SLAAEF8 January   2024 MSPM0L1105 , MSPM0L1105

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Function Explanation
  6. 3Single Wire UART
    1. 3.1 Background
  7. 4Power and Communication Logic
  8. 5Software
    1. 5.1 Overall Flowchart
    2. 5.2 IOMUX
    3. 5.3 Power/Communication Software Design
    4. 5.4 Other Resources
  9. 6Hardware
    1. 6.1 Test Results
  10. 7References

2 Function Explanation

The basic function this reference design achieved includes:

  • Power management
    • Device: BQ25628 [charger+boost], BQ51050B [Wireless charger], TPS7A05 [LDO]
    • Function: The most basic function of a TWS earphone case is charging, including charging the battery inside the case and charging the TWS earbuds. In this design, the system can be charged via a wired type-C connection or wirelessly via a wireless coil. The charger steps down the 5V from the type-C (or the wireless charger) to charge the battery, and the LDO stabilizes the battery voltage at 3.3V to power the MSPM0 and other peripheral devices. The Boost is needed to raise the battery voltage to 5V to charge the earphones. Those functions are running without the help of MSPM0 in this reference design, however, MSPM0 can be used to control the charger/boost through enable pin or inter-integrated circuit (I2C) for advanced control if needed.
  • Lid close detection and status indication
    • Device: TMAG5231 [Hall sensor], LED
    • Function: The cradle should be able to detect the lid closing. This can be achieved by detecting the magnetic flux density change through a hall sensor. A magnet is mounted on the lid, hence the magnetic flux density around the TWS case main body also changes with the lid open and closed. The LED is used to indicate the status of the TWS, for instance: low battery, lid open/close, charging status, Bluetooth pairing, and so forth. MSPM0 is able to monitor the status of the TWS and control the LED through GPIO.
  • Earbuds communication
    • Device: TPS22914 [Load switch], MSPM0L1105DGS20 [MCU]
    • Function: The cradle is able to communicate with the earbuds through the pogo pins. Currently, most TWS use two pogo pins, one of them is Ground and the other is for charging and communication. The load switch is used to control when to charge and when to communicate with the earbuds. In this design, communication is based on a single-wire UART communication protocol using MSPM0.

The block diagram of this design can be seen in Figure 2-1.

GUID-20230912-SS0I-VL21-RLCV-7WGG5K1MLCRR-low.svg Figure 2-1 TWS Cradle Based on MSPM0 Block Diagram

The red line in Figure 2-1 indicates the power path while the black line shows the signal path. The corresponding schematic and PCB can be found in the design file. This design supports a 5V wired inputs through a type C port, or wirelessly from BQ51050B, which regulates the wireless AC power into 5V DC. The BQ25628 is highly-integrated 2A switch-mode battery charge management and system power path management device for single-cell Li-ion and Li-polymer batteries, it not only charges the battery but also provides power to the earbuds. MSPM0L here is used for overall board control, for example, it can manage the power and communication logic between the case and the cradle, lit LED, read battery status and control the charger/boost, and so forth. The Hall sensor TMAG5231 is ideal for detecting lid closing in TWS applications due to its small size, low power consumption and low price.