The internal reference mode (default) uses approximately 3mW more power on AVDD (which is already included in all the specification tables). The AFE5801 can operate in external reference mode by programming EXTERNAL_REFERENCE to 1. In this mode, the VREF_IN pin should be driven with 1.4V.
这句话是说明内部参考电压模式下,参考电压就是AVDD吗?可是芯片有AVDD3(3.3V)和AVDD18(1.8V)两种啊。http://www.ti.com/lit/ds/symlink/afe5801.pdf