Speaker
Mr
Flavien DOZOLME
(THALES Communications & Security)
Description
**1.Introduction**
Microcontrollers and DSPs are key components of embedded systems for most applications (space, avionics, industry…). The reliability of these components has to be asserted to ensure the correct working of the system for the duration of its mission while preserving its performances.
Designers are currently greatly tempted to use commercial components for their applications; they are easier to use and buy while providing higher calculation performances. However, these components
generally have not been tested in extreme environments. From these facts, it seems mandatory to
consider the importance of testing microcontrollers and DSPs before employing them in space applications, or any other application that comes with an extreme environment. That is the reason why the electrical test and reliability team of THALES Communications & Security worked on the subject. This document summarizes test methods and shows some results in regards to testing and qualification of microcontrollers and DSPs in high temperatures. Results described in this abstract have been observed by testing ARM M0 & M4 microcontrollers for industrial application.
**2.Characterization**
Characterization tests were performed on a few components to quantify the drift of their
performance and behavior relatively to temperature. In order to obtain the most precise measurements, the part under test is mounted on a daughter board plugged into an ATE (Automatic Test Equipment). High temperature environment is achieved using an air stream temperature forcing system (see picture below).
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*Figure 1: Mutest ATE with ThermoStream to characterize components*
A firmware including several test scenarios is programmed into the device. The ATE then
orders the component to launch perform the various test scenarios with voltage, clock
frequency, and temperature variations. More exactly, the following parameters can be tested:
- Core functionalities (boot sequence, multi-core communication, voltage supervisor, interruption)
- Clock structure (internal clocks, external clocks, PLL, timers) · Processing modules (ALU, FPU,
TMU)
- Internal memory (volatile and nonvolatile, user and program memory)
- Peripheral communication modules (ex: UART, SPI, I2C, CAN, Ethernet)
- Analog blocks (ADC, DAC, comparator, PWM)
- Operating and low power consumption modes
- I/O characteristics (leakage current, input and output voltage) According to the tested device, various
parameters evolve over temperature, the most noticeable one being current consumption (see the chart below):
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*Figure 2: Current consumption of tested microcontroller in low power mode over temperature*
This first chart shows the current consumption of a microcontroller in a low power mode according to voltage (2.5 or 3.3V) setting and temperature. The low power mode displays an obvious temperature limit to its use. Indeed, from 210°C @2.5V and 215°C @3.3V current consumption is the same as in normal mode. This result also highlights the need for a higher voltage supply to function as temperature increases. Nevertheless, a different test performed on another component, points out the decrease of the maximal operating voltage supply as temperature increases. The root cause of this
would be the decrease of the output voltage provided by the internal regulator when current consumption gets too high (higher current consumption as temperature
increases). The application report “Understanding the Terms and Definitions of LDO Voltage” [2] mentions this particular behavior relative to voltage regulators.
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*Figure 3: Regulator output voltage vs output current draw*
This phenomenon can be observed when testing the ADC module by measuring a stable input (VCC/2) while using the internal voltage regulator as voltage reference.
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*Figure 4: ADC measurements with internal reference*
On the other hand, performing the same test with an external reference gives stable result up to at least 190°C. In the case of the internal reference, the ADC output code positive data at high temperature comes from a negative drift of the voltage reference. What’s more, the higher the voltage supply, the higher the ADC code gets.
It goes without saying that these examples are only a few among other parameters to show both functional and parametric behavior changes along with temperature.
**3.Qualification**
Assessing the functional configurations of the device under test is one thing, ascertaining its ability to remain in working conditions for the duration of its application is yet another.
As for the characterization, several scenarios are implemented into the embedded firmware. A digital sequencer in the cold side continuously and sequentially calls all scenarios executed by devices under test in the hot side.
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*Figure 5: SANSA architecture*
This homemade system is named SANSA: Solution to Activate Numerical Systems for Ageing. Its aim is to simulate as well as possible the working conditions of the device under test (extreme environment for thousands of hours).
Such a testing methodology quantifies drifts over time of both parametric and functional performances of the tested parts.
A critical parameter to monitor during such an ageing test is the complete retention of the
program memory embedded in the DSP. Data corruption might reach error rat that
cannot be compensated by correction algorithms (ECC). The JEDEC standard
JESD218 [3] states the decrease in retention time capabilities of a typical FLASH memory
in regards to temperature by using models from the JEDEC standard JEP122G [4]. For
example, the Arrhenius equation can be used to compute the acceleration factor due to a
temperature increase, and to have an estimation of the retention degradation caused by temperature.
**4.Conclusion**
This document summarizes test methods to ensure performance and reliability of a microcontroller or a DSP in high temperatures, and shows some test results.
In addition, this methodology can also be applied to test devices’ behaviors in a radiation environment, especially to test internal memory resiliency.
To finish, this qualification process can just as well be implemented to qualify FPGA devices for space applications, and to compare their performances with DSPs’.
**Reference**
*[1] “Extreme Environment Electronics”, John D. Cressler, Alan Mantooth*
*[2] “SLVA079: Understanding the Terms and Definitions of LDO Voltage Regulators”, Bang S. Lee, Texas Instrument*
*[3] “JEDEC standard JESD218: Solid-State Drive (SSD) Requirements and Endurance Test Method”*
*[4] “JEDEC standard JEP122G: Failure Mechanisms and Models for Semiconductor Devices”*
Primary author
Mr
Flavien DOZOLME
(THALES Communications & Security)
