What capacitor package is the best choice for bypassing the MAX485?
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\$\begingroup\$ This just might be "What item should I buy" kind of question, right? \$\endgroup\$– JustmeFeb 22 at 19:36
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\$\begingroup\$ @Justme No, because if the answer is accompanied by a detailed explanation it is a way to learn something more. It's not about the shopping list. \$\endgroup\$– SimoneFeb 22 at 19:46
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2 Answers
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Absolute maximum supply voltage for the MAX485 is 12 V so 50 V caps are a bit overkill unless you have a bunch of them for something else or don't want to procure another part number; 25 V or 16 V would be suitable here. Two things about supply bypass caps to remember are:
- Unless the device datasheet says otherwise, exact values aren't critical and
- Distance to the device being bypassed should be minimized to minimize parasitics
The MAX485 datasheet says nothing about decoupling capacitors so in terms of value, the 4.7 uF cap should be fine. However, it's in a ridiculous 1812 package and is rated for 50 V so you can do better. The 50 V 1206 10 uF will also work but here's where point (2) comes into play: physically larger capacitors have more lead inductance and it's usually harder to find that much real estate close to the pins of the device being bypassed.
Looking at the 100 nF caps, again 50 V is overkill and an 1812 package is far far too large. 0603 strikes a good balance between size and workability with hand tools. You might consider getting the 10 uF cap in this size.
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The exact package choice for a low frequency part like this is not critical so you have some freedom to choose what you like. However, my general recommendation in this case is to use either 0402 or 0603, with 0603 being a bit easier to hand solder but sometimes a bit more awkward to fit in close to the power/ground pins.
In this case though the IC itself is relatively large, and you'll probably be putting the decoupling cap on the backside, so either size would be easy to route.
