Electronic Component Selection Guide

The component selection is the most important and crucial part for the designer in the product development cycle.

Process of Component selection:


Parameter of Component Selection

There are various parameters to be considered for component selection. The parameters to be considered for component selection can be broadly classified as technical parameters and non-technical parameters. The selection process is many a time, a fine balancing act between the technical and non-technical aspects.

  1. Technical Parameters 

Functionality: The first and foremost question to be asked by the designer is whether the component under consideration meets all the functions desired by the application. An example could be whether a certain power supply IC meets the voltage and current requirements of the application. 

DC Electrical Characteristics: The most important DC Electrical Characteristic of the device to be considered is the supply voltage(s) at which the device operates. In systems with multiple supply voltages, it is important to check the device’s input-output voltage tolerance to decide whether voltage translators are needed between the various components. The logic levels of the input and output lines (VIH, VIL, VOH, VOL) decide how the component fits into the overall system. 

AC Electrical Characteristics: The important AC Electrical Characteristics to be considered are the frequency of operation, rise time, fall time, propagation delay, setup and hold times. It is important to consider the minimum and maximum values of these parameters and not just the typical values. While interpreting the datasheet, it is important to note the conditions under which these parameters are measured. 

Power Consumption: The general guideline for this parameter is that it should be as low as possible. This becomes the decisive factor in choosing components for portable, battery-operated systems. The designer could look at special features such as availability of sleep modes, idle modes, etc that enable to reduce the power consumption when the device is not active. For example, in a portable audio player, it would be ideal to choose a codec chip that not only has lower active power but also supports switching to a low power mode when not playing back music. 

Supporting Circuit Elements: While choosing a component, it is essential to consider the additional circuitry that allows the component to operate. With the levels of integration going ever higher, it would be better to choose components that support greater on-chip features so that the number of external components is reduced. Greater the on-chip features, lesser the cost, physical size, and power consumption of the system. For example, when choosing a processor IC, the designer could look for the set of peripherals supported such as DMA Controllers, on-chip memory etc also in addition to the core processor function. When choosing Switched Mode Power Supply (SMPS) IC, the designer could look for ICs with built-in MOSFET. Another important factor to be considered is the number and type of power supplies required for the operation of the IC. For example, when choosing an Analog to Digital Converter (ADC), it would be essential to consider the Power Supply Rejection Ratio (PSRR) to decide on the ripple specification of the power supply that drives the ADC. 

Operating Environment requirements: Every component is specified to operate in a certain temperature and relative humidity range. Based on this criterion, components are classified as belonging to the Commercial grade, Industrial grade, and the Military grade. The designer could choose the appropriate grade component based on the system’s operating environment. 

Regulatory Requirements: Regulatory requirements of different national regulatory bodies place constraints on the choice of components. An example of this is the Restriction on the use of certain Hazardous Substances (RoHS) directive of the European Union. This directive bars the usage of Lead (Pb) and other hazardous substances in electronic systems. Support for Pb-free soldering and compliance to RoHS directive could be an important criterion for choosing a certain component. Another example is to verify whether a module or subassembly like AC-DC Converter, being considered is certified to meet FCC, CE, or UL requirements. 

Reliability Data: Comparison of component reliability parameters such as the Mean Time Between Failure (MTBF) of different components being considered would be essential for the design of high reliability systems. While the MTBF data is not generally available from a component datasheet, this could be obtained from the manufacturer. 

IP Availability: When the component under consideration is a Processor or a Programmable Logic Device such as CPLD or FPGA, availability of Intellectual Property (IP) that can be licensed from the IC vendor or third parties is a critical choice that enables faster time-to-market. For example, availability of different operating systems on a processor, availability of audio or video codec software IP on a Digital Signal Processor etc., enable the system to hit the market faster. 

Development Tools: Availability and quality of development tools is a very critical parameter for certain types of components such as Microprocessors, Microcontrollers, Programmable Logic devices etc. Scope for enhancement 

Physical Size: Size of a component is another critical parameter for system design especially in the case of hand held and portable systems. 

        2. Non-Technical Parameters 

Cost: Cost is a critical constraint in any component selection. The important point to be seen is the cost of the total solution than just the cost of the particular component under consideration. 

Multiple Sources: For mass production, having multiple suppliers and manufacturers for the component is a desirable feature since it eases procurement and lowers cost due to competition. Also, the risk of component obsolescence is reduced. A good guideline to follow for the selection of components like buffers, logic gates, operational amplifiers etc., is to choose those packages that are made by multiple vendors. 


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