DAC (Digital-to-analog) question

[Kingpin094]

I have a TI DAC7541 that is a 12 bit digital to analog converter. I am feeding the output of a CD4040 which is a 12 bit counter. The idea is to compare the output of the DAC to the output of an analog sensor and when the difference between the to signals is zero you have the binary value of the analog voltage. The porblem that I am having is that the output of the DAC seems to be nonlinear? Has anyone played with a similar chip? The circuit has be checked and debug so that all the signals are being feed into the right pin. Thanks to anyone who can shed some light on the problem.

 

[kinjalgp]

What is the output of DAC? Current or voltage?

 

[Kingpin094]

The output of the DAC is two current pins. The two pins are hooked up to a opamp as described in the chip datasheet. The output is pretty linear until it hit about 1 volt then it goes unstable.

 

[bogdanfirst]

you might test the 4040. and the connections, i once had a problem in the connection it just didnt make a contact so i spend a few hours trying to figure it out.

 

[kinjalgp]

Or the other reason may be that one of the pin of 4040 has been connected wrongly on DAC. Like bit 7 connected as bit 10 or something of that sort. Hope I am making myself clear.

 

[Kingpin094]

I hooked up 12 leds to the outputs of the CD4040, everything woks fine on that side. Then using the pin numbers from the DAC I hooked up the leds on that end, the leds still came on in the right order. Do you think that I could have a bad track in the board? The thing isn't that old but how long do they last?