DDC114: Noise issue in Test mode

Part Number: DDC114

Hi,

I am currently working with a DDC114 with a custom board.

I get the following value in TEST mode in RANGE 7 on channel 1. When i read the datasheet, on range 7 with 0pF detector the noise shall be 3.7 RMS noise (PPM FSR).

At 3 sigma it should translate into 11.1  peak to peak (PPM FSR). Now with 2^20 FSR x 11.1ppm = 11.64 count noise peak to peak.

I get about 20-25 on my custom board (this the graphic below).

Could you confirm that my calculation is good and that i have an issue on my board? 

Thanks in advance, Cyril.