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 additional 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 for 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 sub-
assembly 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 design of high
reliability systems. While the MTBF data is not generally available from a component
datasheet, this could be obtained from the manufacturer.