How to choose MCU in applications running at high temperature

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How to choose MCU in applications running at high temperature [Copy link]

Electronic controls are intrusive mechanical systems in fields ranging from automotive to industrial, military, and aerospace. The shift to electromechanical systems means that microcontrollers (MCUs), the workhorses of electronic systems, must serve in extremely difficult environments. A study of selected high-temperature and high-temperature MCU products from leading suppliers will illustrate the design options available to embedded system developers. Additionally, this article will discuss the separate but intertwined issues of high-temperature operation and automotive certification.

First, we should define what qualifies as extended and high temperature, and be forewarned that there is little consistency in the industry. Many IC vendors use the term "high temperature" to describe products that operate at ambient temperatures up to 125°C. Other companies call it "extended temperature," reserving 150°C for the "high temperature" designation.

Typically, products that operate in the 0°C to 70°C or 85°C range are considered consumer grade. Products that operate in the -40°C to 85°C range are considered industrial grade. As mentioned above, the real confusion comes with higher temperatures. For clarity, here we will specify the temperature at which the part operates. Typical levels above 85°C are 105°, 125°, and 150°C, although there are cases where other values come into play.

IC manufacturers may use the term "automotive grade" to describe a product. This may or may not imply high-temperature capability. Certainly, automotive applications in the engine compartment require electronics with high-temperature tolerance. However, automotive-grade or automotive-qualified ICs are typically ICs that have been tested to the AEC-Q100 standard.

AEC-Q100 qualified

The Automotive Electronics Council (AEC) was originally created by Chrysler, Ford, and General Motors to establish common standards for part certification and general system-level quality. The AEC-Q100 standard, or a more precise set of standards, defines the stress limits for ICs.

The AEC-Q100 qualification includes some items that apply only to specific types of ICs. For example, Q100-005 focuses specifically on the endurance of nonvolatile memory with respect to write/erase cycles. Obviously, this document applies to flash-based MCUs, but not so much to other ICs. Other Q100 documents apply broadly to things like Q100-001 shear testing of wire bonds. Other specific documents cover tolerance to electrostatic discharge, solder ball shear, and many other potential failure modes.

Still, IC manufacturers can test to AEC-Q100 at lower temperature ranges while providing components that do not meet AEC-Q100 standards for higher temperatures. Let's consider Texas Instruments (TI) and the company's widely used 16-bit MSP430 MCU family, which is targeted at low-power applications.

Figure 1 depicts a typical product in the MSP430F20x branch of the family. As you can see, the MCU integrates a typical peripheral set, including an 8-channel, 10-bit A/D converter. The CPU operates at 16 MHz.

Figure 1: The 16-bit MSP430 MCU family from Texas Instruments (TI) can be specified for application temperatures up to 150°C

Automobile cab application

TI offers MSP430F20x MCUs that operate up to 85°C or 105°C. However, TI recently announced that it is making its MSP430F2x and MSP430G2x MCUs available for AEC-Q100 for quite a while. Still, that certification is limited to the 105°C temperature level identified as Grade 2 in AEC-Q100. This means you won't find the MCUs in the engine compartment. But the MCUs will be used in cabin applications, from lighting controls to HVAC controls to remote keyless entry systems.

At the same time, TI supports high-temperature operation for some MCUs in the same series. For example, the MSP430F249MPMEP operates at 125°C. The MSP430F2619SPM can operate at 150°C. But for now, these high-temperature parts do not meet the AEC-Q100 standard.

Before we move on to the topic of AEC-Q100, you may find that specifying qualified parts is a good approach even if you don’t work in the automotive space, but your application requires high reliability and tolerance environments. For example, qualified components can tolerate vibration. In addition, other industries are beginning to rely on automotive-centric standards rather than developing their own requirements from scratch. We will also continue to discuss automotive applications through the rest of this article, as it serves as a perfect canvas to illustrate high temperature issues.

Returning to TI, the company has two other MCU families that offer high-temperature support. The TMS570 MCU family is rated for 125°C operation and is specifically targeted at automotive and transportation applications, where safety is also a key issue. In fact, the TMS570 integrates dual cores based on the ARM Cortex-R4F architecture (Figure 2). These cores can operate in what is known as “lockstep mode,” where both cores perform the same operation in parallel and the results are compared in real time to detect any failures. The MCUs are a good choice for any application that requires high temperatures and mission-critical safety.

Figure 2: The TMS570 MCU family from Texas Instruments offers extended-temperature operation and redundant cores to ensure safe operation in mission-critical applications.

There are also a wide range of industrial applications that require extended temperature support. Examples include motor control and industrial drive control. TI targets these applications with the TMS320F282x fixed-point MCUs and TMS320F280x Piccolo MCUs, both of which are rated for 125°C. These products are part of the company's product line for DSPs, sometimes referred to as digital signal controllers (DSCs).

Determine Your Temperature Needs

At this point, one could ask why you would need more than 125°C. The answer is complicated.

Customer demand has prompted Microchip to support 150°C operation on a fairly broad product line. In fact, there are 8-bit PIC12 and PIC16 MCUs available in stock that are rated for 150°C and meet AEC-Q100 standards at that temperature—known as Grade 0 qualification. Figure 3 depicts the PIC12F615 MCU, which packs a large feature set into an 8-pin package, including 1.75 KB of flash, multiple timers, and a four-channel, 10-bit A/D converter.

Figure 3: Microchip offers 150°C support and AEC-Q100 Grade 0 qualification in many of its MCUs, including the PIC12F615 described here.

Microchip's 8-bit and 16-bit product lines offer a wider range of 150°C products. There are also 16-bit PIC24 MCUs and dsPIC33 DSCs available from stock with a 140°C rating. In the 125°C class, the company offers 8-bit PIC10, PIC12, PIC16 and PIC18 MCUs, 16-bit PIC24 MCUs, and 16-bit dsPIC30 and dsPIC33 DSCs. In the 32-bit realm, the company recently announced a PIC32 MCU rated for 105°C.

Qualifying 150°C MCUs

Back to the high-temperature end of the spectrum. According to Microchip’s Termer, developing 150°C support was a complex process. He said that while customers were asking for such parts, “we didn’t have the data.” He also said the company had to go through a lengthy characterization process first.

Supporting 150°C requires qualification of the manufacturing process, especially for ICs that require high-temperature ratings. Termer said Microchip runs test structures through process qualification but will soon run real MCUs through the process.

There are many critical issues with high-temperature operation of MCUs that do not exist for low-temperature complex ICs. Termer said that accurate data retention in flash memory is a particularly difficult problem at high temperatures. Likewise, supporting a large number of flash write/erase cycles at high temperatures is even more difficult. A failure in either of these two areas will result in absolute system failure.

There are also issues with getting some analog peripheral functions to work properly at high temperatures. For example, integrated oscillators are susceptible to temperature effects. And A/D converters are also susceptible. However, in the analog area, failure modes are more likely to be loss of fidelity than complete failure. Chip design and process-qualified components must be optimized to achieve reliable high-temperature operation.

Indeed, it is important to make sure that when evaluating extended or high temperature MCUs, you consider the datasheets specific to the higher temperature parts. In some cases, MCU manufacturers will reduce certain specifications at higher temperatures. If you are using the low temperature spec sheet, you may get unpleasant surprises when testing your design at temperature.

Application and Temperature

Now let’s consider the types of applications that might require an MCU to operate in the temperature range we’ve discussed. Bill Hutchings, product marketing manager at Microchip, says 105°C MCUs are being used extensively in the renewable energy sector. For example, power inverters and control system displays for solar systems must operate for long periods of time in direct sunlight.

Sangmin Chon, C2000 marketing manager at TI, sees the industrial space as a primary target for 125°C products. Specific applications include power conversion, and such temperatures may also be required in large data center applications. Chon also sees 125°C MCUs serving a large portion of the automotive market, where 125°C-class, AEC-Q100-compliant products are referred to as Grade 1.

The market area for 150°C MCUs is well-established, and despite automotive being the primary consumer, the market is still large. But there are other 150°C applications. Microchip's Termer identified various drilling applications in the oil and gas industry. He said an MCU is often installed on the drill bit to capture and pre-process data that is then sent to the surface.

MCU availability

The available MCU families rated for 125°C and 150°C are perhaps more extensive than you might think. Therefore, if you have questions about whether temperature might be an issue in your design, do not hesitate to specify a high-temperature MCU; while these products cost more, they are less expensive than you might first guess. For example, Atmel offers 150°C-rated MCUs in its ATtiny and ATmega families (Figure 4). These products are based on the 8-bit AVR processor architecture. The maximum clock speed is 16 MHz. You can choose products with flash memory ranging from 2 to 64 KB. Figure 4 contains a block diagram of an ATmega MCU.

Figure 4: In its 8-bit ATmega and ATtiny MCU families, Atmel supports 150°C operation and an AVR CPU core.

Summarize

One challenge you may face when searching for an MCU that can run at higher temperatures is the often inconsistent way in which this feature is represented in the part number. Going into an IC vendor's website and searching for an extended or high-temperature MCU is often not simple, and inconsistent part numbers don't help.

With multiple manufacturers offering high-temperature MCUs at relatively affordable prices, electronic control will continue to pervade mechanical systems even in the harshest environments. The MCU is the hardest part of this equation due to the complexity of the IC, and MCU manufacturers are solving this problem for the industry. Just be sure to accurately identify the maximum operating temperature of your product. Don't forget that in some applications, such as our desert car example, when your system is powered down, elevated temperatures may be an issue. But you'll likely find that the MCU architecture you're already familiar with can meet your high-temperature requirements.

led2015

Today's chips have achieved a uniform temperature range, but in fact, when an abnormality is encountered, the chip will change.

okhxyyo

Thank you for sharing, I will save a copy

alan000345

Very good, it is really good to share. The chip design for use under high temperature conditions is very good.