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

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • RGC|64
Orderable Information


Layout Guidelines


  1. 9.53K +/-1% resistor connected to pin USB_R1 should be placed as close as possible to the TUSB8042.
  2. A 0.1 µF should be placed as close as possible on each VDD and VDD33 power pin.
  3. The 100 nF capacitors on the SSTXP and SSTXM nets should be placed close to the USB connector (Type A, Type B, and so forth).
  4. The ESD and EMI protection devices (if used) should also be placed as close as possible to the USB connector.
  5. If a crystal is used, it must be placed as close as possible to the TUSB8042 XI and XO pins.
  6. Place voltage regulators as far away as possible from the TUSB8042, the crystal, and the differential pairs.
  7. In general, the large bulk capacitors associated with each power rail should be placed as close as possible to the voltage regulators.

Package Specific

  1. The TUSB8042 package has a 0.5-mm pin pitch.
  2. The TUSB8042 package has a 6.0-mm x 6.0-mm thermal pad. This thermal pad must be connected to ground through a system of vias.
  3. All vias under device, except for those connected to thermal pad, should be solder masked to avoid any potential issues with thermal pad layouts.

Differential Pairs

This section describes the layout recommendations for all the TUSB8042 differential pairs: USB_DP_XX, USB_DM_XX, USB_SSTXP_XX, USB_SSTXM_XX, USB_SSRXP_XX, and USB_SSRXM_XX.

  1. Must be designed with a differential impedance of 90 Ω ±10%.
  2. In order to minimize cross talk, it is recommended to keep high speed signals away from each other. Each pair should be separated by at least 5 times the signal trace width. Separating with ground as depicted in the layout example will also help minimize cross talk.
  3. Route all differential pairs on the same layer adjacent to a solid ground plane.
  4. Do not route differential pairs over any plane split.
  5. Adding test points will cause impedance discontinuity and will therefore negative impact signal performance. If test points are used, they should be placed in series and symmetrically. They must not be placed in a manner that causes stub on the differential pair.
  6. Avoid 90 degree turns in trace. The use of bends in differential traces should be kept to a minimum. When bends are used, the number of left and right bends should be as equal as possible and the angle of the bend should be ≥ 135 degrees. This will minimize any length mismatch causes by the bends and therefore minimize the impact bends have on EMI.
  7. Minimize the trace lengths of the differential pair traces. The maximum recommended trace length for SS differential pair signals and USB 2.0 differential pair signals is eight inches. Longer trace lengths require very careful routing to assure proper signal integrity.
  8. Match the etch lengths of the differential pair traces (i.e. DP and DM or SSRXP and SSRXM or SSTXP and SSTXM). There should be less than 5 mils difference between a SS differential pair signal and its complement. The USB 2.0 differential pairs should not exceed 50 mils relative trace length difference.
  9. The etch lengths of the differential pair groups do not need to match (i.e. the length of the SSRX pair to that of the SSTX pair), but all trace lengths should be minimized.
  10. Minimize the use of vias in the differential pair paths as much as possible. If this is not practical, make sure that the same via type and placement are used for both signals in a pair. Any vias used should be placed as close as possible to the TUSB8042 device.
  11. To ease routing, the polarity of the SS differential pairs can be swapped. This means that SSTXP can be routed to SSTXM or SSRXM can be routed to SSRXP.
  12. To ease routing of the USB2 DP and DM pair, the polarity of these pins can be swapped. If this is done, the appropriate Px_usb2pol register, where x = 0, 1, 2, 3, or 4, must be set.
  13. Do not place power fuses across the differential pair traces.

Layout Examples

Upstream Port

TUSB8042 upstream_layout_sllsee6.gif Figure 46. Example Routing of Upstream Port

Downstream Port

TUSB8042 downstream_layout_sllsee6.gif Figure 47. Example Routing of Downstream Port

The remaining three downstream ports routing can be similar to the example provided.