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AD7367 draws excessive current from AVCC/DVCC when VDD and VSS are missing

Question asked by jimpap on Jun 14, 2016
Latest reply on Jun 15, 2016 by jcolao

Hello all. I have the following issue with AD7367: The current consumption on any power line (Idd, Iss, Icc, Idrive) is as expected when all power supply voltages are at normal operating levels (i.e. VDD=13V, VSS=-13V, AVCC=DVCC=5V, VDRIVE=3.3V). However, when VDD & VSS are missing, Icc jumps to ~140mA (Icc returns to normal when VSS and VDD appear). This is not mentioned nor implied on "Table 6. Pin Function Descriptions" or "Table 5. Absolute Maximum Ratings" of the datasheet.

 

The difficulty in my application is that VSS voltage is derived by a separate power supply that ramps up approx. 0.5 sec after the ramping up of the other supply voltages. The resulting dissipation on the AVCC/DVCC, when VSS is missing, is 5V * 160mA = 0.8 Watt. It seems rather too high. So the question is: Is it normal to leave the application as it is, considering the small duration (0.5 sec) of this overcurrent situation, or should I have to modify the AVCC regulator so that it supplies AVCC/DVCC *after* the appearance of the VSS voltage?

 

NOTE: On the AD7367 evaluation board, the power sequence is controlled by an ADM1185 as following:

1) AVCC, DVCC

2) VDD, VSS

3) VDRIVE

So it seems that I have correctly followed the eval. board scenario. But I'm getting this overcurrent issue!

 

Thank you in advance

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