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DC/DC ConvertersMarkus Friedl (HEPHY Vienna)
B2GM, 14 March 2012
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 Converters 2
Rcable
Rcable
RloadPloss = 2 x Rcable x I
I
I
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
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 3
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 Converters 4
S
Vin D C
+
−
+
−
Vout
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 Converters 5
In reality, bothswitch and diodeare MOSFETtransistors
Duty cycle D = t1,on/T; 1/D = Iout/Iin = Vin/Vout = r (K.Klein, Aachen)
T1 open, T2 closedT1 closed, T2 open
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 )W L = a few 100nH, coil RL = a few 10mW Efficiency = 50..90%
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 6
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 Converters 7
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 Converters 8
ASIC: AMIS Family
Being developed since 2007 AMIS5 now being produced, expected back in
summer 2012
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 9
AMIS4 (almost final)2.56 x 2.87 mm2
0.35µm ON Semiconductor(S. Michelis, CERN)
AMIS4 Measurements
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 10
Efficiency vs. Iout Efficiency vs. TID
80…85% Rad-hard beyond 100MradAlso tested: no SEB or SEGR
(S. Michelis, CERN)
CERN DC/DC Module
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 11
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 ASIC28.4mm
13.5
mm
SM01C Converter Module
Tests with DC/DC Converter and APV25
Performed in Aachen (K. Klein et al) – references: appendix
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 12
6.16.4 6.3 6.2
Motherboard
Ring 6 modules
TEC petal
2 Converters(2.5V and 1.25V)very close toAPV25 chips
Impact on APV25 Noise (2009)
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 13
• Noise of (old) AC1 converter increased with conversion ratio r = Vin / Vout
• AC2-StandardC with Mini Toroid and -filter exhibits no significant additional noise for all accessible conversion ratios
¾ 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!
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 Converters 14
1748APV25chips
Front-endhybrids
Rad-hardvoltage
regulators
Analog level translation,data sparsification andhit time reconstruction
Unified Belle IIDAQ system
~2mcoppercable
Junctionbox
~10mcoppercable
FADC+PROCUnified optical
data link (>20m)
Finesse Transmitter Board (FTB)
CO
PPER
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 2012
Markus Friedl (HEPHY Vienna): DC/DC Converters 15
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 Converters 16
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&material
Id=slides&confId=113796 (2011)
https://indico.cern.ch/contributionDisplay.py?contribId=21&confId=120853 (2011)
14 March 2012Markus Friedl (HEPHY Vienna): DC/DC Converters 17