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Power AD7685 - Multiple Supplies - Power Sequence

Question asked by CRFA on Feb 21, 2012
Latest reply on Mar 15, 2012 by CRFA



I would like to know if there's a recommended practice for power-up the different supplies of the AD7685. I'm designing a battery operated device which has the following sections: Sensor, Signal Conditioning Circuitry, AD7685 and MCU.


I have three supplies:

- Vref. 3.0 V. Connected to Sensor and Vref pin on AD7685.

- 3.3V Analog. Connected to VDD on AD7685 and to supply the signal conditioning circuitry (op amps, filters,...).

- 3.3V Digital. Always On. Connected to VIO on the AD7685 and the rest of digital circuitry, including MCU.


What I would like to do, is the possibility to turn OFF/ON the Analogue section (Vref and 3.3 V Analog) while leaving always ON the digital circuitry.


It's okay to leave the VIO power ON and cutting the supply to VDD and Vref ? Or should I connect VIO to VDD (then becoming part of the 3.3V Analog supply)?


The lines: SDI, SCK, SDO and CNV are connected to pull-up resistors to the 3.3V Digital Supply and to a MCU.