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Bypass Capacitors on Mixed-Voltage Shield
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Please be positive and constructive with your questions and comments.

Bypass Capacitors on Mixed-Voltage Shield

by BobGreenwade on Fri Jul 03, 2020 12:09 pm

I'm working on designing a Shield (regular Arduino type), and I've come across something that has me a tad worried.

The Shield uses several chips (of course), one of which is Maxim's MAX11312 (a 12-channel I2C multi-I/O hub). This chip requires a 5V power to at least two of its pins, with a pair of bypass capacitors for ground. All of the other chips use 3.5V, and a couple of those also have bypass capacitors.

Should I be worried about that? Would I be better off putting a diode, resistor, or some other component in place to limit the voltage? Or should I look around to replace the MAX11312?

BobGreenwade
 
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Re: Bypass Capacitors on Mixed-Voltage Shield

by dastels on Fri Jul 03, 2020 12:27 pm

What are you worried about?

Different types of components do different things and can't be randomly interchanged. Bypass capacitors provide capacitance to "absorb" electrical noise. That's why they are there. Other types of components won't do that.

Dave

dastels
 
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Re: Bypass Capacitors on Mixed-Voltage Shield

by BobGreenwade on Fri Jul 03, 2020 5:44 pm

What I'm worried about is that the 5V bypass could "leak" through the capacitors to the 3.5V power supply, and fry the 3.5V chips. Am I worrying about that over nothing?

BobGreenwade
 
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Re: Bypass Capacitors on Mixed-Voltage Shield

by dastels on Fri Jul 03, 2020 6:08 pm

The bypass caps will be between 5v and ground, or 3.3v and ground. There's no worry about the higher voltage getting to the 3.3v parts.

Dave

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Re: Bypass Capacitors on Mixed-Voltage Shield

by BobGreenwade on Fri Jul 03, 2020 8:28 pm

I thought that probably was the case (else I probably would've gotten a warning about it somewhere) but I wanted to be sure. Many thanks!

BobGreenwade
 
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Re: Bypass Capacitors on Mixed-Voltage Shield

by dastels on Fri Jul 03, 2020 9:03 pm

No problem. have fun!

Dave

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Please be positive and constructive with your questions and comments.