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FMC DEL 1ns 4cha
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  • #14

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Opened Apr 19, 2013 by Tomasz Wlostowski@twlostow
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V5-0 - P8V power supply startup problems

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.

Actions:
1. Replace all 47 uF POSCAPs with 10 uF POSCAPs (10 pcs / board)
2. Update the PTS to characterize TDC jitter of each card.

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Reference: project/fmc-delay-1ns-8cha#14