Re: Questions about SMD passive components

"Antti Keskinen" <antti.keskinen@xxxxxxxxx> writes:

> Hello !
>
<SNIP>
> This isn't what I meant, exactly. You see, I know resistors come in specific
> package sizes, such as the ones you listed above. It is the type of the
> resistor, and technology, which puzzle me so greatly and make my strip my
> hair out. Should I, for example, choose a thick film or a thin film resistor
> to act as a serial resistor in an RC-circuit ? Or should it be a ceramic
> resistor ? Can ceramic resistors be film-based at all ? What are metal film
> resistors then ? Should I choose a similar type resistor to act as a signal
> line terminator ?

I think you will find metal film tend to be the better ones (better
tolerance, temperature coefficient, noise). So use these unless you
have a good reason not to. You would need to be making an awful lot of
product in order for the slightly higher cost to be
significant. 0805's are about $15 for 5k!

<SNIP>
>
> Again, it's not the size or the capacitance which puzzle me, since
> capacitance category (pF, nF, uF) mostly goes hand-in-hand with the size.
> It's the same with non-SMD capacitors. But, there are tantalum capacitors,
> aluminium ones, ceramic ones, multi-layer ones etc etc.

It is hard to make general rules about capacitors, since they have so
many different parameters which may be irrelevant to you, or may be
critical in your particular application. Some non-obvious ones to be
aware of might be:

Ceramic
voltage,temperature coefficient (C0G best, X7R OK, Y5V poor)

Alumininium Electrolytics
lifetime vs temperature
ripple current
impedance

> Which one should I choose as a bypass capacitor for an IC then ?

Probably X7R or Y5V ceramic.

> Should I use a similar capacitor to filter an audio signal that
> exists an IC and enters another ?

Probably C0G. I think the other types could distort the signal if
there is significant voltage accross it.

> Is such "filter capacitor" even needed ?

Depends on the application and what you mean by "filter" I think!

> The problem is that with the current knowledge I have, I cannot efficiently
> browse the manufacturer pages for capacitors or resistors. I don't know
> which technology options I should tick in order to be even able to select
> the resistance/capacitance ranges :)

My sympathies...

--

John Devereux
.

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