How Datasheets Make Engineering Possible

Electronic components provide definable functions; they are the building blocks of design, and electronic design is all about putting those blocks together in the right way. However, unlike conventional building blocks that fit together with regularity, every electronic component is different. Part of the challenge for engineers is matching the component’s function to the design objective – and it’s not always a simple process.

In order to understand the functions, capabilities and limitations of a component, engineers use datasheets. These don’t simply provide the information (data) an engineer needs to select or reject a component – they are also an integral part of the design process.

Datasheets are technical reference documents, so they won’t contain time-sensitive or commercial information such as unit price or availability, but they will provide engineers with the information they need to compare and contrast different products that offer similar functionality. Parameters may vary between alternatives, such as operating temperature, package options or amount of integrated memory; these are just some examples of how engineers use the design-critical information provided.

Pin Definitions

Although their format varies depending on the device, most datasheets will include sections covering a component’s functionality, electrical specifications and pin definitions. The functionality will define the component’s primary purpose and explain how its functions are accessed, while the electrical specifications will define the manufacturer’s recommended operating parameters (see below for more details).

One of the most useful features a datasheet provides is pin definitions, normally in the form of a table which will include each pin’s location on the device, and its function. Design notes may also be included – for example, an output may be open drain, in which case it would need a pull-up resistor on its output. This information would only be available in the datasheet and if this requirement isn’t observed during design it would likely result in a fault.1Figure 1(a): The part numbering system for thick-film resistors from Panasonic

While a pin’s function will be consistent across different package outlines, its position will likely change. A datasheet will document these variations and show how they are defined by the part number. Most components are supplied in a range of package options as well as temperature grades, or (for programmable devices) memory sizes – parameters that are reflected in the part number. Understanding how a part number is formed, therefore, allows engineers to define the right part for their application. This is true for all components from discrete passives to integrated circuits. For example, Figure 1(a) shows a part numbering system for thick-film chip resistors from Panasonic, while Figure1(b) shows the part numbering system for the EFR32 microcontrollers from Silicon Labs. For more information about understanding IC packages, checkout the Octopart Guide to IC Packages.2Figure 1(b): The part number system for the EFR32 family of microcontrollers from Silicon Labs

Input and Output Characteristics

Datasheets also define a device’s operation, which will be dependent on how the device has been manufactured and how it is operated. Operation may change between devices, even in the same family, and it should never be taken for granted that one device will act the same as another of similar design. This can be critical when selecting alternative devices or second sources.3Figure 2: An example of the standard input characteristics for a CMOS port on a microcontroller, as shown in a datasheet

For example, Figure 2 shows the standard input characteristics for a CMOS port on a microcontroller manufactured by STMicroelectronics. It clearly shows how the minimum-logic high voltages and maximum-logic low voltages vary over supply voltage, and includes the operating areas within which the manufacturer cannot guarantee correct operation. This is the kind of operating characteristic that engineers must observe during design, or they risk introducing a design fault that could cause project delays. This information can only be found in a datasheet.4Figure 3: Example of how the active current consumption for a microcontroller is detailed in a datasheet

Understanding the electrical characteristics of individual components is essential at a system level. Figure 3 shows the current consumption for a microcontroller from Silicon Labs, clearly displaying how the supply current (Idd) increases with both operating temperature and supply voltage (Vdd). An engineer would use this information to work out how much current the device would require in the application, by referencing the relevant supply voltage curve at the typical operating temperature. This information would be used when designing the system power supply but can also help engineering teams work out if forced air cooling is required in the application. Of course, every component’s datasheet will be different in this respect but the information will always be provided and presented in the same way – in a table of maximum/minimum parameters and as transfer curves.5Figure 4: Example of how a datasheet documents the characteristics of a peripheral

Electrical characteristics will also be given for specific features of a device. Figure 4 shows how the output of the analog-to-digital converter (ADC) on the same microcontroller from Silicon Labs varies with supply voltage for given reference voltages. This information is critical in design, as it allows engineers to make provision (perhaps in software) for known possible variations (in this case it is in the Least Significant Bit of the digital output). Note that information provided as transfer curves in this form are normally specified as ‘typical’ and is not intended to be guaranteed; often the data is further classified as only being representative at a given operating temperature (in this case, 25°C).

Programmer’s Guides

For more complex devices that are configurable by firmware, the datasheet will include details of how it is programmed and its debug interface. However, very complex devices, such as SoCs that contain multiple processor cores, will normally be supported by an additional document such as a programmer’s guide. This would cover in more detail how the software/firmware is used to configure and control the device. If the processing core at the heart of the system is provided by third party company (such as ARM), the programmer’s guide may also be supplied by that company.

A programmer’s guide complements a datasheet by focusing on how the SoC is configured. Often this will include information that, unlike a datasheet, extends beyond the device itself, to include the software ecosystem that supports the device, including open source software (and where to find it) and the development environments that support the device. Increasingly, this will include partners who may provide an operating system or middleware, for example. A programmer’s guide has greater scope than a datasheet and is subject to more frequent changes. As such, some manufacturers now choose to publish them as wikis instead of ‘static’ documents, such as the CC3200 programmer’s guide from Texas Instruments.

Functionality6Figure 5(a): Datasheets will normally include a functional block diagram for the parts they cover, as show here for a Real-Time Clock/Calendar (RTCC) manufactured by Microchip

In most cases a datasheet will strive to cover every aspect of a device and how it is used. As an example, the block diagram in Figure 5(a) is for a real-time clock/calendar from Microchip, which represents how the device’s functions are accessed. Figure 5(b) shows how the same device might be used in a circuit. This information is provided in the device’s datasheet, and while it may also be available in an application note, not all manufacturers provide one.

The information provided in a datasheet will be relevant to using the device but it may not go into great detail about how its functionality is achieved. This is particularly true if the function provided is formalized under a recognised standard. An example may be a USB port; an integrated device may offer USB functionality, but the datasheet is unlikely to explain in detail how USB works. In this respect, engineers cannot substitute experience or knowledge for the information found in a datasheet; moreover it is a reference to knowledge an engineer may need in order to use a particular component.7Figure 5(b): Datasheets will often provide examples of how a device should be designed in, as shown in this extract from a datasheet for the RTCC from Microchip

In some cases, a device will provide access to functionality as a ‘black box’, which is particularly true for a device designed to work ‘out of the box’. In this case, the datasheet will still be essential, as it will explain how to access that functionality without the engineer needing to understand how it works. This is increasingly the case with highly integrated SoCs which may provide functions such as bluetooth connectivity, for example.

A datasheet is often the first piece of information an engineer will search for when considering a component, so it’s no surprise that references to datasheets are now appearing in more places. Online access to datasheets is seen as an inflection point in design; it gives more people from different backgrounds the opportunity to explore and get involved with electronic engineering.

The information it contains may not be available from any other source, making it practically impossible to use a component without referring to its datasheet. As such, every engineer working on a design project should have access to the datasheet for every component in that project. Today that may take the form of a digital library on a shared server, rather than a binder full of printed sheets.

Although it’s true to say datasheets have changed little over the years, they have evolved. The datasheet remains as essential as a circuit diagram, bill of materials or code listing. In fact, designing a circuit without the datasheets for each component would be incredibly difficult.

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A deep reflection on equivalent circuit thoughts

Abstract: “Equivalent” in the development of circuit theory plays a very important for use, this article from the concept of “equivalent”, the premise of equivalent application ideas, and circuit in the circuit model and analysis method of equivalent to illustrate the from beginning to end in the circuit is “equivalent”, by thinking, we can exactly underground

conclusion: circuit “equivalent” Want to have to exist already, also can’t be replaced.

Keywords: equivalent; Circuit model; Analysis method preface

Introduction

After a full year of study on the theoretical basis of circuit theory, I feel a deep sense that for the theory of circuit, the thought that it contains is the “equivalent” idea. Through equivalent thoughts, we can put the complex circuit simplification, the unknown into an equivalent circuit of the circuit, the communication into a phasor to simplify the calculation to choose a suitable text book of equivalent thoughts cause my interest, so that inspired me to more in-depth thinking of circuit equivalent thought, wrote the paper, if there are any errors or deficiencies, please correct me.

First,the concept of equivalence

For the concept of equivalent, the interpretation in the dictionary is to treat different things as the same thing. But, in the circuit theory, we can understand the concept of “equivalent” that is without changing the circuit itself characteristics at the same time, some of the specific functions of components or models with some to have the same function but different in the configuration of components or models to replace. Therefore, the equivalent transformation of circuit is also realized under certain conditions. Only by truly understanding the concept of equivalence can we correctly use the idea of equivalent transformation in circuit theory.

Second:the equivalent precondition of the circuit

In circuit theory, the concept of equivalent resistance, whether in series resistors or parallel resistors, can be used to convert it into a simple resistor. In the case of three resistors R1, R2 and R3, the equivalent resistance formula is derived.

The U = (R1+R2+R3)I

and U = RI

R is supposed to be another resistor. These two formulas are actually the volt-ampere relation between the volt-ampere relations of the series resistance circuit and the resistance R.

Derivation of the formula for equivalent resistance, is the requirement based on the two volt-ampere relations on the basis of the same, when the condition was established, we can use R to equivalent resistor R1, R2, R3 series. Here, I this simple example is not only to explain the process of the equivalent series resistance and more mainly want to point out that for equivalent looks be like simple, actually is set up under certain conditions, not to conduct an equivalent conversion can at any time. , for example, some problems, the definition of two-port network definition requires 22 port volt-ampere relations are the same, and not to say that an external one the same circuit requires equal voltage, current, respectively. If 22 port volt-ampere relation is the same, any external circuit, the same port must be equal to the current and voltage, but on the other hand, if an external one same electric road port voltage and current are equal does not guarantee that an external another same circuit port equal voltage, current, respectively. As shown in figure 1, when a and b on the left side of the two ends are composed of an external 1 Ω resistance, the voltage between a and b is 1 v, current is 1 a, but when all external 10 Ω resistance is no longer valid. Therefore, for equivalent circuit, it is necessary to make sure that it can be applied before the application, which can be determined according to different circumstances and cannot be carried out in an arbitrary way.

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Third:the equivalent of circuit model in circuit

For the equivalent circuit model, the most common way we line resistor, capacitor, inductor and power, etc., especially the resistance, for any components, in fact, there are certain resistance, therefore, the equivalent resistance is the most popular, is also the most essential. For the theoretical basis of the circuits we study, the equivalent of the resistance model is mainly reflected in the transformation of the resistance star and the triangle connection. As shown in FIG. 2, the star connection and triangle connection of the resistance are equivalent to each other through the following equation:

TU3

For inductive components, the equivalent

conversion Is reflected in the equivalent of

coupling inductance change Change, coupled inductor in series and parallel coupling  inductance

TU2

(Figure 2 The star connection of resistance is connected to a triangle)

can be covered by the inductance can be covered by the corresponding equivalent transformationof the original reason for circuit model.

In the case of uncoupled inductance and capacitance, the equivalent transformation and resistance have the same relationship, so it is no longer described here. For the equivalent of a simple power supply, we usually mention relatively few, so I will give a detailed introduction here:

(1)Series parallel and equivalent power supply of ideal voltage source:

①several voltage source in series can use a voltage source and its equivalent to replace, the electromotive force of equivalent power equals the algebraic sum of the electromotive force, and the equivalent electromotive force reference polarity and the same positive power supply, the opposite is negative.

② only the electromotive force equal and polarity of the same voltage source is allowed in parallel, the equivalent of parallel after the power is going to be any one of them, through the equivalent voltage source current is equal to the total/current; The voltage source of unequal size and polarity is not allowed in parallel, which will violate KVL.

(2) the parallel and equivalent power of the ideal current source:

① several current source in parallel can use a instead of the equivalent current source instead of the equivalent current source current is equal to the algebraic sum of the current source, the current source reference direction same as the equivalent source is positive, the opposite is negative.

② only the equal and same direction current source can be in series, a series of equivalent current source is going to be any one of them, at the ends of the equivalent source voltage is the same as external circuit, and alternative at the ends of the former part of the current source voltage is not the same. The current source that varies in size and direction does not allow concatenation, which is contrary to KCL.

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(3) ideal voltage source and current source series: When the ideal voltage source is in series with the current source, the voltage source can be removed and replaced with an equivalent current source. The equivalent current source is the original current source. The terminal voltage of equivalent current source is not equal to the voltage of the former current source, which is equal to the external voltage, as shown in FIG. 3.

(4) parallel between ideal voltage source and current source: When the ideal voltage source is in parallel with the current source, the current source can be removed and replaced with an equivalent voltage source, which is the original voltage source. The current flowing through the equivalent voltage source is not equal to the current flowing through the original voltage source, which is equal to the current of the external circuit, as shown in figure 4.

Fourth,the equivalent of the analytical method in the circuit

Actually, for the equivalent circuit of ideas, I personally think that the most main is not on the circuit model, but reflect on the method of circuit analysis, reflect on the understanding and awareness of the circuit, so to speak, the circuit of a theory of the “equivalence” has become a kind of brand-new theory, through this brand-new theory, we has a more profound understanding and knowledge of circuit, it is also caused me to think the main reason for the equivalent circuit theory.

For complex circuit, we do not need the model simplification, but we will analyze a method of transformation, so that it can also achieve the purpose of understanding and awareness circuit, even can deepen our understanding of circuit all details. On the basis of circuit theory, we illustrate this “equivalent” idea through a chapter, which is the circuit theorems that we are applying all the time. Including substitution theorem, homogeneity theorem and superposition theorem, the theorem of equivalent source and, theorem of root, the dual reciprocity theorem, the all draw circuit theorem, application of the theory of equivalent in different extent. Take the substitution theorem, for example,in any linear and nonlinear circuits, if the voltage and current of a port for U and I, usable Us = U voltage source or Is = I have current source to replace this port, as shown in figure 5 circuit, R1, R2, known to Us, I1 and I2 R3, if the application into an equivalent substitution theorem to the R3 current source, the calculation more simple. But at the end of the day, I would like to add that the equivalent of the method of circuit analysis is still the basic principle of the circuit, the essence of the equivalent before and after the equivalence.

In addition, the theory ofthe analysis of the sinusoidal ac voltage or current transformation

in the circuit is considered as a distinct example of the circuit equivalent idea.Although on the surface, it is only a data representation,but it will contain a into an equivalent ac dc’s thought,through the special equivalent, let us understanding of circuit and data analysis have a simpler, more clear understanding, at the same time, also for us to solve the problem of the circuit provides a simple method. So I think that this is the equivalent idea in a circuit, the equivalent of a circuit analysis method.

Conclusion

Through deep thinking, I can come to the conclusion that, always exist in the equivalent circuit theory, circuit theory contains the equivalent everywhere, the equivalent thought has become an integral circuit theory thoughts, it can make a complex transformation into a simple circuit, it can make a analysis method into another kind of simple method, it is for us to analysis and solve the problem of circuit provides a great help, to study the basic theory of the whole of the circuit provides a shortcut, I believe, it will also circuit theory is a charm can attract people.

References

[1] Zhou ping, Huang haiyan. Analysis of the equivalent transformation of circuits. Journal of Zhangjiakou agricultural science and technology. 2004.20(2).66-69
[2] Chen rare. Basis of circuit theory
[3] Li han-sun. The reference direction and circuit equivalent concept in circuit analysis
[4] Zhang yongzhao, Li jingmin, Yang wanming. The expression and application of circuit equivalent conditions. Journal of Hebei coal building engineering college