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DRV8825 doesn't turn or engage motor, just overheats!!

Dmitry Ponomarev
Prodigy 140 points
Other Parts Discussed in Thread: DRV8825

Good afternoon,

I've tested about 5 different DRV8825 chips with 3 different circuits, I've connected everything exactly as shown in the manual including all of the capacitors, 

The issue is, whenever I supply more than 15 volts to VMA and VMB and I pull nSLEEP high, the motor controller begins to overheat, and causes nFAULT to go low. 

The coils of the motor never engage, and I never see any motion.

I've tried different MODE combinations, I've set DECAY to Mixed

This happens even when the motor is not connected. I've checked for any short circuits and did not find any. I also used this only with a lab power supply and did not see any current draw above 10ma. 

The overheating takes 5-10 seconds from when nSLEEP is pulled high.

I have a small heat sink on the bottom pad, and it IS connected to ground. I've turned AVREF and BVREF anywheref rom 3.3V to  0.5 volts, the overheating happens at about the same time regardless of this voltage supply. The only thing that affects it is the VMA and VMB voltage.

I've looked on the Pololu website schematic (md20a) and noticed that there is an additional power supply connection for Unipolar Stepper Motors for the centers of the coils. Does this mean that AOUT1, AOUT2, BOUT1, BOUT2 do not supply their own voltage to drive the motor? Is there a connection I am missing, because at no time did I see the motor coils engage at all.

My only possible explanation for this is that I got a batch of faulty chips from DigiKey. Is that a possibility?

Thanks,

  • 0
    TI__Guru** 114905 points

    Hi Dmitry,

    Sorry to hear about your problem. The device should not overheat when the motor is not connected. Normally when a device overheats as described, excess current is being consumed by the device. Have you tried to determine if there is excess current and where is it going?

    Would you provide more information, such as any schematics and layouts of the different circuits used? Also, would you measure the current when nSLEEP is low  and when nSLEEP is pulled high?

    Thanks.