The DACx1001 require external references (REFPF and REFNF) to operate. See the Recommended Operating Conditions for VREFPF and VREFNF voltage ranges.
The DACx1001 also contain dedicated sense pins, REFPS for REFPF and REFNS for REFNF. The reference pins are unbuffered; therefore, use a reference driver circuit for these pins. Set the VREFVAL bits (address 02h) as per a reference span equal to (VREFPF – VREFNF). For example, the VREFVAL bits must be set to 0100 for VREFPF = 5 V and VREFNF = –5 V.