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Component designators have largely been omitted from the layout due to space constraints. The usefulness of designators decreases with increasing board size, as having “C57” among hundreds of 0603 parts does not make it easier to find. Eventually the “Top Designator” layer will be updated with all designators so that they are included in the PDF export.
Issues
1 - VIN Short
Symptom: Both 12V inputs were shorted to ground. When injecting current to try and find the short, the impedance of the short was so low that no significant heat was generated.
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Resolution: Holes were drilled out, and jumper wires were soldered to make up for the missing vias. NC drill file was regenerated which resolved the issue.
2 - Startup Inrush
Symptom: When 12V power is applied to either input while a controller board is connected to a programmer, the board makes a buzzing noise and 12V fails to reach the output of the power path ICs
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Resolution: Since there will be no programmer connected to the controller board in the vehicle, no hardware changes will be made.
3 - Source Switching
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Symptom: Switching sources at > 3A load current is unsuccessful. As soon as the higher priority source is connected (purple), the output (yellow) starts to fall. Overshoot caused by inrush is also very high, peaking at 18V.
Cause: It seems that the excessive inrush from connecting the new source messes something up inside the IC, causing it to think that the original source is out of the valid window and shutting it down. CH2 shows that the original source does not go outside the valid window. This is backed up by the fact that when the bench supply is made to be the original source and the aux battery the new source, switchover happens successfully and the issue only exists when the sources are swapped (bench is new, and IC switches from battery to bench). Presumably this is because the internal resistance of the battery is much higher than the ESR of the output caps on the bench supply, so when the aux is connected the inrush is much lower.
I could have verified this by connecting the power supply while it is off, and then turning it on, rather than having the power supply on before hand and then connecting it to PD. This would have greatly limited the slew rate of the source, and thus the inrush as well. Due to dumb reasons this test was not performed.
Resolution: In the vehicle, this shouldn’t be an issue since PCS would always be connected first and then turned on, so there wouldn’t be any significant inrush. Nevertheless input capacitance can be reduced by depopulating a 10uF input cap.
Change Log
Rev 2.0
Rev 1.0 was a copy of the MSXIV, and did not fit into the MSXV system. Rev 2.0 should really be “1.0”.
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It was found that the 5V buck ICs were damaged (shorted) when testing the OVP. As such, the OVP was lowered from 15 to 14V. The aux battery when fully charged settles over time to ~13.75V so it should still be okay.
Wack vias were fixed by regenerating NC drill files
Pulldowns for all the EN pins added, since if the controller board is not flashed and the output to the IO expanders are floating, all the outputs are on in their default state.
Slew rate limiting added for power path fets
To accommodate for potentially reducing input capacitance (issue 3)
Decoupling cap on load switch from 100nF to 10uF to add additional bus capacitance
To accommodate for lower slew rate limiting above. Adds ~1.5uF @ 12V DC bias per cap, +4x caps for normally aux and +6x caps for normally pcs buses.
Changed input TVS from 14V to 13V rated diodes
Min reverse breakdown is 15V which is a little lower than the previous 14V diodes but still higher than operating voltages. Inrush from the connector had the voltage spiking up to 18V, this should help clamp that down a little better
Added indicator LEDs to power input