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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
current/voltage output in a compact, galvanically isolated form factor. This design uniquely fits
programmable logic controllers (PLC), distributed control systems (DCS), and other industrial
applications. Hardware and firmware design files and lab measurements are provided for rapid
prototyping and development. The board is also available for purchase.
Introduction
In PLC and DCS systems, analog
output currents and voltages
provide critical control and
actuation functions. The Carmel
(MAXREFDES18#) reference
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
output conditioner. The MAX14850 galvanically isolates data communication between the subsystem and
the system controller. Optionally, the subsystem also integrates an isolated and regulated power supply
by using the MAX13253 transformer driver and the MAX1659 and MAX1735 low -dropout (LDO) linear
regulators.
The subsystem features all typical bipolar current and voltage output ranges, and appropriate subsets,
with less than 0.105% total unadjusted error (TUE). The circuit also provides short - circuit and overcurrent
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.
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Figure 1. The Carmel subsystem design block diagram.
Features Applications
Programmable high -accuracy current/voltage output
Current output drives 0 to 1kΩ
Voltage output drives loads down to 1kΩ
Extensive error reporting
Isolated power and data
Small printed circuit board (PCB) area
Device drivers
Example C source code
Pmod- compatible form factor
PLCs
DCS
Distributed I/Os
Embedded systems
Industrial control and automation
Industrial sensors
Competitive Advantages
Flexibility
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.
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The power requirements are shown in Table 1. Note that the
external AVDD and AVSS power rails are required for full system
operation. The currently supported platforms and ports are shown
in Table 2.
Table 1. Power Requirements for the Carmel Subsystem
Reference Design
Power
Name Jumper
Shunt
Input
Voltage
(V)
Input
Current
(mA, max)
3.3V Pmod
Power
Supply
JU4: 1-
23.3 49.0
AVDD 15.0 to
32.5 25.0
AVSS - 15.0 to
-32.5 25.0
Table 2. Supported Platforms and Ports
Supported Platforms Ports
LX9 platform (Spartan®-6) J5
ZedBoard platform (Zynq ®-7020) JA1
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 MAX15500 protects against overcurrent and short-circuit conditions when OUT goes to ground or a
voltage up to ±32.5V. The device also monitors for overtemperature and supply brownout conditions. The
supply brownout threshold is programmable between ±10V and ±24V in 2V increments. The MAX15500
provides extensive error reporting of short-circuit, open - circuit, brownout, and overtemperature conditions
through the SPI interface and an additional open-drain interrupt output (ERROR). The MAX15500 also
includes an analog 0 to 3V output (MON) to monitor the load condition at OUT.
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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.
The MAX13253 (U4) provides an isolated, functional insulation class power solution that accepts 3.3V
and converts it to ±6V using an isolation transformer. Post- regulation is accomplished using the
MAX1659 LDO (U5) for the 5V output, and the MAX1735 (U6) for the - 1.25V output.
Data isolation between the subsystem and the controller is accomplished using the MAX14850 (U7)
digital data isolator. The combined power and data isolation achieved is 600VRMS.
Detailed Description of Firmware for LX9 and ZedBoard
Platforms
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.
The Carmel firmware released for the LX9 development kit targets a Microblaze soft- core
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
(SoC).
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
Eclipse open source standard. Custom Carmel-specific design functions were created utilizing the
standard Xilinx XSpi core version 3.03a. The SPI clock frequency is set to 3.125MHz.
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Figure 2. The Carmel firmware flowchart.
The complete source code is provided to speed up customer development. Code documentation can be
found with the corresponding firmware platform files.
Quick Start
Required equipment:
Windows® PC with two USB ports
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
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Lab Measurements
Equipment:
Carmel (MAXREFDES18#) board
FPGA development kit
One 750Ω, 0.25W resistor load
Agilent 3458A digital multimeter
Agilent E3631A DC power supply (any ±24V, 25mA minimum DC power supply works)
National Instruments GPIB card and cable
Thermonics T-2800 precision temperature forcing system
Perl script for controlling the FPGA development kit and measurement equipment
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
3, Figure 4, and Figure 5, respectively. The data was taken at +25°C in the -10V to +10V voltage
output mode, with 5% overrange.
Figure 3. DNL for - 10V to +10V output range, with 5% overrange.
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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
shown in Figure 6, Figure 7, and Figure 8, respectively. The data was taken at +25°C in the 0mA to
20mA current output mode, with 5% overrange.
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Figure 6. DNL for 0 to 20mA output range, with 5% overrange.
Figure 7. INL for 0 to 20mA output range, with 5% overrange.
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Figure 8. Output error for 0 to 20mA output range, with 5% overrange.
All Design Files
Download All Design Files
Hardware Files
Schematic
Bill of materials (BOM)
PCB layout
PCB Gerber
PCB CAD (PADS 9.0)
Firmware Files
LX9 Platform (Spartan- 6)
ZedBoard Platform (Zynq-7000)
Buy Reference Design
Buy Direct: Carmel (MAXREFDES18#)
Or
Order the Carmel reference design (MAXREFDES18#) from your local Maxim representative.
ARM is a registered trademark and registered service mark of ARM Limited.
Cortex is a registered trademark of ARM Limited.
Eclipse is a trademark of Eclipse Foundation, Inc.
Halo is a registered trademark of Halo Electronics, Inc.
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MicroBlaze is a trademark of Xilinx, Inc.
Pmod is a trademark of Digilent Inc.
Spartan is a registered trademark of Xilinx, Inc.
Windows is a registered trademark and registered service mark of Microsoft Corporation.
Xilinx is a registered trademark and registered service mark of Xilinx, Inc.
ZedBoard is a trademark of ZedBoard.org.
Zynq is a registered trademark of Xilinx, Inc.
Related Parts
MAX13253 1A Spread-Spectrum Push -Pull Transformer Driver for
Isolated Power Supplies Free Samples
MAX14850 Six- Channel Digital Isolator
MAX15500 Industrial Analog Current/Voltage Output Conditioners Free Samples
MAX1659 350mA, 16.5V Input, Low -Dropout Linear Regulators Free Samples
MAX1735 200mA, Negative- Output, Low-Dropout Linear Regulator
in SOT23 Free Samples
MAX5316 16-Bit, ±1 LSB Accuracy Voltage Output DAC with SPI
Interface Free Samples
MAX6126 Ultra-High- Precision, Ultra -Low- Noise, Series Voltage
Reference Free Samples
More Information
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For Samples: http://www.maximintegrated.com/samples
Other Questions and Comments: http://www.maximintegrated.com/contact
Application Note 5742: http://www.maximintegrated.com/an5742
SUBSYSTEM BOARD 5742, AN5742, AN 5742, APP5742, Appnote5742, Appnote 5742
© 2013 Maxim Integrated Products, Inc.
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