SLUSBS9A February 2014  – July 2014


  1. Features
  2. Applications
  3. Description
  4. Simplified Schematic
  5. Revision History
  6. Device Comparison Table
  7. Pin Configuration and Functions
  8. Specifications
    1. 8.1Absolute Maximum Ratings
    2. 8.2Handling Ratings
    3. 8.3Recommended Operating Conditions
    4. 8.4Thermal Information
    5. 8.5Electrical Characteristics
    6. 8.6Typical Characteristics
  9. Detailed Description
    1. 9.1Overview
    2. 9.2Functional Block Diagram
    3. 9.3Feature Description
      1. 9.3.1 Dynamic Rectifier Control
      2. 9.3.2 Dynamic Power Scaling
      3. 9.3.3 VO_REG and VIREG Calculations
      4. 9.3.4 RILIM Calculations
      5. 9.3.5 Adapter Enable Functionality
      6. 9.3.6 Turning Off the Transmitter
        1. End Power Transfer (EPT)
        2. EOC
      7. 9.3.7 CM_ILIM
      8. 9.3.8  PD_DET and TMEM
      9. 9.3.9 TS, Both WPC and PMA
      10. 9.3.10I2C Communication
      11. 9.3.11Input Overvoltage
    4. 9.4Device Functional Modes
    5. 9.5Register Maps
  10. 10Application and Implementation
    1. 10.1Application Information
    2. 10.2Typical Applications
      1. 10.2.1Dual Mode Design (WPC and PMA Compliant) Power Supply 5-V Output With 1-A Maximum Current
        1. Requirements
        2. Design Procedure
          1. Output Voltage Set Point
          2. Output and Rectifier Capacitors
          3. Maximum Output Current Set Point
          4. TERM Resistor
          5. Setting LPRB1 and LPRB2 Resistors
          6. I2C
          7. Communication Current Limit
          8. Receiver Coil
          9. Series and Parallel Resonant Capacitors
          10., Boot and Clamp Capacitors
        3. Curves
      2. 10.2.2bq51221 Embedded in System Board
      3. 10.2.3bq51221 Implemented in Back Cover
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1Layout Guidelines
    2. 12.2Layout Example
  13. 13Device and Documentation Support
    1. 13.1Trademarks
    2. 13.2Electrostatic Discharge Caution
    3. 13.3Glossary
  14. 14Mechanical, Packaging, and Orderable Information

1 Features

  • Robust 5-W Solution With 50% Lower Losses for Improved Thermals
    • Inductorless Receiver for Lowest Height Profile Solution
    • Adjustable Output Voltage (4.5 to 8 V) for Coil and Thermal Optimization
    • Fully Synchronous Rectifier With 96% Efficiency
    • 97% Efficient Post Regulator
    • 79% System Efficiency at 5 W
  • WPC v1.1 and PMA Compliant Communication
  • Patented Transmitter Pad Detect Function Improves User Experience
  • I2C Communication with Host

2 Applications

  • Smart Phones, Tablets, and Headsets
  • Wi-Fi Hotspots
  • Power Banks
  • Other Handheld Devices

3 Description

The bq51221 device is a fully contained wireless power receiver capable of operating in both the WPC and PMA protocols which allows a wireless power system to work with both WPC and PMA inductive charging standards. The bq51221 device provides a single device power conversion (rectification and regulation) as well as the digital control and communication for both standards. It also has autonomous detection of protocol and requires no additional active devices. The bq51221 device complies with the WPC v1.1 and PMA communication protocol. Together with the WPC or a PMA primary-side controller, the bq51221 device enables a complete wireless power transfer system for a wireless power supply solution. The receiver allows for synchronous rectification, regulation and control and communication to all exist in a market-leading form factor, efficiency, and solution size.

Device Information(1)

bq51221YFP (42)3.586 mm × 2.874 mm
  1. For all available packages, see the orderable addendum at the end of the data sheet.

4 Simplified Schematic


bq51221 Dual Mode Efficiency 5-V Out