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DRV8825 heating up when connected with the motor

Sebastian Turner
Intellectual 315 points
Other Parts Discussed in Thread: DRV8825

Hello all

I am designing a stepper motor kit for students using DRV8825. I powered up the trainer kit with 12V, 2A, the datasheet says that the operating current should be 8mA maximum, but i don't think giving 2A would cause any issues since the chip should draw the current it needs. The reason I am pondering over this point is the fact that whenever i connect my stepper with the kit the chip (DRV8825) starts heating up. 

I am using a Vref of 1.65V and Rsense of 0.2 ohms. What do you think might be the cause of the chip heating up?

  • 0
    TI__Guru** 114905 points
    Hi Arhez,

    I am assuming that the DRV8825 outputs are enabled when heating up. Is that true?

    The 8mA current is the amount of current the DRV8825 consumes when powered up and the stepper motor is either not connected or disabled.

    Once the stepper motor is enabled, each winding will be regulated to approximately 1.1A initially. This current translates into approximately 1.2W, which causes the DRV8825 to heat up.
  • 0 in reply to Rick Duncan
    Intellectual 315 points

    Yes the outputs are enabled. Okay if that is normal then shouldn't the chip cool down after that? Or does it stay heated the entire time the motor draws current from it? Is that right?

    Also I was not sure if I have used the right capacitors, like I have used a ceramic capacitor of 0.01uF between CP1 and CP2. The datasheet 16V ceramic capacitor at VCP I might have used a higher rating. And I have used an electrolytic capacitor of 0.47uF, 50V at the V3P3OUT pin instead of a 6.3V ceramic. Do they all make a difference? 

  • 0 in reply to Sebastian Turner
    TI__Guru** 114905 points

    Hi Arhez,

    Arhez said:
    Yes the outputs are enabled. Okay if that is normal then shouldn't the chip cool down after that? Or does it stay heated the entire time the motor draws current from it? Is that right?

    As long as the DRV8825 is providing current to the motor, the internal FETs are generating heat.

    Arhez said:
    Also I was not sure if I have used the right capacitors, like I have used a ceramic capacitor of 0.01uF between CP1 and CP2. The datasheet 16V ceramic capacitor at VCP I might have used a higher rating. And I have used an electrolytic capacitor of 0.47uF, 50V at the V3P3OUT pin instead of a 6.3V ceramic. Do they all make a difference? 

    Using a higher rated capacitor is OK for VCP.

    For V3P3OUT, an electrolytic may work. A ceramic is preferred because it has lower ESR (equivalent series resistance) and smaller size. The lower ESR generally results in less voltage ripple when current is required.

  • 0 in reply to Rick Duncan
    Intellectual 315 points

    Hey Rick

    Thanks for the follow up over the design issues. Just a slight update on the heating problem, this time I used a motor of 24V,0.22 A  motor with a 240 ohms resistance per phase and powered it up with Vm = 12V and the chip did not heat up at all! Previously I was using a motor with less resistance. I dont know how it relates, maybe you can help.

  • 0 in reply to Sebastian Turner
    TI__Guru** 114905 points
    Hi Arhez,

    At 12V, a motor with a 240 Ohms resistance will require 50mA in each winding. This current is much less than the prior motor, and much less power. A conservative estimate is 6mW versus the 1.2W originally stated at 1.1A. The device and the motor will not generate much heat in this condition.