max232 circuit!

[t.man]

hey guys i have these questions for u


1. how do we choose the values of the four capacitors of a max232.

2. are they have to be only polarised ones?

3. i sometimes see V+(pin 2) connected to Vcc via a capacitor or connected to GND via that capacitor- is there any good practice btw the two?

4. thank you

 

[mrmonteith]

Have you looked at the datasheet for the Max232? It shows a typical application. They used 1uf caps all around. I'd go ahead and use polarized ones at least for the charge pumps.

To reduce noise on most ICs it's always a good policy to connect up a decoupling capacitor which is tied from Vcc to Ground. A .1uf ceramic does the trick and they are pretty small. It protects the IC from noise imposed by other circuitry connected to that supply.

Hope that helps. Most of the issues you wouldn't see unless you had an oscilloscope. But the more complex your circuit is the more potential for noise there is and problems that crop up.

Michael

 

[Mike - K8LH]

The MAX232A (and ST202 and some others) can actually use 0.1-uf (100nf) monolythic caps (inside of the machined pin socket in the picture below).

 

[t.man]

i'm sorry, i don't really get you abt Q.3. r u trying to say the best practice is to connect V+ and Vcc with a capacitor? or V+ to ground via decoupling capacitor(o.1uf)?