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DC/DC Converters

B2GM, 14 March 2012. DC/DC Converters. Markus Friedl (HEPHY Vienna). What’s It All About?. We need to bring power to the front-end There is a significant power drop in the cables Limited space and material budget Low voltages required by modern electronics

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DC/DC Converters

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  1. B2GM, 14 March 2012 DC/DC Converters Markus Friedl (HEPHY Vienna)

  2. What’s It All About? • We need to bring power to the front-end • There is a significant power drop in the cables • Limited space and material budget • Low voltages required by modern electronics • In CMS and ATLAS Trackers, ~50% of total power (tens of kW) is burnt in the cables I Rcable Rload Ploss = 2 x Rcable x I Rcable I Markus Friedl (HEPHY Vienna): DC/DC Converters

  3. How to Avoid This? • Lower Rcable: hardly possible  • Serial powering: deliver constant current at higher voltage, needs shunt regulator for each serially connected unit • DC/DC converters: deliver higher voltage, needs converter for each parallel unit • Both methods reduce I and thus power loss at constant Rcable Markus Friedl (HEPHY Vienna): DC/DC Converters

  4. Serial Powering vs. DC/DC Converters • Both options have pros and cons and are intensively studied for S-LHC upgrades • Serial powering: • no common ground: requires level translation for I/O • generally easier for digital output – ATLAS • DC/DC converters: • switching device: requires careful design to avoid noise • generally easier for analog output – CMS Markus Friedl (HEPHY Vienna): DC/DC Converters

  5. DC/DC: How Does It Work? • Buck converter (aka step-down converter): Essentially a kind of pulse width modulation of primary voltage, smoothened by LC filter • L, C: the bigger, the better • Higher switching frequency allows lower L,C values T1 open, T2 closed T1 closed, T2 open In reality, both switch and diodeare MOSFETtransistors Dutycycle D = t1,on/T; 1/D = Iout/Iin= Vin/Vout = r (K.Klein, Aachen) Markus Friedl (HEPHY Vienna): DC/DC Converters

  6. DC/DC: Reality is Not Ideal • Efficiency is <100% (but much better than linear regulator) • Losses occur in several places: • Every coil has an Ohmic resistance • Ohmic resistance when MOSFET switch is on • Capacitive switching losses  frequency • Control circuit also needs power • Typical DC/DC converters for our application have • Vin/Vout = 2..10, Iout = O(1A) • f = 1..5 MHz, switch Ron = O(10mW) • L = a few 100nH, coil RL = a few 10mW • Efficiency = 50..90% Markus Friedl (HEPHY Vienna): DC/DC Converters

  7. DC/DC Challenges in HEP • DC/DC converters are very common (e.g. PC power supply), but we have some special issues in the front-end of HEP experiments • Radiation • Commercial integrated circuits are usually not rad-hard, they typically die after 10…100 kRad •  Needs customized, rad-hard ASICs • Magnetic field • Presence of static B field saturates coil core •  Needs air coil  low L  high switching frequency • Material budget •  Needs small, light-weight materials • Noise emissions (conductive and radiated) •  Needs proper circuit design, layout and shielding Markus Friedl (HEPHY Vienna): DC/DC Converters

  8. R&D at CERN and Aachen • All those issues (previous page) are addressed, there are no showstoppers • CMS (and ATLAS) Tracker group have been studying the use of DC/DC converters for future S-LHC upgrade • CERN Microelectronics group is developing rad-hard DC/DC converter ASICs and air coils • Intensive tests with existing Tracker modules (APV25) and rad-hard DC/DC converter prototypes at Aachen Markus Friedl (HEPHY Vienna): DC/DC Converters

  9. ASIC: AMIS Family • Being developed since 2007 • AMIS5 now being produced, expected back in summer 2012 AMIS4(almost final) 2.56 x 2.87 mm2 0.35µm ON Semiconductor (S. Michelis, CERN) Markus Friedl (HEPHY Vienna): DC/DC Converters

  10. AMIS4 Measurements (S. Michelis, CERN) Efficiency vs. Iout Efficiency vs. TID 80…85% Rad-hard beyond 100Mrad Also tested: no SEB or SEGR Markus Friedl (HEPHY Vienna): DC/DC Converters

  11. CERN DC/DC Module • Final AMIS chip not yet available, but substitute is • CERN group developed a DC/DC module (SM01C) based on commercial converter chip (LTC3605) with similar performance as AMIS, but not rad-hard • Optimized design & layout • Shielded air core coil • Available for tests • Chip will later be replaced by rad-hard AMIS ASIC SM01C Converter Module 13.5mm 28.4mm Markus Friedl (HEPHY Vienna): DC/DC Converters

  12. Tests with DC/DC Converter and APV25 • Performed in Aachen (K. Klein et al) – references: appendix TEC petal 2 Converters (2.5V and 1.25V) very close toAPV25 chips Ring 6 modules 6.4 6.3 6.2 6.1 Motherboard Markus Friedl (HEPHY Vienna): DC/DC Converters

  13. Impact on APV25 Noise (2009) (K. Klein, Aachen) • Noconverter • AC1 (2008) •  AC2-StandardC with Mini Toroid • AC2-StandardC with Mini Toroid + filter 2 • Noise of (old) AC1 converterincreasedwithconversionratio r = Vin / Vout • AC2-StandardC with Mini Toroidand-filter exhibitsnosignificant additional noisefor all accessibleconversionratios  APV25 + DC/DC work together without noise penalty!  Markus Friedl (HEPHY Vienna): DC/DC Converters

  14. Belle II SVD • Originally (TDR), we have forseenrad-hard voltage regulators close to the front-end (“Junction box”=DOCK box) Finesse Transmitter Board (FTB) FADC+PROC 1748APV25chips ~2mcoppercable Junctionbox ~10mcopper cable Unified opticaldata link (>20m) COPPER Front-endhybrids Rad-hardvoltageregulators Analog level translation,datasparsificationandhit time reconstruction Unified Belle IIDAQ system Markus Friedl (HEPHY Vienna): DC/DC Converters

  15. Motivation for DC/DC @ Belle II SVD • Due to financial constraints, we have to re-use Kenwood power supplies of Belle I (SVD2) • Problem: • Belle I: 864 VA1TA chips, ~200W (+ repeater power) • Belle II: 1748 APV25 chips, ~600W • Existing Kenwood supplies are not sufficient for linear regulators & APV25, but more than enough with DC/DC • Now designing junction box with CERN DC/DC modules • Similar space requirements, less cooling needed @ DOCK Markus Friedl (HEPHY Vienna): DC/DC Converters

  16. Summary & Outlook • Cable losses can be reduced by serial powering or DC/DC • DC/DC is baseline for CMS Tracker upgrade • CERN & Aachen are developing • Rad-hard ASIC, air core coils, shields, circuit and layout • APV25 + DC/DC converter: no noise penalty • Now designing Junction box with CERN DC/DC modules • Existing Kenwood power supplies are enough for future SVD • I will meet CERN guys in late April for discussion • Anyone (besided SVD) interested in DC/DC converters? Markus Friedl (HEPHY Vienna): DC/DC Converters

  17. Some References • Wikipedia: http://en.wikipedia.org/wiki/Buck_converter • CERN Microelectronics: http://project-dcdc.web.cern.ch • K.Klein (Aachen): • https://indico.cern.ch/contributionDisplay.py?contribId=56&confId=49682 (2009) • https://indico.cern.ch/contributionDisplay.py?contribId=47&confId=104062 (2011) • F. Faccio, S.Michelis (CERN): • https://indico.cern.ch/contributionDisplay.py?contribId=92&confId=83060 (2010) • http://indico.cern.ch/getFile.py/access?contribId=39&sessionId=7&resId=0&materialId=slides&confId=113796 (2011) • https://indico.cern.ch/contributionDisplay.py?contribId=21&confId=120853 (2011) Markus Friedl (HEPHY Vienna): DC/DC Converters

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