The scope shot below shows DIAG_OUT signal with Hercules RM48 ADC input with 2x 10nF connected and with open circuit (liftted pin 7 of TPS65381). Other than noise level, there is no significant shift in mean voltage levels, so I would assume that ADC input impedance doesn not have much influence on DIAG_OUT voltage.
On the other side, when board is tested over temperature, there is a significant variation of the reading, particularly at MUX-ed voltages with high output impedance. Same board was tested cool (25c), warm (55C) and hot (+85C). VBAT/VBAT_SAFING dropped by almost 300mV over temperature. But was still far from expected reading of 1.000V, for VBAT=10Vas used in this test.
