DRV8243-Q1: DRV8243-Q1 nFAULT is constantly triggered

Hey Avi,

Have you confirmed that your nSLEEP reset pulse is ~30us?

Regards,

Jacob

Thank you for your answer!
Yes we have verified that the pulse is ~30us, you can see that in the provided image. the "HW Variant Wave-up Transient" is exactly what we've been following with no success. It does reset the nFAULT because it's rising up, but it drops again right after (after ~300us).
Everything seems to be in line with your answer, are we missing anything else? I suspect that perhaps it was not wired correctly.

Hey Avi,

Okay good, yeah then the device should be active.  

I see your pull up resistors for nFAULT and DRVOFF say "103", is that 103Ω or 10^3 = 1kΩ?  100Ω might be too strong of a pull-up resistor for nFAULT.  I think it needs to be at least 1kΩ.  InFAULT_PD (Sink current to GND on nFAULT pin when asserted low) is >5mA, so for 3.3V R=V/I --> 3.3V/5mA = >660Ω.  Recommend using 10kΩ value 

Just my notes while looking through schematics

• MODE pin GND --> Device in PH/EN mode
• DRVOFF 103Ω(?) to GND --> whether this is 1k or 103Ω, this does not fall in any of the RLVLxOF6.   Recommend changing this to match one of these levels:
• 
  • Resistor is not needed for short to GND
• ITRIP 22kΩ to GND --> Rlvl3of6 -->1.98 V ITRIP. 
• DIAG 8.2k to GND --> RLVL2OF6 ---> in PH/EN mode, Off-state diagnostics enabled, fault reaction is latched fault.  
• SR to GND --> 1.6V/us slew rate

Try changing that DRVOFF resistor and see if that solves it, I'm not sure why that would cause nFAULT to stay low.  

Given that your off-state diagnostics are enabled, I wonder if those diagnostics are causing this fault indication.  You could try connecting DIAG direct to GND to disable off-state diagnostics to see if that makes the nFAULT issue go away.  

Regards,

Jacob

Hello and thank you for your response!

103 is 10Kohm, it's an SMD resistor code. 

I already tried 2 things today that did not work:

1. Wired the DRVOFF straight to the GND. I also noticed that there should not be a resistor there, unfortunately that didn't do the trick.

2. Set the R_MODE to >250Kohm to enable the PWM mode, unfortunately I got the same output on nFAULT.

I will try to wire the DIAG pin to the GND in the morning and post my results!

I tried wiring DIAG straight to the GND but that didn't work out. nFAULT still drops after the reset operation.
I also tried wiring ITRIP to the GND, to disable the regulation, interestingly nFAULT still drops just the same.
Is there anything else I could be trying?

Hey Avi,

Do you have a motor or resistive load connected to the outputs of the device?  Have you tried to go ahead and send output signals and see if it starts working when you send the appropriate input signals?  

And could you try removing and replacing the DRV8243 driver out, and tried another PCB?  Just to rule out faulty device or fine solder short. 

Regards,

Jacob

Hi Avi,

It is likely that the device needs a clear fault command after the nFAULT is triggered. This is a common occurrence during the power on reset (POR) of the device. 

Best,

David