SLAA897 June 2019 MSP430FR2353 , MSP430FR2355
Handheld small pulse oximeters are typically powered using two AAA batteries. The discharge in battery voltage (can go till 1.8 V) may lead to improper functioning of the MCU and the transmit chain may shut down. Hence, to ensure proper functionality, designers need to regulate the battery voltage and boost it up to 3.3 V to maintain sufficient margin. (Typical MCU working voltage range is 1.8 V to 3.6 V).
The battery voltage can be increased by either using a dedicated boost converter device (Figure 5) or using discrete boost converter (Figure 6).