eRTM15: improvements on dc/dc noise
Problems and solutions:
- If the power supply is above 12.3V, noise is injected to CLKA/CLKB. The issue is noticeable on the backplane clocks and on the front-panel connectors. Unfortunately, NAT-RPM-AC600 provide a 12.4 voltage. Solution: use one BAS3010A-03W to reduce the voltage to the DC/DC (P12V).
- if the power supply has ripple noise, the DC/DC is producing more noise than expected. The issue has been detected with a chinese switching supply attached to the backplane. With CPX400DP it is fine. NAT-RPM-AC600's perfomance are worse that CPX400DP (70mv vs 3 mv). Solution: another LC filter near the mTCA connector, that will clean MTCA_PP12V.
- A 700 kHz phase noise spur is detected only at CLKA/CLKB front-panel connector. Small issue. Minimize P3V6 area (L4_PWR) near CLKA/CLKB traces and LTC6950 is desirable but not mandatory.