Harmonizing Circuit Design and EMC DesignPart 5 Product Specifications (2) ?How to Read Product Specifications

Hello! This is Inagaki of ROHM.

In this Part 5, we consider how to read product specifications. We’ll focus on “electrical characteristics”, which the last time we explained are the most important. Normally, standards may include any or all of minimum values, typical values, and maximum values. It is important to correctly understand what each of these means; if they are misunderstood, design problems may occur. I’ll explain them based on specific examples.

The first important point to understand is that, while minimum values (min.) and maximum values (max.) are guaranteed, typical values (typ.) are not guaranteed values. In many cases, typical values, indicated by “(typ.)”, are representative values at or near the center of a distribution, and are considered to be reference values.

Example 1:

This first example is a reference voltage; shown are the minimum value, the maximum value, and a typical value. In design, 1.250 V is the central value for this particular reference voltage, which can range from a minimum of 1.225 V to a maximum of 1.275 V; that is, we see that there is a tolerance of ±2%.

Example 2:

This second example is of the Low level of an output voltage; in this example, a maximum value and a typical value are presented, but no minimum value is stipulated. To put it this way is somewhat convoluted, but if the “Low” level voltage is too high, it no longer functions as a “Low” level, and so a maximum voltage for the Low level is guaranteed. A minimum value is not stipulated because the level cannot be at ground voltage or lower. In design, it should be understood that the central value for the Low output voltage is around 0.1 V, but voltages of up to a maximum 0.5 V are included. Intuitively, one can say that Low levels for the output voltage of up to a maximum 0.5 V are ensured.

Example 3:

This example is the opposite of Example 2: only a minimum value and a typical value are stipulated. What this means is that a minimum value of 1 A is guaranteed for the output current, with a typical value of about 1.2 A or so. However, when in the design stage an output current of 1 A or greater is required, a device with these specifications cannot be used. If 1.2 A is necessary, a device with a minimum value of 1.2 A or greater is selected.

Example 4:

In this example, minimum and maximum values are stipulated, but no typical value is given. In many cases, such specifications indicate the usage range of an input voltage, a power supply voltage, or the like. In this example, even for a power supply voltage of 5 V, the common-mode input voltage must be in the range 0 to 3 V, with no deviations from this range allowed.

Example 5:

Finally, in this example only a typical value is given. The typical value is not a guaranteed value, and so in this case nothing is guaranteed. A “design value” appearing in conditions is nearly always either a theoretical value on the IC design which the deviation is probably about 2% if the IC is not defective, or a value based on the results of evaluations of characteristic distribution in a transition to volume production. Where design values are concerned, there are cases in which appropriate values are informally set as the minimum and maximum and outgoing tests are performed. In general, this procedure is applied to items for which measurement is difficult using IC outgoing test equipment, and to items verified in design and through statistical management.

Up to this point I have been discussing general electrical characteristics; how about electromagnetic compatibility (EMC)?

In fact, almost no guarantees are made in the form of standards. There are cases in which product specifications describe electromagnetic compatibility (EMC) characteristics. but these are in essence reference values, and no guarantees are made.

Moreover, in electromagnetic compatibility (EMC), most measurement values are for N=1 (measurements are made for a single sample chosen at random), and the temperature characteristic is not measured. The reason for this is that a long length of time is required for a single measurement, and it is difficult to change the ambient temperature in the measurement setup state, among other issues. These facts are well-known and can be said to more or less apply to all the semiconductor integrated circuit manufacturers.

Thank you for your kind attention.