DRV8874 Motor Driver and Arduino Nano Issues

Other Hardware Hardware Development
1

Ive been working on a project revolving around RC control using an Arduino Nano, a custom PCB and a DRV8874 Motor Driver. The custom PCB utilises 2N2222 transistors to control components with an external battery (Li Ion 4S) with paired 1K resistors. A 47µF capacitor is used for decoupling and filtering for the DRV8874. Appropriate headers are used for RC Receiver jumper cables and connecting external components, buzzer etc. A buck converter is used to reduce the 14.4v down to 7.5v for the Vin of the Nano with a Schottky diode to prevent back feeding.

Ive had two issues with my setup. The primary issue ive encountered is that something is frying my Nanos.
Ive currently been through 3 Nanos (Clones). The first and last I don't believe had circuit protection however the 2nd one did and refused to output any serial communication when plugged into the daughter board.
When the first and last Nano's were plugged into the daughter board after an average time of 60 to 90 minutes, the Nano pops with a puff of smoke. The power supply doesn't seem to change the outcome as this has occurred when powered via USB or the buck converter separately.
Whilst the second Nano refused to work, that died due to a PC crash corrupting the bootloader. I tried to burn a new bootloader onto the target board however It couldn't be recognised in any scenario suggesting a hardware failure.
Ive tried to examine and troubleshoot the PCB but I haven't been able to find the cause. I have a feeling its something simple that ive completely overlooked.

The second issue is that the DRV8874 doesn't have any voltage output on either OUT1 or OUT2. With the code ive uploaded to my Arduino Nano, Ive had almost full functionality however, when it came to the DRV8874, no output voltage to the motor was detected across all scenarios.
Ive conducted some diagnostic tests to try and pinpoint the issue:

  1. Ive found that with the last Nano, I received accurate pulse data in the serial monitor from all three channels.
  2. DRV8874 receives 10v to VM.
  3. nFAULT read 5v to GND suggesting the DRV8874 didn't detect any problems within the chip.
  4. nSLEEP is correctly tied to GND and reads 0v.
  5. I tested continuity between multiple pins and the outlier was OUT2 to VM which read 15Ω instead of the expected open state.
    Since the DRV8874 is small and I have limited equipment, I suspect this might be related to a short circuit created during reflow and the main cause as to the OUT1 and OUT2 problems.

These are links to my schematic, board layout and the code ive used for this project.

Imgur
Imgur

I was hoping someone could look at my PCB schematic and my board schematic to spot anything wrong with it.

Thanks

2

What is the maximum load current on all of the Nano's output pins + 5V pin?
If more than about 400mA, you may be overloading the Nano's 5V regulator.
Why not drop the 14.4V to 5V and connect to Nano's 5V pin?

3

Since I don't have any more Nanos I'm not able to check however looking at documentation on the Planet TS2+2 Transmitter and Receiver I'm using for this project, theoretically the maximum load from the receiver and the nSLEEP of the DRV8874 on the Nano's 5v rail would be around 200mA to 250mA. I doubt this is the issue, unless there is a short within the PCB?

I thought about using the buck converter at 5v for the Arduino however this was after I got the PCB fabricated. That being said, Ive discovered that trying to get an exact output voltage on a buck converter is surprisingly difficult. I originally ran the buck converter at 11.5v, then realised that this may overheat the voltage regulator so I lowered it to 7.5v. Ive had it at 7.5v since the first Arduino.

As I have been having countless issues with this PCB I'm tempted to do a redesign as I would like to properly add a 3rd channel header. Additionally, due to an oversight, the Power-IN header doesn't have any functionality as its safer to connect the battery and a switch externally and then to the SWITCH header. (There is a jumper cable on the POWER header to close the circuit)

I'm hoping someone can find any issues with my PCB design so I don't repeat the mistake In the future.