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TUSB2036 DP0PUR Question

Scott Burton
Prodigy 230 points
Other Parts Discussed in Thread: TUSB2036, TINA-TI

Hello Again Forum,

Thanks very much for all your help with my previous questions on this device. Now I need your assistance again in understanding the purpose of the DP0PUR output so I ensure I'm using it correctly on my design.

I understand from the TUSB2036 datasheet, and the USB2.0 standard section 7.1.5, that D+ must be pulled high through a 1.5kohm resistor to indicate a full-speed device. But, from the TUSB2036 datasheet, whenever a system reset  or logic level change on BUSPWR occurs ... "DP0PUR output goes to inactive low until the internal counter reaches a 3ms time period. After the counter expires, DP0PUR is driven to the VCC (3.3V) level ... until the next system reset event ..."

1/  From this I gather that DP0PUR is normally high. Is this correct?

2/  Why, when a logic level change occurs on reset or BUSPWR, does the TUSB2036 toggle DP0PUR and pull D+ low for 3ms?

3/ Does the DP0PUR output actively pull both high and low, sourcing and sinking 4mA as per the TUSB2036 electrical characteristics table?

Finally, the USB2.0 standard indicates that "The voltage source on the pull-up resistor must be derived from or controlled by the power suupplied on the USB cable such that when VBUS is removed, the pull-up resistor does not supply current on the data line to which it is attached."

4/ I believe this is why the TI application schematics for the self-powered TUSB2036-based hub have this pull-up resistor gated by the 5V USB input feed: It is to avoid driving D+ current from the hub back into an unpowered host. Would this be correct?

I look forward to your responses.

Thank you!

Scott

 

  • 0
    TI__Guru 60870 points

     

    1/  From this I gather that DP0PUR is normally high. Is this correct?

    [JN] Yes, during normal operation DP0PUR is normally high.

    2/  Why, when a logic level change occurs on reset or BUSPWR, does the TUSB2036 toggle DP0PUR and pull D+ low for 3ms?

    [JN]  Removal of the pullup on DP indicates to the host that the TUSB2036 has been removed from the bus, which is the expected operation when there is a logic level change on reset or BUSPWR.

    3/ Does the DP0PUR output actively pull both high and low, sourcing and sinking 4mA as per the TUSB2036 electrical characteristics table?

    [JN] DP0PUR actively pulls high only.

    Finally, the USB2.0 standard indicates that "The voltage source on the pull-up resistor must be derived from or controlled by the power suupplied on the USB cable such that when VBUS is removed, the pull-up resistor does not supply current on the data line to which it is attached."

    4/ I believe this is why the TI application schematics for the self-powered TUSB2036-based hub have this pull-up resistor gated by the 5V USB input feed: It is to avoid driving D+ current from the hub back into an unpowered host. Would this be correct?

    [JN] Yes.

    Regards,

    Julie Nirchi

  • 0 in reply to JMMN
    Prodigy 230 points

    Thank you very much Julie.Two follow-up questions for you please.

    5/ You indicate that DP0PUR pulls active high only. Unfortunately, the datasheet is very vague  on its behaviour in the opposite direction, indicating that "DP0PUR output goes to inactive low". I think its low state behaviour would be important in evaluating the operation of the transistor circuit shown in the reference designs. For example, TINA-TI shows that the impedance of DP0PUR to ground wound need to be less than 5k to meet the USB D+ VIL limit of 0.8V (USB2.0 Table 7-7).

    Could you tell me what the impedance and/or current sinking capability of DP0PUR is in its "inactive low" state?

    6/ The TUSB2036 datasheet indicates that "DP0PUR makes it much easier to implement an on-board bus/self-power dynamic-switching circuitry."

    If such switching functionality isn't required, can D+ be simply tied to 3.3V?

    Thanks very much in advance.

    Regards,

    Scott

    JMMN said:

     

    1/  From this I gather that DP0PUR is normally high. Is this correct?

    [JN] Yes, during normal operation DP0PUR is normally high.

    2/  Why, when a logic level change occurs on reset or BUSPWR, does the TUSB2036 toggle DP0PUR and pull D+ low for 3ms?

    [JN]  Removal of the pullup on DP indicates to the host that the TUSB2036 has been removed from the bus, which is the expected operation when there is a logic level change on reset or BUSPWR.

    3/ Does the DP0PUR output actively pull both high and low, sourcing and sinking 4mA as per the TUSB2036 electrical characteristics table?

    [JN] DP0PUR actively pulls high only.

    Finally, the USB2.0 standard indicates that "The voltage source on the pull-up resistor must be derived from or controlled by the power suupplied on the USB cable such that when VBUS is removed, the pull-up resistor does not supply current on the data line to which it is attached."

    4/ I believe this is why the TI application schematics for the self-powered TUSB2036-based hub have this pull-up resistor gated by the 5V USB input feed: It is to avoid driving D+ current from the hub back into an unpowered host. Would this be correct?

    [JN] Yes.

    Regards,

    Julie Nirchi

     

  • 0 in reply to Scott Burton
    TI__Guru 60870 points

    Scott,

     

    5) When the TUSB2036 does not have the pull-up enabled on the DP line it isn't "seen" by the USB host, so the USB connection is not active.    When DP0PUR is not active, the pullup resistor is not connected to the 3.3V rail, but it doesn't drive the DP line low.

     

    6) Yes, DP can have a 1.5K pull-up to 3.3V in lieu of DP0PUR if that is preferred.

     

    Julie