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Unread 21-06-2016, 20:55
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Re: SD540 Motor Controller

Quote:
Originally Posted by Jared View Post
17 mOhm Rds on is really high for this type of motor controller. At 30 amps, which FRC robots will draw for a few seconds, you're dissipating 15.3 watts in your FETs!

It seems weird to have this so high - you'd almost have to go out of your way to find FETs with 8 mOhm Rds. There are tons of FETs designed for motherboard switching power supplies that do much, much better. It seems more likely there's some other issue, like V_gs dropping on the high side FET, or insufficient gate current, or possibly even thermal issue.
I agree it's too high. Looking at the pictures more closely, it looks like this is the MOSFET: http://www.nxp.com/documents/data_sh...N1R0-30YLD.pdf All looks fine to me (in fact, I think it's the same as, or at least related to, the one used in the Talon SRX as shown in this teardown: http://imgur.com/gallery/2xqoU). The current sense resister seems odd to me. I'm trying to make sense of the marking. The SRX uses a 0.5mOhm sense resistor (M50), but the SD540 has a marking of "50m", which doesn't make any sense to me since the math wouldn't add up (50mOhm). Is there an alternate interpretation of that marking?

Large picture of the SD540 here: https://images-na.ssl-images-amazon....1X6vyE3RyL.jpg
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