Strange issue with Custom PCB Carrier for TMC2208 + Arduino Nano  - Page 1
Forum section: electronics / projects

author: jbf
author_rank: Contributor
timestamp: June 17, 2023, 09:51:20 pm
content: Hi all,So I have been working on a project driving a A4988 stepper driver with arduino nano. I made two custom PCBs one as a button board (to control the stepper) another as the main control carrier which holds a socketed Arduino Nano, regulator, and the stepper motor driver. A 12v supply feeds a regulator and power for the stepper.At the stepper driver's VDD, I have a switch to cut power to the 5V logic of the board, which prevents the driver from powering motors.When using the A4988 chip, it works as expected (perfectly).However when swapping out the A4988 with a TMC2208 in legacy mode, the switch does not work as expected. When connected I'm seeing around 5v. When VDD is cut, I'm still seeing 4v at this pin.Can anyone provide some guidance on this? Shouldnt this have zero volts going to it? Why in the world would it still be showing 4v? Would this be an example of the board designers forgetting to add pull-down resistors for the VDD pins? Also to add this same issue happens on the EN pin on the TMC2208's I have.

author: CountChocula
author_rank: Unknown
timestamp: June 17, 2023, 11:16:42 pm
content: I wonder if perhaps your chip is just drawing power from one of its other pins. Davedid a video on thisa while back.I just took a quick glance at the datasheet for that motor driver… why aren't you using the ENN pin to disable power? That seems to be its intended purpose.—CC

author: jbf
author_rank: Contributor
timestamp: June 18, 2023, 12:14:16 am
content: EN has the same issue. When power cut it still reads ~4v on a DMM.I wanted a dumb physical switch with no connection to the Nano in order to kill power to the driver.

author: jbf
author_rank: Contributor
timestamp: June 18, 2023, 12:31:39 am
content: So was doing some digging and found a TMC2208 stepper driver maker thatmentioned this little nugget:Quotehttps://learn.watterott.com/silentstepstick/protector/schematics.pngNow I'm using a no-name amazon version of this stepper driver, but I wouldnt be surprised if this is the same exact circuit design.Do you think this could be the issue? If so, is this snippet saying I can literally place a schottky diode on my carrier PCB that goes from VDD (AKA VIO) to VMOT (VM) with the cathode side on VM to solve this problem?

author: CountChocula
author_rank: Unknown
timestamp: June 18, 2023, 01:46:39 am
content: Quote from: jbf on June 18, 2023, 12:14:16 amIf you want to use ENN, you have to drive it high—connecting it through a resistor to VDD should cut off all power to the motors, which I think is what you're trying to achieve. The documentation you linked to calls this “emergency stop,” and it just completely disconnects the output drivers from the motor, allowing to freewheel.QuoteThe datasheet doesn't say anything about this requirement (though, admittedly, I only quickly skimmed it and I'm not at all familiar with this chip), and there is no diode in any of the reference schematics they show. In either case, this wouldn't help you—a diode in that position would simply ensure that you can't turn off VM before turning off VDD.—CC