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I've spent the past week or so working on my first circuit board project, and I'm wondering what resources are available online or otherwise for reviewing and checking my design. I want to check to make sure that the parts I've selected are suitable, that there are no better (cheaper, more efficient) alternatives, and that they are wired correctly. I'm a mechanical engineer, with very basic knowledge of electrical circuits, so the whole process is a learning experience. I've followed the data sheets to the best of my knowledge, but there's still a lot of potential for error.

I've sought quotes on Fiverr, but most come back offering to redesign the whole thing for several hundred dollars. Given that this is a private project and that it's not that large, I can run a few trial-and-error iterations for that price. Having said that, the component cost isn't insignificant with some components costings tens of dollars.

The project is fairly simple - it's a 4-axis stepper motor controller, driven by a Raspberry Pi Zero. I'm happy enough with the stepper driver portion of the circuit, but I've also had to incorporate 2x voltage regulators - one for 12 V, 5 A and one for 5 V, 1 A. Until now, I've never tried to design a voltage regulator, so I've followed the TI documentation as closely as I could understand it.

For anyone interested, here's the design:

  • [02/08/23 - Updated to include feedback from user1850479.]
  • [03/08/23 - Updated to include feedback from Jens. Added copper layer images - Top (Red) and Bottom (Blue).]
  • [04/08/23 - Updated with inspiration from Jens' layout (Solid Areas). Corrected SW/EN Logic. Corrected VLDOIN trace and revised 12V Reg layout to suit. Added UART trace]

Schematic PCB Top Layer Copper Bottom Layer Copper

To clarify - this question is mostly about the process of error checking, and less about the specific project. However, I'll accept answers for either.

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    \$\begingroup\$ Your 5v regulator will not work with the inductor not hooked up to the switch, so definitely double check your schematic. You also have 5v passing through a capacitor, but capacitors cannot pass DC voltages \$\endgroup\$ Aug 2, 2023 at 0:14
  • \$\begingroup\$ Thanks for pointing that out. That was a decision I made myself as a deviation from the schematic. The TI schematic didn't have provisions for a physical switch. I'll look into that further. \$\endgroup\$
    – G.H.
    Aug 2, 2023 at 0:16
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    \$\begingroup\$ Switch in this case refers to the switching element (transistor) in the switching power supply. It is not an on/off switch and you must wire it up as in the datasheet or it won't work. \$\endgroup\$ Aug 2, 2023 at 0:24
  • \$\begingroup\$ Thanks for the feedback. I've updated my original post to include your feedback. \$\endgroup\$
    – G.H.
    Aug 2, 2023 at 4:06
  • \$\begingroup\$ Fix the switch pin on the 12v regulator too. The layout of the 5v converter isn't great. I don't like the one in the datasheet that much but it's better than what you have so it's a good starting point. C1-C4 should be between the power and ground pins of those socketed PCBs otherwise they don't do much. \$\endgroup\$ Aug 2, 2023 at 6:26

1 Answer 1

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Some thoughts about this design:

There is a misunderstanding about the use of enable inputs, related to the stepper module and the 12 V regulator. Such inputs do not sink or source a significant current, so an LED in series with an enable input will not indicate anything. This is the correct use for active high enable (TPSM63608) and active low enable (TMC2208 module):

schematic

simulate this circuit – Schematic created using CircuitLab

You accidentially interchanged VMOT and VDD of the stepper driver module.
VMOT (original name is VS) is the motor supply, here 12 V.
VDD (original name is VCC_IO) is the digital I/O voltage, here 3.3 V.

The SW signal of the TPSM63608 is not a switch input, it its a diagnostic output of the internal switching node. Do not connect anything here.

R5 will burn, use 3.3 kohm ore more there.

You want to insert a resistor between RBOOT and CBOOT of TPSM63608 to reduce EMI emissions.

To the layout:

If this is a 2 layer board without a dedicated GND plane, you can expect trouble. The GND connections are way too small. These tracks cannot carry the motor current and will act as small inductors all over the place. It is possible to route this with 2 layers, but then use broad > 3mm wide, shortest way tracks and jump with the signal tracks over them.

The switching regulators cry for a proper GND strategy.

Keep the 4 motor tracks close to each other, so the magnetic fields cancel out. Don't walk in a big extra loop with M2A of AXIX3.

Check the motor connector signal assignment. The sequence 1B 1A 2B 2A is often used.

UPDATE

You still use the SW pin as on/off input in your layout. This will probably kill the regulator. The connections of the TPSM63608 look mirrored to me and the VLDOIN needs a connection to VOUT.

I made a test layout, because I think this may become useful to me as well.

QuadTMC2208-1200

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  • \$\begingroup\$ Thanks - this is great feedback. I'll update the original post once I've updated the design. \$\endgroup\$
    – G.H.
    Aug 3, 2023 at 2:38
  • \$\begingroup\$ The GND area around the regulator chips must also take away the heat, so arrange a large copper area there. \$\endgroup\$
    – Jens
    Aug 3, 2023 at 2:54
  • \$\begingroup\$ Thanks - I had ground planes top and bottom. The datasheet for the 12V reg suggests tieing those together with several thermal vias around the regulator and output capacitors (I haven't added those in yet). I've made the other updates you suggested, they were substantial. Hopefully the update looks better, that took all day! \$\endgroup\$
    – G.H.
    Aug 3, 2023 at 8:02
  • \$\begingroup\$ Yes, looks much better now. Put 10-20 vias in the GND area of TPSM63608 and > 50 vias to connect top and bottom GND in the area of the stepper modules. \$\endgroup\$
    – Jens
    Aug 3, 2023 at 14:38
  • \$\begingroup\$ Great, thanks for you feedback! \$\endgroup\$
    – G.H.
    Aug 3, 2023 at 20:51

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