DRV8825 motor controller driver power on issues

• DRV8825 motor controller driver power on issues
  Posted by newtekuser on 31 Mar, 2024 17:41
• Hello All,
  
  I'm putting together a motor controller board using the DRV8825 IC and having some issues with power on. I'm measuring 12.2V at the input cap C5 as well as on C1, C3 and C4, but the internal regulator V3P3OUT does not produce anything. None of the IC pins are shorted and no motor is connected to VMA and VMB pins. nReset and nSleep pins are tied to VP3OUT via 10K pull-ups and the enable pin is floating. Per the data sheet, this configuration should enable the IC.
  Attached my schematic and board layout (2 layer with solid GND on bottom). The IC was purchased from DigiKey and should be good.
  
  I know that the calculation for Vref is now slightly off because I designed it for 12V not 12.2V but my understanding it is that if it affects anything that would be the current limitation.
  
  Is there anything that stands out as an issue with the schematic, or board layout that would cause this?
  
  
  
• #1 Reply
  Posted by DavidAlfa on 31 Mar, 2024 18:39
• Maybe adding a 100nF cap between nRST and gnd so it resets at power-on?
• #2 Reply
  Posted by newtekuser on 31 Mar, 2024 20:14
• Quote from: DavidAlfa on 31 Mar, 2024 18:39

  Maybe adding a 100nF cap between nRST and gnd so it resets at power-on?
  

  
  That did not do it unfortunately.
  
  I found an article describing how to use the DRV8825 controller and they're tying reset and sleep pins to 5V instead of 3.3V. However, in my case I do not connect to the MCU (PIC) just yet which operates on 5V logic anyways.
  
  

  Quote

  You need to connect RST (reset) and SLP (sleep) to 5 V otherwise, the driver won’t turn on.

  
  Would this be the issue? https://www.makerguides.com/drv8825-stepper-motor-driver-arduino-tutorial/
  
  Or is it a catch 22 issue because I'm connecting it to 3.3V when there's no 3.3V voltage because the regulator is not enabled? If that's the case reasoning tells me I should drive these pins (RST, SLEEP) high from the MCU.
• #3 Reply
  Posted by DavidAlfa on 31 Mar, 2024 21:09
• Your problem is nSleep, it turns off V3P3OUT, so trying to get power from that pin will never work.
  nRST and nSleep have a 100K pulldowns, connect 12V to each pin through a 330K resistor.
  This will make a voltage of (12/(330+100))*100 = 2.8V.
  
  
• #4 Reply
  Posted by newtekuser on 31 Mar, 2024 23:58
• Quote from: DavidAlfa on 31 Mar, 2024 21:09

  Your problem is nSleep, it turns off V3P3OUT, so trying to get power from that pin will never work.
  nRST and nSleep have a 100K pulldowns, connect 12V to each pin through a 330K resistor.
  This will make a voltage of (12/(330+100))*100 = 2.8V.
  

  
  Thank you! I ended up tying sleep and reset pins to another 5V rail I have in the circuit and it now works. Motor also spins fine in both directions