Hi,
I have designed PCB for ADS1299 (referring to ADS1299EEG-FE schematics) which mounts on Arduino UNO. I have designed the PCB such a way that, I can unplug the ADS1299 and replace it with another. I have populated three such similar boards. Supply voltages for ADS1299 on all boards are fine. (AVSS = -2.5, AVDD = 2.5, DVDD = 3.3). I have even measured the internal clock source. It is around 2.048MHz as given in the datasheet. Input referred noise is around 0.14uV (250Sps, gain =24 ) for all the channels in all the three boards which is again matching with the datasheet value.
But, each board has different problems.
1) Board1: It always gives zeroes when configured for internal test pulse. But this ADC works fine for an external input signal. All the default register values when read by a sample program gives out correct values (as given in the datasheet)
2) Board2: It gives sudden spikes/ peculiar signals when configured for internal test pulse. When configured for external input signal, it gives zeros as output. All the default register values when read by a sample program gives out correct values (as given in the datasheet)
3) Board3: Internal test pulse doesn't work. Gives zeros when configured for an external input signal. Default register values are wrong.
When I unplug the ADS1299 and replaces with a new one, the problem still persists. It is same with all the three boards. Can someone please help me to solve this problem. I am attaching my schematics and layout files.
Thanks in advance