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AMC1303M2510: Fail-safe output issue

Part Number: AMC1303M2510

Hi  Experts:

My customer is using the AMC1303M2510 for the in-phase current measurement in the servo drives. However, the device usually entered the fail-safe mode like the captured picture below:

you can the data out is hang on "1" before clock for 256 cycles (10MHz) , however, in the fail-safe mode, the CLK will hang on "1" for 70uS , is that correct ?

The device is in the fail-safe mode when the system is normally working , this is not we want to see because It will be false to drive the motor.

I checked the condition to trigger this mode :

a) The missing on the AVDD   b) The VCM > Vcmv (3V,  5V-2V)

My questions are:

1)  We checked the waveform of the AVDD , Vin+,Vin- with respect to the GND1, there is a little switching noise but is not sufficient to trigger the safe-fail mode ,

is there any factor to trigger this mode except for the two ones I listed?

2) We tried the value of the input capacitor on the AVDD , Vin+,Vin- as the datasheet recommended , but it has no effect. How to calculate the input capacitor to eliminate the common/differential mode noise effectively ?  

yellow: Data output    green: CLK out   Blue: phase current (DC current)