Accurate and stable, how would you rate this combination?

Industrial processes require precise and robust control of actuators to manage process parameters such as flow, temperature, and pressure. Precision analog output modules, also known as programmable logic controllers (PLCs) or distributed control systems (DCSs), can generate voltage or current outputs for controlling such actuators. These modules need to provide stable, reliable, and accurate outputs in harsh industrial environments.

The combination of ADI's single-channel 16-bit I/V output DAC AD5423 and overvoltage protection SPST switch ADG5401F meets this type of 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 is as low as ±0.01% at 25°C (±0.05% over temperature), with a typical output drift of 0.35 ppm FSR/°C. In current output mode, TUE is also ±0.01% at 25°C, 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 (RO) of 6Ω and integrates an auxiliary feedback channel to connect the channel IOUT/VOUT to the +VSENSE input of the AD5423, thus eliminating any errors associated with the on-resistance variation 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.

steady

ADG5401F Overvoltage Protection SPST switches are used on the analog outputs of the AD5423 DAC to provide overvoltage protection in both the powered and unpowered states. The source (S) and source feedback (SFB) pins of the ADG5401F can withstand overvoltages up to ±60 V. This protects the precision analog output nodes from damage due to system power loss, wiring errors, power supply timing, etc. Figure 1 shows in detail how the AD5423 and ADG5401F should be connected in the analog output module.

Figure 1. AD5423 and ADG5401F configuration.

The ADG5401F power supplies set the overvoltage fault threshold. If the voltage on the source pin (S or SFB) exceeds the ADG5401F supply voltage, a fault is considered to have occurred and the main switch channel and the auxiliary feedback channel are automatically disconnected.

When the switch channel is open during a fault, any large fault current is prohibited from flowing back to the DAC output and the system power supply. No large fault current flows 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 the current limiting resistor in the output signal path, which can cause load margin issues in some applications.

ADG5401F integrates an anti-open-loop switch. If the VOUT /IOUT node is subjected to an overvoltage signal, the ADG5401F will start the overvoltage protection mode, and both the main channel and the auxiliary feedback channel switches will be opened. At the same time, the internal anti-open-loop switch (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 supply rail.

To implement 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 should be used to 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.

Figure 2. ADG5401F circuit diagram.

Figure 3. AD5423 functional block diagram.

Table 1. High Voltage Transient Protection

diagnosis

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

On-chip diagnostic registers contain flags to indicate various fault conditions, as well as a FAULT pin that triggers 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) that verifies received data and triggers the FAULT pin if the current packet does not appear to be correct. It also provides temperature monitoring, and a fault is logged if the chip temperature exceeds a set limit.

in conclusion

The AD5423 and ADG5401F work together to provide the precision and robustness required for industrial process applications.

The 16-bit I/V outputs of the AD5423 provide the precise control signals required by modern analog output modules, while the ADG5401F maintains this accuracy and provides robust protection in harsh environments to prevent external influences from causing system failure or degradation of accuracy.