“Industrial processes require precise and robust control of actuators in order to manage process parameters such as flow, temperature and pressure. Precision analog output modules, so-called programmable logic controllers (PLCs) or distributed control systems (DCS), can generate voltage or current outputs for controlling such actuators. These modules need to provide stable, reliable and accurate output in harsh industrial environments.
Industrial processes require precise and robust control of actuators in order to manage process parameters such as flow, temperature and pressure. Precision analog output modules, so-called programmable logic controllers (PLCs) or distributed control systems (DCS), can generate voltage or current outputs for controlling such actuators. These modules need to provide stable, reliable and accurate output in harsh industrial environments.
The combination of ADI’s single-channel 16-bit I/V output DACAD5423 and overvoltage protection SPST switch ADG5401F meets this type of control requirement and can meet the requirements of analog output modules.
Precision is a key feature of the AD5423. In the voltage output mode, the TUE at 25°C is as low as ±0.01% (the entire temperature range is ±0.05%), and the typical output drift is 0.35 ppm FSR/°C. In the current output mode, the TUE at 25°C is also ±0.01%, and the typical output drift is 2 ppm FSR/°C. The differential non-linearity (DNL) in all output modes is ±1 LSB, ensuring monotonicity.
The on-resistance (RON) of the precision switch ADG5401F is 6Ω, and an auxiliary feedback channel is integrated to connect the channel IOUT/VOUT to the +VSENSE input of the AD5423. This eliminates any errors related to changes in the on-resistance of the ADG5401F. The maximum on-leakage current of the ADG5401F over the entire temperature range is 40 nA. 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 affected, and the dynamic range can be maximized.
The ADG5401F overvoltage protection SPST switch is used on the analog output of the AD5423 DAC to provide overvoltage protection in both power-on and no-power 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 node from damage due to system power failure, wiring errors, power timing and other issues. Figure 1 shows in detail how AD5423 and ADG5401F should be connected in the analog output module.
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, it is considered a fault and the main switch channel and auxiliary feedback channel will be automatically disconnected.
When the switch channel is disconnected during a fault, any large fault current is prohibited from flowing back to the DAC output and system power supply. During the overvoltage event, no large fault current flows, so the system power consumption is no longer constrained by the fault power consumption, and the design work required for the system power supply can be reduced. The ADG5401F allows the system to remove the current-limiting resistor in the output signal path, which may cause load margin issues in some applications.
ADG5401F integrates an anti-open loop switch. If the VOUT/IOUT node suffers from an overvoltage signal, the ADG5401F will activate the overvoltage protection mode, and the main channel 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 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 should be used The (TVS) device implements a circuit similar to that 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 system output.
Figure 2. ADG5401F circuit diagram
AD5423 has a built-in 12-bit internal diagnostic ADC that can provide diagnostic information about user-selectable inputs (such as power, ground, internal die temperature, and voltage reference).
The on-chip diagnostic register contains flags for indicating various fault conditions, as well as the FAULT pin triggered by any fault. The short-circuit detection is monitored in the voltage output mode, and the open-circuit detection is monitored in the current output mode. AD5423 also provides a cyclic redundancy check (CRC) to check the received data; if the current data packet does not look correct, the FAULT pin is triggered. It also provides a temperature monitoring function, if the chip temperature exceeds the set limit, it will record the fault.
Figure 3. Functional block diagram of AD5423
The AD5423 and ADG5401F cooperate with each other to provide the precision and robustness required for industrial process applications. The 16-bit I/V output of the AD5423 can provide the precise control signals required by modern analog output modules, while the ADG5401F can maintain this accuracy and provide strong protection in harsh environments to prevent external influences from causing system failures or reduced accuracy.