Re: DAC
- From: "PeteS" <ps@xxxxxxxxxxxxxxxxxxx>
- Date: 26 Aug 2005 01:42:55 -0700
I am not sure you understand the functioning of the DAC. Vref in
requires a stable 2.5V reference. Whether you want to apply that to the
Offset in pin is another matter.
The DAC outputs a nominal 5V span, and applying 2.5V to the Offset in
pin sets the output range at -2.5 to +2.5. Note that if you are only
going to -2.4V, your supplies to the DAC may be a little low (it can
only get within 2V of the power supply rails)
The output is -2.5V for a code of 0 and +2.5 for a code of 0x3FFF (14
bit device) with Voffset = 2.5V. It would be 0V for a code of 0 with
Voffset(in) = Ground, and 5V (assuming your power supply is >7V for the
analogue section) for a code 0f 0x3FFF. If you just turn the device on,
I would expect it to have 0 in the DAC register, so you could expect
the output to be at the negative maximum.
The output voltage of the device is given by:
Vo = 2 x V(DAC) - V(offset_in)
Where V(DAC) = [Vref(in) x Code] / 2^14
If you want to output zero from the device at power up, then tie
Voffset(in) to ground.
Cheers
PeteS
.
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