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Does the CPDM have USB short circuit protection?

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  • Does the CPDM have USB short circuit protection?

    Today, we found our PDM failed and was completely unable to provide power to USB ports. Quick inspection with a voltmeter showed a very odd voltage of 0.35 V across the USB port's 5V and GND pins when the PDM was powered. Additionally, when we inspected the internals of our PDM, we found one IC (labeled U1) with a large gash near one of its leads. it appears to have been caused by a catastrophic overcurrent (as per archimedespi's suggestion that the die physically exploded or expanded). Due to the damage, we're unable to determine what the part number is to look up a datasheet, so we don't know exactly what it does.

    I have a few questions as a result:

    * What is the part number or function of the IC labeled U1 on the PDM board?
    * What fault conditions will cause an overcurrent on it?
    * Will a USB short circuit of 5V to ground be handled by an overcurrent protection mechanism of any sort?

    I have a suspicion that the legacy module we have could be related to this. We're finding that it's dropping out and also operating intermittently. Although I don't have exact records, the only interaction since both the legacy and PDM were both working was physically attaching it using mounting screws to TETRIX. This raises a few additional questions: Could the legacy module plausibly intermittently short 5V to ground without suffering catastrophic damage like in the PDM? We've found that the LED in it tends to flicker during operation, with it connected straight to the phone.

    In this configuration (no PDM, straight connection) I have a strong hunch that overcurrent protection is triggering, because when we lose the legacy module, we need to disconnect the OTG cable at the PHONE side and NOT the legacy side. I am thinking that this releases the OTG port's ID pin and "resets" the USB controller causing it to provide power again. I'll have to check on whether after a failure, if we plug a different device into that cable, it gets power or not. I didn't get a chance to do that today.

    if someone could shed some light on these questions it would be much appreciated. Thanks!
    FTC6460 mentor (software+computer vision+electronics), FPGA enthusiast. In favor of allowing custom electronics on FTC bots.
    Co-founder of ##ftc live chat for FTC programming--currently you may need to join and wait some time for help--volunteer basis only.

  • #2
    Originally posted by hexafraction View Post
    Today, we found our PDM failed and was completely unable to provide power to USB ports. Quick inspection with a voltmeter showed a very odd voltage of 0.35 V across the USB port's 5V and GND pins when the PDM was powered. Additionally, when we inspected the internals of our PDM, we found one IC (labeled U1) with a large gash near one of its leads. it appears to have been caused by a catastrophic overcurrent (as per archimedespi's suggestion that the die physically exploded or expanded). Due to the damage, we're unable to determine what the part number is to look up a datasheet, so we don't know exactly what it does.

    I have a few questions as a result:

    * What is the part number or function of the IC labeled U1 on the PDM board?
    * What fault conditions will cause an overcurrent on it?
    * Will a USB short circuit of 5V to ground be handled by an overcurrent protection mechanism of any sort?

    I have a suspicion that the legacy module we have could be related to this. We're finding that it's dropping out and also operating intermittently. Although I don't have exact records, the only interaction since both the legacy and PDM were both working was physically attaching it using mounting screws to TETRIX. This raises a few additional questions: Could the legacy module plausibly intermittently short 5V to ground without suffering catastrophic damage like in the PDM? We've found that the LED in it tends to flicker during operation, with it connected straight to the phone.

    In this configuration (no PDM, straight connection) I have a strong hunch that overcurrent protection is triggering, because when we lose the legacy module, we need to disconnect the OTG cable at the PHONE side and NOT the legacy side. I am thinking that this releases the OTG port's ID pin and "resets" the USB controller causing it to provide power again. I'll have to check on whether after a failure, if we plug a different device into that cable, it gets power or not. I didn't get a chance to do that today.

    if someone could shed some light on these questions it would be much appreciated. Thanks!
    Question... were you using the legacy module to run Legacy Motor controllers, or just sensors?

    Phil.

    Comment


    • #3
      Originally posted by Philbot View Post
      Question... were you using the legacy module to run Legacy Motor controllers, or just sensors?

      Phil.
      The module was connected to four motor controllers (which were not behaving erratically in any way) and two servo controllers (which were also working fine before). No sensors were attached. The controllers were powered from the PDM, and the PDM is still distributing power. Neither the battery nor the PDM fuse blew.

      I'll look for an NXT and our motor controller testing routine for the time being.
      FTC6460 mentor (software+computer vision+electronics), FPGA enthusiast. In favor of allowing custom electronics on FTC bots.
      Co-founder of ##ftc live chat for FTC programming--currently you may need to join and wait some time for help--volunteer basis only.

      Comment


      • #4
        Originally posted by hexafraction View Post
        Today, we found our PDM failed and was completely unable to provide power to USB ports. Quick inspection with a voltmeter showed a very odd voltage of 0.35 V across the USB port's 5V and GND pins when the PDM was powered. Additionally, when we inspected the internals of our PDM, we found one IC (labeled U1) with a large gash near one of its leads. it appears to have been caused by a catastrophic overcurrent (as per archimedespi's suggestion that the die physically exploded or expanded). Due to the damage, we're unable to determine what the part number is to look up a datasheet, so we don't know exactly what it does.

        I have a few questions as a result:

        * What is the part number or function of the IC labeled U1 on the PDM board?
        * What fault conditions will cause an overcurrent on it?
        * Will a USB short circuit of 5V to ground be handled by an overcurrent protection mechanism of any sort?

        I have a suspicion that the legacy module we have could be related to this. We're finding that it's dropping out and also operating intermittently. Although I don't have exact records, the only interaction since both the legacy and PDM were both working was physically attaching it using mounting screws to TETRIX. This raises a few additional questions: Could the legacy module plausibly intermittently short 5V to ground without suffering catastrophic damage like in the PDM? We've found that the LED in it tends to flicker during operation, with it connected straight to the phone.

        In this configuration (no PDM, straight connection) I have a strong hunch that overcurrent protection is triggering, because when we lose the legacy module, we need to disconnect the OTG cable at the PHONE side and NOT the legacy side. I am thinking that this releases the OTG port's ID pin and "resets" the USB controller causing it to provide power again. I'll have to check on whether after a failure, if we plug a different device into that cable, it gets power or not. I didn't get a chance to do that today.

        if someone could shed some light on these questions it would be much appreciated. Thanks!
        I don't have a module at hand to look at the PCB for a label, but we've had two PDM's fail at the same location, which was a small square IC. Both times we were asked by MR if we had somehow reversed the polarity on the battery, which was not the case. I would really like to see some kind of statement addressing the HW issues comprehensively, what is known vs. what is speculation. Candidly.

        Comment


        • #5
          Originally posted by Robert Van Hoose View Post
          I don't have a module at hand to look at the PCB for a label, but we've had two PDM's fail at the same location, which was a small square IC. Both times we were asked by MR if we had somehow reversed the polarity on the battery, which was not the case. I would really like to see some kind of statement addressing the HW issues comprehensively, what is known vs. what is speculation. Candidly.
          We also did not reverse the battery polarity to the best of my knowledge. I obviously cannot keep my eyes glued to our team's PDM so I can't say for sure though, although we don't have any batteries with modified connectors. However, I believe that reversed battery should be something protected at the input, or at least documented in a reasonable datasheet that includes info such as max electrical ratings, typical operation, etc.
          FTC6460 mentor (software+computer vision+electronics), FPGA enthusiast. In favor of allowing custom electronics on FTC bots.
          Co-founder of ##ftc live chat for FTC programming--currently you may need to join and wait some time for help--volunteer basis only.

          Comment


          • #6
            Originally posted by hexafraction View Post
            * What is the part number or function of the IC labeled U1 on the PDM board?
            * What fault conditions will cause an overcurrent on it?
            * Will a USB short circuit of 5V to ground be handled by an overcurrent protection mechanism of any sort?

            U1 appears to be a TI TPS5450 buck regulator, or some equivalent (it might not be made by TI). TI's data sheet is here:

            http://www.ti.com/lit/ds/symlink/tps5450.pdf

            This is the device that takes the battery input and generates the 5V output. The large inductors (L1, L2), capacitors, and the diode (D2) are on the output side of that. Best guess that R3 and R4 are the resistors that set the output voltage.

            This regulator, like many similar ones, does have overcurrent and thermal protection. I guess the switching transistor (Typically a FET) is inside the TPS5450, and that's probably what exploded.

            I don't see any evidence on the PDM that there is individual overcurrent protection for the USB ports. In fact, there are no signals connected to the USB chip's power power output controls (and no transistors near the ports).

            If 12V from the battery somehow made it onto the USB power input (so 12V fed _into_ the output of the regulator), bad things could definitely happen. The regulator would be very unhappy, I don't know enough about switching regulators to know for sure, but it can't be good.
            Mitch Lichtenberg
            Technical Mentor, Saratoga High School Mechanical Science and Engineering Team (M-SET)
            FRC 649
            FTC 6165, 7641, 7390

            Comment


            • #7
              Originally posted by hexafraction View Post
              We also did not reverse the battery polarity to the best of my knowledge. I obviously cannot keep my eyes glued to our team's PDM so I can't say for sure though, although we don't have any batteries with modified connectors. However, I believe that reversed battery should be something protected at the input, or at least documented in a reasonable datasheet that includes info such as max electrical ratings, typical operation, etc.
              Reversing the 12V input would be bad, by the way. That'd definitely break something. There's no reverse protection on the PDM, even though there appears to be some on the motor controller modules.

              /Mitch.
              Mitch Lichtenberg
              Technical Mentor, Saratoga High School Mechanical Science and Engineering Team (M-SET)
              FRC 649
              FTC 6165, 7641, 7390

              Comment


              • #8
                Thanks for that info; we have only used MR devices and previously known good Hitechnic controllers with it. I'll get the photos posted tomorrow and contact modernrobotics as well when I get a chance.
                FTC6460 mentor (software+computer vision+electronics), FPGA enthusiast. In favor of allowing custom electronics on FTC bots.
                Co-founder of ##ftc live chat for FTC programming--currently you may need to join and wait some time for help--volunteer basis only.

                Comment


                • #9
                  Originally posted by Mitch View Post
                  Reversing the 12V input would be bad, by the way. That'd definitely break something. There's no reverse protection on the PDM, even though there appears to be some on the motor controller modules.

                  /Mitch.
                  Yes, it is definitely bad. I've had two PDMs handed to me that have been blown up by various teams connecting the power backwards. Normally this isn't possible, but modifying the connectors to Powerpole makes this pretty easy to do if you're not paying attention. All you have to do is slide the black and red connectors together wrong and then plug that into something wired correctly.

                  If you do reverse the power, it does indeed immediately destroy the 5V regular chip as described earlier in this thread. The fuse will not blow.

                  There is no protection in the MR design against this. Bizarrely, there is a big diode AFTER the regulator, that protects the downstream components (everything on USB) but that's no help to the regulator itself.

                  I can see this will be a common occurrence, especially since FIRST is recommending a separate power switch between the battery and PDM which gives the kids more opportunity to get it backwards. Even using the standard Tetrix power switch will not be immune since adding that requires some manual wiring.

                  Comment


                  • #10
                    Would it be a good idea to connect a diode (or maybe an LED if we want to signify that everything should have power) to wire before the PDM to reduce the likelihood of blowing the PDM by reversing the polarity of the power given?

                    Comment


                    • #11
                      Originally posted by ViperMentor View Post
                      All you have to do is slide the black and red connectors together wrong and then plug that into something wired correctly.
                      This is a lot harder if you purchase the red and black connectors already bonded as a pair. Then you physically have to put the wrong color wires in the terminals.

                      Phil.

                      Comment


                      • #12
                        For such an unreliable (and seemingly unnecessary) device, <RE01b> doesn't seem to make much sense. it has less safety protections than other cheap USB hubs and doesn't do much useful stuff for us that we can't do with simple hubs and simple wiring distribution. Is there any chance that either the PDM would be modified to actually justify its requirement, or the requirement be lessened in light of the failures that we and other teams are having?
                        FTC6460 mentor (software+computer vision+electronics), FPGA enthusiast. In favor of allowing custom electronics on FTC bots.
                        Co-founder of ##ftc live chat for FTC programming--currently you may need to join and wait some time for help--volunteer basis only.

                        Comment

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