TIDUEY1C November   2020  – June 2025 BQ25798

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 TPS25751D
      2. 2.3.2 BQ25798
    4. 2.4 System Design Theory
      1. 2.4.1 TPS25751D PD Controller
      2. 2.4.2 BQ25798 Battery Charger
      3. 2.4.3 TPS54531 Buck Converter
      4. 2.4.4 TLV75533 LDO
      5. 2.4.5 USB Type-C® Receptacle
      6. 2.4.6 Supporting Components for Programming
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware and Software Requirements
    2. 3.2 Application Customization Tool
    3. 3.3 Test Setup
    4. 3.4 Test Results
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 Altium Project
    2. 4.2 Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author
  12. 6Revision History

3.4 Test Results

On power-up, the TPS25751D configures the BQ25798 over I2C, configuring the charge current, pre-charge current, termination current, charge voltage, and control settings. These initial writes are based on the answers provided in the Web-based Application Customization Tool. When a 5V sink PDO Contract is negotiated, the PD controller sets up the buck-boost battery charger BQ25798 for a VIN of 5V and charging the battery at1A based on this particular configuration.

TIDA-050047 Power On Reset (POR) CommandsFigure 3-8 Power On Reset (POR) Commands
TIDA-050047 Example of a 5V Sink Contract Charging a BatteryFigure 3-9 Example of a 5V Sink Contract Charging a Battery
TIDA-050047 20V Sink Charging at 1AFigure 3-10 20V Sink Charging at 1A

Similarly, when a 20V sink PDO contract is negotiated, the same behavior can be seen where the PD controller sets up VIN at 20V this time, while maintaining charging at 1A.

TIDA-050047 Sourcing 5V With BQ25798 in OTG ModeFigure 3-11 Sourcing 5V With BQ25798 in OTG Mode

When the TPS25751D negotiates a source PDO contract, the device configures the BQ25798 to operate in OTG mode so that the battery can source the power needed for the port partner. In this case, the BQ25798 needs to boost up the battery voltage up to 5V to source power to the other device.

TIDA-050047 Sourcing 20V With BQ25798 in OTG ModeFigure 3-12 Sourcing 20V With BQ25798 in OTG Mode

The same behavior can be observed when the port partner and the TPS25751D negotiate a 20V contract using the TPS25751D as a source.

One feature of USB Type-C PD is the ability to perform power role swaps. Figure 3-13 shows a power role swap from source to sink.

TIDA-050047 Power Role Swap from 20V Source to 20V SinkFigure 3-13 Power Role Swap from 20V Source to 20V Sink

TIDA-050047 is initially sourcing 20V on VBUS. A power role swap is initiated, and VBUS transitions to 0V as the port stops sourcing. The far-end USB-C port becomes the new power source, and a 20V PD contract is negotiated, with TIDA-050047 now acting as the power sink. Once the power role swap has successfully completed, the TPS25751D configures the BQ25798 for charging mode.

Similarly, Figure 3-14 shows a power role swap from sink to source can occur.

TIDA-050047 Power Role Swap from 20V Sink to 20V SourceFigure 3-14 Power Role Swap from 20V Sink to 20V Source