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

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


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


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


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%


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


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


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)

AMIS4 Measurements


Efficiency vs. Iout Efficiency vs. TID

80…85% Rad-hard beyond 100MradAlso tested: no SEB or SEGR

(S. Michelis, CERN)

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 ASIC28.4mm

13.5

mm

SM01C Converter Module

Tests with DC/DC Converter and APV25

Performed in Aachen (K. Klein et al) – references: appendix


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)


• 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)


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?


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)


http://en.wikipedia.org/wiki/Buck_converter

http://project-dcdc.web.cern.ch/

https://indico.cern.ch/contributionDisplay.py?contribId=56&confId=49682



http://indico.cern.ch/getFile.py/access?contribId=39&sessionId=7&resId=0&materialId=slides&confId=113796

http://indico.cern.ch/getFile.py/access?contribId=39&sessionId=7&resId=0&materialId=slides&confId=113796


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

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