ELECTRONIC PROGNOSTICS FOR DC to DC CONVERTERS

www.Ridgetop-Group.com

ELECTRONIC PROGNOSTICS FOR DC to DC CONVERTERS

Ridgetop Group, Inc. Tucson, Arizona


Acknowledgements

• Work was funded by JSF Program Office and the associated SBIR.

• Lockheed Martin/Ft. Worth

• C & D Technologies/Tucson


Ridgetop Background• Tucson-based firm, five

years of growth!• Government customers

include DARPA, Navy, DOE, NASA, Missile Defense

• Strong in Analog/Mixed-Signal design and test.

• Staff backgrounds from Tektronix, Hughes, Credence, Honeywell


Joint Strike Fighter (JSF)• 75% of the Fighters

by 2020• Employs advanced

Prognostics/Health Management (PHM)

• Use of Commercial Off the shelf (COTS) Products

• Lockheed Martin is the Prime Contractor


JSF PHM Vision

Source: A. Hess, JSF Program Office


Ridgetop’s JSF-Funded Project

• Develop Electronics PHM to a widely used module within Mil/Aero Systems

• Test bed is a Commercial High Efficiency DC to DC Converter (Forward Converter)

• Develop techniques and modular, reusable, methodologies that can be widely applied in EW Systems.

• Snap on to existing diagnostics backbone


Ridgetop’s Project - PHM• Navy has determined significant

problems with Power converter modules’ reliability.

• To examine electronics-module PHM, a simple DC-DC power converter was selected.

• SBIR introduces a new PHM approach and applies the efficacy on Forward Topology, a variation of the buck, ( 80% of Navy’s converters).


Features of C&D WPA50 Supply

• 50W, 5V output• Vin range = 36V-

75Vdc• Under voltage and

high Temperature protection

• 400 kHz switching• 200ms turn-on time


Lifetime Model

“Bathtub Curve”

Failure Rate

Time


Failure Rate Mapping

Reliability

“Bathtub Curve”

Cumulative Probability of Failure

Prognostic “distance”


Electronics Prognostics Approach

SMPS Key Failure Modes

Pareto Ranking

Gate Oxide Hot Carrier Radiation

Step 2: Extract Precursors to Failure

Step 3: Calculate Remaining Lifetime (using CPU)

Ripple Current (Cap) Semi Faults

End of Life

Step 1: Characterize SMPS Power System Failures

Degradation

Lifetime of SMPS Power System

Failure Rate

Advanced Warning Point


Prioritize Precursor Observations


Pareto Analysis


CRITICAL COMPONENTS• Primary MOS• Secondary Sync.

Forward and catch rectifier

• Opto Isolator• PWM controller• Input capacitor• Output CapacitorForward Converter

Input= 48Vdc

Output= 5V, 10A max


Precursor MethodologyCan pre-cursors be measured during normal operating

conditions?

Measure pre-cursor voltage or currents to predict failure during normal operating conditions

Can pre-cursors be measured under different

operating conditions?Apply new operating conditions to measure pre-cursors to failure

Can Statistics predict the failure of the component?

Apply physics of failure model, using known statistics to predict failure of component


Physics of Failure


Power MOSFET failure• High dv/dt variations

due to fast switching• Slow reverse

recovery of body diode parasitic bipolar turn on

• Higher on-resistance at high T. Thermal runaway possible

BREAKDOWNRepresented by a low but finite impedance of the short-circuit path


Power MOS failure (Contd.)FAILURE MECHANISMS

• Short-circuit induced over-currents

• Over-Voltage induced over-currents

CONCLUSION• Failure probability depends

on the distance of the operating point from the SOA Boundary

Source: Hower P.L., “Safe Operating Area – a new frontier in LDMOS design”


Power MOS failure (Contd.)Prognostic Technique

• Formulate mathematical model incorporating the time-to-breakdown based on the Physics-of-Failure approach

• Add Sacrificial MOS Prognostic Cell, subjected to higher stress conditions, so that it’s operating point is closer to the SOA boundary

Increased StressConditions


Failure DistributionsPrognostic Cell Approach

Prognostic Cell Host MOSFET

Time

Prognostic Distance

Techniques previously applied to CMOS IC’s:

• Hot carrier damage

• TDDB Gate Oxide Failure

• Metal Migration

• Radiation Effects


Opto-Isolator failure

A degradation of 50% in the CTR is usually considered the failure point of the opto-isolator

Source: Fairchild Application note AN3001 “Optocoupler Input Drive circuits”


Opto-Isolator Prognostic Solution

Prognostic technique

• Monitor the fall in output current due to CTR degradation

• Solution: Current monitor (QT-1410)


Capacitors

• Electrolytics – Large capacity, but prone to problems in aging. – Aluminum – Reform dielectric problem; fail

shorts– Tantulum – aging of electrolyte; heating

• Ceramic (this SMPS)– Capacities have grown in recent years– Difficult to extract in-situ precursors


Ceramic Capacitor failure

Degradation of Insulation Resistance (IR)

• High temperature and high voltage stresses

• Power dissipation due to current through ESR

• Pre-cursor – Capacitor displays an equivalent parallel resistance of about 1 MΩ.Source: Munikoti, Dhar, “Low voltage failures in MLCC: A

New accelerated test screen”


Capacitor Prognostics Soln.

Disconnect load and ground gate of primary and secondary MOS switch, apply a small DC current to the capacitor and observe voltage at this node.

Φ1

Φ2


Simulated results of Prognostics Solution

Simulated output voltage as the insulation resistance of thecapacitor degrades. The applied current to the capacitor is 1 µA.

0

1

2

3

4

5

6

100000 1000000 10000000 1E+08

IR (Ohms)

V(ou

t)


PWM controller

• Breakdown of the discharging transistor inside the oscillator due to rapid charge-discharge


PWM controller (Contd.)

Precursor• Increase in IDDT from

the supply

Solution• Current monitor


QT-1410 (Current Monitor)High speed (5 MHz), High resolution (5µA)measurementPeak (IDDT) and/or charge (IDDQ) measurementSerial / Parallel measurement50 MHz Data sampling rate


Voltage Monitor

• Isolation Amplifier– Optical isolation– Capacitive isolation

• ADC of QT-1410 is utilized


Prognostic processing schemeWeighting fusion

(Implemented in software)• Weights based on

accuracy of prognostic technique.

• Determines how reliable the sensor is, in the range of measurement


Data Extraction

P C R R e g is te rT A P C o ntro lle r

T D I

T D O

T C K

T M S

T A P – T e s t A c c e s s P o rtT D I – T e s t D a ta InT D O – T e s t D a ta O utT C K – T e s t C lo c kT M S – T e s t M o d e S e le c tP C R – P ro g no s t ic C e ll R e g is te r

P r in te d C irc u it B o a rd w ith IC ’sa nd E m b e d d e d P ro g no s t ic s

P ro g n o s tic C e lls

JTAG


Possible Software Framework• Flexibility of adjusting

prognostic distance • Automatic/Manual

weight selection option

• Investigate ability to detect false alarms


Phase I Items DeliveredAnalyzed components susceptible to failureDeveloped physics of failure models for those componentsDetermined precursors to failureDeveloped prognostic designs for the deviceThe proposed solution covers >80% of failures at low cost


Phase II Objectives• Implement Phase I Electronic Prognostics Design using a COTS

DC to DC power converter

– Extract the necessary sensor information from the DC to DC Converter using a COTS backbone. Process the sensor information using a prototype software program

– Validate system performance of Electronic Prognostics via HALT tests on the DC to DC Converter

• Showcase concept of Electronic Prognostics for the JSF Aircraft and potential extensions to other electronic modules.

• Evaluation of weight reduction of JSF using prognostics to augment TMR Redundancy.


Next Steps

• Invitation for SBIR Phase II Proposal is pending from JSF Program Office.

• Continuing work in semiconductor faults and prognostics with NASA and NAVY/Crane.

• Proposal pending for extensions to handle FPGA Failures with Raytheon Missile Systems and Honeywell.

• Have additional concepts and ideas to apply for other funded activities, for example:

– Continuous readout of remaining useful life using “Picket Fence” approach.– More work on FPGA and Memories Physics of Failure and precursor extraction– More work in mechanical faults (connectors and solder joints via partners)– Apply prognostic techniques to additional types of Avionics or EW modules.

• Ridgetop is looking for Development Partners !

ELECTRONIC PROGNOSTICS FOR DC to DC CONVERTERS

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