Charles Douvier of PNW/Electronics writes:
Turns out the DAC is probably the easiest peripheral I’ve used on the PIC. It took me longer to wait for the PICKit to update from 18F configuration to 16F. BUT.. if you’re having issues.. here you go:
A simple voltage follower (or however you want to buffer the output) is needed on the DAC output. It’s not designed to drive anything.
Don’t expect screaming speeds out of this thing…it’s just not going to happen. I ran mine up to 1.3KHz, which is more than enough for what I’m trying to accomplish. If you put an A/D converter in you could use that to control your ramp speed and you’d have yourself a nice driver for your VCO input on test equipment with properly conditioned output.
I feel very uneasy with the “Don’t expect screaming speeds” bit.
The PIC16F1509 data sheet gives the max settling time of the DAC as 10us. Yet the writer is talking about ~1kHz speeds. He should take a long, hard look at the LM358 data sheet. We’re talking about maybe (TI’s LM358A) 0.3V/us at unity gain and… wait for it… a load of 1M ohm! Load the thing and… ouch. I’m sure a few FET switches and a resistive string can go faster than a few kHz.