Bombproof coupling for A4988 /

Im currently working on a board design where centerpiece will be A4988 / DRV882x.
Input voltage on the carrier board will be limited to 6-32V.

As suggested in description, I added 100uF, 100V, RAD ALU ELEC CAP, but I wonder if more can be done to make an near “bulletproff” design.
Since it will be a mass produced board, I would really love to have as solid solution as possible. A4988 will be pluged into the board and will be “disposable” - but it would be nice to have a solid solution.

Also I wonder if it would help to have a cutout underneath the A4988 - the idea is to aid in air circulation. Or maybe bunch of via’s would do the trick?

Any ideas is highly appreciated! :slight_smile:

What parts are you trying to bulletproof?

I’d suggest adding a TVS diode to clamp over-voltage input. This diode will also forward-conduct (like a crowbar circuit) when reverse connected.
Also add some kind of fuse, or a polyswitch-type PTC resettable fuse rated for whatever your max amperage is.

For the control inputs, you’ll want to protect them from the external world with between 20 and 220 Ohm resistors. You could make those be resettable fuses, too. After the resistor, you also want a Zener diode to prevent against overvoltage and clamp/crowbar reverse polarity connections.

So, reasonable power input protection looks like:

  • electrolytic capacitor
  • PTC resettable fuse at 3 A hold / 6 A trip
  • TVS diode with 30V rating

Reasonable signal input protection looks like:

  • 220 ohm / 15 mA PTC resettable fuse
  • 5.1V zener

Just make sure you choose a low-capacitance Zener so you don’t make the control signals rise time too slow.

Thank you so much for the answer!

One last quastions, in my 3D printer today (it has RAMBo 1.2), when I acidentially manualy move print table, it controller temporary powers up from motion of the board. And now Im designing a time-lapse solution where people will most probobly want to move camera carrier manually - can it cause problems to A4988? Ideally I would like to prevent any backwards current flow back to the system.

You’ll want a unidirectional TVS between VMOT or GND, not bi-directional. Bi-directional would work on the output side to protect the driver, though, although generally this is not needed.
I wouldn’t think the temporary power-up of the A4988 would be a problem, but if you want to prevent that, you have to de-couple the motor leads using a relay or similar that only turns on when the system is powered.