3.3v MAX232?

Oznog

Active Member

• Apr 6, 2006

• #1

I am looking at a system where I need to lower Vdd from 5v to 3.3v. However the ST232 (same as a MAX232), but that's rated only for 5v. Even if the logic works the same since it's a capacitive charge pump obviously any change in Vdd will be reflected in its output level which could make its output levels unreadable by another receiver.

I don't want to use 2 regs. Is there a RS232 transceiver that runs on 3.3v? It would preferrably need to be a very low current device like the ST232.

 

Mike - K8LH

Well-Known Member

• Apr 6, 2006

• #2

This might not be exactly what you're lookin' for but the open-drain outputs and pull-ups work great on anything (PC or laptop) I've connected to at data rates up to 115-kbaud... I've used VDD=5v and VDD=3.3v on the PIC side and the pull-up on the RS232 side can often be 5v on some laptops all the way up to 13v on some desktops...

Regards, Mike

 

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justDIY

Active Member

• Apr 6, 2006

• #3

Texas Inst has a few (11) 3.3v compatible rs232 drivers ... this link is for the cheapest one

http://focus.ti.com/docs/prod/folders/print/sn75c3221.html

Maxim (for whom the MAX232 was named?) has a bunch

**broken link removed**

 

DirtyLude

Well-Known Member

• Apr 6, 2006

• #4

Best/cheapest one I've found is the ST3232. $1.66 if you are willing to go SMD, otherwise $2.60 for DIP.

https://www.electro-tech-online.com/custompdfs/2006/04/246.pdf

I use these all the time.

 

Papabravo

Well-Known Member

• Apr 6, 2006

• #5

The MAX3221 works just fine at the lower Vcc. It has one TX and one Rx. We pay $1.37 It probably has a brother with two Tx and Two Rx.

 

DirtyLude

Well-Known Member

• Apr 6, 2006

• #6

Papabravo said:

The MAX3221 works just fine at the lower Vcc. It has one TX and one Rx. We pay $1.37 It probably has a brother with two Tx and Two Rx.

Click to expand...

Where do you get that from? The ST3232 above has 2 TX and RX lines, but I've never actually needed 2, so it seems like a waste.

 

Papabravo

Well-Known Member

• Apr 6, 2006

• #7

You can get them at Arrow, Digikey, and Maxim.

 

DirtyLude

Well-Known Member

• Apr 6, 2006

• #8

Nice. It's $1.25 from Digikey in TSSOP package.

 

Oznog

Active Member

• Apr 6, 2006

• #9

Thanks! I should be able to get a part that fits my needs then.

 

Papabravo

Well-Known Member

• Apr 7, 2006

• #10

Glad I was helpful.