I need help creating a discrete DAC for an old project

[DaveHardy]

Hello, I'm trying to recreate a Burr Brown DAC 71 CSB I for a project I'm in the middle of.  The DAC itself is relatively easy and straight forward.  The problem is that this old DAC doesn't require a clock / latch instruction to output data, and I'm having trouble finding a primitive replacement or one that would allow me to tie the latch low for constant output. 

Any suggestions or comments will be appreciated.

[moffy]

The DAC71 doesn't have a latch on its input, so whatever digital word is present on its input is converted to an analogue output. If you want a fixed value just provide a 16 bit latch or 2 eight bit latches. What logic are we talking here, 5V TTL/CMOS, 3.3VCMOS, FPGA etc.

[Benta]

Perhaps you should read the OP's question again...

[moffy]

Perhaps you should read the OP's question again...

Perhaps you could help the OP since you understand the question better than I do.

[PCB.Wiz]

Hello, I'm trying to recreate a Burr Brown DAC 71 CSB I for a project I'm in the middle of.  The DAC itself is relatively easy and straight forward.  The problem is that this old DAC doesn't require a clock / latch instruction to output data, and I'm having trouble finding a primitive replacement or one that would allow me to tie the latch low for constant output. 

Any suggestions or comments will be appreciated.

If that settles in 5us, can you not simply clock almost any suitable DAC at 200kHz or above, to emulate the same action ?

[DaveHardy]

Thanks for the comments everybody!  Regarding clock timing, I don't want to go that route unless I absolutely have to.  I found this IC.  It's V out instead of current out.  I think I can make it work in this circuit.  According to the datasheeet, holding everything low will create a pass through device.  I'll post the circuit next.

https://www.analog.com/media/en/technical-documentation/data-sheets/1657lfa.pdf

[DaveHardy]

Gain adjust is supposed to be calibrated for 5V + offset  from zero at pin 6 of U347.   I could install an op amp on a minature board with the DAC and a gain trimmer to get V out and omit U347.  Is this a good idea? What could go wrong?

[DaveHardy]

This might be an even better part!  This is a current DAC.

https://www.analog.com/media/en/technical-documentation/data-sheets/AD7538.pdf

[moffy]

You have a latch signal that feeds into the 74174, if you wanted to you could forward that signal to the DAC and use anyone you liked.

[DaveHardy]

Those are separate latches for upper and lower byte.  If some parts in the program alternate high and low latches, I'm screwed.  I'd rather avoid all complications first. 

[moffy]

Those are separate latches for upper and lower byte.  If some parts in the program alternate high and low latches, I'm screwed.  I'd rather avoid all complications first.

Nasty. There is the possibility to forward both latch signals and combine them into a single latch signal that updates on any change.