DAC

Exactly what problems are you having? I've used one of the same family, and although I had no real problems, you have to be a little careful about source impedance on those pins.

Cheers

PeteS

Hello,

The ouput of the DAC is going to the non- inverting input of an op amp. Now, when I apply 2.5 volts to the " Ref_in" and " "Offset" pins of the DAC, the DAC outputs -2.4 volts , and in return my opamp outputs the

-15 volts. Opamp has dual power supply of + - 15volts. The inverting input of the opamp is grounded. I need to output zero from this DAC at the power up when its not getting any digital data. Please advice thanks Regards John

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