Defining the problem: A step by step tutorial on EMI, ESD, and EFT problems in embedded designs and a range of possible solutions.
When it comes to protecting their designs from a variety of transient electrical disturbances, developers of microcontroller-based embedded systems in consumer, industrial, and automotive electronics are caught between the rock and the hard place.
On the other, increased competition, as well as market regulatory pressures, are forcing original equipment manufacturers (OEMs) to reduce the cost of their products. As a result of this focus on cost control, implementing the necessary transient immunity protections to prevent application malfunction due to transients on power and signal lines is becoming ever more challenging.
The impact of increasing MCU sensitivity and low-cost application design is being felt in all markets: consumer, industrial, automotive, etc. While there are significant differences in the design and use of products for these markets, the susceptibilities induced in all microcontroller-based applications are essentially the same. Typical susceptibilities include unexpected state changes on input pins (reset, interrupt request, or general purpose inputs), corruption of on-chip clock signals, or even damage to the silicon.
The pervasive impact of EMI and ESD transients
In consumer electronics applications, transient immunity is a challenge for both battery powered and AC mains powered products. Battery powered products such as keyboards, mice, remote keyless entry systems, and remote controls are challenged by ensuring the immunity of the application to ESD transients.
For example, an ESD directly to the product or to a nearby coupling plane has been seen to assert the reset function of an MCU by temporarily changing the state of the RESET pin. In these cases, there is typically a long trace between the RESET pin and an in-circuit programming header that serves as an antenna to receive the ESD energy and couple it to the RESET pin.
Likewise, an electrical fast transient (EFT) injected on the AC power plug of an AC mains powered product can couple to a reset trace by either radiation or conduction resulting in susceptibility. Self-compatibility is also of great concern where the product contains inductive loads (motors, compressors, etc) that are switched.
Since electronics for industrial applications is typically powered only from the AC mains, they have similar issues to those of consumer electronics products powered from the AC mains. However, these issues are typically more severe than in residential applications due to the presence of heavy machinery (large inductive loads) switching on and off the power distribution system for the factory.
The transient immunity issues in automotive electronics applications are also similar to consumer electronics applications except for being powered by DC mains. This is because automobiles contain numerous switching inductive loads (alternator, compressor, solenoids, etc) that put transients on the DC mains. In addition, automotive applications are becoming increasing concerned with ESD.
For example, a new application for MCUs is in remote tire pressure monitoring systems (TPMS). This is a novel innovation but introduc
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