ZWorld Exp-A/D12, User Manual

Page: 26 / 111

XP8500 26 s I/O Configurations
selected. The normal operating current of the A/D converter chip is 1 mA
to 2.5 mA. This consumption drops to 4 µA to 25 µA when the chip is in a
power-down mode. The reduction represents only about 10–20 percent of
the XP8500 board’s analog supply current and none of its digital supply
current
Drift
The AD680JT voltage reference experiences a voltage drift of 10 ppm/°C
(typ) to 30 ppm/°C (max). This drift corresponds to 25 mV/°C to 75 mV/°C,
or 1.75 mV to 5.25 mV over the temperature range of 0°C to 70°C.
The LMC660C op-amp has an offset-voltage drift of 1.3 µV/°C (typ), or
91 µV over the temperature range of 0°C to 70°C.
A greater contribution to overall drift arises from differences in the
temperature coefficients of the gain and bias resistors, and the fixed 10 k
Ω
resistors in resistor packs RP3 and RP4. These resistor networks and the
one used for the ratiometric voltage divider have a temperature coefficient
of 200 ppm/°C. Because the packages are small, the resistors within each
package are always at essentially the same temperature and their deviations
track closely.