The USB transceiver on the test board failed, shorting or backfeeding 5V onto the USB data lines (D+ and/or D−), which caused electrical overstress to the host PC’s USB controller, resulting in complete system failure.
More info it is on a Teensy 4.1 and when the transceiver shorted out it fryed the PC along with it.
Where did the 5 volts come from? The Teensy doesn’t produce any voltage on it’s own to back feed.
I have buck convertors in my system that provide 5v to power the teensy and 3.3v for some logic.
This sounds like your circuitry might have been wonky - share a photo of your setup/wiring
How does this work? I apply a 5v and ground from another source, I removed the 5v supply from the USB cable so there is D+, D-, and Ground on the cable going to the Teensy and it still burns out the USB transceiver chip?
There is no other wiring or logic going into it just 5v from a power source no 5v from the computer with data lines and ground from the computer. What am I missing here for this to make the chip fail?
You’d need to separate GND too; see this page’s “Power” section
Power
USB Power
Normally Teensy is powered by your PC or USB hub, through a USB cable. The USB power arrives at the VUSB pin, which is connected VIN and powers the entire board.
VIN Pin
When USB power is not used, 5V power may be applied to the VIN pin. Because VIN & VUSB are connected, power should not be applied to VIN while a USB cable is used, to prevent the possibility of power flowing back into your computer. Alternately, a pair of pads on the bottom side may be cut apart, to separate VUSB from VIN, allowing power to be safely applied while USB is in use. (TODO: VUSB-VIN pads photo, right side)
3.3V Power
Teensy 4.1 has a voltage regulator which reduces the 5V VUSB / VIN power to 3.3V for use by the main processor and most other parts. Additional circuitry may be powered from the 3.3V pin. The recommended maximum for external 3.3V usage is 250mA. Teensy 4.1 is not meant to receive power on its 3.3V pin, but this can be done with special modificaton.
USB Host Hot Plugging
Power to USB devices connected on the USB host port is provided through a current limited switch and a large capacitor. The current limit lessens the disruption to Teensy’s power when a USB device is hot plugged and needs a sudden inrush current to charge up all its capacitors.
Power Consumption
When running at 600 MHz, Teensy 4.0 consumes approximately 100 mA current. Reducing CPU speed to 528 MHz or lower reduces power consumption.
Low Power Features
Snooze library (TODO: more info here…)
CPU Voltage Control
A DC-DC buck converter creates lower voltage needed for the CPU. Software can control this voltage, in 50 mV steps. At 600 MHz, the CPU runs on 1.25V. For 528 MHz and lower, 1.15V is used. At 24 MHz, the CPU runs on only 0.95 volts. When overclocking, higher voltages are automatically used.
VBAT
A 3 volt coin cell may be connected to VBAT & GND to allow the RTC to keep track of date / time while power is off. A CR2032 type battery is recommended, though other 3V coin cells may also be used.
On / Off Pin and Power Control
A special low power state which turns off the 3.3V power can be controlled by the On/Off pin. A pushbutton is meant to be connected between On/Off and GND. While running, holding the button for 4 seconds turns off power. Pressing for 0.5 seconds while power is off turns the 3.3V power back on and reboots the processor. If a coin cell is connected to BVAT, the power state is retained when main power is disconnected. Without VBAT, the power state always defaults to 3.3V power on, even if the On/Off button had been used to turn off 3.3V before main VIN/VUSB power was removed.
I am further testing power supplys that come into the board. But I know that I have to disable the 5v input from the PC if I choose to use the Vin thats why it is there. I need it to be powered all the time from that Vin heince the 5v power supply that I am using. Also my needs are to communicate to the PC via the USB for program information that I loaded on the Teensy. What is happening is that the USB transceiver is still burning out shorting out or open condition. I had one Teensy that shorted out the USB transceiver sending 5v down the Data line of the USB and killing 2 computers. Since everything is supposed to isolated how did that happen?
Mark, we have your E-mail in our system. We can continue this conversation over there.
I just sent you a reply.
1 - There’s no USB transceiver chip on the Teensy 4.1, USB goes straight into the microcontroller.
2 - Every computer I’ve seen in the last 25+ years has protection logic built into it’s USB ports that prevent damage from shorts to ground or back feeding 5 volts on any of the data or power lines from affecting the system. It’s part of the USB standard to do this.
3 - “Fancy” computers will even let you know theres a problem with a USB device and usually tell you what it is before disconnecting that port from the system. On “Dumb” comcomputers, the affected USB port just stopps working until you power cycle the machine.
How about you provide photos and schematics showing your setup, that way we might be able to figure out what happened and prevent it from happening again?
Hi Mark (@MLarson ),
I suggest checking the common mode voltage between your 5V power supply and your PC.
Plug in the power supply and turn it on. Likewise for your PC. Connect the Teensy to the PC only using your USB cable (D+ / D- / GND). Then measure the voltage between the power supply 0V / GND and the PC / Teensy 0V / GND. Measure both the DC voltage and the AC voltage - using a standard multimeter. If you see more than a volt or two, that may explain the failure.
On isolated power supplies, the 0V can float at a voltage higher than Earth initially. But that voltage difference collapses when you connect the two parts together. Importantly, ~zero current should flow when that happens. I suspect your buck converters maybe aren’t isolated - and significant current has flowed when you connected the two.
I hope this helps,
Paul
As it stands right now there is a issue going on with my buck convertor preventing it from fully connecting to the PC. I have tried a testing power supply at 5v going directly into the Teensy with no errors but when connecting it to my buck converter it is not happy. If I use a USB isolator before going into the computer it shows it as a unrecongized device but if i plug it straight into the PC then nothing shows up. I understand that the USB goes directly into the chip but there is something wierd going on with it. I have 1 board that does not connect to the PC via the USB but the LED flashes near the USB port on the board when I hit the reset button on the board. I have one good one left that I am trying to figure out what the issue is. The reason why I am not understanding what is happening is because I have built another project pretty close to the one I have made now and it works without any issues. Thats why I am here trying to understand what is going on especially when it fries 2 PCs. All I am doing now is trying to do now is getting it to work with my buck converter. The aother teeny that I have working uses the exact same thing with no issues and is being used heavily 45 hours a week. I just want to understand.