Hi,
I’m trying to put together a two layer motor driver board with a DRV8833. I layed out what was written in the datasheet, where it says the chip itself gets hot during usage and needs a groundplate as big as possible. So on the front and back side I made a filled area connected the layers under DRV8833.
My question would be: what padding do I need to have in order to distribute the heat to these filled areas on the top and bottom? Currently it looks like this: attached
thx!
Not sure what you mean by padding ? you need many more vias to connect the “heatsink” on the top and bottom layers . . . and ideally use 2oz copper, and make these areas as big as you can, you still have room . . . these devices, despite their thermal protection and over current mechanisms can easily be turned into melted plastic, I know from personal experience.
Did you already read https://www.ti.com/document-viewer/DRV8833/datasheet/layout#SLVSAR14931 ? At least you don’t have large ground areas but you have used tracks for GND everywhere. Instead, you should add GND zones to both sides drawing them around the board and stitch the two layers together everywhere with vias.
Now you have stitched the two layers only directly under the DRV, and the GND zone is restricted to small area.
You also have two pin header connectors which may have unconnected pins. Use unconnected pins as GND connections if possible. Wires and other metal connections between different devices conduct heat.
You also have non-optimal connections with the capacitors. None of the three capacitors which look like those which are needed by the DRV are “as close as possible”, especially C13. Those which are connected to GND should be connected to the zone, too, not just to traces.
Thank you all for your fast answer. I’ve changed a few things according to your reply. This is how it looks like now:
Are you sure the vias are correct? You seem to have several shorts or at least DRC violations caused by vias. Have you run DRC?
Putting the C’s any closer to the DRV doesn’t necessarily have noticeable effect, but I would do it routinely.
I once read in some TI document about capacitor placement a phrase: “as close as humanly possible”. That sounds funny considering the technical nature of the PCB design process, but here there’s certainly room to move the capacitors much closer by moving the tracks from the two upper and the two lower pins. You can probably move the small capacitors almost their own width.
How is the board assembled? If you solder manually you should probably have thermal reliefs for all pad-zone connections, also in SMD pads.
As far as I can see, all the current goes through the VM track which is relatively narrow. It doesn’t help to have good thermal dissipation for the IC if the current burns the track. I’m not any good at circuit design but you should probably take a second look at that.
Thanks,
I double checked the vias and corrected 'em. I also made the VM beefier. And moved the capacitors closer to the DRV.
Here’s an older thread which focuses mostly on the GND planes/zones and options for how to place vias and tracks: Beginner's questions before sending for print - #13 by eelik. You, too, could add something like 100 vias and all empty areas would be covered by copper.
(Personally I wouldn’t use 0R resistors to jump over tracks. There are also contradicting opinions about putting tracks together vs. keeping them apart. This depends on the circuitry and how it works.)
Yup . . . add more vias, get the heat away from the device to BOTH sides of the PCB . . . MORE vias.
Thanks for the link, it helped a lot. Now my board looks like a slice of emmental cheese 
Out of curiosity… DRV8833 Vs SN754410 (both by TI)
Been planning to build an Astro-Photography Tracking gizmo (have built several tracking gizmos for Telescopes but none for Astro-Photography).
In preparation, I pulled out some of my older homemade Stepper Motor control gizmos to review, selected one that uses TI, SN754410 and, out of concern re overheating, I tested it. I don’t have any DRV8833 but, have plenty SN754410 so, can’t compare them…
I added Loading to the motor by holding the shaft to near-stalling (for one minute) and checked the Temperature. No problem. The Chip never got higher than 190ºF (having to let go so I could film video, it cooled down to 185ºF). PCB was cooler than the chip.
The boards I designed for them are Single-Layer, no Via’s. I did create a Pad underneath attached to GND (GND is the heat-transfer vehicle). Photo and Video (for your amusement)…
Driving Stepper 17HS16-2004S1. No cheese…
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