Circuit functions and advantages

The circuit shown in Figure 1 is a fully functional, flexible and programmable analog output solution using only two simulator devices, which meets most of the requirements of programmable logic controller (PLC) and distributed control system (DCS) applications. The ad5660-1 is a low-power (2.8 MW @ 5 V), rail to rail output, 16 bit nanodac ®, Ad5750-1 is an industrial current / voltage output driver. The combination of the two can provide all typical current and voltage output ranges, 16 bit resolution without code loss, 0.05% linearity and less than 0.1% output error. The circuit also has some important characteristics to support industrial applications, such as on-chip output fault detection, CRC verification to prevent packet error (PEC) and flexible power on options. It is very suitable for building a robust industrial control system. In mass production, it can maintain consistent performance without external precision resistance or calibration program, so it is an ideal choice for PLC or DCS module.

  Figure 1. Basic analog output circuit for single channel (schematic diagram, not showing all connection and protection circuits)

Figure 1. Basic analog output circuit for single channel (schematic diagram, not showing all connection and protection circuits)

Circuit description

AD5750 / ad5750-1 is a single channel, low-cost, precision voltage / current output driver designed to meet the needs of industrial process control applications. The voltage output range can be programmed for standard output ranges for PLC and DCS applications: 0 V to 5 V, 0 V to 10 V, − 5 V to + 5 V, and − 10 V to + 10 v. A 20% out of range setting is also provided for the standard range, resulting in the following options: 0 V to 6 V, 0 V to 12 V, − 6 V to + 6 V, and − 12 V to + 12 v.

The current output is provided through separate pins and can be programmed into the following ranges: 4 mA to 20 mA, 0 Ma to 20 mA, − 20 mA to + 20 mA, 0 Ma to 24 Ma, and − 24 Ma to + 24 ma. The unipolar range has an out of range setting of 2%. Because the current output of AD5750 / ad5750-1 can be either source current or suction current, it can interface with a wide range of sensors or actuators. If necessary, the voltage and current output pins can be connected together to configure the terminal system as a single channel output.

Ad5660-1 is a single channel, low-cost, low-power, rail to rail voltage buffered output nanodac with an integrated 1.25V, 5 ppm / ° C reference voltage source. Ad5660-1 has a built-in power on reset circuit to ensure that the DAC output is powered up to 0 V and maintained at this level until an effective write operation is performed.

The interface between ad5660-1 DAC and ad5750-1 driver is simple without external devices. The output voltage range of ad5660-1 is 0 V to 2.5 V, which matches the input range of ad5750-1. In addition, the reference output voltage of ad5660-1 is 1.25 V, which fully matches the reference input requirements of ad5750-1.

ESD protection and overvoltage protection required by devices used in PLC and DCS applications are generally much higher than the formal recommended requirements. Each pin of ad5750-1 has built-in ESD protection diode, which can prevent 3 kV transient from damaging the device (manikin). However, the industrial control environment may subject I / O circuits to much higher transients. Eval-cn0203-sdpz circuit board has built-in external 30 V / 600 W transient voltage suppressor (TVS), 50 MA / 30 V self recovery fuse (PolySwitch) and Schottky Power Diode to provide higher voltage ESD protection, 50 Ma overcurrent protection and 30 V overvoltage protection. The schematic diagram in Figure 1 does not show the optional external protection circuit, but can be found in the detailed schematic diagram of cn0203 design support package (eval-cn0203-sdpz-sch PDF file):

The circuit must be built on a multilayer circuit board with a large area of ground plane. For optimum performance, proper layout, grounding and decoupling techniques must be used (refer to tutorial mt-031 – “grounding data converters and solving the mystery of agnd and DGND” and tutorial MT-101 – “decoupling techniques”).

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