It is not good practice to use an unregulated power source to power the VLED+ of the MAX30102. It is recommended to use a regulated voltage reference for the VLED+ supply because you want a steady current for the LEDs in order to receive a clean PPG signal from the photodiode. An LED with an unregulated supply will make the PPG signal more noisy than it needs to and this will affect HR and SpO2 calculations.