The DAx0501 family of devices includes a 2.5-V precision band-gap reference that is enabled by default. Operation from an external reference is supported by disabling the internal reference in the REF_PWDWN bit (address 3h). The internal reference is externally available at the VREFIO pin, and can be used to drive external circuitry. At power-on reset, the internal reference is enabled. This enabled reference can result in current being sunk or sourced from the device to an external reference source. When using an external reference, use a series resistance that is larger than 1 kΩ to reduce the current at start-up to be less than 5 mA. After the internal reference is disabled, the input becomes high impedance. For noise filtering, use a minimum 150-nF capacitor between the reference output and AGND.

The reference voltage to the device, either from the internal reference or an external one, can be divided by a factor of two by setting the REF-DIV bit (address 4h) to 1. The REF-DIV bit provides additional flexibility in setting the full-scale output range of the DAC output. Make sure to configure REF-DIV so that there is sufficient headroom from VDD to the DAC operating reference voltage, VREFIO (see Equation 1). See Section 7.3 for more information. The short-circuit current of the internal reference is limited by design to approximately 100 mA.

Improper configuration of the reference divider triggers a reference alarm condition. In this case, the reference buffer is shut down, and all the DAC outputs go to 0 V. The DAC data registers are unaffected by the alarm condition, thus enabling the DAC output to return to normal operation after the reference divider is configured correctly.