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TUSB2036 RESET Function

Scott Burton
Prodigy 230 points
Other Parts Discussed in Thread: TPS2553, TUSB2036, TPS3809, TPS2042, TUSB2046B

Hello Forum,

I hope someone can help me with a question regarding this device.

I'm doing a two-port design with the TUSB2036 and want to ensure that the two TPS2553 port protection devices are held disabled until the 5V power rail is present and stable. I don't want a heavy load on the 5V USB rail as it is ramping up to its regulated value.

To disable the TPS2553 I'm connecting its ENABLE pin to the PWRONn_b pin of the TUSB2036. Then I'm connecting the RESET_b pin of a TPS3809 voltage supervisor to the RESET_b pin of the TUSB2036. The supervisor will hold the RESET_b signal LOW for 200ms after the USB power rail reaches its regulated level.

My question is: What is the state of the PWRONn_b pins when the TUSB2036 is in RESET? Are they held HIGH until the TUSB2036 RESET_b is released HIGH?

I was also wondering about the interaction between the port protection device and the TUSB2036 in the event of a USB port power overload. In the reference design, when such an over-current condition occurs,  TPS2042 OCn_b output will toggle LOW and in so doing will pull the corresponding OVRCURn_b input LOW on the TUSB2036. As a result the PWRON_b output will toggle HIGH and disable the TPS2042. With the inter-dependence of these two ICs, does the TPS2042 output just cycle ON and OFF until the over-current condition is removed?

Any assistance with these questions would be much appreciated!

Scott

 

 

  • 0
    TI__Guru 60870 points

    Hi Scott,

    I'll need to verify this in the lab, but the PWRONz outputs are probably not actively driven high during reset.  How long do you plan on having the TUSB2036 held in reset?

    When the TUSB2036 sees one of the OVRCURz inputs driven low, it will disable the related PWRONz output and report the error condition to the host.  The port power will not be re-enabled until the host gets an updated status that the over current condition has been resolved and sets the port power.   Power management for over current is dictated by the USB host, not the TUSB2036.

    Regards,

    Julie Nirchi

  • 0 in reply to JMMN
    TI__Guru 60870 points

    Scott,

    I checked this out on the TUSB2046B which has similar PWRONz circuitry.  The PWRONz outputs are not enabled when the device is held in reset.

     

    Regards,

    Julie

  • 0 in reply to JMMN
    Prodigy 230 points

    Hi Julie,

    Thank you for your response!

    With the PWRONz outputs disabled when the TUSB2036 is held in reset I'll be able to use a PWRONz signal to keep the TPS2553 USB port power switch off until the voltage supervisor detects the USB power rail is present and stable. Excellent!

    Regarding the over current condition, though, I'm still a bit confused.

    In the TI TUSB2036 reference design, the TUSB2036 receives the over current indication from the TPS2042 USB power switch and, in turn, controls the state of that switch via the PWRONz signal.  As such, it seems to me that if a port of the TI TUSB2036 reference circuit were under a sustained over current condition, the TI TUSB2036 would actually cycle power to that port. I believe this would occur because, in response to the over current, the TPS2042 port power switch would toggle OVRCURz LOW resulting in the TUSB2036, in concert with the USB host, then toggling the associated PWRONz signal HIGH. This would disable the TPS2042 and, as a result, the over current condition would then effectively cease to exist. I assume OVRCURz would then toggle HIGH indicating that the over current condition had been resolved. In response to this the TUSB2036 and USB host would then toggle PWRONz LOW, thus re-enabling the TPS2042 into the still-present over current condition, and the cycle would repeat.

    I'm probably missing something here but I do want to ensure I'm using the PWRONz and OVRCURz signals correctly. Is my logic correct?

    Thanks!

    Scott

  • 0 in reply to Scott Burton
    TI__Guru 60870 points

    Scott,

    You are implementing the OVRCURz and PWRONz signals correctly, but you are assuming the TUSB2036 is smarter than it is.  The TUSB2036 will disable the PWRONz if it sees that OVRCURz is asserted, but it will not turn on PWRONz if OVRCURz is deasserted.  Only the USB host can force the TUSB2036 to assert PWRONz.  The host will not turn power back onto the port just because the over current condition is gone, there are a series of commands / checks that it goes through.  The host also flags a lot of error messages, so the overcurrent condition will be very apparent to an end user.

    Julie