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AN-1265 APPLICATION NOTE One Technology Way • P AN-1265 APPLICATION NOTE One Technology Way • P. O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com Isolated Motor Control Feedback Using the ADSP-CM402F/ADSP-CM403F/ ADSP-CM407F/ADSP-CM408F Sinc Filters and the AD7403 By Dara O’Sullivan, Jens Sorensen, and Aengus Murray INTRODUCTION MOTOR CURRENT CONTROL APPLICATIONS This application note introduces the main features of the sinc Figure 1 shows a simplified schematic of an isolated current filters of the ADSP-CM402F/ADSP-CM403F/ADSP-CM407F/ feedback system for inverter fed motor drives. The system ADSP-CM408F microprocessors, with a focus on high overcomes the difficulty of isolating the analog signal that is performance motor control applications. generated across the current shunt from the high voltage common The purpose of this application note is to highlight the key signal that is generated by the switching power inverter. The capabilities of the sinc filter module and to provide guidance system converts the signal using isolated Σ-Δ modulators and on how to configure the sinc filter through software. For more then transmits a digital signal across the isolation barrier. information about the full range of sinc filter features and The Σ-Δ modulators generate a modulated bit stream as a function configuration registers, see the ADSP-CM40x Mixed-Signal of the input voltage and transmit the signal across the isolation Control Processor with ARM Cortex-M4 Hardware Reference barrier to a filter circuit on the low voltage side. The sinc filter and the documentation within the ADSP-CM40x Enablement filters the bit stream from a second-order modulator, such as the Software package. AD7403, to recover a 16-bit digital signal that represents the motor The sinc filter of each ADSP-CM402F/ADSP-CM403F/ winding current. ADSP-CM407F/ADSP-CM408F microprocessor is part of a complete motor current feedback subsystem that includes a current shunt, a modulator to digitize and isolate the signal, and the sinc filter to decode the bit stream and present it to the controller. This application note describes how to set up the sinc filters. U ISOLATING R GATE DRIVERS S V AC MOTOR RS W ISOLATION BARRIER AD7403 DV PWM Σ-Δ TRIP CLK CTL CPU SINC3 FILTER DW IRQ Σ-Δ SRAM DMA IV, IW CTL ADSP-CM40x 11801-001 Figure 1. Isolated Current Feedback Using the AD7403 Rev. B | Page 1 of 20 AN-1265 Application Note TABLE OF CONTENTS Introduction ...................................................................................... 1 Primary Filter Scaling ...................................................................9 Motor Current Control Applications ............................................. 1 Secondary Filter Scaling and Overload Configuration ......... 10 Revision History ............................................................................... 2 Sinc Module Fault Detection Functions .................................. 13 Sinc Filter Module Overview .......................................................... 3 Sinc Filter Setup .............................................................................. 14 Current Feedback System Overview .............................................. 4 Pin Multiplexer Configuration ................................................. 14 Current Shunt Selection .............................................................. 4 Data Buffer Memory Allocation .............................................. 14 Modulator Clock, Primary Filter Decimation, and Data Interrupt and Trigger Routing .................................................. 15 Interrupt Rate Selection ............................................................... 5 Primary and Secondary Filter Configurations ....................... 16 Aligning Sinc Impulse Response to PWM ................................ 6 Sinc Filter Software Support ..................................................... 17 Implementation of Impulse Response Alignment to PWM ... 7 Sinc Data and Interrupt Rate ...................................................... 8 REVISION HISTORY 4/15—Rev. A to Rev. B Added Figure 23, Figure 24, and Figure 26 ................................. 12 Changed AD7401A to AD7403 ........................................ Universal Changes to Figure 27 ...................................................................... 13 Changes to Introduction Section and Figure 1 ............................. 1 Added Figure 28 ............................................................................. 13 Changes to Current Shunt Selection Section, Figure 3, and Changed Sinc Filter Setup and Software Driver Functions Figure 4 .............................................................................................. 4 Section to Sinc Filter Setup Section ............................................. 14 Changes to Modulator Clock, Primary Filter Decimation, and Changes to Data Buffer Memory Allocation Section, Data Interrupt Rate Selection Section, Figure 5, Figure 29, and Figure 31 ................................................................ 14 and Figure 7 ....................................................................................... 5 Changes to Interrupt and Trigger Routing Section Added Figure 6; Renumbered Sequentially .................................. 5 and Figure 32 ................................................................................... 15 Added Figure 8, Aligning Sinc Impulse Response to PWM Changes to Primary and Secondary Filter Configurations Section, Figure 9, and Figure 10 ..................................................... 6 Section .............................................................................................. 16 Added Figure 11, Figure 12, and Implementation of Impulse Changes to Sinc Filter Software Support Section ....................... 17 Response Alignment to PWM Section .......................................... 7 Added Table 3; Renumbered Sequentially .................................. 17 Added Figure 13, Figure 14, and Sinc Data and Interrupt Rate Section ................................................................................................ 8 11/13—Rev. 0 to Rev. A Changes to Figure 15 ........................................................................ 9 Changes to Figure 1 ........................................................................... 1 Changes to Figure 16 and Feedback Scaling Calculations Changes to Figure 4 ........................................................................... 4 Section .............................................................................................. 10 Changes to Table 1 ............................................................................. 5 Changes to Figure 17 and Figure 19 ............................................. 11 Added Figure 18, Figure 20, and Figure 21 ................................. 11 9/13—Revision 0: Initial Version Changes to Figure 22 and Figure 25 ............................................. 12 Rev. B | Page 2 of 20 Application Note AN-1265 SINC FILTER MODULE OVERVIEW The sinc filter block performs two functions: it generates a high The filter enable function assigns sinc filter pairs to one of two fidelity feedback signal for the motor control algorithm, and it configuration register groups to set the filter parameters. The provides rapid detection of overload currents in the case of fault expectation is that the motor current control requires multiple conditions. Connecting the overload fault signal to the pulse-width current or voltage filters configured in the same way. The sinc modulator (PWM) block can shut down the PWM inverter filter module supports control of two motors with one group of without any software intervention. The sinc filter transfers data two filter pairs assigned to each motor. The primary filter settings directly to memory using direct memory access (DMA), and a are the filter order, decimation rate, offset bias, and gain scaling. processor interrupt can be generated when a preset number of The secondary filter settings are the filter order, decimation samples is ready. The interrupt minimizes the software overhead rate, overload trip levels, and glitch filter settings. to service the sinc filter after it is configured. The same feedback Other configuration functions include modulator clock circuit applies to isolated dc bus voltage feedback and dc bus frequencies, interrupt masking, and DMA data transfer. The current measurements. other control peripherals required to set up the sinc filter are the Figure 2 shows a block diagram of the sinc filter module. The port controller, which connects external pins to the sinc filter sinc filter module has four sinc filter pairs that implement inputs, and the trigger routing unit (TRU), which connects feedback signal filtering and overload detection on the digital output signals of the sinc filter to the appropriate peripheral. bit streams connected to the inputs. SINC PAIR 0 DMA PRIMARY LIMIT TO TRU FROM GPIO OVERLOAD INDICATOR SECONDARY SINC PAIR 1 PRIMARY LIMIT TO TRU FROM GPIO OVERLOAD INDICATOR SECONDARY TO MEMORY AXI MASTER INTERFACE SINC PAIR 2 PRIMARY LIMIT TO TRU FROM GPIO OVERLOAD INDICATOR SECONDARY SINC PAIR 3 PRIMARY LIMIT TO TRU FROM GPIO OVERLOAD INDICATOR SECONDARY CONTROL FOR GROUP 0 FROM PROCESSOR MMR ACCESS TO GPIO MODULATOR CLOCK 0 APB SLAVE CONTROL FOR GROUP 1 SINC MODULE TO PROCESSOR TO GPIO MODULATOR CLOCK 1 INTERRUPT REQUEST 11801-002 Figure 2. Sinc Filter Module Overview Rev. B | Page 3 of 20 AN-1265 Application
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