• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 33 subscribers
  • Views 322 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TUSB4020BI: TUSB4020BI with downstream power switching and overcurrent reporting. Without External EEPROM

Bojan Jovanovic
Prodigy 145 points
Part Number: TUSB4020BI

Hello there!

We want to use TUSB4020BI Hub in configuration with downstream power switching and overcurrent reporting, without external EEPROM. Our schematic looks like this:      TUSB4020BI_Hub.pdf

The board is manufactured but we have a hard time making the Hub work.

By following this TUSB4020BI Schematic Checklist document, it is clear that, for configuration with external EEPROM or no EEPROM, we should either connect a 4.7K pull-up resistor to SMBUSz pin (pin 22) or leave it floating. We have a pull-down there which means that the Hub will wait in programming mode (link1, link2). We can easily fix that issue and remove resistor R41 from the board leaving SMBUSz floating and using an internal pull-up resistor. This will put the Hub in I2C master mode.

The second issue we have, it seems, is around reset. We applied the same passive reset approach with 1uF capacitor connected to GRST_n (pin 11) and an internal pull-up resistor as we noticed is applied in TUSB4020BPHP Evaluation Module (pages 9 and 10 of this document).  Our power-on sequence is completely the same as in the case of TUSB4020BPHP Evaluation Module: VDD voltage (1.1V) is obtained from V33 voltage. This is not in accordance with the datasheet which says that VDD must be stable before V33 (Chapter 7.7).

How the Evaluation module is working fine with passive reset and V33 stable before VDD? If the Hub on our board is not working properly when we remove resistor R41 from the board, does it make sense we increase the value of 1uF capacitor connected to GRST_N pin (C22) in order to get a slower charge time and thus keep the Hub longer in reset state?

Thanks in advance for your time and efforts.

Sincerely,

Bojan.

  • 0
    TI__Guru 60870 points

    Hi Bojan,

    1.  Yes, if the hub is not being configured by a SMBUS host, then SMBUSz must be high or the hub waits to be configured.

    2.   As long as 3.3V and 1.1V are ramping together, there is no issue using the passive reset circuit. Since we were concerned about customer delaying the 1.1V ramp after
    the 3.3V ramp, the wording was added to the datasheet. The potential issue with 3.3V ramping before the 1.1V is that the passive reset circuit relies on the external
    capacitor and an internal pullup to 3.3V, if the 1.1V ramps well after the 3.3V ramp there is a chance the reset would end before the hub is fully powered.  A 1uF capacitor on GRSTz is fine for most applications, but if the power supply ramp time is long, you may need to increase it to 2 uF to meet the power on reset timing conditions.

    What occurs on the DP/DM lines of the upstream port of the hub when it is connected to a host?  Do you have a good thermal pad connection under the hub?  This is often the root cause of bring up issues.

    Please be aware that you are enabling battery charging on the downstream ports, but then limiting current to 500 mA.  Battery charging can draw up to 1.5A.  Also, although USB 2.0 devices should be limited to 500 mA, some draw more for short periods of time.

    Do you see anything reported on the host when the hub is connected?  Please check the voltage levels on USB_VBUS and USB_R1. 

    Regards,

    JMMN

  • 0 in reply to JMMN
    Prodigy 145 points

    Hello, .

    Removing R41 resolved the issue. Thank you very much for your assistance!

    Cheers,

    Bojan