The device features an internal reference source with a nominal output value of 4.096 V. On power-up, the internal reference is enabled by default. A minimum 1-µF decoupling capacitor, as illustrated in Figure 35, is recommended to be placed between the REFIO and REFM pins. The capacitor must be placed as close to the REFIO pin as possible. The output impedance of the internal band-gap circuit creates a low-pass filter with this capacitor to band-limit the noise of the reference. The internal reference is also temperature compensated to provide excellent temperature drift over an extended industrial temperature range of –40°C to +125°C. By default the internal reference is on and the voltage at REFIO is 4.096 V. The REFIO pin has ESD protection diodes to the AVDD and GND pins.
The initial accuracy specification for the internal reference can be degraded if the die is exposed to any mechanical or thermal stress. Heating the device when being soldered to a PCB and any subsequent solder reflow is a primary cause for shifts in the internal reference voltage output. The main cause of thermal hysteresis is a change in die stress and is therefore a function of the package, die-attach material, and molding compound, as well as the layout of the device itself.