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Keywords:
Petaluma MAXREFDES30, 16-bit 8-channel simultaneous-sampling analog front end
SUBSYSTEM BOARD 5827
Petaluma (MAXREFDES30#): 8-Channel Simultaneous-
Sampling Analog Front End
Apr 28, 2014
Abstract: The Petaluma (MAXREFDES30#) subsystem reference design is a cost optimized, high-speed and high-accuracy analog
measurement solution for three-phase power monitoring applications. Hardware, firmware, design files, and lab measurements
provide complete system information for rapid prototyping and development.
Introduction
Three-phase power measurement applications require
multiple analog inputs for voltage and current
measurements on each line of the three-phase system. A
power monitoring system must sample all of the analog
inputs simultaneously to accurately calculate the
instantaneous power consumption.
The
Petaluma (MAXREFDES30#)
subsystem reference
design provides eight high-speed, 250ksps, 16-bit
simultaneous-sampling analog input channels that accept
±10V input signals.
The Petaluma design utilizes two quadruple ultra-precision,
ultra-low-noise input buffers (MAX44252); an 8-channel,
16-bit simultaneous-sampling ADC (MAX11046B); an ultra-
high precision 4.096V voltage reference (MAX6126); and
regulated +10V, -10V, and +5V power rails (MAX1659,
MAX765/LM337, MAX8881).
In addition to three-phase
power measurement applications, this subsystem also
performs well in any application that requires multiple
simultaneous sampling of analog inputs, such as
multiphase motor control and industrial vibration sensing.
More detailed image
(JPG)
Page 1 of 10
Figure 1. The Petaluma subsystem design block diagram.
Features
High precision, 8-channel, simultaneous-sampling inputs
High-speed 250ksps sampling rate
High-accuracy 16-bit resolution
Device drivers
Example C source code
Configuration files for ZedBoard™ platform
FMC-compatible
Competitive Advantages
High-performance energy measurement subsystem
Cost optimized
Energy efficient
Applications
Three-phase power measurement
Power grid protection
Multiphase motor control
Vibration and waveform analysis
Detailed Description of Hardware
The Petaluma subsystem is optimized for applications that use multiple high-speed, high-accuracy, simultaneous-sampling analog
inputs.
Figure 1
shows the block diagram of the Petaluma reference design.
The MAX44252 devices (U1 and U2) are quadruple ultra-precision, low-noise op amps. The op amps attenuate and buffer the
±10V input signals to match the input range of the ADC (MAX11046). The MAX44252 devices are set up in the inverting
configuration, so the polarity of the signal is reversed at the input of the ADC. The formula to convert the ADC code to voltage is:
10-CODE/65536*20.
Page 2 of 10
The MAX11046 (U3) is a low-cost, 8-channel, 250ksps, 16-bit, single-supply, bipolar, simultaneous-sampling ADC.
Although the MAX11046 ADC has an internal 4.096V voltage reference, Petaluma uses an external MAX6126 (U4) voltage
reference to provide the highest possible accuracy. The MAX6126 has an initial accuracy of 0.02% and a 3ppm/°C maximum
temperature coefficient (tempco).
By default, the Petaluma is powered from the 12V and 3.3V outputs of the FMC connector on the ZedBoard, if all shunts are
installed in the 1–2 position. The MAX1659 (U5) and MAX8881 (U6) provide post-regulated 5V and 10V rails. The MAX765 DC-DC
inverter and LM337 negative LDO produce the -10V rail. To use external power supplies, move the shunts on all jumpers to the 2–
3 position. Connect the ground terminal of the external power supplies to the GND connector. Connect the 3.3V, 5V, 10V, and -10V
supplies to the corresponding connectors on the board.
Petaluma connects to FMC-compatible field-programmable gate array (FPGA)/microcontroller development boards. Petaluma
requires supply voltages of 3.3V and 12V from the FMC connector and uses the pin assignments illustrated in
Figure 2.
Page 3 of 10
Figure 2. FMC connector pin connections.
Table 1
shows the power requirements.
Table 2
shows currently supported platforms and ports.
Page 4 of 10
Table 1. Power Requirement for the Petaluma Subsystem Reference Design
Power Type
On-board power
Jumper Shunt
JU1–JU4: 1–2
Input Voltage (V)
3.3
12
3.3
External power
JU1–JU4: 2–3
5
10
-10
Table 2. Supported Platforms and Ports
Supported Platforms
ZedBoard platform (Zynq
®
-7020)
Ports
J1
Input Current (mA, typ)
6.2
70
6.2
41.4
9.4
9.4
Detailed Description of ZedBoard Firmware
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 Petaluma firmware released for the ZedBoard kit targets an ARM
®
Cortex
®
-A9 processor placed inside a Xilinx Zynq system-
on-chip (SoC).
The firmware is a working example of how to interface to the hardware, collect samples, and save them to memory.
Figure 3
shows the process flow. The firmware is written in C using the Xilinx SDK tool, which is based on the Eclipse open source
standard. Custom Petaluma-specific design functions were created utilizing the AXI MAX11046 custom IP core. The firmware
supports the maximum ADC sampling rate at 250ksps.
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