SLUAA04A june   2020  – may 2023 BQ25150 , BQ25155 , BQ25618 , BQ25619 , TS5A12301E , TS5A3157 , TS5A3159A , TS5A6542

 

  1.   1
  2.   High-Efficiency Charging for TWS Using a 2-Pin Interface
  3.   Trademarks
  4. 1 Introduction
  5. 2 System Overview
    1. 2.1 Charging Case
      1. 2.1.1 BQ25619
      2. 2.1.2 TLV62568P
      3. 2.1.3 TPS22910A
      4. 2.1.4 TS5A12301E
      5. 2.1.5 MCU
    2. 2.2 Earbuds
      1. 2.2.1 BQ25155
      2. 2.2.2 TPS22910A
      3. 2.2.3 TS5A12301E
      4. 2.2.4 BT/SOC
  6. 3 Charging Case Algorithm Implementation
    1. 3.1 Initialization and Main Code
    2. 3.2 UART Interrupt and Output Voltage Adjustment
  7. 4 Earbud Algorithm Implementation
    1. 4.1 Initialization and Main Code
    2. 4.2 Interrupt and Transmission
  8. 5 Test Procedure
  9. 6 Test Results
    1. 6.1 Dynamic Voltage Adjustment
    2. 6.2 BQ25619 with 4.6-V Output
    3. 6.3 Standard Boost with 5V Output
  10. 7 Summary
  11. 8 Schematics
  12. 9 PCB Layout
  13. 10Software
    1. 10.1 Charging Case main.c
    2. 10.2 Earbuds main.c
  14. 11Revision History

3.2 UART Interrupt and Output Voltage Adjustment

When the UART RX interrupt is triggered, the interrupt will check if a charge complete byte has been received. If the charge has been completed, the MCU will set the case to low power mode and wait for a system state change. If a charge complete byte was not received, the MCU will store the received earbud battery voltage and continue the interrupt.

The PWM duty cycle will then be calculated with the newly received earbud battery voltage. This calculation is based on resistor divider and filter that are connected to the feedback pin of the TLV62568P. An excel calculator, Design Tool for Output Voltage Adjustment using a DAC, for these values can be found here.

Equation 1. P W M D u t y   =   ( 7 . 607 - ( 1 . 434 × ( V b a t   +   0 . 33 ) ) ) × 40 3 . 3

The calculation needs to be adjusted to produce an output voltage of approximately 200 mV above the current earbud battery voltage to account for the headroom needed by the earbud battery charger. After this calculation is done, the PWM duty cycle value is qualified to prevent a voltage under 3 V or over 4.5 V from being applied. If the value is found to be good, the MCU will adjust the PWM duty cycle and the output voltage will follow.

To re-enter charging mode, the analog switch is toggled off and the load switch is re-activated. The interrupt will then terminate.

GUID-DB5DBED9-8114-48EF-A46A-DDA1AFDF4B9E-low.svg Figure 3-2 PWM Algorithm