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Precision, Robust Solution for Process Control Analog Outputs with Protection

Posted by: Yoyokuo 2022-08-30 Comments Off on Precision, Robust Solution for Process Control Analog Outputs with Protection

Industrial processes require precise and robust control of actuators to manage process parameters such as flow, temperature and pressure. Precision analog output modules, so-called Programmable Logic Controllers (PLCs) or Distributed Control Systems (DCSs), generate voltage or current outputs for controlling such actuators. These modules are required to provide stable, reliable, and precise output in harsh industrial environments.

The combination of ADI’s single-channel 16-bit I/V output DACAD5423 and overvoltage-protected SPST switch ADG5401F meets such control needs and can meet the requirements of analog output modules.

Precision

Precision is a key feature of the AD5423. In voltage output mode, TUE at 25°C is as low as ±0.01% (±0.05% over temperature) with typical output drift of 0.35 ppm FSR/°C. In current output mode, TUE at 25°C is also ±0.01% with a typical output drift of 2 ppm FSR/°C. Differential nonlinearity (DNL) is ±1 LSB in all output modes and monotonicity is guaranteed.

The precision switch ADG5401F has an on-resistance (RON) of 6Ω and integrates an auxiliary feedback channel for connecting channel IOUT/VOUT to the +VSENSE input of the AD5423, which eliminates any errors associated with the ADG5401F on-resistance variation. The ADG5401F has a maximum on-drain current of 40 nA over temperature. For a 16-bit 4 mA to 20 mA current output DAC, this leakage current is less than 1 LSB, the accuracy of the output signal chain is not compromised, and the dynamic range is maximized.

steady

The ADG5401F Overvoltage Protection SPST switch is used on the analog output of the AD5423 DAC to provide overvoltage protection in both powered and unpowered states. The source (S) and source feedback (SFB) pins of the ADG5401F can withstand overvoltages up to ±60 V.

This will protect the precision analog output nodes from damage due to system power loss, wiring errors, power sequencing, etc. Figure 1 details how the AD5423 and ADG5401F should be connected in the analog output module.

Precision, Robust Solution for Process Control Analog Outputs with Protection

Figure 1. AD5423 and ADG5401F Configuration

The ADG5401F power supply sets the overvoltage fault threshold, if the voltage on the source pin (S or SFB) exceeds the ADG5401F power supply voltage, a fault is considered, and the main switch channel and auxiliary feedback channel will automatically disconnect.

When the switch channel is disconnected during a fault, any large fault currents are inhibited from flowing back to the DAC output and system power supply. There is no large fault current flowing during an overvoltage event, so the system power consumption is no longer constrained by the fault power consumption and the design effort required for the system power supply is reduced. The ADG5401F allows the system to remove current-limiting resistors in the output signal path that can cause load margin issues in some applications.

The ADG5401F integrates an anti-open loop switch. If the VOUT/IOUT node experiences an overvoltage signal, the ADG5401F will initiate overvoltage protection mode and both the primary and auxiliary feedback channel switches will be turned off. At the same time, the internal anti-open loop switch (the internal connection between D and DFB) will be closed. This anti-open-loop switch keeps the DAC output feedback loop intact and prevents the DAC from clamping the output to the supply rails.

For protection against high voltage transients such as IEC 61000-4-2 ESD, IEC 61000-4-4 Electrical Fast Transient Burst (EFT) and IEC 61000-4-5 surge, discrete resistors and transient voltage suppression should be used (TVS) devices implement a circuit similar to that shown in Figure 2. Place the resistor within the feedback loop of the system so that the resistor does not add any error to the system output.

Precision, Robust Solution for Process Control Analog Outputs with Protection

Figure 2. ADG5401F circuit diagram

Table 1. High Voltage Transient Protection

Precision, Robust Solution for Process Control Analog Outputs with Protection

diagnosis

The AD5423 contains a 12-bit internal diagnostic ADC that provides diagnostic information on user-selectable inputs such as power, ground, internal die temperature, and voltage reference.

On-chip diagnostic registers contain flags to indicate various fault conditions, as well as the FAULT pin that is triggered for any fault. Short circuit detection is monitored in voltage output mode, and open circuit detection is monitored in current output mode. The AD5423 also provides a Cyclic Redundancy Check (CRC), which verifies the received data; if the current packet does not appear to be correct, the FAULT pin is toggled. It also provides temperature monitoring, and if the chip temperature exceeds a set limit, a fault is logged.

Figure 3. AD5423 functional block diagram

in conclusion

The AD5423 and ADG5401F work together to provide the precision and robustness required for industrial process applications. The AD5423’s 16-bit I/V output provides the precise control signals required by modern analog output modules, while the ADG5401F maintains this accuracy and provides robust protection in harsh environments against external influences that could cause system failure or loss of accuracy.

About the Author

David Forde graduated from Carroll Institute of Technology in 2006 with a Bachelor of Science degree in integrated circuit design. After graduation, he joined Analog Devices as a layout engineer. In 2011, he graduated from the University of Limerick with a master’s degree in engineering specializing in VLSI systems; in 2015, he joined the Instrumentation and Precision Technology Division as an application engineer, supporting the analog switch and multiplexer product lines.

Claire Croke joined Analog Devices in 1999 and is currently a Marketing Engineer in the Precision Switches and Multiplexers division in Ireland. Claire previously worked on the Precision Converters Applications team at Analog Devices. She graduated from the University of Limerick, Ireland, with a BA in Electrical Engineering.

Jean McAdam is Process Control and Automation Strategic Marketing Manager at Analog Devices. Prior to that, she was responsible for the marketing activities of ADI Platform’s customer assessment solutions and worked as a software systems engineer and software developer. She graduated from the University of Limerick with a BA in Electrical and Computer Engineering.

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