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TM4C1231H6PM: GPIO setting

zhimin xia
Prodigy 230 points
Part Number: TM4C1231H6PM

we use TM4C1231H6PMI7 in a gate control product, we get some failure samples returned by end customer, we found some output IO which will output with 3.3V has dropped to around 1.0V. if we reset the system, these GPIO can recover to 3.3V,

GPIO setting is setting to pull-up(GPIOPUR set to 1), output IO, but not set GPIO to open drain(GPIOODR is in default 0), we also find if we add a noise to these GPIOs, the failure will happen in these setting. 

we doubt about the GPIO setting, so we change the GPIO to open drain(GPIOODR set 1), and keep rest setting, the failure will not happen.

Can you help support below question?--Thank you.

1. if we use pull up setttng in output GPIO, is it necessary to set the output port to open drain? if we do not set to open drain, is it possible to have the same failure?

2. why these failure will happen? is it related with TI's errata file" GPIO #10" ?  if so, if we set the output to open drain, can it solve the problem?

  • 0
    TI__Guru 72500 points
    My guess is that this may be related to high currents turning on an internal parasitic SCR. The short high currents can be caused by driving a low impedance load or injected noise. If the problem is current out of the device, then switching to open drain mode will eliminate the problem as the current will be limited by the internal pullup resistor. That would work if the rise time of the signal is fast enough. The best solution however, would be to increase the load resistance by adding a current limiting resistor in series with the output pin.
  • 0 in reply to Bob Crosby
    Guru 117855 points

    Along w/Vendor Bob's good direction - would it not always prove 'preferable' to ... 'BUFFER the MCU's GPIO from any/all 'potential' Output stress?'

    Our firm ALWAYS imposes some form of 'Buffer-Driver" between the Power Stage (even the intermediate, Power (Pre-Amp) Stage) and MCU.

    Indeed - such results in a 'cost/size ADDER'  ...   Yet what is the cost of a System Failure - Travel to Repair - and the (likely) 'Loss of Reputation?'

    The MCU IS an intelligent device - and its "Conversion to Beast of Burden" - even when operated in 'Open Drain' - invites 'issues!'      (Especially so w/the passage of time - and the (expected) increase in 'Power Switched, Transient Spikes!'