Hardware techniques should be maximized to ensure desired electromagnetic compatibility (EMC) performance before attempting any software techniques. This is important because software techniques do not reduce the level of immunity signals to which the MCU is exposed " they only reduce the impact of these signals on system operation. Even though the application performance may not be degraded, exposure to immunity signals can adversely affect long-term reliability.

In order to produce an application that meets both the mandated EMC requirements and minimizes cost, the design process must be both methodical and iterative. Rigorous system and PCB design methodologies are required to ensure quality and consistency in the design process. Without such methodologies, achieving EMC compliance will be accidental and unrepeatable. The design process must also be iterative to ensure the best possible system design and PCB layout at the lowest cost.

A design that minimizes cost cannot be completed properly in one pass " regardless of the quality of personnel or tools. An EMC-compliant, low-cost application is the result of close and consistent collaboration between the EMC engineer and all other engineering disciplines (i.e. " electrical engineers, mechanical engineers, PCB layout engineers, etc).

Building Blocks of Transient Suppression and Control
Components used to suppress or control transients can be grouped into two main categories: 1) components that shunt transient currents (voltage limiters), and 2) components that block transient currents (current limiters).

Note that depending on the rise time (frequency bandwidth) of the transient, a component may function as either a shunt or a block. For instance, at a slow rise time (low frequency bandwidth) an inductor will have little impedance (a shunt). At faster rise times (higher frequency bandwidth), an inductor will have greater impedance (a block).

As a result, transient suppression components must be carefully selected for the optimal operating conditions. The actual performance of the component in the application will depend on the radio frequency (RF) characteristics of the component and the physical geometry of the board layout.

Resistors. A series resistor between two nodes can provide inexpensive and effective transient protection. Resistance can be used to create low-pass filters and to decouple power domains.

In these applications, a series resistor is used to block or limit transients with frequency- independent resistance. Series resistance is primarily suited to protecting digital or analog signals that carry low currents and can accept a modest voltage drop (across the series resistance). Typically, wire wound or carbon composition resistors are used due to their ability to survive large transient currents.

Important characteristics to consider when selecting resistors are the steady-state maximum power rating, maximum working voltage, and dielectric withstand voltage. The parasitic shunt capacitance and series inductance of a resistor do not require special consideration in transient protection applications.

Capacitors. Capacitors are used in a variety of transient protection roles: bypassing or charge storage (as a limiter of voltage variations) and power decoupling (as a shunt element in a low-pass filter or a series element in a high-pass filter).