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TUSB2036 SUSPEND pin

Jon Sonnenberg
Prodigy 40 points
Other Parts Discussed in Thread: TUSB2036

I have a circuit with the TUSB2036 IC.  I am able to connect to a computer and the computer recognizes the device as a generic USB hub.  My problem is that after 7.6 seconds, the suspend pin goes high and the crystal stops oscillating.  When I look through the datasheet and other post on the forum, most of the solution seems to be the timing of the reset circuit.  I am using a 150k resistor with a 1uF cap.  What possibilities would make this shut off after 7+ seconds of operation? 

  • 0
    TI__Guru* 76130 points

    Hello,

    The power-on reset timing should be from 1ms to 4ms (recommended), your RC circuit will give a power-on reset of about 150ms, you have to change this, by USB spec, a device should be able to respond to the host within 100ms after power is applied.

    A USB device should enter in suspend mode when there is more than 3ms of no bus activity, it should exit SUSPEND mode with a general reset.

    If you want the hub to never go into SUSPEND mode, connect the 1.5K pull-up from DP to 3.3V instead of connecting from DP to DP0PUR.

    Regards.

  • 0 in reply to Elias Villegas M.
    Prodigy 40 points

    Thanks.  I will try this.  Unfortunately, I was sharing the reset timer with other devices so I may just have to set up another RC reset circuit for this device.  What are the actual limits for this device not to enter the suspend mode?  Are 1ms and 4ms the hard limits? 

  • 0 in reply to Jon Sonnenberg
    Prodigy 40 points

    One of the things that I find puzzling is that I have an earlier prototype of this circuit with the same device and same reset circuit.  It does not go into the suspend mode. 

  • 0 in reply to Jon Sonnenberg
    TI__Guru* 76130 points

    The limit for the power-on reset timing is the specified on the datasheet, the 1ms to 4ms is just a recommendation based on the 100ms max limit by USB spec and the time it takes to the hub to configure itself, you can relax this 1-4ms limit based on your testing.

    Regards.

  • 0 in reply to Elias Villegas M.
    Prodigy 40 points

    I am still having the IC turn off after several seconds.  I even pulled DP up to 3.3V instead of DP0PUR as you stated and it still shuts down.  What could be causing this failure?