Folks
Bit of a noob and still struggling with electronics 101.
I'm trying to build my own serial to USB breakout circuit for use with a Pro Mini. I'm just going to use the stock circuit provided in the FT232RL data sheet but this circuit (page 23 of http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdf shows a 10uF polarised capacitor between Vcc and GND.
I'm working on the assumption that a polarised capacitor means either an Aluminium Electrolytic or Tantalum, is this correct?
I can't find a 10uF polarised SMD cap at either RS or Farnell. I know there are other suppliers but if neither of them have it I have to think there's a fair chance I'm barking up the wrong tree?
Any suggestions?
Thanks
I can't find a 10uF polarised SMD cap at either RS or Farnell.
I don't believe you. What about this:-
http://uk.farnell.com/sanyo/10svp10m/capacitor-10uf-10v/dp/9188878
Anyway the value is not critical just make it bigger than 10uF.
I had to take a closer look at this because I don't remember ever needing a 10uF cap in a FT232 circuit.
It is actually a 10nF... which is .01 uF.
And IIRC polarised capacitors are not there for the design of the circuit but because certain capacitors are polarised by design. And I don't see why a capacitor this small would be polarised. Maybe look at some other FT232 designs. You should be able to replace that cap with a .1 uF ceramic and you can probably get rid of the ferrite bead. I haven't seen many designs using it.
Thanks Guys
Not sure where my head was last week, was trying to order a lot of components to meet a deadline and must have a brain freeze.
Just out of interest, why would you use a polarised cap, for example the 4.7uF one also needed? I have them and will use them, just wondering for my own education, I'm still putting myself through Capacitors 101 (I still have to check if uF is bigger or smaller than nF :))
tg
Perhaps more than you wanted to know
Not at all, a straighforward and well explained answer, many thanks.
I take that to mean that if the schematic shows a polarised cap but I can get a standard ceramic one with the same value then I could probably substitute it?
Just talking generally, I'll be sticking to the schematics until I know what I'm doing a bit better :-?
I take that to mean that if the schematic shows a polarised cap but I can get a standard ceramic one with the same value then I could probably substitute it?
One of the problems with high value ceramic capacitors is that there value is not that stable with temperature and it could be up to 20 to 60% less than the nominal value. This depends to some extent on the dielectric used. Dielectric - Wikipedia.
For decoupling then electrolytics are always to be preferred at values over 4u7
Thanks Mike
I also found another article, by sticking "capacitors 101" into Google :), that mentions the relative speeds of the different types.
It seemed to be electrolytic = slow, tantalum = a bit faster and ceramic = fastest which would explain the use of both a 100nF and 4.7uF in parallel in the FT232R reference circuit.
Finally, absolute newbie question but I'm assuming the use of the these capacitors in this circuit is voltage smoothing, is this correct? Is this the same as the de-coupling Mike mentions?
Thanks
Tommy
Decoupling is localise voltage smoothing of noise caused by the activity of the components, not necessarily the ripple in smoothing and rectification. But broadly speaking they are the same.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html