The integrated circuit (IC) described herein lowers the start-up voltage to, for example, 50 mV, compatible for starting a DC-DC converter from a thermoelectric generator (TEG), even with a small temperature gradient. The IC further improves end-to-end efficiency of the energy harvester by improving power efficiency of the DC-DC converter while ensuring maximum power transfer from the TEG at low voltages. The IC uses a low voltage integrated charge pump that can boost sub-100 mV input voltage. A startup clock is generated by a ring-oscillator that begins operation with low supply (e.g., 50 mV or less), and which allows for one inductor to be used for DC-DC converter and for startup of the converter. The IC can be configured between the TEG and any downstream sensor or communication circuits to provide an acceptable (e.g., greater than 1 V) voltage for powering the downstream circuits from a low-voltage (e.g., less than 200 mV) TEG energy source.