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

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 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters2 R cable R load P loss = 2 x R cable x I I I

3. How to Avoid This?  Lower R cable : 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 R cable 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters3

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 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters4

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 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters5 In reality, both switch and diode are MOSFET transistors Duty cycle D = t 1,on /T; 1/D = I out /I in = V in /V out = r (K.Klein, Aachen) T1 open, T2 closed T1 closed, T2 open

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(10m   L = a few 100nH, coil RL = a few 10m   Efficiency = 50..90% 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters6

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 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters7

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 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters8

9. ASIC: AMIS Family  Being developed since 2007  AMIS5 now being produced, expected back in summer 2012 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters9 AMIS4 (almost final) 2.56 x 2.87 mm 2 0.35µm ON Semiconductor (S. Michelis, CERN)

10. AMIS4 Measurements 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters10 Efficiency vs. IoutEfficiency vs. TID 80…85%Rad-hard beyond 100Mrad Also tested: no SEB or SEGR (S. Michelis, CERN)

11. CERN DC/DC Module 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters11  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 28.4mm 13.5mm SM01C Converter Module

12. Tests with DC/DC Converter and APV25  Performed in Aachen (K. Klein et al) – references: appendix 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters12 6.1 6.46.36.2 Motherboard Ring 6 modules TEC petal 2 Converters (2.5V and 1.25V) very close to APV25 chips

13. Impact on APV25 Noise (2009) 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters13 Noise of (old) AC1 converter increased with conversion ratio r = V in / V out AC2-StandardC with Mini Toroid and  -filter exhibits no significant additional noise for all accessible conversion ratios  No converter AC1 (2008)  AC2-StandardC with Mini Toroid AC2-StandardC with Mini Toroid + filter 2 (K. Klein, Aachen)  APV25 + DC/DC work together without noise penalty!

14. Belle II SVD  Originally (TDR), we have forseen rad-hard voltage regulators close to the front-end (“Junction box”=DOCK box) 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters14 1748 APV25 chips Front-end hybrids Rad-hard voltage regulators Analog level translation, data sparsification and hit time reconstruction Unified Belle II DAQ system ~2m copper cable Junction box ~10m copper cable FADC+PROC Unified optical data link (>20m) Finesse Transmitter Board (FTB) COPPER

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 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters15

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? 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters16

17. Some References  Wikipedia: http://en.wikipedia.org/wiki/Buck_converterhttp://en.wikipedia.org/wiki/Buck_converter  CERN Microelectronics: http://project-dcdc.web.cern.chhttp://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=56&confId=49682  https://indico.cern.ch/contributionDisplay.py?contribId=47&confId=104062 (2011) https://indico.cern.ch/contributionDisplay.py?contribId=47&confId=104062  F. Faccio, S.Michelis (CERN):  https://indico.cern.ch/contributionDisplay.py?contribId=92&confId=83060 (2010) https://indico.cern.ch/contributionDisplay.py?contribId=92&confId=83060  http://indico.cern.ch/getFile.py/access?contribId=39&sessionId=7&resId=0&materialId= slides&confId=113796 (2011) http://indico.cern.ch/getFile.py/access?contribId=39&sessionId=7&resId=0&materialId= slides&confId=113796  https://indico.cern.ch/contributionDisplay.py?contribId=21&confId=120853 (2011) https://indico.cern.ch/contributionDisplay.py?contribId=21&confId=120853 14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters17