The absolute maximum rating listed in the datasheet of ADS7828-Q1 for the input pins is as below -
Digital Input Voltage to GND ................................. –0.3V to +VDD + 0.3V.
When the ADC is OFF (not powered) and the input channel pins of the ADC are connected to voltage not exceeding 5V will damage the IC due the fact that from the above statement where the Vdd = 0 and the input voltage connected to the ADC input channels are above than 0.3V (0+0.3V), violating the condition.
Is my understanding is correct ? if so then can you explain me how does it damage the IC.