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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
This application note introduces the main features of the sinc
filters of the ADSP-CM402F/ADSP-CM403F/ADSP-CM407F/
ADSP-CM408F microprocessors, with a focus on high
performance motor control applications.
The purpose of this application note is to highlight the key
capabilities of the sinc filter module and to provide guidance
on how to configure the sinc filter through software. For more
information about the full range of sinc filter features and
configuration registers, see the ADSP-CM40x Mixed-Signal
Control Processor with ARM Cortex-M4 Hardware Reference
and the documentation within the ADSP-CM40x Enablement
Software package.
The sinc filter of each ADSP-CM402F/ADSP-CM403F/
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.
MOTOR CURRENT CONTROL APPLICATIONS
Figure 1 shows a simplified schematic of an isolated current
feedback system for inverter fed motor drives. The system
overcomes the difficulty of isolating the analog signal that is
generated across the current shunt from the high voltage common
signal that is generated by the switching power inverter. The
system converts the signal using isolated Σ-Δ modulators and
then transmits a digital signal across the isolation barrier.
The Σ-Δ modulators generate a modulated bit stream as a function
of the input voltage and transmit the signal across the isolation
barrier to a filter circuit on the low voltage side. The sinc filter
filters the bit stream from a second-order modulator, such as the
AD7403, to recover a 16-bit digital signal that represents the motor
winding current.
11801-001
ADSP-CM40x
PWM
CPU
SRAM
AC
MOTOR
SINC3
FILTER
ISOLATION BARRIER
U
V
W
R
S
R
S
D
V
CLK
D
W
TRIP
IRQ
DMA I
V
, I
W
AD7403
ISOLATING
GATE DRIVERS
CTL
Σ-Δ
CTL
Σ-Δ
Figure 1. Isolated Current Feedback Using the AD7403
Rev. B | Page 1 of 20
