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Texas Instruments AM335x Reliability Considerations in PLC Applications (Rev. A) Application notes
Application Report
SPRABV9A – April 2014 – Revised September 2015
AM335x Reliability Considerations in PLC Applications
Ron Eller
ABSTRACT
Programmable Logic Controllers (PLC) are used as the main control in an automation system with highreliability expectations and long life in harsh environments. Processors used in these applications require
an assessment of performance verses expected power on hours to achieve the optimal performance for
the application.
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Contents
Overview of PLC Applications..............................................................................................
PLC Critical Requirements .................................................................................................
Trade-Offs for Best Performance ..........................................................................................
Summary ......................................................................................................................
Reference .....................................................................................................................
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List of Figures
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Reliability Curve .............................................................................................................. 2
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Chart 1
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Chart 2
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Overview of PLC Applications
The programmable logic controller (PLC) is the main control system in an automation system that
implements the proper sequencing and control of different I/O nodes. PLCs are typically benchmark in the
number of I/O’s in both size and through-put. Typically the PLC run-time on an embedded platform is
managed over the Ethernet and is used in factory, building, mobile, and process and energy automation.
In the past, many PLC systems utilized custom designed ASICs to obtain the system and environment
requirements. Today, many manufacturers are looking for off-the-shelf processing solutions such as
application processors or FPGAs with embedded cores.
This document describes some of the challenges in meeting the reliability and environmental requirements
for types of logic controllers with commercially available processors.
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PLC Critical Requirements
PLC applications generally require high reliability from both the hardware and software. The Soft Error
Rate (SER) across all used device memory and logic must be low. Generally, the low SER failure rates
are expected to be in the 130 to 240 FITs.
These applications are expected to have a long lifetime typically in the 100,000 power-on hours or 11.4
years of continuous use (24 hours/7 days per week) at a high operating temperature with little or no air
flow. In some applications, the PLC life expectancy may exceed the 100,000 power-on hours.
In addition to the reliability expectations, PLC applications typically utilize low latency access to the I/O
interfaces and processor through-put.
Low power is also a critical requirement as many of the PLC applications are designed to minimize space,
which results in the use of a processor without a cooling fan or heat sink. Generally, PLC applications
need low power and smaller footprints to achieve better overall efficiency.
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Trade-Offs for Best Performance
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Trade-Offs for Best Performance
Reliability is the probability of meeting specifications or requirements over time. This is often measured in
FIT (Failure In Time). The FIT rate is the number of failures in 1,000,000,000 device operating hours and
is a time dependent value. The reliability performance of a semiconductor device can be influenced by
changes in material properties and application conditions.
Wear-Out Region
Useful Life Region
Failure Rate
Early Life
Failure
Region
Time
Figure 1. Reliability Curve
Application temperature, voltage and activity can have a large impact on the intrinsic or wear-out
associated with the semiconductor device reliability performance. One of the most influential factors in
effecting a products overall life expectancy is the operating junction temperature in the application. This is
the temperature of the device silicon during operation. As the junction temperature increases, the overall
product life expectancy will decrease. Voltage also has an impact in product performance over time. In
much the same way as junction temperature, as the voltage increases, the product life will decrease.
Finding the right balance in product performance verses reliability expectations is critical in optimizing the
application goals.
The Texas Instruments AM335x products are designed to support an intrinsic reliability goal or wear-out
rate of 50 FIT (MTBF = 2 e7 hours) for 100,000 power-on hours (POH), when used at a junction
temperature of 105°C and nominal core voltage as defined by the device-specific data sheet.
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AM335x Reliability Considerations in PLC Applications
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Trade-Offs for Best Performance
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Figure 2 demonstrates the effect of temperature and estimated FIT rate when operated at the defined
junction temperatures for 100,000 power-on hours.
Figure 2. Chart 1
Many processors, such as the TI AM335x products, have multiple operating performance points which
may be utilized depending on the application needs.
For example, the following operating performance points are from the April 2013 revision of the Sitara™
AM335x ARM® Cortex™-A8 Microprocessors (MPUs) Data Manual (SPRS717).
The power-on hours (POH) information in Table 1 is provided solely for your convenience and does not
extend or modify the warranty provided under TI's standard terms and conditions for TI semiconductor
products.
To avoid significant degradation, the device power-on hours (POH) must be limited to the following:
Table 1. Reliability Data
Commercial
(1)
Industrial
Operating
Condition
Junction Temp
(Tj)
Lifetime (POH)
Extended
Lifetime (POH)
(1)
Junction Temp
(Tj)
Lifetime (POH)
(1)
Junction Temp
(Tj)
37K
(1)
Nitro
0°C to 90°C
100K
-40°C to 90°C
100K
-40°C to 105°C
Turbo
0°C to 90°C
100K
-40°C to 90°C
100K
-40°C to 105°C
80K
OPP120
0°C to 90°C
100K
-40°C to 90°C
100K
-40°C to 105°C
100K
OPP100
0°C to 90°C
100K
-40°C to 90°C
100K
-40°C to 105°C
100K
OPP50
0°C to 90°C
100K
-40°C to 90°C
100K
-40°C to 105°C
100K
POH = Power-on hours when the device is fully functional.
NOTE: Logic functions and parameter values are not assured out of the range specified in the
recommended operating conditions.
The above notations cannot be deemed a warranty or deemed to extend or modify the warranty under TI's
standard terms and conditions for TI semiconductor products.
In looking at the various operating conditions and assuming a target FIT rate of 10 FITs, Figure 3 would
be the estimated reliability performance in power-on hours as it relates to the junction temperature. This
model assumes constant operation at the specified junction temperature and power-on hours.
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Summary
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Figure 3. Chart 2
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Summary
In conclusion, selecting the appropriate operating performance point to best meet the application needs for
life expectancy targets and environmental conditions is critical in attaining the application goals. Trade-offs
between frequency and junction temperature can greatly influence the product life expectancy.
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Reference
•
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Sitara™ AM335x ARM® Cortex™-A8 Microprocessors (MPUs) Data Manual (SPRS717)
AM335x Reliability Considerations in PLC Applications
SPRABV9A – April 2014 – Revised September 2015
Submit Documentation Feedback
Copyright © 2014–2015, Texas Instruments Incorporated
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