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I'm planning a project involving the ADNS-5050 optical mouse sensor package. The data sheet for this package says that it needs to be combined with 4 capacitors, and it has a diagramme that I think is supposed to tell me what capacitors to use, but I don't have a great deal of experience with electronics and don't know exactly how to interpret it.

The relevant part of the diagramme is:

(circuit diagramme for ADNS-5050 connection to power and LED)

As far as I can tell, the document does not elaborate on these four capacitors. Obviously, the 0.1, 3.3 and 4.7 are measures of capacitance, but I don't know what the units are, or even if they are all the same units. I do recognize from the symbols that two of them are polarized and two are non-polarized, but I am kind of floundering at figuring out what exactly I need to hook up.

What capacitors exactly is this diagramme calling for, and how might I have figured it out by myself? :-)

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That's a terrible diagram, it should really say what the units of these are. (also, when you compare the symbol of C1 and C3, it seems like it wasn't drawn with software that has component symbols, but by hand ... not a good sign for documentation quality.)

However, seeing the values: Unit is most likely µF. Watch out, C2 and C4 are polarized caps (i.e. electrolytic ones) and thus their orientation matters.

Also, note that if a device needs both such large capacitances as 3.3 µF and 4.7 µF in electrolytic capacitors as well as high-frequency 0.1 µF (= 100 nF) capacitors, at least the ceramic capacitors should be placed very close to the chip. (The schematic "suggests" that wrong, and this raises even more questions about documentation quality).

The company was later bought by Avago, then that got bought by Broadcom. They reworked the datasheets for most devices from the ADNS-series, but it seems they never got around to fixing the ADNS-5050 data sheet schematics. It's not the same device, so don't take anything said there as true, but you might want to also browse the Broadcom ADNS-5070 datasheet if any concepts remain unexplained in the ADNS-5050 datasheet.

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  • \$\begingroup\$ Thanks very much :-) \$\endgroup\$ – Jonathan Gilbert Oct 7 '20 at 16:06
  • \$\begingroup\$ I'm curious, can you tell me why it's important for the ceramic capacitors to be placed very close to the chip? \$\endgroup\$ – Jonathan Gilbert Nov 15 '20 at 9:01
  • \$\begingroup\$ because their purpose is to stabilize the supply voltage when the current draw by the chip drastically changes in short time. If you put a long trace between the supply pin of the IC and the capacitor, that acts as an inductor – thus reducing or even nullifying the ability of the capacitor to hold the voltage at the pin stable. Look for "decoupling capacitors" on here or generally the internet for more in-depth explanations. \$\endgroup\$ – Marcus Müller Nov 15 '20 at 11:27
  • \$\begingroup\$ Thanks very much :-) \$\endgroup\$ – Jonathan Gilbert Nov 15 '20 at 15:48

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