6-bit dac in comparator on K64 and k66

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tenkai

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Does anyone know how to access the 3 6-bit DACs that are part of the 4 Analog comparators on the K66 and K64?

I was thinking of trying to add voltages from two 6 bit dac and two of the 12 bit dacs to get 2 outputs with 18 bits of resolution.

Does this sound feasible?
 
I may have answered my own question from the K64 manual, which states:

The 6-bit DAC is 64-tap resistor ladder network which provides a selectable voltage reference for applications where voltage reference is needed. The 64-tap resistor ladder network divides the supply reference Vin into 64 voltage levels. A 6-bit digital signal input selects the output voltage level, which varies from Vin to Vin/64. Vin can be selected from two voltage sources, Vin1 and Vin2. The 6-bit DAC from a comparator is available as an on-chip internal signal only and is not available externally to a pin.

Still, I'd like to hear any suggestions. Perhaps I could use the comparator to a static reference?
 
Screen Shot 2018-04-19 at 3.53.00 PM.png

then again, I see this diagram, and it appears that the dac has another output, besides into the comparator. Can I get to it somehow? I wonder!
 
Yup, sad to confirm this would be fruitless indeed. That 6 bit DAC is internal only.

Even if you could access it, somehow combining it with the 12 bit DAC won't give you a DAC with 18 bits resolution. There are all sorts of analog problems with combining 2 DACs that way.
 
Paul,

I have another idea to increase bit depth of the dacs, using Teensy hardware.

Take a few PWM pins, put them through RC circuits to get constant DC voltage. These would be static voltages, dialed in based on a calibration routine, and switched with a transistor controlled with a GPIO pin. For a ±10v signal, they would be 5v, 2.5v, 1.25v.. sum those with the output of on board Teensy DACs to get 14-16 bits of DAC resolution.... I hope...

Since they are switched, the settling time wont be much of an issue. I would just have to worry about the settling time of the transistor switch. I can adjust PWM on the outputs to calibrate the entire system, since they are controlling the MSB of the dac system.

Gonna try this one out :)

T
 
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