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TSB81BA3E based repeater to repeater start-up problem

Mitchell Kary
Intellectual 630 points
Other Parts Discussed in Thread: TSB81BA3E

Hello,

I have system that includes two repeater boards connected as part of a system, both of which using the TSB81BA3E phy.I can confirm that they both adhere to the TI recommended termination networks in the data sheet.

If the first repeater is always powered and I then cycle power on the second repeater (as might happen in my system initially) while scoping the TPB pins, I observe that the TPB pair starts toning and then turns off and is pulled to 1.86V.

Cycling power on the second repeater does not change the state of these TPB pins (other than being pulled up to 1.86V). If I remove the 1394 connector from while observing these pins (with the second repeater powered or un-powered) they start toning again as soon as the plug is pulled.

Its obviously a power-up sequencing issue, but I don't quite understand what mechanism would cause the TSB81BA3E to disable toning and tri-state the TPB outputs. I also don't understand why disconnecting the now tristated TPB pair from the other TPA termination restores TPB operation.

I would appreciate any information you could provide on what would cause this behaviour in the PHY so I can work backwards to come up with a system cause and solution.

Thanks,

Mitch

  • 0
    TI__Guru* 76130 points

    Hello,

    Can you provide your schematic?

    Are the two TSB81BA3E connected in parallel or are they connected to each other?

    Are you terminating the unused ports?

    What is the state of LPS?

    The 1.86V you are seeing on TPB is the TPBIAS of the other end of the 1394 interface, it is possible that the PHY is entering in low power mode, can you send a scope capture of the power-up sequence showing RESET#, Vcc and XI, you should follow the below power up sequence:

    "Power-up: 1.8V should ramp after the 3.3V supply reaches at least 2.5V. At no time should the 1.8V supply have a higher voltage than the 3.3V supply."

  • 0 in reply to Elias Villegas M.
    Intellectual 630 points

    Ellias,

    The connection schematic is pasted below.

    The unused ports of the repeater(s) not being used are just like the ones shown, but nothing is connected to them externally.

    LPS is held low by a resistor and I verified that it never changed state during the problem.

    So I did some experiments and have pasted pictures below. The summary is as follows:

    In my system, the two repeaters are connected by a 1394 cable which does NOT carry power or ground. The two repeaters are powered locally and the grounds on each are isolated from each other. I believe this to be the root of the problem as when I connect the two grounds together things work.

    Having said that, I was just trying to get some insight into why TPA of this PHY goes to 3.3V and TPB behaves as shown in the attached picture below after I attach the second (un-powered) repeater to the powered on. When I then apply power to the second repeater , the TBP of the first repeater goes to 1.86V (from the now biased TPA of the second repeater) as initially described in the previous post.

    Thanks,

    Mitch