• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 32 subscribers
  • Views 1405 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.

TUSB2036: DP0PUR and prolonged RESET

maxtch
Prodigy 60 points
Part Number: TUSB2036

In the datasheet a maximum RESET time of 1ms is specified. However for my specific design the system-wide POR signal is a bit longer than that. Will connecting the DP0PUR help that by delaying the pull up resistor?

  • 0
    TI__Mastermind 18655 points
    Hello maxtch,

    How long are you holding the reset in your system?

    For the RESET terminal, our TUSB2036 has RC circuit with a 15KOhm pull-up resistor and a 0.1uF capacitor. This circuit will hold the reset terminal low about 3 ms. This delay shouldn't be a problem with a standalone hub. There are concerns with using long resets in embedded systems because you don't want other portions of the USB system to time out.

    Regards
  • 0 in reply to Joel Jimenez0
    Prodigy 60 points

    Joel Jimenez0 said:
    Hello maxtch,

    How long are you holding the reset in your system?

    For the RESET terminal, our TUSB2036 has RC circuit with a 15KOhm pull-up resistor and a 0.1uF capacitor. This circuit will hold the reset terminal low about 3 ms. This delay shouldn't be a problem with a standalone hub. There are concerns with using long resets in embedded systems because you don't want other portions of the USB system to time out.

    Regards

    I need to hold the hub in RESET until the main MCU starts, since the main MCU's PLL is used to clock the hub. It can be somewhere around a few tens of milliseconds depending on how the final code turns into.

  • 0 in reply to maxtch
    TI__Mastermind 18655 points
    Hello maxtch,
    I suggest keeping the hub turned off until your MCU and code are completely initialized and then be able to follow the sequence as per the datasheet.
    The passive reset circuit is not a defined resistor/capacitor value because those values will vary depending on the length of time that the 3.3V rail takes to ramp up. I would recommend making sure that the reset input is held low (below Vil) for 1 ms after the 3.3V rail reaches 3.0V.
    The clock start requirement with regards to power on reset applies to cases where the clock is driven from another source or an oscillator that has to get enabled.
    Regards
  • 0 in reply to Joel Jimenez0
    Prodigy 60 points
    So I cannot leave the power on but RESET low? (As the MCU and hub can share power domain?) If I let power on, is there a maximum time before the MCU starts the clock and releases RESET? (The MCU in question is STM32F042, which starts at 8MHz and later switched to 48MHz clock.)
  • 0 in reply to maxtch
    TI__Mastermind 18655 points
    Since this is an embedded system application, we recommend you having a minimum of 100 µs to a maximum of 1 ms of reset timing after Vcc reaches its 90%. If the hub is held in reset for a longer period of time, it can fail to respond promptly to USB host signaling and not a complete enumeration.
    No there is not a maximum time. The only requirement is the minimun in the datasheet (60us).
    Regards