The datasheet states:
The ADP130 has an internal undervoltage lockout circuit that
disables all inputs and the output when the input voltage is less
than approximately 2.1 V. This ensures that the ADP130 inputs
and the output behave in a predictable manner during power-up.
Do you refer to VBIAS or to VIN (or both) in this section when you say "input
voltage"? I think
there should be not be a 2.1V undervoltage lockout for VIN as this does not
make sense considering the VIN range spec of 1.2V to 3.6V?
The UVLO monitors the voltage on the VBIAS pin. If VBIAS and VIN are tied
together, the minimum operating voltage will be 2.1V. If VBIAS and VIN are
powered from different sources, the LDO will be disabled when VBIAS falls below
2.1V. VIN can go as low a 1.2V in this case.