I have an ADV7280 connected to the host processor Nuvoton N32926 which shares 1,85V regulated power supply with the ADV.
Due to a more narrow voltage range specification of the new processor version, I had to modify the power supply voltage level, bringing the previous 1,85V to the new 1.79V.
This voltage rail applies to PVDD, DVDD and AVDD of ADV7280 (DVDDIO is at 3,3V). The regulator is a DCDC 1MHz 1,5A which can supply ADV current as requested in the datasheet and hardware guide.
At this new 1.79V voltage, ADV does not talk appropriately via I2C interface by blocking the SDA signal to a low level and showing "deal with nack" error in the processor console. This also affects communicating with other I2C devices.
To unlock the situation a reset signal must be asserted to ADV and SDA will be released, but at the new I2C writing, the error appears again frequently.
I monitored the voltage rail but I have not found fast voltage drops during the I2C initialization phase, just a steady reduction of 20mVdc during ADV startup due to copper rail resistance from the regulator to ADV supply pins.
However, I believe the voltage is far from the 1,71V indicated in the datasheet as the minimum request. If I revert the modification, the ADV works well again.
I found in a few samples that the voltage must not be under 1,81-1,82V to work properly, otherwise, the communication problem occurs.
Could someone help me to understand the problem?