ADS122C04: ADS122C04 AVDD Power Supply Off

Hi Atsushi,

Welcome to the E2E forum!  Here are my comments to your questions:

1. Is is allowed for this condition, DVDD is on and AVDD is off. [Bob] Yes this is allowed as long as the Absolute Maximum Ratings are not exceeded.  The main concern is if one of the analog inputs will still have a voltage applied while AVDD is off.  Another option is to issue a POWERDOWN command which will turn off the analog portion of the device.  Some small current will flow to maintain internal state, but this is typically only 100nA.  Depending on the amount of off time for AVDD, it may actually use less overall current consumption using the POWERDOWN command.  The reason is external caps will need to recharge when the supply collapses and then power is reapplied.  Also there is time required to reconfigure the device.

2. In this condition, any additional current will flow ? [Bob] If a reference or analog input has a voltage or a capacitance that may have existing charge, current could flow into the ADC from external sources.  If the current through the inputs exceed the Absolute Maximums the device can be damaged. 

3. In this condition, register data are kept and accessible ? [Bob] If you turn off AVDD the ADC will be held in a reset state until the supply reaches nominal operating voltage.  When the ADS122C04 is released from reset, the configuration registers will also return to the reset values.  So if you turn off either of the supplies, the device will return to the reset state and the registers to the reset values. 

By the way, in my system, DVDD=3.0V and AVDD= 2.5V.

Best regards,

Bob B