Author: David Forde, ADI – Claire crocke, Application Engineer – Jean McAdam, Application Engineer – Strategic Marketing Manager
In order to manage process parameters such as flow, temperature and pressure, precise and robust control of actuators is needed in industrial process. Precision analog output module, the so-called programmable logic controller (PLC) or distributed control system (DCS), can generate voltage or current output for controlling such actuators. These modules need to provide stable, reliable and accurate output in harsh industrial environment.
The combination of ADI’s single channel 16 bit I / V output dacad5423 and overvoltage protection SPST switch adg5401f meets the requirements of this kind of control and the requirements of analog output module.
Precision is a major feature of ad5423. In voltage output mode, 25 ° The Tue was as low as 0 ± 01% (the whole temperature range is 0 ± The typical output drift is 0.35 ppm FSR/ ° C。 In current output mode, 25 ° Tue at C is the same ± The typical output drift is 2 ppm FSR/ ° C。 The DNL of all output modes is 0 ± 1 LSB to guarantee monotonicity.
The on resistance (RON) of adg5401f is 6 Ω， An auxiliary feedback channel is integrated to connect the channel IOUT / Vout to the + VSENSE input of ad5423, thus eliminating any errors related to the on resistance change of adg5401f. The maximum conduction leakage current of adg5401f is 40 Na in the whole temperature range. For 16 bit 4 mA to 20 mA current output DAC, the leakage current is less than 1 LSB, the accuracy of the output signal chain is not affected, and the dynamic range can be maximized.
The adg5401f over-voltage protection SPST switch is used in the analog output of ad5423 DAC, which can provide over-voltage protection in both on and off state. The source (s) and source feedback (SFB) pins of adg5401f can withstand the highest load ± Over voltage of 60 v.
This will protect the precision analog output node from damage due to system power failure, wiring error, power timing and other problems. Figure 1 shows in detail how to connect ad5423 and adg5401f in the analog output module.
Figure 1. Configuration of ad5423 and adg5401f
If the voltage on the source pin (s or SFB) exceeds the power supply voltage of adg5401f, the main switch channel and auxiliary feedback channel will be automatically disconnected.
When the switch channel is disconnected during the fault, any large fault current will be forbidden to flow back to the DAC output and system power supply. There is no large fault current flow during the overvoltage event, so the system power consumption is no longer constrained by the fault power consumption, and the design workload of the system power supply is reduced. The adg5401f allows the system to remove a current limiting resistor from the output signal path, which may cause load margin problems in some applications.
Adg5401f integrates an anti open-loop switch. If the Vout / IOUT node suffers from overvoltage signal, adg5401f will start overvoltage protection mode, and the switches of main channel and auxiliary feedback channel will be disconnected. At the same time, the internal anti open loop switch (internal connection between D and DFB) will close. The anti open-loop switch keeps the DAC output feedback loop intact and prevents the DAC from clamping the output to the power rail.
To achieve high voltage transient protection, such as IEC 61000-4-2 ESD, IEC 61000-4-4 electrical fast transient (EFT) and IEC 61000-4-5 surge, discrete resistors and transient voltage suppression (TVS) devices shall be used to implement circuits similar to those shown in Figure 2. Put the resistor in the feedback loop of the system, so that the resistor will not add any error to the output of the system.
Figure 2. Adg5401f circuit diagram
The ad5423 has a built-in 12 bit internal diagnostic ADC that provides diagnostic information about user selectable inputs such as power, ground, internal die temperature, and voltage reference.
The on-chip diagnostic register contains flags to indicate various fault conditions and a fault pin triggered by any fault. Short circuit detection is monitored in voltage output mode and open circuit detection is monitored in current output mode. Ad5423 also provides cyclic redundancy check (CRC), which can check the received data; If the current packet does not look correct, the fault pin is triggered. It also provides temperature monitoring function, if the chip temperature exceeds the set limit, it will record the fault.
Figure 3. Ad5423 function block diagram
Ad5423 and adg5401f work together to provide precision and robustness for industrial process applications. The 16 bit I / V output of ad5423 can provide the precise control signal required by modern analog output module, while adg5401f can maintain this precision and provide strong protection in harsh environment to prevent system failure or precision reduction caused by external influence.
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 ADI as a layout engineer. In 2011, he graduated from Limerick university with a master’s degree in VLSI system engineering; In 2015, he joined the instrumentation and precision technology division as an application engineer, providing support for analog switch and multiplexing products.
Claire Croke joined ADI in 1999 and is currently a marketing engineer in the Irish precision switches and multiplexers division. Claire previously worked in ADI’s precision converter application team. She graduated from the University of Limerick in Ireland with a bachelor’s degree in electronic engineering.
Jean McAdam is the strategic marketing manager for process control and automation at ADI. Prior to that, she was responsible for the marketing activities of ADI platform customer evaluation solutions, and served as a software system engineer and software developer. She graduated from Limerick university with a bachelor’s degree in electronic and computer engineering.