I am working with ADP5090 -2-EVALZ to generate voltage using Teg(SP1848) as a input source. The issue i am facing is with Cold start voltage i.e 380 mV ,the output only generates if my TEG provides input voltage greater than 380 mV.i used external battery to bypass this as you mentioned in data sheet.i connected 400mV dc supply to Back_up battery terminal acting as battery.but still no output was coming to my Vout(sys pin).My super cap voltage was 1.48v at that time.Why the output is not coming at my Vout ?.like it gives when input voltage reaches above 380 mV. The super cap i am using is 5v/2.5f.
You need a high back_up battery voltage to bypass the cold start. so you can try to increase the voltage.
Btw, ADP5091 is more suitable for supercap storage as charging efficiency is much better than ADP5090.