As given in the Datasheet for using internal reference, we need to short VrefN to AVSS= -2.5V (Provided supply voltage is +-2.5V) and add a capacitor at VCAP1 and VrefP.
I made a circuit keeping in mind the above conditions. When I measured voltage at VCAP1 it is -1.3V and at VrefN is -2.49V and as per the ADS1299 datasheet section 9.3.1.3.4., on solving the circuit for VrefP it should come at +2V. Which also satisfies the relation VrefP-VrefN=4.5V.
But when I actually measured voltage at VrefP (w.r.t Gnd=0V) the multimeter showed -2.42V which makes Vref=VrefP-VrefN=70mV. How is that possible? There is no additional components other than capacitors attached to these pins i.e. VCAP1, VrefP. I have attached schematic for the same below.
I was suspecting IC is damaged but I am able to set its registers, read registers, take raw EEG data samples. So suspecting just the VrefP generating op-amp is faulty would be lame. Can someone please help me with what's going on in the circuit?
