INDUSTRY 4.0 u ANALOG DEVICES


Due to variances across different systems and machines, typically, a programmable logic controller (PLC) can be used to control the many complex parameters.


sensors. Furthermore, allocating some of these channels to lower input ranges is useful for current measurements with an external sense resistor. In modern multiplexed ADCs, like some of the AD411x family, such sense resistors are incorporated into the component. AFEs integrated with critical passive components, like accurate low drift matched 1MΩ and 10MΩ voltage dividers with Analog Devices’ iPassives®


technology, eliminate the


need for costly external components. This enables higher density and at the same time, more spatially optimised solutions by minimising the solution footprint, weight, and board space. The newest multiplexed ADCs, like the AD4116, have a low power, low noise, 24-bit, sigma-delta (∑-�) ADC that integrates a very high impedance AFE. Figure 1 shows the internal structure of the part. For utmost flexibility, the inputs can be configured independently. Each setup allows the user to enable or disable the buffer, correct the gain and offset, select the filter type, select the output data rate (ODR), and select the reference source. The flexibility in selecting different voltage


reference sources makes the design task easier. These multiplexed ADCs have versatile reference source options, like an internal low drift 2.5V source, an external reference via differential Ref+ and Ref- pins or using analogue power supply (AVDD-AVSS). For an external reference, such ADCs have


true rail-to-rail, integrated precision unity gain buffers on both reference inputs. These buffers with high input impedance allow high impedance external sources to be directly connected to these inputs. Similarly, the user of modern ADCs can select the clock source from an internal oscillator, an external crystal, or an external clock; a flexibility that eases the design process. On the analogue side, the input is a crucial


part that determines the robustness of a multiplexed ADC, as it receives external voltages from peripherals. With a single 5V supply, a modern multiplexed ADC like the AD4116 can achieve input ranges


18 March 2024 Irish Manufacturing Figure 2: A typical connection diagram


up to ±20V. This ADC can even accommodate input voltages beyond these voltages, due to ±65V absolute maximum ratings, without incurring damage to the device. However, in this input range, there may be


trade-offs in accuracy. An external protection device like a TVS, shown in Figure 2, can protect the ADCs beyond the absolute maximum ratings. On the digital side, a CRC checksum reinforces the robustness of the interface. The RC low-pass filter at the inputs of the


ADC, as shown in the Figure 2, assists with anti- aliasing and noise filtering. An important point is that the filter resistor is placed in series with the input impedance of the ADC. This resistor will affect the internal voltage divider ratio resulting in a gain error. Nevertheless, with very high input impedance


like 10MΩ of the ADC, the voltage division error will be very small. For example, if 180Ω is used, the error will be only around 0.0018%. Moreover, this error can be removed by a system calibration or adjustment of the gain settings. The former can be completed by utilising the calibration mode offered by the newest multiplexed ADCs. These modern ADCs have four sub-


calibration modes: internal zero-scale, internal full-scale, system zero-scale, and system full-scale. In addition to calibration mode, for normal


operation, other options include continuous conversion mode, continuous read mode, or single conversion mode. To save power in systems with constricted power budget, the user can also activate standby or power-down modes.


EXTRA INTEGRATED FUNCTIONS The high integration of the newest multiplexed ADCs allows for greater flexibility especially in typical automation applications. For example, there are four integrated general-purpose input output (GPIO) pins, two of which can be configured as digital inputs or outputs, while two others can be configured solely as digital outputs (GPO). These GPIO or GPO pins can be used for controlling an extra external multiplexer. With an external multiplexer, one can increase the channel count even further. Another integrated feature is a programmable delay block that can be enabled before the ADC begins to take samples. This delay allows an external multiplexer or amplifier to settle. The latest ADCs generate, by default, 24-bit conversions. However, the width of the conversions can be reduced to 16 bits via a control bit for easier data processing in some microcontrollers. An integrated temperature sensor can help monitor the ambient temperature at which the device is operating. It may also be used for diagnostic purposes, or as an indicator of when the application circuit must do a calibration routine due to possible shifts in operating temperature.


CONCLUSION The latest multiplexed ADCs are highly accurate and can be easily integrated, meeting the increasing need for performance and robustness in modern production plants and industrial applications. At the same time, designers gain greater flexibility and meet system performance requirements more quickly and easily.


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