Argonne National Laboratory is a U.S. Department of Energy laboratory managed by U Chicago Argonne, LLC.

– Failures over useful life are random but have an average rate: Poisson Process

– Probability of k failures between time t and t+t: Poisson Distribution

The TileCAL Low Voltage System

Reliability Analysis Methodology

Calculations

• 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

End of Long Barrel Detector Section

LVPS Access

on Detector Drawer Electronics

LVPS Box8 bricks per Box

LVPS Brick

Reliability Analysis of a Low Voltage Power Supply Design

for the Front-End Electronics of the ATLAS Tile Calorimeter

Abhirami Senthilkumaran, Bruce Mellado, Anusha Gopalakrishnan, Sanish MahadikUniversity of Wisconsin-Madison, Madison, WI

USAOn Behalf of the ATLAS Tile Calorimeter System

Gary Drake, Member IEEE, James Proudfoot

Argonne National Laboratory, Lemont, IL USA

2. Series-Parallel Model and Voltage De-rating for Capacitor– Tantalum capacitors most critical– Rated for 35V, used at <= 15V– Higher voltage rating reduces failure

When a capacitor fails– Probability of short = 0.75; Probability of open = 0.25 Also include 4 caps in parallel + diodes + LC filter

• Failures in Electronics– Failures generally described by the Bathtub Curve

– Interested in region of Constant Failure Rate

1. Series Reliability Model– Any single failure can cause brick to fail– Use only critical parts in model

Assume – Part failures are independent & random Start with single tantalum cap Parts Count Method– Use FITS values for each part

• Mean Time Between Failures MTBF– Expected time between failures– MTBF = 1 / l – This is not “useful lifetime”

• Probability of Failure-Free Operation– Probability of no failures at time t– R(t) = e-lt

Must calculate l for the entire unit

3. Comparison with Previous Design– Rated voltage of capacitor is 20V– Calculated failure rate: 12.4 bricks/year

– Observed failure rate: 5.2 bricks/year– From 3 years of operation

# Failures/yr = #Units * S li = 7.20

Dominated by Tantalum Reliability

Result #1: # Failures/yr = #Units * S [li * wi] = 5.03

Still Dominated by Tantalum Reliability

Result #2: Result #3:

We have performed a reliability analysis on the new upgraded supplies 2048 Bricks in the detector system

Expect 2.11 failures per year in the system

– l = Average number of units failing per unit time– Measured in Failures In Time FITS (# / 109 hrs)

Part Failures/109 hrIR2110S FET Driver 43.6IRFS9N60 MOSFET 0.544Inductor 470 uH 10Capacitor 47 uF 288HCPL7800 Opto-Isolator 52LM6142 Op-Amp 2LT1681 Controller Chip 6.04

# Failures/yr = # Units * S [li * wi] X x

Statistical Analysis– Poisson distribution; Neyman procedure

Use observations as a correction

R(t = 2 yrs) R(t = 5 yrs) R(t = 10 yrs) R(t = 20 yrs)

0.992992 0.982573 0.965450 0.932094

R(t = 2 yrs) R(t = 5 yrs) R(t = 10 yrs) R(t = 20 yrs)

0.995097 0.987788 0.975727 0.952049

R(t = 2 yrs) R(t = 5 yrs) R(t = 10 yrs) R(t = 20 yrs)

0.997938 0.994853 0.989732 0.979569