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AMC7836EVM: Faulty SDM-USB-DIG?

Lucas Berezy
Prodigy 90 points
Part Number: AMC7836EVM

Hello,

I have two AC7836EVM kits. One of them is working just fine, the other appears to have problems that I've traced back to the supplied SDM-USB-DIG dongle.

I've tried using the dongle from kit A with the board from kit B and everything works as expected. Using the dongle from kit B with either board A or board B results in unexpected behaviour. I'm using the supplied evaluation GUI as well as a serial terminal to manually send command strings to the dongles. Drivers are installed.


Both dongles enumerate as expected and I can connect to the the exposed virtual com ports. When I have the problem dongle connected to a board either board, sending the sequence "04000003GG0C03\r\n" (which would usually initialise the power for the DUT and result in the 3 leds on the EVM board turning on) results in the dongle latching up (all J3 pins are 3V3 high and both leds on the dongle are on, as well as the USB device dropping off the bus).

I can open a serial terminal and send commands to the dongle (with echo back) when the dongle isn't attached to any board. I've only once been able to successfully send the aforementioned power up command once (other commands such as SPI transfers do not seem to cause latch up) and shortly after the dongle did latch up.

I feel the dongle may have been damaged in transit and is defective as it clearly doesn't work as expected compared to the other identical EVM kit I have. Are there any more tests I can do to help narrow down the issue or anyone I can contact for a replacement dongle?

  • 0
    Prodigy 90 points
    Is there anyone that can help with this issue?

    I've done a little bit more testing and have been able to consistently replicate the device latch up condition when giving the dongle commands that specifically change the output pin voltage compatibility levels.


    When issuing either of the following commands, the device latches up:

    04 00 00 01 GG (set 3V3 logic level mode)
    04 00 00 01 GH (set 5V logic level mode)

    however, when using the command 04 00 00 01 GI (set output logic level converter OFF), the device DOES NOT latch up.

    I've tried these same commands on another known-good dongle and the dongle behaves appropriately without latch up.


    Are these dongles available to either purchase individually or for individual replacement? I am reluctant to go through the ordeal of returning the entire kit just for the faulty dongle.
  • 0 in reply to Lucas Berezy
    TI__Genius 11750 points
    Howdy Lucas,

    I apologize for the late reply, actually just returning from holidays :) One thing to note is that special care must be taken when switching between voltages. An "OFF" command is generally sent when switching from one voltage value to another (3.3V to 5V, or 5V to 3.3V). If the "OFF" command is not sent, both voltages may be simultaneously active and damage the dongle. This "OFF" command can be found if you were to sniff the line when exiting the GUI. When the GUI [x] button is pressed, the GUI exits and this "OFF" command is sent.

    We can take this conversation offline, in which I can ask for your address for a replacement dongle.

    Best Regards,
    Matt
  • 0 in reply to Matthew Sauceda
    Prodigy 130 points

    Thanks for getting in touch and thank you for that bit of information. The dongles have over ever been exposed to switching between off and 3V3 in use and switching between voltages during testing has been from the off state.