SLLSET2 August 2017 TUSB8042


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Description (Continued)
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1Absolute Maximum Ratings
    2. 7.2ESD Ratings
    3. 7.3Recommended Operating Conditions
    4. 7.4Thermal Information
    5. 7.5Electrical Characteristics, 3.3-V I/O
    6. 7.6Timing Requirements, Power-Up
    7. 7.7Hub Input Supply Current
  8. Detailed Description
    1. 8.1Overview
    2. 8.2Functional Block Diagram
    3. 8.3Feature Description
      1. 8.3.1Battery Charging Features
      2. 8.3.2 USB Power Management
      3. 8.3.3One Time Programmable (OTP) Configuration
      4. 8.3.4Clock Generation
      5. 8.3.5Crystal Requirements
      6. 8.3.6Input Clock Requirements
      7. 8.3.7Power-Up and Reset
    4. 8.4Device Functional Modes
      1. 8.4.1External Configuration Interface
      2. 8.4.2I2C EEPROM Operation
      3. 8.4.3Port Configuration
      4. 8.4.4SMBus Slave Operation
    5. 8.5Register Maps
      1. 8.5.1 Configuration Registers
      2. 8.5.2 ROM Signature Register
      3. 8.5.3 Vendor ID LSB Register
      4. 8.5.4 Vendor ID MSB Register
      5. 8.5.5 Product ID LSB Register
      6. 8.5.6 Product ID MSB Register
      7. 8.5.7 Device Configuration Register
      8. 8.5.8 Battery Charging Support Register
      9. 8.5.9 Device Removable Configuration Register
      10. 8.5.10Port Used Configuration Register
      11. 8.5.11Device Configuration Register 2
      12. 8.5.12USB 2.0 Port Polarity Control Register
      13. 8.5.13UUID Registers
      14. 8.5.14Language ID LSB Register
      15. 8.5.15Language ID MSB Register
      16. 8.5.16Serial Number String Length Register
      17. 8.5.17Manufacturer String Length Register
      18. 8.5.18Product String Length Register
      19. 8.5.19Device Configuration Register 3
      20. 8.5.20USB 2.0 Only Port Register
      21. 8.5.21Serial Number String Registers
      22. 8.5.22Manufacturer String Registers
      23. 8.5.23Product String Registers
      24. 8.5.24Additional Feature Configuration Register
      25. 8.5.25SMBus Device Status and Command Register
  9. Applications and Implementation
    1. 9.1Application Information
    2. 9.2Typical Application
      1. 9.2.1Discrete USB Hub Product
        1. Requirements
        2. Design Procedure
          1. Port Implementation
          2. Port 1 Implementation
          3. Port 2 Implementation
          4. Port 3 Implementation
          5. Port 4 Implementation
          6. Power Switch Implementation
          7., Reset, and Misc
          8. Power Implementation
        3. Curves
  10. 10Power Supply Recommendations
    1. 10.1TUSB8042 Power Supply
    2. 10.2Downstream Port Power
    3. 10.3Ground
  11. 11Layout
    1. 11.1Layout Guidelines
      1. 11.1.1Placement
      2. 11.1.2Package Specific
      3. 11.1.3Differential Pairs
    2. 11.2Layout Examples
      1. 11.2.1Upstream Port
      2. 11.2.2Downstream Port
  12. 12Device and Documentation Support
    1. 12.1Receiving Notification of Documentation Updates
    2. 12.2Community Resources
    3. 12.3Trademarks
    4. 12.4Electrostatic Discharge Caution
    5. 12.5Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Power Supply Recommendations

TUSB8042 Power Supply

VDD should be implemented as a single power plane, as should VDD33.

  • The VDD pins of the TUSB8042 supply 1.1 V (nominal) power to the core of the TUSB8042. This power rail can be isolated from all other power rails by a ferrite bead to reduce noise.
  • The DC resistance of the ferrite bead on the core power rail can affect the voltage provided to the device due to the high current draw on the power rail. The output of the core voltage regulator may need to be adjusted to account for this or a ferrite bead with low DC resistance (less than 0.05 Ω) can be selected.
  • The VDD33 pins of the TUSB8042 supply 3.3 V power rail to the I/O of the TUSB8042. This power rail can be isolated from all other power rails by a ferrite bead to reduce noise.
  • All power rails require a 10 µF capacitor or 1 µF capacitors for stability and noise immunity. These bulk capacitors can be placed anywhere on the power rail. The smaller decoupling capacitors should be placed as close to the TUSB8042 power pins as possible with an optimal grouping of two of differing values per pin.

Downstream Port Power

  • The downstream port power, VBUS, must be supplied by a source capable of supplying 5V and up to 900 mA per port. Downstream port power switches can be controlled by the TUSB8042 signals. It is also possible to leave the downstream port power always enabled.
  • A large bulk low-ESR capacitor of 22 µF or larger is required on each downstream port’s VBUS to limit in-rush current.
  • The ferrite beads on the VBUS pins of the downstream USB port connections are recommended for both ESD and EMI reasons. A 0.1µF capacitor on the USB connector side of the ferrite provides a low impedance path to ground for fast rise time ESD current that might have coupled onto the VBUS trace from the cable.


It is recommended that only one board ground plane be used in the design. This provides the best image plane for signal traces running above the plane. The thermal pad of the TUSB8042 and any of the voltage regulators should be connected to this plane with vias. An earth or chassis ground is implemented only near the USB port connectors on a different plane for EMI and ESD purposes.