mega16l usart max 232 with vcc=3.3v

[khatarat]

mega16l usart vcc=3.3v

hi
i want to create a circuit that have an atmega16l to send some information via usart using max232.
my circuit work when i use 5v as supply power but not when i use 3.3v
i use 6 mh ocilator
what should i do. is there a specific work should be don with lower voltage than 5v like 3.3v?

 

[Tahmid]

mega16l usart vcc=3.3v

Hi,
This is because the MAX232 doesn't work below 4.5v.
focus.ti.com/lit/ds/symlink/max232.pdf
Hope this helped.
Tahmid.

 

[khatarat]

Re: mega16l usart vcc=3.3v

it means that input should be more than 4.5v or suppluy power should be more than 4.5v?

 

[Tahmid]

mega16l usart vcc=3.3v

You can power the ATmega with 3.3v, but the MAX232 must be given a supply power voltage with at least 4.5v, most suitably 5v.
For 3.3v operation, you can use a boost chip, like LT1073 or something like this.
Hope you got it.
Tahmid.

 

[khatarat]

Re: mega16l usart vcc=3.3v

i have tested max232 with 3.3v its worked well
can i chat with u(google talk or yahoo messenger?)

 

[Tahmid]

mega16l usart vcc=3.3v

I don't use IM.
According to datasheet, MAX232 is not to work at 3.3v.
I don't think there's a problem with code as it works at 5v.
Tahmid.

 

[khatarat]

mega16l usart vcc=3.3v

recomended voltag is 5v but it work with lower powers
i think that problem is from output of micro
when i use 5v out put is about 5 and circiut work well but when i use 3.3v output is abut 2v and max232 cannot get it

 

[Tahmid]

mega16l usart vcc=3.3v

Hi,
I think that's why 5v is stated in datasheet.
Why do you need 3.3v, will it not do with 5v?
Tahmid.

 

[matbob]

Re: mega16l usart vcc=3.3v

Hi khatarat,

You may use MAX3232 designed to operate at 3.3V. The min input high requirement is 2V, which is available in your case.