SLAA897 June   2019 MSP430FR2353 , MSP430FR2355

 

  1.   MSP430’s Analog Combo Enables True Single-Chip Pulse Oximeter Designs
    1.     Trademarks
    2. 1 Introduction
    3. 2 Proposed Single-Chip Design
      1. 2.1 Using SAC to Generate the LED Drive
      2. 2.2 Using SAC as TIA and Gain Stage
      3. 2.3 Power Management
    4. 3 Key Benefits
    5. 4 Summary
    6. 5 References

2.3 Power Management

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).

  • TPS613221A is a synchronous boost converter with only 6.5-μA quiescent current.
    • slaa897-using-tps613221a-to-boost-the-battery-voltage.gifFigure 5. Using TPS613221A to Boost the Battery Voltage
  • A discrete boost converter can be implemented by controlling the gate switching through a PWM signal generated from the timer of the MCU and sensing the output voltage by the ADC and varying the duty cycle of the PWM accordingly.
    • slaa897-discrete-boost-converter-implementation.gifFigure 6. Discrete Boost Converter Implementation