DRV 8805 runs for few seconds then pause for a fraction of a second then runs then pause then run

Hi Sijo,

Based on your description, it appears like the device is entering thermal shutdown. Once it cools, it then starts again.

Can you provide more information?

What are the settings used on your board?

What are the motor parameters?

Thank you.

Hello,

The VM and VCLAMP are +12V in series with 1A slow blow fuse.

The RESET pin is connected to GND through 10K resistor.

The nEnable pin is connected to GND.

The DIR pin is connected to GND

The  STEP input is 1KHZ square wave from the signal generator.

I tried SM1 and SM0 connected to GND ( 2 phase drive full step)

I tried SM1 connected to GND and SM0 connected to Vcc through 3.3K resistor( 1-2 phase drive half step)

I hold my finger on the chip while the motor spins. The chip was at room temperature. when the motor pause the chip gets warm then cool down the motor spins fine then pause. This phenomena repeats.

The nFault pin is connected to LED cathode and the anode is connected to  +5V through a 3.3k resistor. So, I can see the LED blinks after few seconds or when the motor goes to pause the LED turns ON with full brightness.

Thanks

Sijo

Hi Sijo,

Would you measure the motor resistances, and report them? It still appears to be thermal shutdown. Knowing the motor resistance will help determine the maximum current through the windings.

Also, you can try to lower VM and VCLAMP. This will reduce the current in the windings. It will also affect the maximum speed.

Hello Rick,

Yes the motor resistance is 3.9ohm +_0.1.

The fuse in series to VM and VCLAMP is 1A slow blow!!

The VM and VCALMP is 9V, frequency is 1KHZ square wave. The other parameters are same.

I kept my finger on the chip to see, getting warm but not. The chip will get warm only when it goes to pause!!

Regards

Sijo

Sijo,

Thanks for sharing the motor data.

As Rick has pointed out, it appears that device is entering in fault condition either over-temperature or over-current. At 9Vm with 3.9 ohm, over-current protection is also possibility becuase it near to 2.3amp over-current trip.

 To indetify the real issue, can you help with following:

1. If  PWP (16-pin) version of IC is used, make sure that thermal pad is soldered to GND properly.

2. Reduce the Vm to absolute minimum 8V or better at VM of 9V, add 1-2 ohm in series resitance with motor winding, re-test the circuit. This will help to clearly indentify if fault is triggered due to over-current or over-temperture.

3. Sometime running direclty with higher step frequency, motor may loose steps while cathcing up with required speed and go to halt condition. Re-test the circuit at lower step frequency, lets say at 200Hz step and see the behaviour.

Best Regards

Milan-Motor Application Team

Thanks guys! but that is not the way we want.

I will check with series resistors. If I put a series resistor, may be I will loose the steps!!

The motor should run with good torque.

I will check for the current through the individual coils and will let you know.

Do you have any suggestion for the alternate chip with higher current carrying capacity?

Thanks 

Hi Sijo,

How much current do you need? The target motor should have a rated current and voltage specification.

With that information, we can suggest an alternate device.

Thanks. 

Hello,

Here is the motor specs. Please suggest the appropriate chip.

Step angle 1.8 degree

Rated Voltage  4V

Rated Current 1.2A

Phase resistance 3.3+_10% ohm

Phase Inductance 2.8+_20% mH

Holding torque 3200g-cm

Detent Torque 280g-cm

Number of leads 6

I am also thinking of another stepper motor which has 10.5ohm phase resistance and 760ma phase current for DRV8805DW

Thanks

Hi Sijo,

Based on the motor specs, you need a device that regulates the current. The DRV8805 does not have current regulation. When you put activate an output, the winding current can exceed 3A. This is well above the motor specs.

The second motor will do a little better, but it is still above the motor ratings.

There are two options.

1) If you want to use the motor as a unipolar, consider making the followin modifications to your board:
      a. Separate VM of the device and motor.
      b. Connect VM of the DRV8805 to >8.2V (minimum operation voltage) This could be a boost regulator off the main power.
      c. Connect the motor  and VCLAMP to 4V (rated motor voltage). This should be the main power

2) Configure your motor as a bipolar motor. Use a bipolar stepper driver, such as the DRV8846, to drive the new configuration. Our bipolar stepper drivers have current regulation which allow you to limit the current into the motor. Configuring your motor as a bipolar stepper may result in reduced performance. The DRV8846 can run up to 18V and regulate the current as desired.

Please review the post https://e2e.ti.com/support/applications/motor_drivers/int-motor_drivers/f/40/p/62381/223979.aspx for instructions on connecting the motor.

Thanks! let me go through the possibilities!!

Hello Guys,

I dropped the VCLAMP voltage to 5V and VM +12V step frequency 600Hz square wave. The motor is working fine.

Thanks

Sijo

Hi Sijo,

That is good to hear. Please note that your are still above the motor manufacturers specifications at 5V. This may be a long term reliability issue.