Betev, B L

Denes, P

Djambazov, L

Dröge, M

Faure, J L

Iliev, Bozhidar Z

Lustermann, W

Nanov, I

Raykov, P

Shivarov, N

CERN Document Server

Low Voltage Supply System for the Very Front End ReadoutElectronics of the CMS Electromagnetic CalorimeterB. Betev3, P. Denes1. L. Djambazov3, M. Droge3, J.-L. Faure3, B. Iliev2,W. Lustermann3, I. Nanov2, P. Raykov2, N. Shivarov21Princeton University, Princeton, NJ 08544, USA.2Bulgarian Academy of Sciences, Central Laboratory of Mechatronics andInstrumentation, BG-1113 Soa, Bulgaria.3Eidgenossische Technische Hochschule, ETH-Zurich, CH-8093 Zurich, Switzerland.October 14, 1999AbstractWe use a two stages low voltage power supply systemwith remote sensing. Linear low voltage power sup-plies outside the cavern feed local voltage regulatorshoused in water cooled boxes inside the detector withsignicant power losses over around 120m of thereforecooled cables. All voltages are oating and providedindependently to groups of 50 crystals, two trigger tow-ers. They are grounded at the detector end. Controls,overvoltage and overcurrent protection and fuses areintegrated into the power supplies. Radiation tests onthe low voltage regulator components were performed.A low voltage regulator has been built and tested.1 IntroductionThe barrel part of the CMS [1] ElectromagneticCalorimeter (ECAL) is composed of 61200 lead-tungstate crystals arranged in 36 super modules (SM)housing 1700 crystals each [2]. There are two end capscomposed of 16000 crystals. After the crystal's scin-tillation light is converted into an electrical signal, thereadout electronics in the barrel and the end cap regionare identical. Throughout this article mainly the bar-rel region is considered supposing a low voltage system(LVS) for the end caps will be derived from the barrelone at a later stage.Groups of 5 2 crystals in    form a submoduleread out by a Very Front End (VFE) module. A triggertower consists of 55 crystals. Their energy is summedto provide rst level trigger information. The LVS willbe subdivided into independent Low Voltage Channels(LVCH). Each of them will power groups of 50 crystalscorresponding to 2 trigger towers, corresponding to 5VFE modules.1.1 Requirements for the Very FrontEnd ElectronicsThe VFE electronics requires four independent lowvoltages, +5V and  2V for the analog part and +5Vand +2V for the digital part. Their expected currents(I) and the resulting power consumptions (P) are sum-marized in the following table:Voltage [V] +5  2 +5 +2ILV CH[A] 7.8 1.3 1.5 3.3ISM[A] 264 43 51 111IBarrel[A] 9486 1530 1836 3978PLV CH[W] 38.8 2.5 7.5 6.5PSM[W] 1318 85 255 221PBarrel[W] 47430 3060 9180 7956The VFE electronics will be very sensitive to noise,especially to correlated noise as introduced by thepower supplies because the energy of 25 crystals issummed as the trigger towers energy. Therefore lin-ear power supplies are proposed in order to avoid allpotential problems arising from the use of switchingmode ones.1.2 Environmental ConstraintsThe ECAL barrel is located inside the 4Tesla super-conducting magnet [3]. Behind the crystals an inte-grated dose up to 2Mrad and up to 51013n=cm2areexpected at an integrated luminosity of 5  105pb 1.In addition the available space inside the detector isvery limited. There is no space for the low volt-age power supplies inside the SM's and only about(800  500  150)mm3per SM about 4m away fromFigure 1: Two stage power supply system with remote sensing.the SM's but still in the CMS magnet. Outside the de-tector radiation levels and the magnetic stray eld arestrongly depending on the location. There is suÆcientspace at the galleries but still in a radiation environ-ment of 100 rad absorbed dose and in a moderate mag-netic eld of 0:05T. An important point is also theaccessibility of the system. To access the electronicsinside the detector, the entire end caps have to be re-moved. Also the access to the electronics in the cavernis limited to the shutdown periods of the accelerator. Incontrary there is always access to the counting house,where radiation and magnetic eld are negligible.2 Low Voltage System LayoutThe LVS is very complex taking into account the largenumber of channels, 1224 for the barrel, the total re-quired power of 74 kW for the ECAL barrel only andthe problems of radiation and magnetic eld. So anychosen solution includes advantages and disadvantages.In addition the nal LVS performance strongly dependson its behavior in the CMS environment including theinterference with other parts of the detector and notonly on single blocks specications.We propose a two stage power supply system withoating voltages and remote sensing in both stages,as sketched in Figure 1. In the rst stage linear lowvoltage power supplies (LVPS) located outside the cav-ern feed low voltage regulators inside the detector over 120m long cables. The LVR's regulate the voltageat the load in a distance of 7m, constituting the sec-ond stage. This conguration is identical for all fourvoltages required by the VFE modules. The groundingwill be performed at the detector end.The major disadvantage of this solution is the hugepower loss in the system. In order to minimize this lossthe cables cross sections are increased in three stepsfrom the load back to the LVPS. A minimal power lossat the LVR is achieved by regulating its input voltage.But still the power losses in the cables and the LVR'sare signicant.In table 1 the dierent cross sections (A) of the cop-per cables and the resulting voltages (U) and powerlosses (P) for a single LVCH are summarized, withthe variables as dened in Figure 1. With 34 LVCH'sU0[V] 5 -2 5 2A1[mm]21.0 1.0 1.0 1.0A2[mm]21.5 1.5 1.5 1.5A4[mm]28.0 4.0 4.0 8.0U2[V] 6.4 -2.2 5.3 2.6U3[V] 7.9 -3.7 6.8 4.1U4[V] 11.9 5.0 8.3 5.8P1[W] 4.9 0.13 0.18 0.9P2[W] 5.7 0.15 0.21 1.0P3[W] 11.6 1.9 2.3 4.9P4[W] 31.0 1.6 2.3 5.5Table 1: Cable cross sections, voltages and power lossesin the low voltage system.in a SM this leads to power losses of  200W in thecables inside the SM,  240W between the SM patchpanel and the LVR box, 700W in the LVR box and1400W from the LVR box to the LVPS. Assuming aneÆciency of 50% for the linear LVPS's the total powerconsumption of the ECAL barrel will be  350 kW,leading to an overall eÆciency of 25%.It is obvious that the entire system, including thecables and the LVR's requires water cooling. The cool-ing system of the SM's will remove the additional en-ergy lost in the cables inside the SM's themselves. TheLVR's will be housed in water cooled boxes and thecables are placed into water cooled channels. We areinvestigating the possibility to use the return ow ofthe SM cooling system for this purpose.3 The Low Voltage Regulators3.1 Radiation TestAs the low voltage regulators will be located insidethe detector it is mandatory that they survive radia-tion doses up to 1Mrad. Therefore a set of commer-cial components was tested using the PSI Optis beam[4] with 1:25  109protons=(cm2s) of 64MeV. Thissimulates at the same time ionizing and nonionizing012345670 20 40 60 80 100 120 140 160T / minU / V VinVoutVgsbeam  ON OFF ONFigure 2: Irradiation test: SIPMOS SPP30N03L.-50-40-30-20-1000 20 40 60 80 100 120T / min∆U / mV∆Vref∆VoutFigure 3: Irradiation test: MC1723CP.irradiation. About 2 hours operation at Optis beamcorrespond to 10 years of the expected irradiation forthe ECAL VFE electronics at LHC. In particular wetested a SGR117A three terminal type, positive, ad-justable voltage regulator from Linnity, a TLE4270xed voltage regulator from Siemens, a MC1723CPtype regulator from Motorola, a SIPMOS-SPP30N03Lpower transistor from Siemens, a BTS640S2 [5] semi-conductor smart switch from Siemens and a IRFZ24N-HEXFET transistor from International Rectierer.The components were tested on experimental setupsunder working conditions equivalent to their future use.All of them but the BTS640S2 switch survived a mini-mum of 2 hours of irradiation. In Figure 2 the behaviorof the SPP30N03L during 140minutes of irradiationis drawn for an output current of Iout= 8A and anoutput voltage of +5V, for an input voltage voltageof Uin= 6:28V. The shift of the gate-source voltage,Vgs, is tolerable as it enables always a safe operation ofthe pass transistor. The output voltage was constantat (5:001 0:001)V. Figure 3 presents the results forthe MC1723CP low voltage regulator from Motoroladuring  120minutes of irradiation. The output volt-age decreased nearly linearly with the irradiation byFigure 4: LVR prototype layout for one LVCH.about 50mV. This change is clearly correlated withthe change in the reference voltage Vref.3.2 Prototype LayoutThe failure of the BTS640S2 switch, which also in-cludes fault protection features, in the irradiation testlead to a very simple design of the LVR. All addi-tional functionality like switching of the output volt-ages, overvoltage and overcurrent protection and out-put current measurement were moved into the LVPS.The LVR serves one LV channel with a single PCB of10477mm2containing four independent voltage reg-ulators based on the MC1723CP type regulator and theSiemens-SIPMOS SPP30N03L pass transistor. Theschematic layout is given in Figure 4.It is forseen to add some means to measure thesensed voltage at the load and the Vgsand to trans-fer them to the LVPS rack controllers.3.3 Prototype Test ResultsThe LVR's frequency response was studied at the pro-totype board and with a SPICE model. Therefore theinput to output transfer functions, the +15V to outputtransfer functions, the output dynamic impedances,the output noise and the cross talk between the dif-ferent channels for all four independent voltages weremeasured.The LVR unity gain cross over frequency is about afew kHz depending on the gain of the MOSFET. Theinput to output transfer functions showed two maximaone just above the unity cross over frequency and thesecond one around (100  500) kHz due to the self res-onance of the regulator. The output noise was foundto be around a few V=3 kHz. The cross talk increasedwith the frequency.3.4 LVR housingFor one ECAL super module 34 of the above describedLVR boards are needed. As they will be located insidethe cryostat it is mandatory that they are water cooledin order to remove the energy of 800W per SM. There-fore a special housing, the LVR box, is constructed. ItOver current?Under Voltage?Over Voltage?Over current?Under Voltage?Over Voltage?Over current?Under Voltage?Over Voltage?Over current?Under Voltage?Over Voltage?+5V analogLVR120m power and sensMain TransformerRectifiersSwitch ON/OFFInterlock CircuitryFaulty StatusTransformerOperativeExternal Emergency?Over Temperature?StabilizerLow VoltageLow VoltageStabilizerLow Voltage+5V analogStabilizerLow VoltageStabilizer-2V analog+5V digital+2V digitalMain Power Supply220V ACLocal / RemoteLVR for one LVCHLVPS for one LVCHRack ControllerInterface to theRack ControllerInterface to the-2V analogLVR120m power and sens+5V digitalLVR120m power and sens+2V digitalLVR120m power and sens4 x 15V DC auxilliary voltage, 120m cableFigure 5: Block diagram of the low voltage system for one LVCH.is based on two aluminum plates, sandwiching a cool-ing pipe. Two rows of up to 9 LVR boards can bemounted on each side of the cooling plate. The passtransistors are directly screwed onto it. The box has asize of 800 500 150mm3and the two smallest sidepanels serve as input and output patch panels.4 Low Voltage Power Supplies4.1 General LayoutThe LVPS's have to match the modularity of theLVCH's, in order to enable an individual control of thevoltages and a measurement of their output currents.Thus the LVPS has to provide 4 voltages correspondingto +5V,  2V, +5V and +2V at the load. One trans-former is feeding 4 independent channels composed ofrectier, lter and low voltage regulator with a passtransistor. Four additional windings with followingrectiers and stabilizers provide four +15V auxilliaryvoltages for the LVR. The system performs overvoltage,undervoltage and overcurrent protection and reacts onthe over-temperature and other emergency signals. Ablock diagram is sketched in Figure 5.The current and voltage protection functionality isbased on the BTS640S2 smart power switch. It hasground referenced input for switch ON/OFF, a diag-nostic feedback status output and a sense voltage out-put proportional to the output current.Figure 6: LVR box with LVR modules and coolingplate.4.2 Technical SpecicationsEach LVCH as described above provides the follow-ing main voltages: (+8:0  1:0)V, ( 3:9  0:5)V,(+7:5  0:9)V and (+4:1  0:5)V, with the followingmaximal currents respectively: 12:0A, 2:0A, 2:3A and5:0A. The input is standard AC 220V. The line reg-ulation for +10% and  20% of the AC input voltagehas to stay below 0:5% and the load regulation be-low 1% of the output voltage. A maximum ripple andnoise of 3mV RMS and 30mV peak to peak at thepower supply output is tolerable. The supply providesadjustable overvoltage and undervoltage protection, athermal shutdown at 85ÆC, soft turn on 0:5 s, fast turnFAN UNITFAN UNITModulesRegulatorCrate with 6FAN UNITRackControllerECAL LVPS REGULATORCMLI Sofia, ETH ZurichResetRemoteLocalOn / Off+15 V+15 V+15 V+5 V analog+15 V-2 V analog+5 V digital+2 V digitalfault statusfault statusfault statusfault statusFigure 7: LVPS rack layout (left) and regulator modulefront panel (right).o (< 100ms) and a hardware interlock circuitry sen-sitive to overvoltage, overcurrent and undervoltage sig-nals for all main voltages, to over-temperature condi-tions and to an external emergency signal. In addition4 auxilliary voltages of +15V, 100mA are providedwith 0:2% line regulation 0:4% load regulation, 0:2mVRMS and 2mV peak to peak ripple and noise. Allpower supplies in one rack are connected to a LVPSrack controller which measures and displays all mainand auxilliary voltages, the sensed voltages at the LVRinputs and the currents of the main voltages. It readsthe status information of the interlock circuitry andmeasures the temperature in the rack. It receives thevoltages and currents from the corresponding LVR'sand displays them. The rack controller is accessiblevia a front panel connector. It connects the rack toa main LVS controller in a local network. The powersupply can be operated in local or remote mode. Inremote mode the rack controller can turn ON or OFFindividual channels while in local mode a front panelbutton is used. It provides means to dispatch the ON,OFF and RESET signals from single front panel but-tons to all LVPS voltages in all regulator modules. Theoutput voltage status is controlled by switching the in-put AC voltage of the main transformer exclusively,thus all outputs are always switched in parallel.An additional transformer provides power to the ACinput switch and to the interlock circuitry in order toallow the startup of the system.4.3 LVPS housingEach ECAL barrel SM requires 34 of the above spec-ied LVPS's. They will be mounted into a 19" racktogether with the rack controller. Having in mind thesizes of the main transformers and of the electrolyticcapacitors it is possible to house six LVPS's in one 19"4 to 5 units high crate. Hence 6 crates per rack allowthe installation of 36 LVPS's. Their total power losswill be below the admissible 8 kW. Each crate con-sists of a mechanical support structure with a connec-tor backplane and built in AC/DC conversion units for6 LVCH's in the back part. In the front up to 6 Regu-lator modules can be inserted, serving one LVCH each.The front panel of them provides a status informationvia LED's and contains all necessary switches and but-tons. In addition the rack will contain the required fanunits. The rack controller will be housed in a 4 to 5units high crate. It includes a front panel display withcontrol buttons, a rack ON/OFF button, a rack resetbutton and power and reset switches for the auxilliaryvoltages and the controller itself. A possible layout ofthe LVPS rack and the regulator module front panel isgiven in Figure 7.5 ConclusionThe system design of a linear low voltage system for theCMS ECAL has been shown. Active components forthe LVR withstanding the radiation have been identi-ed. A prototype of the LVR board has been built andtested. The LVPS specications are basically knownand its design is in progress. We conclude that a linearLVS is feasable with the known dissadvantages of largepower losses and thus a huge amount of cables.References[1] CMS Collaboration, G.L. Bayatian et al., Techni-cal Proposal, CERN Report No. CERN/LHCC94-38, LHCC/P1, 15. Dec. 1994.[2] CMS Collaboration, G.L. Bayatian et al., TheElectromagnetic Calorimeter Project Tech-nical Design Report, CERN Report No.CERN/LHCC 97-33, CMS TDR 4, 15. Dec. 1997.[3] CMS Collaboration, G. Acquistapace et al., TheMagnet Project Technical Design Report,CERN Report No. CERN/LHCC 97-10, CMS TDR1, 2. May. 1997.[4] PSI Users Guide, Paul Scherrer Institute Villi-gen, Switzerland, 1994.[5] 7. Internationale Fachtagung Elektronik imKraftfahrzeug, Baden-Baden, Germany, Sept.1996.

Low voltage supply system for the very front end readout electronics of the CMS electromagnetic calorimeter

Low voltage supply system for the very front end readout electronics of the CMS electromagnetic calorimeter

Abstract

Similar works

Full text

Available Versions

CERN Document Server