3.3v MAX232? - Electronic Circuits Projects Diagrams Free

Oznog · 6th April 2006, 08:01 AM

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 · 6th April 2006, 09:59 AM

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

justDIY · 6th April 2006, 02:56 PM

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

http://focus.ti.com/docs/prod/folder...sn75c3221.html

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

http://para.maxim-ic.com/cache/en/results/5020.html

DirtyLude · 6th April 2006, 03:17 PM

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

http://www.mouser.com/catalog/625/246.pdf

I use these all the time.

Papabravo · 6th April 2006, 05:46 PM

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 · 6th April 2006, 07:36 PM

Quote:

Originally Posted by Papabravo

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.

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 · 6th April 2006, 08:43 PM

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

DirtyLude · 6th April 2006, 09:45 PM

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

Oznog · 7th April 2006, 05:16 AM

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

Papabravo · 7th April 2006, 01:59 PM

Glad I was helpful.

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6th April 2006, 08:01 AM	#1
Oznog	3.3v MAX232? 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. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

6th April 2006, 09:59 AM	#2
Mike, K8LH	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 Attached Thumbnails

6th April 2006, 02:56 PM	#3
justDIY	Texas Inst has a few (11) 3.3v compatible rs232 drivers ... this link is for the cheapest one http://focus.ti.com/docs/prod/folder...sn75c3221.html Maxim (for whom the MAX232 was named?) has a bunch http://para.maxim-ic.com/cache/en/results/5020.html

6th April 2006, 03:17 PM	#4
DirtyLude	Best/cheapest one I've found is the ST3232. $1.66 if you are willing to go SMD, otherwise $2.60 for DIP. http://www.mouser.com/catalog/625/246.pdf I use these all the time. __________________ Mark Higgins

6th April 2006, 05:46 PM	#5
Papabravo	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.

6th April 2006, 08:43 PM	#7
Papabravo	You can get them at Arrow, Digikey, and Maxim.

6th April 2006, 09:45 PM	#8
DirtyLude	Nice. It's $1.25 from Digikey in TSSOP package. __________________ Mark Higgins

7th April 2006, 05:16 AM	#9
Oznog	Thanks! I should be able to get a part that fits my needs then. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.