The bipolar output span can be calculated through Equation 4 by defining a few parameters, the first being the value for the reference voltage. Once a reference voltage is chosen, the gain resistors can be set accordingly by determining the desired VOUT at code 0 and code 2n. For a VREF of 2.5 V and a desired output voltage range of ±10 V the calculation is as follows.
CODE = 0:
Setting the equation to minimum output span, VOUT(0) = –10 V, will reduce the equation to: R3/R1 = 4:
CODE = 4096:
Setting the equation to maximum output scan, VOUT(4096) = 10 V, and R3/R1 = 4 will reduce the equation to: R3/R2 = 3
It is important to note that the maximum code of a 12-bit DAC is 4095; code 4096 was used to simplify the equation above. For practical use, the true output span will encompass a range of –10 V to (10 V – 1 LSB), which in this case is –10 V to 9.995 V.