1. Status and future perspectives
R&D on power supply distribution systems for calorimeters and muon detectors at the LHC phase II
Status and future perspectives
Research team:
M. Alderighi(1,^), S. Baccaro(2,^), F. Belloni(3), M. Bernardoni(5), G. Busatto(6), S. Buso(7), M. Citterio(4), P. Cova(5), N. Delmonte(5), F. Iannuzzo(6,10), A. Lanza(9,*), P. Maranesi(3), R. Menozzi(5), C. Meroni(4), A. Paccagnella(7,8,^), A. Porzio(6), M. Riva(3,4), G. Spiazzi(7), P. Tenti(7), F. Velardi(6)
^ Not partecipating to the PRIN2007 activity
* Speaker
1 – INAF/IASF and INFN Milano, Italy; 2 – ENEA Casaccia and INFN Roma, Italy; 3 – University of Milano, Italy; 4 – INFN Milano, Italy; 5 – University of Parma, Italy; 6 – University of Cassino, Italy; 7 – University of Padova, Italy; 8 – INFN Padova, Italy; 9 – INFN Pavia, Italy; 10 – INFN Pisa, Italy
Research co-funded by Ministero dell’Istruzione, dell’Universita’ e della Ricerca (MIUR) and INFN, under the PRIN2007 programme
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

2. Goals of the collaboration
Investigating the performance of active components available on the market in a sLHC-like environment, selecting the ones suited for the designed DC/DC converters
Designing distribution architectures and DC/DC converters able to cope with the tight requirements in terms of environment (radiation and B field), electrical/mechanical parameters (voltages, currents, dimensions) and thermal management usually found in calorimeters and muon detectors
Prototyping the designed converters and implementing all state-of-the art techniques in order to meet the thermal requirements
Testing the prototypes on the bench and in radiation and B-field environments, modifying their design as a function of the results
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

3. ATLAS Upgrade week - PRIN2007 and Apollo Collaboration
Summary of activity in the past two years Developed under the PRIN2007 programme
The R&D of the years 2009 and 2010 was devoted to the development of a PS distribution system able to cope with the sLHC specifications of the LAr calorimeters, because of the extremely high values of the required radiation tolerance:
Several 30V and 200V power MOSFET from different manufacturers tested up to 10kGy at the ENEA Casaccia 60Co g-ray source, average energy 1.25MeV. Heavy ions irradiations were also performed at the INFN Laboratori Nazionali del Sud, Catania
The chosen distribution system was the Intermediate Bus Architecture (IBA), based on a Main Converter (MC) to reduce the voltage from 280VDC to 12VDC, and several Point of Load (PoL) converters to distribute lower voltages to the electronics
The MC, based on the above architecture, was designed and a prototype partially realized and bench tested
In order to meet the B-field specifications of the MC, a planar primary transformer was designed and a prototype was realized and implemented in the MC prototype
The thermal performance of both the MC and the planar transformer was evaluated by FEM and tested by IR measurements
Two PoL converters were designed and prototypes realized and bench tested
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

4. Radiation tests of power MOSFETs (Univ. of Cassino)
Tests performed at 10Gy/h up to 10kGy
PCB holder capable of hosting up to 88 devices (see picture at the bottom)
Four different polarizations used for each device on the same holder (see here)
11 30V and 9 200V devices of various manufacturers tested with 7 samples each
Post-irradiation annealing performed, T = 100 °C, bias applied, 1 week long (ESA/SSC 22900)
Results of Vth for the best 30V and 200V devices are shown here. The 10kGy limit can be reached with some precautions
No increase of the oxide leakage current was observed during the irradiation (shown here for the best 30V device)
30V
200V
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

5. Distribution architectures
Chosen architecture – IBA with one isolated MC, reducing the voltage from 280VDC to 12VDC, and several non-isolated PoL (niPoL) on boards
Alternative solution – Higher output voltage from MC
Actual present architecture of LAr
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

6. Main Converter 1 (Univ. of Milano)
It consists of three equal modules, each one delivering 1.5kW.
Redundancy n+1 is adopted. The three modules are connected in parallel to provide power up to 3kW. In case of failure of one module, the remaining two can deliver the same power.
33 cm
7 cm
Design is based on the Switch-In-Line Converter (SILC) topology (see below), because of the reduced voltage stress across MOSFETs (reducing their sensitivity to radiation) and zero-voltage commutation at switch turn-on.
A 20W auxiliary converter is included in each module, in order to supply drivers and supervisors at the startup.
13 cm
Main converter module specifications
Input voltage = 280 V
Output voltage (main) = 12 V
Maximum supplied power (main) = 1.5 kW
Switching frequency (main) = 100 kHz
Output voltage (aux) = 5V
Maximum supplied power (aux) = 20 W
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

7. Main Converter 2 (Univ. of Milano)
Primary planar transformer layout is composed of 4 units connected in parallel, each one made of a 22 layers PCB. The turn ratio is 10:2.
The magnetic core is made of Cool-Mu material.
One 1.5kW module equipped with the planar transformer was produced (see pictures).
First bench measurements are reported below.
Global efficiency is included between 80% and 90% for the full power range (no B).
Transient response at full load is also shown.
22 layers
4.71 mm
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

8. Thermal management (Univ. of Parma)
MC simulated with 3D Finite Element Model under the conditions:
Output power = 1200 W
Natural air convection on top and vertical surfaces
Forced convection plate-thin heat sink at the bottom
Ambient temperature = 27°C
Total power dissipation at given conditions 220 W
Simulation results are shown below, compared with IR
measurements on the real module.
Case with three modules inside, of dimensions 150 x 402 x 285 mm3,
2 mm thick stainless steel, was thermally simulated, under the
following conditions:
MC output power = 3 kW • Max case temperature =18°C
• Liquid cooling system delivery = 1.9 l/min • Δp = 350 mbar
Tinlet= 18°C • Toutlet≤ 25°C. Results are shown below for three working modules and two working modules (one fault)
Module simulated results
Module IR measurements
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

9. niPoL converters (Univ. of Padova)
Chosen topology: Interleaved Buck with Voltage Divider (IBVD):
• Zero voltage switch turn-on • High step-down ratio
• Reduced switch voltage stress (Vin/2)
• Interleaved operation with automatic current sharing and ripple cancellation
High current PoL 7 x 3.5 cm2:
Vin = 12V
Vout = 2V
Iout = 20A
Operating frequency = 280 kHz
Ferrite core inductors (2.2 mH)
Prototype and measured efficiency shown here
Low current PoL 6 x 4.3 cm2 (in collaboration with Faccio’s team):
Vin = 12V
Vout = 2.5V
Iout = 3A
Operating frequency = 1MHz
Air core inductors (350 nH) Co C1
Cin L1 L2 S1 S3 S4
Prototype shown below with measured efficiency compared with a single buck S2
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration

10. Future perspectives – The Apollo R&D
From 2011 onward this R&D will be funded by INFN only under the name Apollo
The Apollo working programme for the next two-three years is the following:
Testing the radiation hardness of the present devices with protons and neutrons
Looking for new devices appearing on the market, particularly for new technologies like the GaN and testing them
Concluding the construction of a full MC prototype with three modules, a case and the cooling system, if necessary implementing new cooling techniques like the IMS
Continuing the thermal simulations and measurements of the MC prototype, designing its cooling system
Completing the radiation and B-field tests of the full MC prototype
Modifying its electrical and mechanical parameters for making it suitable for Muon chambers
Designing new PoL converters for use with the Muon chambers in a very high B field, up to 2T, studying new topologies and adopting new devices
Characterizing new core materials able to work up to 2T, or as alternative defining the performance of the best materials available on the market
ATLAS Upgrade week - PRIN2007 and Apollo Collaboration