Yes I got Multisim, Quartus II, and Xilinx...

I already tested the circuit in Multisim however I wanted to hear expert's opinion on this topic as I generally don't trust simulators...

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin

 

Hi,
I agree, sims are just a guide, but they can highlight errors.

Looking at the MAX7400 datasheet says, Vin can be Vdd/2.

So a 3V input will drive it OK, if its powered from 5V..

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

The MAX7400 is a Cmos filter IC. It needs to be clocked with a signal that is 100 times higher than its cutoff frequency by a Cmos square-wave or by its own internal oscillator. The clock signal must be with a low of 0.5V or less and a high of 4.5V or more.

The input signal might need an RC lowpass filter to remove high frequency harmonics that would cause aliasing with the oscillator. Your input square-wave might have harmonics that must be removed ahead of the filter IC. The input level to the filter IC can be any level up to about 4.8V p-p but signals lower than 1V p-p have higher distortion and noise at the output. The gain below the cuoff frequency is 1.0.

Why not use Cmos logic ICs to make a 5V p-p square-wave instead of old TTL that makes a square-wave around 3.4V p-p??

__________________
Uncle $crooge

 

I'm not familiar with that Maxim part, but if it's supposed to be a logic input it will probably work?. Failing that a simple open collector buffer and a pullup resistor to 5V is all that's required.

I've just had a read of the datasheet, I would suggest you simply try it, I suspect it may be perfectly fine.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

The input frequency of the square wave is variable (600Hz - 6Khz). What design of low pass filter can I use (if needed at all) for this aplication ?

Thanks

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin

 

A simple RC lowpass filter starts its rolloff at 1/5th its cutoff frequency. So 6kHz x 5= 30kHz. It won't have much effect on the harmonics of 600Hz.

__________________
Uncle $crooge

 

Thank you for your help. With this info I can hopefully finish my AC motor control project. Personally I think I've gone way 2 far with this but than again, I learned something new doing it

Oh, and thanks for that CMOS IC suggestion, I was able to find variety of 40XX IC's that suite my needs so I won't be needing that blastted 741....

__________________
"The people who cast the votes don't decide an election, the people who count the votes do."
-Joseph Stalin