Correct timing

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Many analog circuits require a clock signal or require that a task be performed after a certain amount of time. For such applications, there are a variety of solutions available. For simple timing tasks, a standard 555 circuit can be used. Using the 555 circuit and appropriate external components, many different tasks can be performed.

However, the widely used 555 timer has a drawback in that it cannot be set very accurately. The 555 timer works by charging an external capacitor and detecting a voltage threshold. This circuit is easy to make, but its accuracy depends greatly on the actual value of its capacitor.

Crystal oscillators are used in applications where accuracy is a must. They may be very accurate, but they have one drawback: reliability. Anyone involved in repairing electrical equipment knows that failures are often caused by large electrolytic capacitors. Crystal oscillators are the second leading cause of failures.

A third way to measure length of time or generate a clock signal is to use a simple small microcontroller. Of course, there are many devices to choose from, and each has its own optimization method. However, these devices need to be programmed, and the user needs to have a certain amount of knowledge to use it; in addition, due to their digital design, they must be used with great care in critical applications. For example, if the microcontroller fails, the entire system will have problems.

In addition to these three basic clock generation building blocks, there are other lesser known alternatives. One such alternative is the TimerBlox modules from Analog Devices. They are silicon-based timing modules that, unlike microcontrollers, are fully analog in operation and can be adjusted via resistors. Therefore, no software programming is required and the functionality is very reliable. Figure 1 provides an overview of the different TimerBlox modules and describes the basic functions of each. Countless other functions can be generated using these basic building blocks.

Figure 1. TimerBlox circuit for generating various timing functions.

Compared to the widely used 555 timer circuit, the TimerBlox circuit does not rely on external capacitor charging. All settings are done in resistors, so its function is more precise. Accuracy can reach 1% to 2%. Crystal oscillators are more accurate, about 100 times, but with all the disadvantages that come with it.

The applications for timing modules are very diverse. Analog Devices has published many example circuits. Figure 2 shows an envelope detector. Several fast pulses are combined to form a longer pulse. The external components of the LTC6993-2 are minimal for this application. The capacitor in the circuit is just a backup capacitor to support the supply voltage and has no effect on the accuracy of the timing module. .

Figure 2. Envelope detector using the LTC6993 TimerBlox integrated circuit.

Other interesting applications include phase-shift synchronization of multiple switching regulators for power supplies, or adding spread spectrum modulation to a switching regulator IC with a synchronization input. Another typical application is the deployment of specified delays, where the timer provides a delayed turn-on function for a specific circuit segment.

There are many different technical solutions for generating clock signals and performing various time-based tasks. Each has its own advantages and disadvantages. Silicon oscillators such as the TimerBlox module, for example, are easy to use, accurate, and reliable because they use variable resistors instead of capacitors.