PDA

View Full Version : increasing output voltage on the prop pins???



RottenJalapeno
02-05-2007, 05:59 AM
does anyone know an easy way to increase the output voltage on the pins from 3.3 to lets say 3.5-3.7 volts?
I'm trying to drive the MAX7219 display driver but its minimum logical high input voltage is 3.5 and so I'm not able to get it to work. If anyone has any ideas please reply

PJ Allen
02-05-2007, 06:11 AM
Attached is Beau Schwabe's 3V I/O to 5V I/O interface.

Beau Schwabe
02-05-2007, 07:12 AM
For this application, I would lean more toward the diode-level shifter rather than the dual gate SCR.

http://forums.parallax.com/showthread.php?p=622466

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

RottenJalapeno
02-08-2007, 03:05 AM
Just wanted everyone to know I got it to work, and thanks for all the help. But I ended up getting it to work just using 10k pullup resistors tied to +5v so when it went low it pulled it low. I'm wondering now is this safe for the chip? will the 5v hurt the props i/o? If not it works great!

Mike Green
02-08-2007, 03:29 AM
The 10K pullup will limit the current into the chip. The protective diode on the input pin will conduct (to shunt the current to the Vcc/Vdd supply line) as it should. The supply line can normally tolerate several tens of milliamps of such current without problems.