V5-0 - P8V power supply startup problems
|Assignee:||Tomasz Wlostowski||% Done:||
The switched mode PSU (LT3503) on some cards (V5+) has problems with starting up: it never exits current limit mode, because of high load capacitance of the decoupling capacitors (10 x POSCAP 47 uF) combined with their very low ESR.
As a result, we get very noisy P8V rail, which disturbs the ACAM delay line PLL linear power supply, increasing the jitter of measured timestamps 3-4 times. The bug was unnoticeable to the PTS because it currently measures only average delay.
1. Replace all 47 uF POSCAPs with 10 uF POSCAPs (10 pcs / board)
2. Update the PTS to characterize TDC jitter of each card.
Also create new production files (V5-1)
- All boards delivered to CERN were repaired
- Documentation updated with new capacitor values in V5-1 EDMS release.