[FAQ] AM625 / AM623 / AM620-Q1 / AM625-Q1 / AM625SIP: MCU_PORz input slew rate

There can be long-term reliability issues associate with the input buffer if the applied signal spends too much time in the voltage region between VIHSS and VILSS. The maximum transition time allowed is 1000ns. I recommend driving the reset input with a push-pull buffer that produces a signal transition rate that is faster than 5ns to eliminate the risk of noise coupling into the signal as it transitions through the input buffer switching threshold.

A 22 pF glitch filter is recommended at the input of MCU_PORz

 another important point about the MCU_PORz input slew rate. It is very easy for noise to couple on slow rising signals such that it creates non-monotonic transitions. Your MCU_PORz reset source needs to be monotonic to prevent the chance of creating glitches on internal reset as it transitions through the input buffer switching threshold. A faster slew rate on the MCU_PORz will increase your system noise immunity. The min slew rate defined in the AM625 datasheet is acceptable to the AM625 device but may not be acceptable for your system noise immunity requirements.

Please keep in mind the AM62x device requires the MCU_PORz input to have a maximum rise/fall time of 1000ns. This may be difficult to achieve with a pull-up on a signal sourced from an open-drain output buffer. You may need to buffer the open-drain signal with a push-pull buffer that has hysteresis on its input to ensure the AM62x device never receives a short reset pulse that violates the minimum pulse duration defined in the "MCU_PORz Timing Requirements" table. For example, it may be possible for noise to couple on the slow rising open-drain signal just as it crosses the input buffer threshold which could cause a short glitch on the reset signal. Normal device operation could be compromised if this occurs.

See the "Input Slew Rate" parameter in the "Fail-Safe Reset (FS RESET) Electrical Characteristics" table.

The MCU_PORz input is the only input on the AM62x device that is fail-safe and 3.3v tolerant. Therefore, you can pull the MCU_PORz signal to 1.8V or 3.3V.

See the "Steady-state max voltage at all fail-safe IO pins" parameter for MCU_PORz in the "Absolute Maximum Ratings" table.

Regards,
Paul