Figure 1. PL Power Down Sequence Diagram
- Carrier asserts PWROFF_C2M_L (t0). Power sequencers immediately begin rolling back all power solutions.
- Upon first power supply not meeting the required stabilization requirements, all status signals and request signaling from the SOM is deasserted (t1)
- At VCCOEN_PL_M2C (t2) deassertion carrier turns off power to the VCCO supplies.
- Carrier remove SOM5V0 (t3).
- SOM5V0 does not have to be removed. However, the discharge of related power supplies and power up rules must be observed before PWROFF_C2M_L (t5) can be deasserted.
- (t4) is observed to be the same point as (t0) in the power up sequence.
- Rails discharge for up to 2 seconds (t5).
Important: It is a good design practice to delay the re-release of PWROFF_C2M_L for
more than 2 seconds. This is because full discharge of the SOM rails depends on many
factors including device temperature, temperature grade, and the performance/power
draw of the software and firmware being run on the SOM at the time of PWROFF_C2M_L
assertion. Failure to provide enough time for the system to discharge rails can
provide a locked state for the power sequencer. Rails powering up under the
incorrect order can cause the sequencer to halt power-up sequence for SOM
protection. The only resolution to this locked state is a complete power down of all
rails, including the main SOM 5.0 V input.