same as the EVM board.
    0.225V(V Limit) / 3A = 0.075
4. The I Drive setting is set to 75k ohm to DVDD, which I think is appropriate, while raising the low value.
    When the I Drive setting is low, the nFault pin goes low and the motor does not turn.
5. When the motor is rotating quickly at a high duty ratio, if an external force is applied to stop it, a current of more than 5A is consumed.
   Shouldn't the current value be limited to 3A by the R sense value?
   The hole sensor and OUT pin are connected in the same way as page 13 of the datasheet.

When I asked FAULHABER about the motor, they said that it should be used at a high frequency of 100 kHz or higher.
Therefore, we are testing at frequencies above 100 kHz, and when I checked the datasheet of CSD88584Q5DC, I found that the switching frequency was up to 50 kHz.
Is the current value high and heat generation severe because it is outside the maximum frequency of the FET?

I wonder if there will be no problem if I change FET to CSD87333Q3D.
Thank you.

(FAULHABER_모터)EN_1645_BHS_FMM.pdf

  • 0
    TI__Intellectual 1240 points

    Hello,

    I will look into this and get back to you by the end of this week.

    Regards,

    Hong

  • 0 in reply to Hong Khor
    Prodigy 20 points

    Thank you.

  • 0 in reply to on off
    TI__Intellectual 1240 points

    Hi,

    Thank you for your patience.

    Regards,

    Hong

  • 0
    Prodigy 20 points

    I have new information.

    For the test, the motor was operated repeatedly at a low duty ratio of 20% to 30% for one day.
    After that, the current value returned to the normal range.
    It does not exceed 800mA at no load.

    I have no idea what caused it.

  • 0 in reply to on off
    TI__Intellectual 1240 points

    Hello,

    Your schematic looks fine. The IDRIVE controls how much sink and source current the gate drivers can produce, so a low setting may not be enough to spin the motor.

    The PWM frequency is above the recommended specification for the half bridge. Since the switching frequency is a NexFET specification, I would recommend asking that team what would happen if the maximum recommended frequency was exceeded; exceeding recommendations could result in unknown behavior. I would recommend to switch to the FET where the PWM frequency is within spec.

    For the current when the motor is stopped by an external force, we can see in the datasheet that the current limit is "cycle by cycle".

    So, it will check every PWM cycle. However, if an external force is stopping the motor, it would draw its maximum stall current consistently. The t_BLANK means that the current limit would not be activated for 5 us at the start of each cycle. If you check the gate current, you could see it turn off after 5 us, but the time in between is enough to bring up the current to 5A.

    Regards,

    Hong

  • 0 in reply to Hong Khor
    Prodigy 20 points

    Hello,

    1. FET will be replaced with CSD87333Q3D.
    CSD87333Q3D looks good because the recommended frequency is 1500kHz.

    2. I want to limit the current to 2A when an external force has stopped the motor.
    0.225V / 2A = 0.1125
    Should I attach about 110m ohm shunt resistor?

    Thank you.

  • 0 in reply to on off
    TI__Intellectual 1240 points

    Hello,

    Since the current limit is cycle-by-cycle, like mentioned above, with a blank time, the stalling current would still likely be much higher than that 2A current limit. Does your application regularly have an external force stop the motor?

    Best,

    Hong

  • 0 in reply to Hong Khor
    Prodigy 20 points

    Hello,
    yes. Even if the motor is stopped by an external force during rotation, I want to give a constant torque.

    I want to limit the maximum current value even with momentary external impact.

    Is it possible?

    Regards,

    on

  • 0 in reply to on off
    TI__Intellectual 1240 points

    Hi on,

    I will consult with my colleagues about this feature and get to you by the end of the week.

    Best,

    Hong

  • 0 in reply to Hong Khor
    Prodigy 20 points

    The Rsense resistor broke during the motor loop test.
    RSense: 75ohm / 3W
    The current seen by the DC power supply is up to 2.5A.
    To the naked eye, the motor driver is fine.
    Other circuits like MCU, hall sensor etc are ok.
    The motor is out of order.
    I don't know what caused it.

  • 0 in reply to on off
    TI__Intellectual 1240 points

    Hi on,

    For DRV8306, you can try configuring the VDS OCP threshold by changing the resistor as specified here in the datasheet:

    Keep in mind that this measures VDS of the FET, so you will need to do the calculation of your peak current * Rdson to find the voltage that VDS should trip on. Therefore, the limit you set here will always apply.

    For the Rsense resistor, excessive heat dissipation can cause mechanical cracks over time. If you are testing the motor and too much current surges through, it will go through the Rsense resistor.

    Regards,

    Hong