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Maxim > Design Support > Technical Documents > Subsystem Boards > APP 5742

Keywords: Carmel, MAXREFDES18, analog output, conditioner, programmable logic controllers (PLC),

distributed control systems (DCS), industrial control and automation

SUBSYSTEM BOARD 5742

Carmel (MAXREFDES18#): High Accuracy Analog

Current/Voltage Output

Sep 23, 2013

Abstract: The Carmel (MAXREFDES18#) subsystem reference design provides a high-accuracy analog

output currents and voltages

provide critical control and

actuation functions. The Carmel

design shown in Figure 1 provides

a flexible and programmable

analog output that meets industrial control requirements.

The buffered voltage output from the MAX5316 16-bit, high -accuracy digital-to-analog converter (DAC)

drives the input of the MAX15500, a programmable analog output conditioner with extensive error

reporting. The MAX6126 ultra-high - precision voltage reference provides references for the DAC and the

protection, open circuit detection, brownout detection, overtemperature protection, all of which are critical

for industrial applications. Flexible power-up options make Carmel an ideal choice for robust industrial

control systems.

Features Applications

Programmable high -accuracy current/voltage output

Current output drives 0 to 1kΩ

Voltage output drives loads down to 1kΩ

Extensive error reporting

Distributed I/Os

Embedded systems

System safety

Small solution size

Low cost

Detailed Description of Hardware

Carmel connects to Pmod-compatible field-programmable gate

array (FPGA)/microcontroller development boards. Carmel

requires a 3.3V supply voltage from the Pmod connector and

uses the SPI pin assignments as illustrated here.

The power requirements are shown in Table 1. Note that the

3.3V Pmod

The MAX15500 (U1) is a single- channel, low -cost, precision analog current/voltage output conditioner

developed to meet the requirements of PLCs and other industrial control and automation applications.

The MAX15500 operates from a ±15V to ±32.5V power -supply range.

The MAX15500 can generate both unipolar and bipolar current and voltage outputs. In current mode, the

device produces currents of - 1.2mA to +24mA or -24mA to +24mA. In voltage mode, the device

produces voltages of - 0.3V to +6V, -0.6V to +12V, or ±12V. To allow for overrange and underrange

capability in unipolar mode, the transfer function of the MAX15500 is offset so that when the voltage at

AIN is 5% of full scale, IOUT is 0mA and VOUT is 0V. Once VAIN attains full scale, VOUT or IOUT

becomes full scale +5% or +20% depending on the state of FSMODE.

The MAX5316 (U2) is a high -accuracy, 16-bit, buffered voltage-output DAC. The device features ±1 LSB

integral nonlinearity (INL) (max) accuracy and a ±1 LSB differential nonlinearity (DNL) (max) accuracy

over the -40°C to +105°C. A separate -1.25V AVSS supply allows the output amplifier to go to 0V (GND)

while maintaining full linearity performance. For lower deadband requirements, the feature -reduced

MAX5216 DAC can be used instead.

The MAX6126 (U3) drives the analog output conditioner and the DAC's reference input with an ultra-

high - precision 4.096V voltage reference with 0.02% initial accuracy and a 3ppm/°C maximum

temperature coefficient (tempco).

The DAC’s output directly drives the conditioner’s input with no external components, making the

interface simple.

Table 2 shows the currently supported platforms and ports. Support for additional platforms may be

added periodically under Firmware Files in the All Design Files section.

microcontroller placed inside a Xilinx® Spartan ®-6 FPGA. The Carmel firmware also supports the

ZedBoard kit and targets an ARM® Cortex®- A9 processor placed inside a Xilinx Zynq system- on-chip

The firmware is a working example of how to initiate the system and wait for a user’s input. A user can

select the output mode and type in the DAC input code. The simple process flow is shown in Figure 2 .

The firmware is written in C using the Xilinx software development kit (SDK) tool, which is based on the

Required equipment:

Carmel (MAXREFDES18#) board

Carmel-supported platform (i.e., LX9 development kit or ZedBoard kit)

One ±24V, 25mA minimum DC power supply

One 750Ω, 0.25W resistor

Download, read, and carefully follow each step in the appropriate Carmel Quick Start Guide:

Carmel (MAXREFDES18#) LX9 Quick Start Guide

Carmel (MAXREFDES18#) ZedBoard Quick Start Guide

Carmel (MAXREFDES18#) board

FPGA development kit

Windows PC

INL, DNL, and total unadjusted error (TUE) are the most important specifications for PLC and other

process control systems. The MAX15500 is highly flexible and configurable to meet the needs of various

applications. Measurements of DNL, INL, and output error for the reference design are shown in Figure

output mode, with 5% overrange.

Figure 3. DNL for - 10V to +10V output range, with 5% overrange.

Figure 4. INL for -10V to +10V output range, with 5% overrange.

Figure 5. Output error for - 10V to +10V output range, with 5% overrange.

In the case of current output, DNL, INL, and output error (without calibration) for the reference design are

Figure 6. DNL for 0 to 20mA output range, with 5% overrange.

Figure 7. INL for 0 to 20mA output range, with 5% overrange.

Figure 8. Output error for 0 to 20mA output range, with 5% overrange.

Bill of materials (BOM)

PCB layout

PCB Gerber

PCB CAD (PADS 9.0)