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MSA301 in a 3.3V system
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MSA301 in a 3.3V system

by cuddy on Sun Dec 20, 2020 4:35 pm

I have a project with a microcontroller that uses 3.3V logic (MSP430), and I got an MSA301 breakout board to add an accelerometer to it. When I connect it up as instructed in the documentation, I can't talk to it at all over I2C. This doesn't particularly surprise me, since feeding 3.3V into a 3.3V regulator is not a recipe for success, and the pull ups don't even manage to get SCK to 1.8V. The AP2112-3.3 datasheet I found specifies a Vin of 4.3V.

I had the brilliant idea of trying to power the breakout board with 5V, which kinda sorta worked at first, but now SDA and SCL are being pulled up to about 4.7V, and suddenly the system draws something like 90 mA and the processor's I2C peripheral stops working as soon as the processor goes into sleep mode.

Has anyone had success using this breakout board in a system with 3.3V logic, or is it really only useful in 5V systems? I was thinking about popping the level shifter and VIN pull ups off, then jumping SDA and SCL straight to their 3.3V versions. Does that seem like a sensible solution, or am I doing something dumb?

I notice the MMA8451 breakout board also purports to be "perfectly safe for use with 3V or 5V power and logic" but seems like it would have the same problem with 3.3V logic.

cuddy
 
Posts: 3
Joined: Sun Dec 20, 2020 3:48 pm

Re: MSA301 in a 3.3V system

by cuddy on Sun Dec 20, 2020 11:22 pm

These are the changes I have in mind.

rework.jpg
rework.jpg (189.44 KiB) Viewed 43 times


Unfortunately, this tiny stuff is beyond the capabilities of my in-house rework technician. I don't even have any solder wick handy. You can see the botchy job of just soldering in the header in that picture.

cuddy
 
Posts: 3
Joined: Sun Dec 20, 2020 3:48 pm

Please be positive and constructive with your questions and comments.