2 nd Measurement – Feb., 2011 Test board with individual components 188 MeV protons

1. Single Event Upset Energy Dependence In a Buck-Converter Power Supply Design LC Filter LC Buck LC Filter + 200V - + Vout - FET Driver Transformer RSHUNT RSHUNT + VPRI - + VSEC - GNDPRI GNDSEC SEC Power PRI Power IIN* VIN* OpAmp VFB Run LT1681 Controller Chip Startup & Shutdown Control OVP, OCP, Temp, & Monitor Stop Opto Isolator Over Temp Startup VOUT* To ELMB (Control Interface) Shutdown IOUT* IFB Opto Isolator Monitor Voltages Primary Isolated Secondary Gary Drake, Member IEEE, James Proudfoot Argonne National Laboratory, Lemont, IL USA Bruce Mellado2, AnushaGopalakrishnan1, SanishMahadik1, Robert Reed2, AbhiramiSenthilkumaran1 1 - University of Wisconsin-Madison, Madison, WI USA 2 – The University of the Witwatersrand, Johannesburg, SA On Behalf of the ATLAS Tile Calorimeter System The TileCAL Low Voltage System LVPS Brick • Power for TileCAL Front-End Electronics • Novel Switching DC-DC Power Supply • Custom, Compact, High-Efficiency, 250 Watt • 8 Different Voltages  Customized Bricks • Water Cooled; System Interface & Monitoring • Environment: Magnetic Field, Radiation Tolerant • 256 boxes on detector, 2048 bricks, + spares • Reliability is Important  Infrequent Access LVPS Box 8 bricks per Box LVPS Access on Detector Detector Section End of Long Barrel Drawer Electronics We have performed a study of the susceptibility to Single Event Upsets (SEU) on the new upgraded supplies Radiation Testing Methodology Block Diagram of Brick • Radiation Tolerance Requirements • 10 Years of Running, L = 1034 cm-2 sec-1 Test Setup at MGH • SEU Testing Program • Proton beam at Mass. Gen. Hospital • 20 – 200 MeV protons • Read out continuously during irradiation Test Setup Configuration Measurements & Results • The Fix • Soft Start not used in brick operation • But, circuit does control startup rate • Want capacitor for cold start • Want capacitor out of circuit for normal operation • Add a diode & resistor: • 4th Measurement – Apr., 2012 Study SEUs as a function of energy • 60 MeV, 80 MeV, 100.5 MeV, 140 MeV, & 216 MeV • Results: See energy dependence • 1st Measurement – Dec., 2010 • Bricks tripped from SEU • 188 MeV protons • SEU Problem • 2nd Measurement – Feb., 2011 • Test board with individual components • 188 MeV protons • Discovered: LT1681 Controller Chip trips & restarts • Soft Start Feature Schematic Soft-start capacitor External component Value controls startup delay • Theory: Bendel Parameters [1] • In general, SEU susceptibility depends on fab tech., feature size, layout, and configuration • Bendel Parameters: Parameterization of form: • Our fit: LT1681 Block Diagram • Diode conducts at cold start • Diode is back biased • SEUs still happen, but recovery is fast SEMI-EMPIRICAL 2 PARAMETER FIT • 3rd Measurement – Apr., 2011 • Fix installed on 3 bricks • No more trips! • A Puzzle • SEUs not seen in earlier tests at 60 MeV • Why?... [1] W.J.Stapor, et al., IEEE Trans Nucl. Sci., Vol. 37, NO.6, pp. 1966-1973, December 1990.