The PDS, or Power Distribution System, is the next step in the power supply system and is located on the ECU.
Its main goal is to regulate the battery voltage to a more usable 5 volt line, which all systems will be supplied from.
The PDS also houses the overall system watchdog. The full design of it is not yet decided upon, but the high level functionality is as follows: every 24h, the watchdog will shutdown both main converters for a few seconds to essentially power cycle the satellite. One hour before the scheduled power cycle, the watchdog will send a warning message to the OBC to signal an imminent power cycle. The OBC can decide to let the timer go through, allowing the satellite to power cycle on schedule, or reset the timer back to 24h if it decides so. This should only be done if a major operation is in progress or will be in the hour following the warning. Lastly, the OBC is able to send a signal to the watchdog to force a power cycle regardless of the status of the timer. This allows the OBC to attempt to fix a system that had a failure.
MSP430FR5989 is placed in the system to monitor the status of all converters and protection systems for redundancy. It is connected on the main I2C buses of the backplane, but not on the LVDS bus considering no significant amount of data will be generated by the PDS.
Two redundant DC-DC switching converters are used to ensure power is always supplied, even in the case of a full converter failure. The specific converters used are the LTC3833 for its high efficiency and flight heritage with the specific GanFETs used. They are both fed with the battery voltage output from the BMS and regulate it down to a stable 5.3 volts to account for loss on the line. Their outputs converge to an ideal diode controller to arbitrate the power supplied to the main 5 volt rail. The last element on the 5 volt rail is an overvoltage protection circuit to ensure the converters never supply a voltage greater than the rated input to the components of the satellite, which could damage them. The circuit will simply block any output to the 5 volt rail until the voltage is reduced back down to the desired level.