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TUSB8020B: Pin termination for unused signals

Ryotaro Fukui
Intellectual 2345 points
Part Number: TUSB8020B

Hello team,

How should I terminate pins for unused signals described below?;

Q1) Unused downstream port pin termination

USB_DP_DN2
USB_DM_DN2
USB_SSTXP_DN2
USB_SSTXM_DN2
USB_SSRXP_DN2
USB_SSRXM_DN2

Q2) Pin termination for other unused signals

USB_VBUS
PWRCTL1/BATEN1
OVERCUR1z
PWRCTL2/BATEN2
OVERCUR2z
SMBUSz/SS_DN2
PWRCTL_POL/SS_DN1
GANGED/SMBA2/HS_UP
FULLPWRMGMTz/SMBA1/SS_UP

Also we assumed signals below should be terminated like followings;

SCL/SMBCLK: left unconnected
SDA/SMBDAT: left unconnected

Please correct if my understanding was wrong.

Best Regards,
Ryotaro Fukui

  • 0
    TI__Guru 60870 points

    Hello Fukui-san,

    Leave the unused port unconnected:

    USB_DP_DN2: left unconnected
    USB_DM_DN2: left unconnected
    USB_SSTXP_DN2: left unconnected
    USB_SSTXM_DN2: left unconnected
    USB_SSRXP_DN2: left unconnected
    USB_SSRXM_DN2: left unconnected

    USB_VBUS - cannot be left unconnected, this is a detection input and must be used for normal operation.
    PWRCTL1/BATEN1: left unconnected
    OVERCUR1z - pullup (there is an internal pullup, but external pullup is recommended for noisy systems)
    PWRCTL2/BATEN2: left unconnected
    OVERCUR2z - pullup (there is an internal pullup, but external pullup is recommended for noisy systems)
    SMBUSz/SS_DN2: left unconnected
    PWRCTL_POL/SS_DN1: left unconnected
    GANGED/SMBA2/HS_UP: left unconnected
    FULLPWRMGMTz/SMBA1/SS_UP: left unconnected

    Yes, this is correct:

    SCL/SMBCLK: left unconnected
    SDA/SMBDAT: left unconnected

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Intellectual 2345 points

    Hello JMMM,

    Thank you for your response. I want to confirm about USB_VBUS.

    As you feedbacked, in datasheet "8.3.1 Battery Charging Features", describes there are functions that require VBUS input.

    But in our case, however, USB_VBUS is monitored by a separate IC and will not use the Battery function too. This IC will just be used as a simple repeater purpose.

    Is USB_VBUS connection still required for this case too?

    Best Regards,

    Ryotaro Fukui

  • 0 in reply to Ryotaro Fukui
    TI__Guru 60870 points

    Hello Fukui-san,

    Yes, the USB_VBUS is required by USB 2.0 / 3.0 specification to be used by hubs to determine the correct operational state.  USB_VBUS should be high whenever a powered host is connected to the upstream port of the hub.

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Intellectual 2345 points

    Hello JMMN,

    Thank you for your response. I understand that VBUS connection is required in this case too.

    But since its function is not used, is it possible to substitute a resistor of 90.9kΩ with near value like 100kΩ?
    When the VBUS voltage is 5V, the USB_VBUS should be 0.495V with 90.9kΩ, and should be 0.455V when changed to 100kΩ.

    90.9kΩ is difficult to obtain in this case, so I would like to make sure if other resister value is usable for USB_VBUS.

    Best Regards,

    Ryotaro Fukui

  • 0 in reply to Ryotaro Fukui
    TI__Guru 60870 points

    Hello Fukui-san,

    Yes, different resistor values can be used.  I would recommend using a smaller resistor than 100K (or changing both resistors) so that USB_VBUS is at 500 mV or higher range when it is on.  455 mV is close to the Vil value (~395 mV).

    Regards,

    JMMN