Reading Datasheets Of Electronic Devices

Most of the present-day electronics designers and application engineers do not find it necessary to look beyond the first page of the datasheets of the electronic components or devices while selecting one for their application. They consider the knowledge of a few major specifications of the device sufficient for the design exercise that they wish to undertake. Though it may be adequate in some cases, the design where the components are chosen without giving due consideration to the information contained in the datasheet may not be the optimal one.

The datasheet of a device reveals its true character and hence its suitability for a given application. In addition to listing down the device parameters, it gives the electrical and environmental conditions at which these parameters have been measured and also contains information on variation of important parameters as a function of other relevant electrical and environmental parameters. It is vital information particularly when you are designing a circuit or a module that has to qualify stringent environment standards. A comprehensive datasheet almost invariably includes application circuits recommended by the manufacturer.

Comprehensive and condensed datasheets

Both comprehensive as well as condensed versions of datasheets are usually available from manufacturers. The word ‘comprehensive’ is used here to differentiate between the datasheet of a device found in a short-form catalog and another datasheet of the same device available in the detailed version. For example, a company manufacturing a range of semiconductor devices may have one condensed catalogue containing data on all categories of devices like diodes, bipolar transistors, MOSFETs and thyristors that it manufactures. It may also offer detailed catalogues separately for each of these categories.

Surely, the technical data of a given device in the short-form catalogue will not be as comprehensive as it would be in the detailed catalogue. In the condensed version, one is likely to find salient features, major performance specifications, package information and electrical characteristics along with the condition for which they are valid. On the other hand, a detailed datasheet offers a range of characteristic curves showing variation of important parameters as a function of other relevant parameters and typical application circuits. 

Common Features

A study of the datasheets of a variety of devices, be they discrete or integrated circuit (IC), reveals a commonality in the type of data and characteristic curves. These common features are outlined in the following paragraphs.Typical applications and outstanding features. All datasheets begin with typical  applications as suggested by the manufacturer and the outstanding features of the device. This information appears on the first page of the datasheet and is an essential part of both condensed and detailed versions. Statements like “It has high dv/dt capability and a low thermal resistance… designed primarily for half-wave AC power control such as motor controls, heating controls… (taken from the datasheet of S2800 series SCR)… high photosensitivity, hermetically sealed… fast optical sensor of high-modulation bandwidth... (taken from the data sheet of PIN photodiode type BPX-65)… single-pulse avalanche energy rated, nanosecond switching speeds, linear transfer characteristics, high input impedance… well suited for applications such as switching regulators, motor drivers, relay drivers… (taken from the datasheet of power MOSFET type IRF250 shown in Fig. 1)” are representative of the first page of the datasheet of the device. This gives designers a fair idea of the important features and applications without going through the whole datasheet.

Device package outline: A sketch with device dimensions and lead identification, outline of the package styles of the device and other mechanical information are included in this part. Quite often a given device is made in more than one package style either with no difference in performance specifications (such as medium-power silicon transistor type 2N6045/MJE6045 made in TO220AB and TO127 package styles),
or with a minor difference (such as bipolar transistor 2N2222 in TO-92 plastic and TO-18 metal can
packages), and occasionally with a major difference (such as IC regulator type 78-series in TO-92 plastic, TO-220 and TO-3 packages).

Fig. 2 shows the package options for the operational amplifier LM741. As you can see from the figure, it is
available in three packages, namely, the metal can package, dual-in-line package and ceramic flatpak package.

Schematic diagram: Detailed schematic of the internal structure of the device is also given in the datasheet.
Fig. 3 shows the internal schematic of operational amplifier LM741. It helps the designer to correlate the electrical features of the device with its internal architecture. This sometimes helps the designer to explain the device behaviour that is otherwise not described in the datasheet.

Absolute maximum ratings: Absolute maximum ratings (Fig. 4) contain information on voltages, currents, powers and temperature range that should never be exceeded. As is evident from the figure, the maximum supply voltage for operational amplifier LF356 is ±18V.

Performance curves.  Performance curves of interest as a function of voltage, current, temperature, etc follow next. These include the characteristics of the device, such as drain current versus drain voltage (drain characteristics) or drain current versus gate voltage (transfer characteristics) in the case of FETs, vemitter voltage versus emitter current in the case of UJTs and forward voltage versus forward current in the case of diodes. Fig. 5 shows the characteristics curves for diodes 1N4001 to 1N4007.

 

Electrical characteristics.  Electrical characteristics are usually given in tabular form indicating spread in parameter values that is likely to occur in a batch of devices in terms of minimum, typical and maximum values. It is a vital design input as in some cases, spread in values could be as much as an order of magnitude.
To substantiate the statement, the datasheet of C122-series of SCRs from RCA tells that its dv/dt rating could
be anywhere between 10V/s and 100V/s. Similarly, the gate-source threshold voltage of power MOSFET
type IRF250 could vary from 2V to 4V (Fig. 7).

Application circuits. These are always Application circuits are usually included only in the detailed version of the datasheet.an asset to the designers, more so for those who are a little short of design experience. Quite of-
ten, expressions used to calculate different component values in a given application circuit are also presented.

Fig. 8 shows some of the application circuits for operational amplifier LF356 given in its datasheet. The information contained in Fig. 8 is reproduced from the detailed datasheet of LF 355/356/357 series of FET input op-amps.

Courtesy : Electronics For You  - www.efymag.com