For AD7991, Vref can use 5V?
With Vref=5V, can i supply Vdd= 5V and how about the I2C signal?
[edited by: jiamin at 6:27 AM (GMT -4) on 13 Jul 2021]
Thanks for your query. Yes the AD7991 supports VREF = 5V.
VDD must be ≥VREF, so this requires that VDD be at least 5V as well.
The AD7991 can be configured to use either VDD or the VIN3 input as the VREF source. This is selected via the REF_SEL bit in the Configuration Register.
The I2C logic levels are set by VDD as well. In the spec table, VINL and VINH specify the logic low and high voltages, and both are a percentage of VDD. On I2C bus, the logic high voltage is achieved when the SDA/SCL drivers are set to open drain mode, and the lines go high via pull-up resistors to VDD. Figure 22 in the data sheet shows these pull-up resistors.