Broadcom ACPL-C799 Evaluation Kit Board: Isolated Sigma-Delta Modulator User manual

Broadcom

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Description

The Avago ACPL-C799 isolated sigma-delta (–) modulator converts an analog input signal into a high-speed (10 MHz typical)

single-bit data stream by means of a sigma-delta over-sampling modulator. The time average of the modulator data is directly

proportional to the input signal voltage. The modulator uses internal speed of 10 MHz. The modulator data are encoded and

transmitted across the isolation boundary where they are recovered and decoded into high-speed data stream of digital ones and

zeros. The original signal information is represented by the density of ones in the data output.

The input signal information is contained in the modulator output data stream, represented by the density of ones and zeros. The

density of ones is proportional to the input signal voltage, as shown in Figure 1. A differential input signal of 0 V ideally produces a

data stream of ones 50 percent of the time and zeros 50 percent of the time. A differential input of –50 mV corresponds to 18.75

percent density of ones, and a differential input of +50 mV is represented by 81.25 percent density of ones in the data stream. A

differential input of +80 mV or higher results in ideally all ones in the data stream, while input of –80 mV or lower will result in all

zeros ideally. Table 1 shows this relationship.

Figure 1 Modulator Output vs. Analog Input

This User Guide is provided to assist you in the evaluation of product(s) currently under development. Until Broadcom releases this

product for general sales, Broadcom reserves the right to alter prices, specifications, features, capabilities, functions, release dates, and

remove availability of the product(s) at anytime

ACPL-C799 Evaluation Kit Board

Isloated Sigma-Delta Modulator

User Guide

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Preparation and Setup

A digital filter converts the single-bit data stream from the modulator into a multi-bit output word similar to the digital output of a

conventional A/D converter. With this conversion, the data rate of the word output is also reduced (decimation). A Sinc3 filter is

recommended to work together with the ACPL-C799. With a 10-MHz internal clock frequency, 256 decimation ratio and 16-bit

word settings, the output data rate is 39 kHz (= 10 MHz/256). This filter can be implemented in an ASIC, an FPGA, or a DSP.

In this evalboard, Sinc3 filter is implemented using Xilinx Spartan XC3S250E FPGA. The FPGA hardware is designed in Verilog/VHDL

environment. Major building block are the Digital Filter and USB interface control as shown in Figure 2. The design is synthesized

and implemented using Xilinx Tool to a bitstream file. This bitstream file can be loaded to FPGA through USB, which is already done

for each evalboard kit shipped to customer.

Figure 2 Digital Filter and USB Interface Control

Preparation and Setup

1. Each complete ACPL-C799 evaluation kit shipment will come with the following items:

— ACPL-C799 evalboard

— Cable with USB / mini USB terminations

— Cable with 3.5mm audio jack / crocodile clip connectors

— Softcopy folder containing drivers and application software programs

2. The softcopy folder contains the following document or software programs:

— ACPL-C799 Xilinx FPGA Evbd Kit User Guide.pdf – evalboard user guide

— CDM20830_Setup.exe – FTDI USB chipset driver for Windows 32-bit and 64-bit operating systems. For other OS, you can

download om the manufacturer's website: http://www.ftdichip.com/Drivers/VCP.htm

— dig_filter_50_rev1.exe – Avago application GUI software.

— dig_filter_50_rev1.bit – FPGA bitfile

— Sinc3_verilog.txt – Sinc3filter codes in Verilog

Table 1 Input Voltage with Ideal Corresponding Density of 1s at Module Data Output, and ADC Code

Analog Input Voltage Input Density of 1s Density of 0s ADC Code (16-bit unsigned decimation)

+Full-Scale +80mV 100% 0% 65,535

+Recommended Input Range +50mV 81.25% 18.75% 53,248

Zero 0mV 50% 50% 32,768

–-Recommended Input Range –50mV 18.75% 81.25% 12,288

–Full-Scale –80mV 0% 100% 0

C799

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Preparation and Setup

— Sinc3_VHDL.txt – Sinc3filter codes in VHDL

— Sine wave files – sine waves configured to different frequencies 500 Hz, 1000 Hz, and 2000 Hz that can be played from any

audio players

3. Save the softcopy folder into a PC directory location. See the appendix for descriptions of the major components on the

evaluation board, the schematic diagrams and PCB layout.

4. Connect the evalboard to the PC using the provided USB cable. Turn on switch SW1. The red "5VIN" LED will light up indicating

the presence of a USB connection. Install the CDM20830_Setup.exe USB chipset driver file. The driver will install two ports, USB

Serial Converter A and USB Serial Converter B. To verify that the installation is successful, open Device Manager (right-click on

Computer, select Properties, then click Device Manager), under "Universal Serial bus controllers", the two ports "USB Serial

Converter A" and "USB Serial Converter B" should appear.

5. Each time the evalboard SW1 is turned on, the board goes through a series of power-on sequences. When completed, the

green "DONE" LED comes on to indicate completion of the power-on sequences.

6. Go to the PC directory, and run the dig_filter_50_rev1.exe application program. Refer to the application GUI screen capture as

shown in Figure 4. If the evalboard is connected and SW1 switched on, Avago-System text message appears on the right of

the Search button. If SW1 is not turned on, an error message appears, as shown in Figure 3. Click OK once, and the application

GUI appears. The text message System not connected!! will appear instead.

Figure 3 Error Message

7. Switch on SW1. Go to the application GUI, and click the Search button once. Now, the text message changes to

Avago-System to indicate that the connection is established.

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Application GUI

Figure 4 Application GUI

The application GUI has three displays, two of the displays showing the signal in time domain and frequency domain, and the

third showing SNR and SNDR historical plots. The time domain signal can be displayed in terms of ADC count or voltage level

(mV) by checking the Display (mV).

On the right of the displays, real time minimum, maximum, and average signal levels are shown in time domain in terms of

either mV or ADC count. SNR, SNDR, 2nd harmonic and 3rd harmonic levels are displayed in frequency domain.

1. Click Start to start capturing the input signal. The configured board frequency is captured under the Frequency box and the

part number or evalboard type in the Board/Product.

2. You can save the signal, FFT and SNR/SNDR history data into text files that are readable and compatible to Microsoft Excel by

selecting the Datalog (signal, fft and snr/sndr history) box. The snr.txt, signal.txt, and fft.txt are stored in the same file

directory as the application GUI.

3. If there is an updated FPGA bitfile or you hae configured a new bitstream file, this can be can be uploaded easily by clicking the

Load FPGA Bit File on the top-left corner of the application GUI. When the bitfile is being uploaded, the green DONE LED goes

off and the red UPLOAD LED comes on. When uploading is completed, the red UPLOAD LED goes off, while the green DONE

LED comes on again to signal completion. The FPGA LOAD Completed! pop-up appears, as shown in Figure 5.

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Application GUI

Figure 5 FPGA LOAD Completed! Pop-up

4. For quick help guide, click Help on the top-right corner of the application GUI, then select setup guide. The help guide also

described the calibration procedure to zero the offset.

Figure 6 Help – setup guide

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Measurement

Figure 7 Measurement

There are few ways to apply the input signal into the evalboard:

 Apply input current signal with Shunt Resistor

One example to select the shunt resistor value is shown below:

If maximum rms current through motor = 100A, 20 percent overloads during normal operation, then, peak current is 170 A

(= 100 × 1.414 × 1.2). Recommended maximum input voltage for ACPL-C799 = ±50mV.

Shunt resistor value = V/I = 50mV/170A ≈ 0.3m

Power dissipation = I

× R = (100)

× 0.3m = 3W

The shunt resistor mounting pad is designed to accommodate various shunt resistor package types. The Kelvin connection

PCB trace connects from the center of the pad to the inputs of ACPL-C799 through the anti-aliasing filters (AAFs). Connecting

from the center of the pads is usually the optimum location for most shunt resistor designs. The evalboard also provides pads

P1 and P2 for soldering thick cables to the motor driving board.

 Apply input voltage signal without shunt resistor

Connect the audio cable with the audio 3.5-mm jack connected to either a PC, smart phone, tablet, MP3 player, or any kind of

audio player device. Then, connect the crocodile clips to the shunt resistor mounting pads.

By checking the 1kHz sine test signal, you can supply a 1 kHz sine wave voltage signal into the evaluation board. Other

methods include running any of the three sine wave files provided from a music player software program in audio player

devices as described previously. Adjust the volume until the signal level is near ±50mV or ±20,000 ADC counts for best

SNR/SNDR performance.

The performance of SNR/SNDR is dependent on a few factors:

— The evalboard

— The sigma-delta modulator used, in this case, the ACPL-C799

— Input signal frequency used

— The decimation ratio, which can be set at the application GUI to 256, 128, 64, or 32.

— The input signal level. ACPL-C799 recommended input voltage range is from –50mV to 50mV. To achieve the best

SNR/SNDR, it is recommended to design the maximum input signal range near to ±50mV (selection of input current range

and shunt resistor value).

— The input signal source.

Table 2 shows a comparison of the SNR/SNDR performance between audio signal source coming from a laptop and a smart

phone.

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Measurement

 Lab bench test: Apply input voltage signal from a function generator with 1 shunt resistor mounted on the input of

evaluation board.

When a voltage signal is sourced from a function generator to the evaluation board without a shunt resistor connected as

shown in Figure 8, input bias current of about 0.18mA from the ACPL-C799 will cause a 9mV offset on the function generator

output due to the 50 source impedance of the function generator.

Figure 8 Sourcing the Voltage Signal from a Function Generator to the Evaluation Board without a Shunt Resistor Connected

A more accurate method to measure the performance of the ACPL-C799 evaluation board is to connect a 1 shunt resistor,

then supply the voltage signal from a function generator that can drive sufficient current through the 1 shunt resistor until

an input signal level of ±50mV is reached. One such function generator is the ultra low distortion DS360 function generator

from Standford Research Systems.

Table 3 shows the SNR/SNDR performance using this method.

If such a function generator is not available, it is best to connect an actual shunt resistor and connect to customer's current sensing

system directly.

Table 2 SNR/SNDR Comparison

ACPL-C799 Board

Audio Signal from Dell Lattitude E7440 Laptop Audio Signal from Samsung Galaxy S6

signal freq=1kHz signal freq =500Hz signal freq =1kHz signal freq =500Hz

SNDR(dB) SNR(dB) SNDR(dB) SNR(dB) SNDR(dB) SNR(dB) SNDR(dB) SNR(dB)

Clock freq = 10MHz 67.55 68.44 66.27 68.06 72.31 74.26 72.05 74.76

Table 3 SNR/SNDR Performance

ACPL-C799 Board

DS360 Stanford Research Systems Ultra Low Distortion Function

Generator

signal freq=1kHz signal freq =500Hz

SNDR(dB) SNR(dB) SNDR(dB) SNR(dB)

Clock freq = 10MHz 74.53 77.42 74.97 78.35

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

PCB Modifications

1. Vdd1 is supplied from the 5V/5V isolated dc/dc converter. You can also supply Vdd1 from a 9V battery through the

L78L05ACUTR LDO regulator. To do that, ensure that R45 is disconnected.

2. The ACPL-C799 Vdd2 is supplied from the 3.3V regulator. If you need to check the performance or troubleshoot the ACPL-C799

component only at Vdd2=5V, you can mount a 0 R47 resistor. In this instance, the Vdd2 is supplied directly from the USB

power, 5VCC. Note that you have to remove R18, R19, and R20 because the FPGA I/O pins may not be able to take 5V.

3. The green LED1 signals the detection of ACPL-C799.

4. LED2, LED3, and LED4 are not defined. If you want to modify the FPG, you can use these LED indicators for other functions.

5. The H1 and H2 connector pins are physically connected to the FPGA. If you want to modify the FPGA, you can make use of

these connector pins for input (I/P) or input/output (I/O).

Troubleshooting

1. After switching on SW1, if the green DONE LED does not come on, reset the FPGA by pressing SW2 once. If the problem still

does not go away, perform a full board reset by pressing SW3 once.

2. Each evalboard sent to the customer is functionally checked and tested. If the problem does not go away, consult a Broadcom

Application Engineer. If need be, Broadcom will send a new board.

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Appendix

PCB Description

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Appendix

Schematic Diagram

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ACPL-C799 Evaluation Kit Board

User Guide

Appendix

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Appendix

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Appendix

PCB Layout

Broadcom

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ACPL-C799 Evaluation Kit Board

User Guide

Appendix

For product information and a complete list of distributors, please go to our web

site: www.broadcom.com.

Broadcom, the pulse logo, Connecting everything, Avago Technologies, and the

A logo are the trademarks of Broadcom in the United States, certain other

countries and/or the EU.

The term "Broadcom" refers to Broadcom Limited and/or its subsidiaries. For

more information, please visit www.broadcom.com.

Broadcom reserves the right to make changes without further notice to any

products or data herein to improve reliability, function, or design.

Information furnished by Broadcom is believed to be accurate and reliable.

However, Broadcom does not assume any liability arising out of the application

or use of this information, nor the application or use of any product or circuit

described herein, neither does it convey any license under its patent rights nor

the rights of others.

pub-005678 – May 13, 2016

Broadcom ACPL-C799 Evaluation Kit Board: Isolated Sigma-Delta Modulator, ACPL-C799 User manual

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