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X_PWRON should at least be delayed long enough for the device to arrive in the OFF state, so a power-up event is recognized properly. With R3 = 55k, the current delay is measured around ~4 ms using real components. It is recommended that R3 be increased even further to provide a safer delay margin. Replacing R3 with a 143k resistor, the delay was measured as ~10 ms. It is recommended to use a 143k resistor for R3.
Note that earlier versions of the AM57x SOM (PCM-057.A5 and earlier) populate C251 with a 1uF capacitor, which is connected between X_PWRON and ground. This capacitor will introduce further delay on the X_PWRON rise/fall time, potentially causing the board not to respond or boot as expected. The design was updated to populate C251 with a smaller 0.1uF capacitor, which results in an X_PWRON response similar to Figure 2. Consider this capacitor value when implementing this design with an older version of the SOM.