I might need run near the 4 A limit or go up to 4.2 A. Would you please provide some specifics on how I might implement some form of passive cooling (i.e., what to use, where to place it, and how to attach it)?. Thanks.
We do not have much specific advice for additional cooling, but it sounds like you are not going that far beyond what we would normally expect the driver to be able to handle in an open, room temperature environment (4A), so there are probably several solutions that would be good enough. If you are adding heat sinks, you will want to attach them to the limiting components, which are the four discrete MOSFETs right next to the motor outputs. Also, make sure you are securing your heat sinks using an adhesive with high thermal conductivity, like thermal tape or paste.
Thank you for that information. I was looking at those chips, but footnote 3 in the spec sheet specifically says “3
With sufficient additional cooling. This limitation comes from the 30 mΩ current sense resistors, which are rated for 1 W.” Doesn’t that mean that I need to cool the resistors?
No, the current sense resistors limit the maximum current per phase to 6A since any currents over that would cause their 1W power rating to be exceeded. The external MOSFETs will be the first component to overheat if the driver continuously supplies more than 4A per phase (or potentially lower currents in applications with reduced heat dissipation), so those are the components you would need to cool. You can find more detailed information in the product page description under the “Power dissipation considerations” header (near the bottom).
Now I understand. Thank you.