DRV8847: DRV8847S outputs lost steps

Hi,

I have a couple questions. 

• How is the customer setting up the driver and the motor? If possible, can you send me a schematic?
• In circuit 1, can you tell me which of the four signals corresponds to OUT1, OUT2, OUT3, and OUT4? It seems to me that the yellow and purple signals are operating correctly but the other two are not. Knowing which two of the four outputs are not behaving properly.
• If you are able to, can you send me a waveform showing one of the output steps, preferably one that contains missing steps, and the corresponding output current. Zoom into the area where there is a gap in the steps and show both the output voltage and current.

Hi,

1. This is the schematic diagram. Three pieces DRV8847S are used. Two pieces used to drive two bipolar steppers. One piece used to drive electromagnetic valve.

2. In circuit1, CH1-BOUT1, CH2-AOUT2, CH3-BOUT2, CH4-AOUT1.

    CH3 signals are also not operating normally. Sometimes the width of pulse changes.

3. Below is the waveform of output voltage and output current.

Hi Pablo, 

This issue is very urgent now, as customer is going to mass production, please help to give us some feedback ASAP.

Thanks a lot!

Hello, 

I am sorry for the delay reply. I see from your schematic that ISEN pins are shorted to ground. The DRV8847 uses a comparator which compares the V_ISENSE and VREF(V_TRIP) (see figure below). The Vtrip is set by the TRQ bit and can have a typical value either of 75mV(TRQ=1) or 150mV(TRQ=0). 

Can the customer check what TRQ value they are using?

If the ground bounce on the ISEN pin goes above 75mV, it cause the comparator to regulate the current for a brief moment (~ns) which might not be visible on the scope due to the 5Ms/sec resolution and time scale and this can make it seem like a step was skipped. 

If the customer has set the TRQ=1 (Vtrip=75mV), can the customer try clearing the bit to zero to change the Vtrip to 150mV and see whether the issue with the missing steps is fixed?

Hello,

Do you have any updates?