SLUA748A December   2015  – April 2016 BQ25120 , BQ51003 , TPS61046 , TPS61240 , TPS62743

 

  1.   Trademarks
  2.   Power Management Reference Design for a Wearable Device with Wireless Charging Using the bq51003 and bq25120
    1. 1 Wearable Power Design
      1. 1.1 Wireless Charging Input
      2. 1.2 Battery Charger, MCU, Radio, and Sensor Power
      3. 1.3 Second Buck Output for MCU, Radio or Sensor
    2. 2 PMOLED Display Power Design
    3. 3 Heart Rate Monitor or e-Ink Power Design
    4. 4 Layout Guidelines for Wearable Design
      1. 4.1 Wireless Receiver (bq51003)
      2. 4.2 Linear Charger (bq25120)
      3. 4.3 Buck Converter (TPS62743/6)
      4. 4.4 Boost Converters (TPS61046 and TPS61240)
      5. 4.5 General Considerations
    5. 5 References
  3. AExperimental Results
    1. A.1 Experimental Results
  4.   Revision History

1.3 Second Buck Output for MCU, Radio or Sensor

While the bq25120 integrates a single, ultra-low power step-down converter for one rail, some systems, such as an MCU, radio or sensor, need a second high-efficiency rail with a different voltage. For these sub-systems, a discrete ultra-low power step-down converter with similar performance to the bq25120 converter is required. PMP11311 includes a TPS62743 which contains a user-selectable choice of 8 different output voltages from 1.2 V to 3.3 V.

If the more common 1.2-V or 1.8-V rail is needed, then the pin-to-pin compatible TPS62746 may be used instead to obtain the extra feature of an input voltage switch (VIN switch). The VIN switch allows a no-leakage measurement of the battery voltage by the host MCU. More details about the TPS62743 and TPS62746 and their implementation are found in the data sheets in the references. Either device requires a total solution size of less than 10 mm2.

schematic_second_buck_slua748.gifFigure 5. Schematic of Second Buck for MCU, Radio or Sensor Power