USING A REF19x AS A POWER SUPPLY FOR THE
Because the supply current required by the AD5620/AD5640/
AD5660 is extremely low, an alternative option is to use a REF19x
voltage reference (REF195 for 5 V or REF193 for 3 V) to supply
the required voltage to the part (see Figure 50). This is especially
useful if the power supply is quite noisy or if the system supply
voltages are at some value other than 5 V or 3 V, for example, 15 V.
The REF19x outputs a steady supply voltage for the AD5620/
AD5640/AD5660. If the low dropout REF195 is used, the current
it needs to supply to the AD5660 is 500 µA. This is with no load
on the output of the DAC. When the DAC output is loaded, the
REF195 also must supply the current to the load. The total current
required (with a 5 kΩ load on the DAC output) is
500 µA + (5 V/5 kΩ) = 1.5 mA
The load regulation of the REF195 is typically 2 ppm/mA,
which results in an error of 3 ppm (15 µV) for the 1.5 mA
current drawn from it. This corresponds to a 0.197 LSB error
for the AD5660.
VOUT = 0V TO 5V
Figure 50. REF195 as the Power Supply to the AD5660
BIPOLAR OPERATION USING THE AD5660
The AD5660 is designed for single-supply operation, but a
bipolar output range is also possible using the circuit in
Figure 51. Figure 51 gives an output voltage range of ±5 V.
Rail-to-rail operation at the amplifier output is achievable
using an AD820 or an OP295 as the output amplifier.
The output voltage for any input code can be calculated as
where D represents the input code in decimal (0 to 65535).
When VDD = 5 V, R1 = R2 = 10 kΩ,
This results in an output voltage range of ±5 V, with 0x0000
corresponding to a −5 V output and 0xFFFF corresponding to a
+5 V output.
Figure 51. Bipolar Operation with the AD5660
Rev. G | Page 21 of 28