COTS Regulator Studies. Derek Donley*, Mitch Newcomer, Mike Reilly *Hospital of the University of Pennsylvania, Radiation Oncology. COTS Radiation survey (Background) .
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COTS Regulator Studies Derek Donley*, Mitch Newcomer, Mike Reilly *Hospital of the University of Pennsylvania, Radiation Oncology
COTS Radiation survey (Background) • It is fairly well known that deep sub micron CMOS processes with thin gate oxide exhibit a fairly strong resistance to radiation*. Also that CMOS processes are not inherently susceptible to bulk damage from Neutrons and Protons. • Along with thinner dimensions comes the benefit of lower capacitance an higher gain gm/i. • One additional characteristic is that silicon has an inherent breakdown field that can not be violated. So thinner gate oxides and feature sizes have resulted in lower supply voltages, mostly a good thing. Although we don’t usually know what manufacturers are putting into their latest designs we thought it would be reasonable to look for fast opamps with low supply voltages to see if they might hold up to under high levels of ionizing radiation. Our first study in 2011 targeting CMOS opamps appropriate for the Phase 1 upgrade of the LAr electronics showed: that all of the opamps we selected meeting these critera were unaffected by a TID of up to 1MRad: OPA2835, LMH6611, THS4520 ADC driver. • See for instance the paper by the CERN micro electronics group: • IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 46, NO 6, DECEMBER 1999
Regulators With the LHC regulator experience behind us in our work on the TRT we thought that it might be useful to apply the same criteria and survey commercial regulators. 1) It wasn’t clear that the ST regulators would be available and 2) We felt that if commercial regulators could withstand the LAr radiation environment we would likely prefer the more modernized LDO’s. Regulators are more complex than opamps alone with internal reference voltages and high current capability so we expanded our study to include higher current transistors, voltage references, opamps and commercial regulators. Based on the criteria of expected thin gate oxide processes and high frequency operation. At the same time we were working with Bob Hollebeek at Penn on the design of a micromegas based proton therapy imaging detector for use at Penn’s proton therapy facility. As a result we have had some access during scheduled R&D periods to their 230MeV protons and the help and Expert for setup, focusing and calibration: Derek Dolney from Penn’s Radiation Oncology group.
Treatment Room (1 of 5) Derek adjust Gurney to hold our apparatus
Hand wired Test Board with provision for 14 test devices. With flood exposure to all active devices we get 3.8 1010 per exposure period. Nov 25, 2013 After 15 runs with full flood exposure the dose was 5.7X1011 *Note that the board shown has only the two devices in the cross hairs mounted .
Graphs of Full Exposure Seconds +2.5V Beam Monitor?? -2.5V
Graphs of Full Exposure Cont. The disturbance at 1800 seconds is due to the failure of the 1735 -2.5 due to over spec input voltage not radiation.
Failed Devices Significant voltage change below 5X1011 protons or 30 KRad BNL* gammas. • ADP3333 300mA positive LDO reg. • LT3032 150mA positive LDO reg. • MIC5271 100mA negative LDO reg. • UCC 284 500mA negative LDO reg. • UCC 384 500mA negative LDO reg. • Jim Kierstead at BNL has been very helpful in receiving our setups, exposing them under power and returning • then to us.
TPS74401 3A and TPS74201 1.5A TI LDO Regulators Pre - Proton Exposure at setup time.
Data Logger 0 1.3X1012 Protons/cm2 1.3 1.5X1012 Protons/cm2
TPS74xxx series Total Proton fluence 1.5X10120.5, 1.5, 3amp Adjustable slow turn on Regulators
Conclusions • This report is on the Survey part of our COTS regulator study. • The next stage is to select devices for use and perform studies on a statistically significant sample. ~20 parts of each candidate device. It looks like there are several candidate positive regulators with the TPS74XXX series being most versatile, stable and radiation tolerant up to the 1.5X1012fluence tested so far. Calculations of an equivalent ionization dose of only 80KRad will require additional ionizing radiation to get to the 300KRad (with safety factor) required for the LAr Front End Crate environment. Only one negative regulator candidate has been identified so far. MAX1735 200mA max regulators. It may be possible to shunt some current around it via resistor to bring the max current drive up to 300mA.