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
filters of the ADSP-CM402F/ADSP-CM403F/ADSP-CM407F/
ADSP-CM408F microprocessors, with a focus on high
performance motor 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 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 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.
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.
U
ISOLATING
GATE DRIVERS
RS
RS
V
AC
MOTOR
W
ISOLATION BARRIER
AD7403
DV
PWM
Σ-Δ
TRIP
CLK
SINC3
FILTER
CPU
CTL
DW
IRQ
DMA IV, IW
ADSP-CM40x
CTL
Figure 1. Isolated Current Feedback Using the AD7403
Rev. B | Page 1 of 20
11801-001
Σ-Δ
SRAM
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 Rate Selection ............................................................... 5 Interrupt and Trigger Routing .................................................. 15 Aligning Sinc Impulse Response to PWM ................................ 6 Sinc Filter Software Support ..................................................... 17 Primary and Secondary Filter Configurations ....................... 16 Implementation of Impulse Response Alignment to PWM ... 7 Sinc Data and Interrupt Rate ...................................................... 8 REVISION HISTORY
4/15—Rev. A to Rev. B
Changed AD7401A to AD7403 ........................................ Universal
Changes to Introduction Section and Figure 1 ............................. 1
Changes to Current Shunt Selection Section, Figure 3, and
Figure 4 .............................................................................................. 4
Changes to Modulator Clock, Primary Filter Decimation, and
Data Interrupt Rate Selection Section, Figure 5,
and Figure 7 ....................................................................................... 5
Added Figure 6; Renumbered Sequentially .................................. 5
Added Figure 8, Aligning Sinc Impulse Response to PWM
Section, Figure 9, and Figure 10 ..................................................... 6
Added Figure 11, Figure 12, and Implementation of Impulse
Response Alignment to PWM Section .......................................... 7
Added Figure 13, Figure 14, and Sinc Data and Interrupt Rate
Section ................................................................................................ 8
Changes to Figure 15 ........................................................................ 9
Changes to Figure 16 and Feedback Scaling Calculations
Section .............................................................................................. 10
Changes to Figure 17 and Figure 19 ............................................. 11
Added Figure 18, Figure 20, and Figure 21 ................................. 11
Changes to Figure 22 and Figure 25 ............................................. 12
Added Figure 23, Figure 24, and Figure 26 ................................. 12
Changes to Figure 27...................................................................... 13
Added Figure 28 ............................................................................. 13
Changed Sinc Filter Setup and Software Driver Functions
Section to Sinc Filter Setup Section ............................................. 14
Changes to Data Buffer Memory Allocation Section,
Figure 29, and Figure 31 ................................................................ 14
Changes to Interrupt and Trigger Routing Section
and Figure 32................................................................................... 15
Changes to Primary and Secondary Filter Configurations
Section.............................................................................................. 16
Changes to Sinc Filter Software Support Section ....................... 17
Added Table 3; Renumbered Sequentially .................................. 17
11/13—Rev. 0 to Rev. A
Changes to Figure 1 ...........................................................................1
Changes to Figure 4 ...........................................................................4
Changes to Table 1.............................................................................5
9/13—Revision 0: Initial Version
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
fidelity feedback signal for the motor control algorithm, and it
provides rapid detection of overload currents in the case of fault
conditions. Connecting the overload fault signal to the pulse-width
modulator (PWM) block can shut down the PWM inverter
without any software intervention. The sinc filter transfers data
directly to memory using direct memory access (DMA), and a
processor interrupt can be generated when a preset number of
samples is ready. The interrupt minimizes the software overhead
to service the sinc filter after it is configured. The same feedback
circuit applies to isolated dc bus voltage feedback and dc bus
current measurements.
Figure 2 shows a block diagram of the sinc filter module. The
sinc filter module has four sinc filter pairs that implement
feedback signal filtering and overload detection on the digital
bit streams connected to the inputs.
The filter enable function assigns sinc filter pairs to one of two
configuration register groups to set the filter parameters. The
expectation is that the motor current control requires multiple
current or voltage filters configured in the same way. The sinc
filter module supports control of two motors with one group of
two filter pairs assigned to each motor. The primary filter settings
are the filter order, decimation rate, offset bias, and gain scaling.
The secondary filter settings are the filter order, decimation
rate, overload trip levels, and glitch filter settings.
Other configuration functions include modulator clock
frequencies, interrupt masking, and DMA data transfer. The
other control peripherals required to set up the sinc filter are the
port controller, which connects external pins to the sinc filter
inputs, and the trigger routing unit (TRU), which connects
output signals of the sinc filter to the appropriate peripheral.
DMA
SINC PAIR 0
PRIMARY
FROM GPIO
LIMIT
TO TRU
OVERLOAD INDICATOR
LIMIT
TO TRU
OVERLOAD INDICATOR
SECONDARY
SINC PAIR 1
PRIMARY
FROM GPIO
SECONDARY
TO MEMORY
AXI MASTER INTERFACE
SINC PAIR 2
PRIMARY
FROM GPIO
LIMIT
TO TRU
OVERLOAD INDICATOR
LIMIT
TO TRU
OVERLOAD INDICATOR
SECONDARY
SINC PAIR 3
PRIMARY
FROM GPIO
SECONDARY
CONTROL FOR GROUP 0
MODULATOR CLOCK 0
CONTROL FOR GROUP 1
TO GPIO
SINC
MODULE
MODULATOR CLOCK 1
Figure 2. Sinc Filter Module Overview
Rev. B | Page 3 of 20
TO PROCESSOR
INTERRUPT REQUEST
11801-002
TO GPIO
FROM PROCESSOR
MMR ACCESS
APB SLAVE
AN-1265
Application Note
CURRENT FEEDBACK SYSTEM OVERVIEW
Figure 4 shows the key elements in the current feedback system.
The shunt senses the winding current as a voltage signal that
scales according to the shunt resistance. The AD7403 modulator
generates an isolated bit stream with a pulse density (MDATW
in Figure 4) that scales according to the full-scale input voltage
range. The sinc filters extract the pulse density information
according to the filter order (O for the primary filter and O' for
the secondary filter) and decimation rate (D for the primary filter
and D' for the secondary filter). The primary filter parameters
optimize the filter for precision and additional bias and scaling
blocks convert the data into a 16-bit, signed integer before it is
transferred to memory. The secondary parameters optimize the
filter for speed, and the outputs pass the signal to digital
comparators that detect overload conditions. Upper and lower
limit comparators detect current overloads, and a glitch filter
waits for a minimum overload count (LCNT) within a specific
window (LWIN) before generating an overload trigger signal. The
overload trigger is a trip input signal for the PWM driving the
motor inverter. The DMA transfer engine generates an interrupt
signal to initiate algorithm execution when the winding current
data is ready in memory.
CURRENT SHUNT SELECTION
The system specifications required to define the feedback are
the peak control current, ICC_PEAK, and the specified maximum
input voltage, VMOD_MAX, for the modulator. The peak current
capability of the power inverter typically defines the control
current range, but other considerations may apply. The specified
maximum operating voltage of the AD7403 modulator is
±250 mV, which is the maximum voltage range within which
the modulator specifications are valid. The maximum operating
voltage is lower than the ±320 mV full-scale range (VFS) of the
modulator because the linearity and signal-to-noise performance
degrades significantly as inputs approach full scale. The shunt
resistance must be less than VMOD_PEAK/ICC_PEAK to satisfy these
constraints, and the closest nominal shunt value is chosen. For
the example in Figure 3, given that the power stage peak current
rating is 8.5 A, the maximum shunt resistance is 29.4 mΩ. For
derating, a smaller standard size shunt is picked. For example, a
25 mΩ shunt yields a specified maximum current of 10 A and a
peak current of 12.8 A.
MDAT
VS
IS
FULL-SCALE INPUT
100% +320mV
12.8A (PEAK)
89.1% +250mV
10.0A (PEAK)
50%
0V
10.9%
–250mV
0%
–320mV
11801-004
SPECIFIED MAX INPUT
Figure 3. Feedback Current Operating Ranges
LCNT, LWIN
OVERLOAD
TRIGGER
GLITCH
FILTER
LMIN
CPU
Σ-Δ
22Ω
VS
47pF
iW
RS
22Ω
CTL
IW
IV
MDATW × D'O'
MDATW
AD7403
BIAS
DATA
INTERRUPT
RAM
SORD, SDEC
SECONDARY
DMA
SCALE
PORD, PDEC
÷2S
PRIMARY
OTHER
CHANNEL
MDATW × DO
CURRENT
FEEDBACK
Figure 4. Sinc Filter Current Feedback Paths
Rev. B | Page 4 of 20
FULL-SCALE RANGE: ±320mV
11801-003
PWM
LMAX
Application Note
AN-1265
MODULATOR CLOCK, PRIMARY FILTER
DECIMATION, AND DATA INTERRUPT RATE
SELECTION
j f
He fM
πf
sin D
πf
f
− j ( D − 1)
1
M
=
fM
×e
×
πf
D
sin
f
M
O
where:
H is the transfer function of the sinc filter in the frequency domain.
f is the frequency.
D − 1 O
τ d =
2 fM
where τd is the filter group delay.
0
−10
−20
−30
0
50
100
150
200
250
300
FREQUENCY (kHz)
11801-028
The frequency of the modulator clock (fM) and the decimation rate
(D) are the parameters that define the sinc filter performance. The
filter order (O) is typically one order higher than that of the frontend modulator. Therefore, when the AD7403 is used, the filter is
third-order. The equations for the filter frequency response and
filter group delay follow. The frequency response shown in Figure 5
and Figure 6 has zeroes at frequencies that are even multiples of the
decimation frequency (fM/D). Therefore, matching the decimation
frequency to the PWM switching frequency substantially reduces
PWM switching harmonics. Other considerations include the
increase in the filter group delay with decimation rate and the
maximum decimation limit of the filter.
PHASE (Radians)
0
Figure 6. Sinc Filter Phase Response
For a given filter order, the decimation rate and filter order are
the filter parameters that define the signal-to-noise ratio (SNR)
and group delay of the filter. Figure 7, Figure 8, and Table 1
show the variation of the SNR, effective number of bits (ENOB),
and group delay vs. the decimation rate for a third-order filter
with a 10 MHz modulator clock. The decimation rate must be
in the range of 85 to 210 to achieve an ENOB of 11 bits to 14 bits
and an SNR of 67 dB to 86 dB, which is the filter performance
range required for current feedback. The group delay is between
12 µs and 32 µs in this decimation rate range. Note that the SNR
and ENOB numbers listed in Table 1 assume an ideal signal
chain. The numbers represent theoretical maximum numbers
and serve to illustrate the trade-off between the SNR/ENOB
and the filter group delay only. Any practical implementation
gives lower performance.
D = 125
100
SNR (dB)
–100
–150
50
–200
0
50
100
150
200
250
FREQUENCY (kHz)
300
MCLK = 10MHz, O = 3
0
0
50
100
150
200
DECIMATION RATE
Figure 5. Sinc Filter Amplitude Response
Figure 7. Sinc Filter SNR
Rev. B | Page 5 of 20
250
300
11801-006
–250
11801-005
GAIN (dB)
–50
AN-1265
Application Note
40
0.10
0.08
AMPLITUDE
GROUP DELAY (µs)
30
20
0.06
0.04
10
0
50
100
150
200
250
300
DECIMATION RATE
11801-019
MCLK = 10MHz, O = 3
0
11801-029
0.02
0
0
Figure 8. Sinc Filter Group Delay
Table 1. SNR, ENOB, and Group Delay with Decimation Rate1
Decimation Rate
85
113
154
210
SNR (dB)
68
74
80
86
ENOB (Bits)
11
12
13
14
Group Delay (µs)
12.6
16.8
23.0
31.4
The test condition is a ±200 mV sine wave at 1.22 kHz.
1
ALIGNING SINC IMPULSE RESPONSE TO PWM
With the selection of decimation rate and modulator clock values,
the characteristics of the filter are set. It is equally important to
match the filter characteristic to the application. A sinc filter has
memory and the current output depends on not only current input
but also previous inputs and outputs. The impulse response is
useful for examining the effect of the sinc filter.
The impulse response of a system is defined as the output sequence
when the system is stimulated by a unit pulse. If the system is
linear and time invariant, the output response to any input
sequence can be determined through convolution of the input
and the impulse response as follows:
10
15
SAMPLE NUMBER
20
Figure 9. Impulse Response of Sinc3 Filter
with Decimation Rate of 16
A third-order sinc filter has a hyperbolic impulse response.
Figure 9 shows a weighted sum, which gives most weight to
samples at the center and less weight to samples at the beginning
and end. The effect of the weighted sum must be taken into
account when measuring motor currents.
The current through a motor driven by a switching inverter can
be split into two components: an average component and a
switching component. For control purposes, the switching
component is unwanted and must be eliminated so only the
average component remains.
Figure 10 shows that there are two instances during a switching
period when the average phase current can be measured. Those
instances are at the beginning and middle of a switching period.
Both instances are indicated by a synchronizing pulse, PWM_SYNC.
Failing to measure at the point of average phase current results
in signal degradation due to aliasing.
PHASE
CURRENT
AVERAGE CURRENT
∞
∑ x [k ] × h [n − k ]
k = −∞
PWM
where:
y is the output sequence.
n is the sample number.
x is the input sequence.
k is the index.
h is the impulse response of the system.
PWM_SYNC
tSW/2
TIME
tSW
11801-020
y [n] =
5
Figure 10. Motor Phase Currents and Relationship to the Inverter PWM
The impulse response, h, when known, can be used to determine
the response to any input. Figure 9 shows the impulse response
for a sinc3 filter with a decimation rate of 16.
With a sample-and-hold-based converter, the average value of
the currents is measured by letting the PWM_SYNC signal
trigger the sample-and-hold circuit. However, due to the
duration of the impulse response of the sinc filter, the task of
suppressing the switching component requires a different
approach when using Σ-Δ converters.
Rev. B | Page 6 of 20
Application Note
AN-1265
The impulse response is symmetrical around the center pin,
meaning the sinc filter gives equal weight to samples before and
after the center pin (see Figure 9). Furthermore, the switching
component is symmetrical around the point of average current.
That is, if x equally spaced samples taken before the point of
average current are added to x equally spaced samples taken
after the point of average current, the result is the average
current. In other words, the switching component sums to zero.
These properties are utilized to extract the average current
while also eliminating the switching component completely. If
the center pin of the impulse response is aligned with the point
of average current, an equal number of samples are taken before
and after the desired sampling point. Because the samples before
and after the center pin are given equal weight and the switching
current is symmetrical around this point, the filter output is the
true average current. This technique is illustrated in Figure 11.
The most weight is given around the desired sampling point. The
further away from this point, the less weight is given to samples.
O×D−2
Therefore, the number of pins in a third-order filter with a
decimation rate of 5 is 13. It is worth noting that the number of
pins is much greater than the decimation rate.
From the number of pins, the length of impulse response, in
seconds, can be calculated as
tM × (O × D − 2)
where tM is the period of the modulator clock.
The duration of the impulse response is important because it
tells how long it takes a sample to make its way completely
through the filter.
The center pin of the impulse response is halfway through the
total filter length. Therefore, the time it takes a sample to
propagate halfway through the filter must be
τd =
SAMPLE POINTS
PHASE
CURRENT
t M × (O × D − 2)
2
IMPLEMENTATION OF IMPULSE RESPONSE
ALIGNMENT TO PWM
IMPULSE
RESPONSE
11801-021
PWM_SYNC
TIME
Figure 11. Aligning the Center Pin of Impulse Response to the Point of the
Average Current, Equal Number of Samples Taken Before and After This Point
Aligning the center pin of the impulse response to the point of
average current is equivalent to aligning the center pin to the
PWM_SYNC pulse. However, to perform the alignment correctly,
the actual impulse response must be known.
In most applications, high decimation rates are used; but, for
simplicity, a decimation rate of 5 is used in the following example.
The impulse response of a sinc3 filter is shown in Figure 12.
0.15
AMPLITUDE
The number of pins in the impulse response is
The Aligning Sinc Impulse Response to PWM section describes
how the impulse response must be aligned to PWM to extract
the true average motor current. This section describes how the
implementation can be performed on the ADSP-CM402F/
ADSP-CM403F/ADSP-CM407F/ADSP-CM408F.
The task is to align the center pin of the impulse response to the
PWM_SYNC pulse. As described in the Aligning Sinc Impulse
Response to PWM section, the center pin is found half of an
impulse response after the first pin of the filter. Measured in
seconds, that is
τd =
t M × (O × D − 2 )
2
In other words, if the feed of input data starts (tM × (O × D −
2))/2 sec before the PWM_SYNC pulse, the center pin aligns
with the PWM_SYNC pulse, as shown in Figure 11. The feed of
data to the filter is controlled by enabling or disabling the
modulator clock.
Advancing enablement of the modulator clock with respect to
the PWM_SYNC pulse is impossible because it requires the generation of a negative delay. That is, when the PWM_SYNC signal
is needed, PWM has not yet been started. However, instead of
advancing the start of the modulator clock, exactly the same effect
can be achieved by delaying the start of the modulator clock by τd.
0.10
0.05
11801-022
As long as the switching period, tSW, is constant and there is an
integer number of data points from the sinc filter per switching
period, delaying the start of the modulator clock gives the same
result as advancing it.
0
0
1
2
3
4
5
6
7
8
9
10
11
12
SAMPLE NUMBER
Figure 12. Impulse Response of a Third-Order Sinc Filter with Decimation
Rate of 5
Rev. B | Page 7 of 20
AN-1265
Application Note
To generate the delay, the ADSP-CM402F/ADSP-CM403F/
ADSP-CM407F/ADSP-CM408F TRU and a general-purpose
timer are used, as shown in Figure 13.
PWM_SYNC
GENERALPURPOSE
TIMER x
TIMER0_TMRx
SINC
t M O D 2
11801-023
PWM TIMER
In Figure 14, note that the general-purpose timer generates a
delay of
Figure 13. Aligning Sinc Impulse Response to PWM Using General-Purpose
Timer and Triggers
The PWM timer block outputs a trigger master, PWM_SYNC,
which is routed to the TRU and onto the trigger slave of a
general-purpose timer, TRGS_TIMER0_TMRx. The generalpurpose timer generates a delay with respect to the PWM_
SYNC pulse, which brings the impulse response in alignment
with PWM. When the delay expires, the general-purpose timer
generates a trigger master, TRGM_TIMER0_TMRx, which again
is routed to the TRU and onto the trigger slave of a sinc filter,
SINC_SYNC. The sequence is illustrated in the timing diagram
in Figure 14.
SAMPLE
TIME
tSW
2
This delay brings the center pin of the impulse response in
alignment with the PWM_SYNC pulse. Because the center pin
is at the midpoint of the impulse response, it takes another half
impulse response before data has propagated through the filter.
In Figure 14, note that the data interrupt occurs half of an
impulse response after the PWM_SYNC pulse.
After the data interrupt is started, there is no need to realign the
center pin to the PWM_SYNC pulse. The filter remains in sync
and, thus, the impulse response is always aligned to PWM.
Therefore, the general-purpose timer used for alignment can be
reused for other purposes.
SINC DATA AND INTERRUPT RATE
It is not possible to match the sinc filter decimation rate with
the typical PWM switching frequencies used in motor drives.
For example, matching a switching frequency of 16 kHz requires a
decimation rate of 625, and the resulting filter group delay is
94 μs. This decimation rate is well above available values, and the
filter group delay limits the bandwidth of the current loop.
SAMPLE
TIME
PHASE
CURRENT
PWM_SYNC
TMRx_CNT
TIMER0_TMRx
MODULATOR
CLOCK
tM × (O × D – 2)
tM × (O × D – 2)
2
2
11801-024
DATA IRQ
Instead, the decimation rate is set to a multiple of the PWM
frequency to lower the group delay and still achieve the target
filter SNR. The control algorithm samples the data at a submultiple
of the decimation frequency matching the PWM switching. This
software decimation process involves transferring multiple data
samples to a circular buffer in memory and reading the most
recent data sample in response to the interrupt generated when the
buffer is full. The DMA engine transfers data from the primary
sinc filter to data memory, and the sinc control unit generates a
trigger every time it transfers a fixed number of samples.
Figure 14. Startup of Sinc Filter Using a General-Purpose Timer and a TRU
Rev. B | Page 8 of 20
Application Note
AN-1265
tSW
PWM_AH
PWM_SYNC
tM
MODULATOR
CLOCK
DEC × tM
DECIMATION CLOCK
tSW/SWDEC
PRIMARY DATA TRANSFER
D(3)
D(4)
D(0)
D(1)
D(2)
D(0)
D(1)
τd
τd
½ IMPULSE
RESPONSE
½ IMPULSE
RESPONSE
11801-025
SINC0_D0 TRIGGER
Figure 15. Modulator and Decimation Clock Timing
Figure 15 shows the alignment between PWM switching, the
modulator clock, the decimation clock, and data sampling. The
synchronizing pulse (PWM_SYNC) from the PWM block aligns
the startup of the modulator clock with the PWM frequency. The
decimation frequency is a submultiple of the modulator clock
and a multiple of the PWM frequency. The SINC0_D0 trigger rate
is at the PWM frequency.
The information in Table 2 illustrates the process of selecting
the decimation rate and the PWM switching frequency. The first
three entries in the table are chip level settings for the core and
peripheral clocks. The maximum core clock rate is 240 MHz,
and it is typically an even multiple of the system (peripheral)
clock frequency. The sinc filter modulator clock derives from the
system clock based on the MDIV register field value, and there
are a limited set of values in the 5 MHz to 20 MHz range. The
primary hardware decimation rate (PDEC) is 125, which sets the
filter SNR at 76.0 dB (>12-bit ENOB) with a filter group delay of
18.6 µs. The modulator clock is 10 MHz; therefore, the primary
decimation clock frequency is 80.0 kHz, and a software decimation
rate (SWDEC) of 5 synchronizes the sample rate with a 16.00 kHz
PWM frequency (PWM). To tune the PWM frequency, adjust
the sinc filter decimation rate.
The equation governing the relationship among the modulator
clock, the PWM frequency, and the hardware and software
decimation rates is
MCLK
PWM
= PDEC × SWDEC
where:
MCLK is the modulator clock.
PWM is the PWM frequency.
PDEC is the primary hardware decimation rate.
SWDEC is the software decimation rate.
The hardware and software decimation rates must be integers.
The PCNT register field value in the sinc filter sets the software
decimation rate. The PCNT register field value loaded in the sinc
filter control register is less than one of the number of sample
delays before an interrupt is generated. The PWM_TM0 register
sets the PWM switching frequency and, therefore, sets the
sample timing.
Table 2. Decimation Rate Selection
Parameter
Core Clock
System Clock Divider
System Clock
Modulator Clock Divider
Modulator Clock (1/tM)
Decimation Rate
Filter SNR
Filter ENOB
Decimation Clock Frequency
Filter Group Delay
Software Decimation Rate
Data Transfer Count
PWM Frequency (1/tSW)
PWM Period Count
Symbol
CCLK
SYSSEL
SYSCLK
MDIV
MCLK
PDEC
SNR
ENOB
DCLK
τd
SWDEC
PCNT
PWM
PWMTM
Value
240
3
80
8
10
125
76.0
12.3
80.0
18.6
5
4
16.00
2500
Unit
MHz
MHz
MHz
dB
Bits
kHz
µs
kHz
PRIMARY FILTER SCALING
The sinc filter order (O) and decimation rate (D) set the
primary filter dc gain (GDC), given by
GDC = DO
The sinc filter block has output scaling and bias functions to
convert the data to a 16-bit signed integer before it is transferred to
memory. The data format is valid as a fractional 16-bit integer
(S.15) in the range of ±1.0 or as a signed 16-bit integer in the
range of ±215, depending on interpretation.
Rev. B | Page 9 of 20
AN-1265
Application Note
The raw filter output is an integer between 0 and DO, where
DO/2 aligns with a 50% pulse density corresponding to 0 A. Adding
a bias value of −DO/2 to the output sets the correct zero level.
Dividing the result by DO/2 scales the full-scale, fractional integer
output to ±1. However, for simplicity, the unit has a simple binary
scale factor (S), where the user selects S to set the gain near 1.0.
Regardless of the scaling, the DMA engine only transfers the
16 least significant bits of the output data; therefore, correct
scaling is essential to avoid loss of precision. The output data is
saturated to prevent data overflow, which inverts the polarity of
the output signal due to incorrect scale factor selection. The
filter sets an overflow fault flag when saturation occurs.
Conversion of the data to a floating point involves scaling by the
inverse of the current shunt gain and adjusting for the
mismatch between the filter dc gain and the scale factor.
Feedback Scaling Calculations
The final system gain from the shunt current to the data-word
in memory derives from the gains of all the elements in the system,
as shown in Figure 16. The isolated modulator in this example
is the AD7403.
iW
RS
AD7403
SINC
BIAS SCALE
Σ-Δ
MDAT
1-BIT
DO
SINC
÷2S–1
32-BIT
UNSIGNED
INTEGER
IW
215
1.15
SIGNED
FRACTION
IW
16-BIT
SIGNED
INTEGER
Figure 16. Sinc Primary Output Data Scaling
VS = iW × RS
The bias and scale functions in the primary output path remove
the bias on the sinc data and rescale the data to a 16-bit signed
integer. The bias value must be −DO/2 to eliminate the offset in
the sinc output for a modulator with a bipolar input range. The
rescaling selects the appropriate bit range from the sinc output
word.
IW =
SINC −
2S − 1
DO
O
2 = D VS
2S VFS
where IW is the winding current (digital).
DO
2
S
IW =
where:
VS is the input voltage.
iW is the winding current (analog).
RS is the resistance of the shunt.
The isolated modulator expects a bipolar input and generates a 50%
pulse density for a 0 V input. The pulse density of the data stream
(MDAT) is a function of the ratio of the input voltage (VS) to the
positive full-scale input (VFS):
In the case of the AD7403, the positive full-scale voltage is
320 mV, and the ones density is 89.1% for the specified
maximum voltage of 250 mV.
This dc scaling applies to the secondary filter outputs, and the
maximum secondary decimation rate restricts the raw output data
range to a 16-bit unsigned integer. The secondary output is 0 at the
negative full-scale input and DO at the positive full-scale input.
<< 1∴ S >>
( )
ln D O
ln 2
The sinc output equation, when reading the data as a signed
integer, adds a scale factor of 215.
The shunt voltage seen by the modulator is
V
MDAT = 0.5 S + 1
V
FS
D O VS
+ 1
2 VFS
The scale factor must set the maximum fractional integer
output at 1.0, which is true when
–DO/2
FS: ±320mV
VS
S/W
SINC =
11801-008
SHUNT
The sinc filter dc gain is DO; therefore, the raw output as a
function of the input voltage is
D O VS 15
×2
2S VFS
The current reading as a function of the actual winding current in
this case is
R DO
IW = iW × S
0.32 2S
15
× 2
SECONDARY FILTER SCALING AND OVERLOAD
CONFIGURATION
The secondary sinc filter data outputs connect directly to overload
comparators and a glitch filter, as shown in Figure 4. The secondary
filter decimation rate is set significantly lower than that of the
primary filter to achieve fast response to fault conditions. The
processor TRU connects the overload trip signal to the PWM
modulator shutdown input to clear the fault. The TRU can also
connect the overload signal to other sources, such as an external
general-purpose input/output (GPIO) used to shut down other
critical circuit elements.
Rev. B | Page 10 of 20
Application Note
AN-1265
Typical power inverter switches can withstand a short circuit for
a few microseconds; therefore, the overload circuit must have a
relatively short detection window. Because the sinc filter can
respond to a step input within three decimation cycles, a response
within 3 μs is possible using a decimation rate of 10, as shown
in Figure 17 and Figure 18. The sinc filter also filters out
inverter switching noise, as shown in Figure 19, Figure 20, and
Figure 21. In Figure 19, Figure 20, and Figure 21, a 10 A peak
test waveform injects 16 A noise pulses of 1.5 μs in duration and
16 A overload pulses of 40 μs in duration. The filter rejects the
short noise pulses, but the circuit detects the 16 A overload pulses.
The maximum and minimum trip levels in this test are at
secondary sinc outputs corresponding to ±16 A.
PHASE CURRENT (A)
16
0
0
2
4
16
6
8
TIME (ms)
10
12
11801-010
MCLK = 10MHz
D = 10, O = 3
–16
Figure 19. Test Current Waveform
COUNT
0
0.100
0.105
TIME (ms)
0
0
Figure 17. Secondary Filter Overload Detection: Test Current Waveform
2
4
6
8
10
12
TIME (ms)
11801-031
–16
0.095
500
MCLK = 10MHz
D = 10
O=3
11801-009
PHASE CURRENT (A)
1000
Figure 20. Secondary Sinc Data with a Decimation Rate of 10
1.0
0.5
TRIP
TRIP
1.0
0.5
TIME (ms)
0
0
Figure 18. Secondary Filter Overload Detection: Overload Trip Signal
2
4
6
TIME (ms)
8
10
12
11801-032
0.095 0.096 0.097 0.098 0.099 0.100 0.101 0.102 0.103 0.104 0.105
11801-030
0
Figure 21. Signal Indicating if Data Exceeds Maximum or Minimum Limits
Rev. B | Page 11 of 20
AN-1265
Application Note
125
A faster response is possible at a lower decimation rate; but, as
shown in Figure 22, Figure 23, and Figure 24, the secondary
sinc output exceeds the trip levels even for a simple sinusoidal
test current of ±10 A. The higher sinc filter noise at a decimation
rate of 5 generates multiple false trip signals. Figure 25 and
Figure 26 illustrate the SNR at high (10) and low (5) decimation
rates and the noise margin for the trip signal.
COUNT
100
75
50
16
–10
–5
0
0
5
10
PHASE CURRENT (A)
11801-012
MCLK = 10MHz, D = 5, O = 3
0
Figure 25. Secondary Filter Gain Curve for Decimation Rates of 5
1000
MCLK = 10MHz
D = 5, O = 3
0
2
4
6
8
10
12
TIME (ms)
750
Figure 22. Test Current Waveform
COUNT
–16
11801-011
PHASE CURRENT (A)
25
500
250
MCLK = 10MHz, D = 10, O = 3
50
–5
0
5
10
Figure 26. Secondary Filter Gain Curve for Decimation Rates of 10
0
0
2
4
6
8
10
12
TIME (ms)
Figure 23. Secondary Sinc Data with a Decimation Rate of 5
1.0
0.5
0
0
2
4
6
8
10
TIME (ms)
12
11801-034
TRIP
–10
PHASE CURRENT (A)
11801-033
COUNT
0
11801-035
100
Figure 24. False Overloads Detected
Rev. B | Page 12 of 20
Application Note
AN-1265
The secondary output glitch filter rejects short overload trips by
eliminating trips with durations less than a minimum count
(LCNT) with a trip count window (WCNT). Figure 27 and
Figure 28 illustrate how the glitch filter eliminates the spurious
overload that is triggered when the decimation rate is 5; however,
there is an additional three cycle delay in the response time.
Therefore, there is no reduction in response time from the lower
decimation rate. Figure 27 and Figure 28 illustrate the ability of
the filter to reject short noise pulses on the analog input. In this
example, the noise pulse is 1.5 µs in duration.
The secondary sinc filter includes a set of history buffers that
capture the eight most recent data samples before a trip is
generated for diagnostic purposes. The data in the history
registers is accessed directly through the device peripheral
memory infrastructure.
0
SINC MODULE FAULT DETECTION FUNCTIONS
MCLK = 10MHz,
D = 5, O = 3
–16
0
2
4
6
8
10
12
In addition to overload faults, the sinc module checks for data
faults that can arise from incorrect filter settings overloading
the chip infrastructure.
11801-013
PHASE CURRENT (A)
There is no extra output scaling on the secondary filters; therefore,
valid minimum and maximum trip levels are within the range
of 0 to DO. The negative, full-scale current maps to 0, and the
positive, full-scale current maps to DO. Setting the minimum and
maximum trip levels to 1 and DO − 1 enables the maximum range
of the trip function. The transfer function shown in Figure 25 and
Figure 26 (for a decimation rate of 10 and a 20 mΩ shunt) shows
that the noise peaks for a 10 A input are within the maximum
(1000 counts) and minimum (0 counts) outputs of the filter. Set
the LMIN and LMAX trip levels to 1 count and 999 counts to
avoid spurious trips for 10 A peak current. The actual current
level at which the trip is triggered ranges between 11 A and the
full scale of 16 A. The likelihood of a trip increases the closer the
current is to the full-scale limits.
The overload circuit operates slightly more precisely within the
specified modulator input range. For the previous case, the peak
noise at 5 A input is 700 counts, which is equivalent to 6.4 A.
Therefore, the trip is set to operate within the range of 5 A to
6.4 A. The LMAX and LMIN settings, in this case, are 700 counts
and 300 counts. Attaining precise trip settings using lower
decimation rates is more difficult.
16
The primary filter detects output data saturation when there is
an incorrect setting of the output bias and scaling. The filter
DMA engine detects a first in, first out (FIFO) error if it fails to
transfer data before the filter writes new data. The ESATx bits
and the EFOVFx bits in the SINC_CTL register mask the
SINC_STAT interrupt generation on saturation and FIFO faults.
TIME (ms)
Figure 27. Test Current Waveform with Overload Events
1.0
TRIP
Secondary Filter Scaling and Trip Level
0.5
0
2
4
6
TIME (ms)
8
10
12
11801-036
0
Figure 28. Overload Trip Signal with a Decimation Rate of 5 and Glitch Filter
with WCNT = 4 and LCNT = 4
Rev. B | Page 13 of 20
AN-1265
Application Note
SINC FILTER SETUP
There are several steps to set up the sinc filter module as well as the
signal routing and data buffers before the filter is ready for use.
After it is configured, the DMA engine automatically streams
primary filter data to memory, and the secondary limit function
shuts down the PWM module in the case of an overload. The
system generates an interrupt when data is ready; therefore, the
processor can execute the control algorithm and update the PWM
duty cycle registers. Figure 29 outlines the interconnections
required between the sinc filter block and the CPU, SRAM, PWM,
and external pins to capture motor current feedback signals.
The following four steps set up current feedback using the sinc
filter:
11801-015
Configure the pin multiplexer.
Allocate the data buffer memory.
Connect the interrupt and trigger routing.
Configure the primary and secondary filters.
Figure 30. Pin Multiplexing Code Generator
DATA BUFFER MEMORY ALLOCATION
This section further describes these steps, detailing the setup
process and programming the sinc filter control registers.
TRIP
GENERAL
PURPOSE
TIMER
CLK
SYNC0
OVERLOAD TRIGGER
CLK0
CLK1
SINC
STATUS INTERRUPT
CPU
D0
D1
D2
D3
DATA INTERRUPT
SRAM BUFFER
CLK1
PIN
MULTIPLEXER
DMA
D0
D1
D2
D3
11801-026
PWM0
SYNC
The primary filter data buffers must be defined and assigned
memory space to allow the control algorithm to use the data.
The software decimation rate and the number of feedback channels
define the buffer size. The data is ordered on a per group basis
in channel sequence. The pointer to the most recent data set is
stored in the SINC_PPTRx register. Figure 31 shows how the
data buffer is organized and how the head and tale specify the
start and end of the buffer, where SINC_OUT_x_M[n] is the
data for the nth most recent sample in the Mth channel in the
filter group x, and n = 0 is the most recent data.
BUFFER ADDRESS
Figure 29. Sinc Filter System Configuration
PIN MULTIPLEXER CONFIGURATION
SINC_PHEADx
The pin multiplexer connects the front-end modulator clock and
data pins to the sinc module. Two modulator clock outputs are
available, the SINC0_CLK0 and SINC0_CLK1 pins. Four sinc data
input pins are available, the SINC0_D0 pin, the SINC0_D1 pin,
the SINC0_D2 pin, and the SINC0_D3 pin. The PORT_
MUX register controls the selection of these pins from four
alternate input or output signals for each of the multiplexed
pins. The PinMux64.jar and PinMux32.jar Java® application
programs, which are supplied with the ADSP-CM40x Enablement
Software package, automatically generate C code to enable the
user port selections. Figure 30 is a snapshot of the PinMux64.jar
Java application window.
Rev. B | Page 14 of 20
BUFFER DATA
SINC_OUT_x_0[3]
SINC_OUT_x_1[3]
SINC_PPTRx
SINC_OUT_x_0[0]
SINC_OUT_x_1[0]
SINC_OUT_x_0[1]
SINC_OUT_x_1[1]
SINC_OUT_x_0[2]
SINC_TAILx
SINC_OUT_x_1[2]
Figure 31. Data Buffer Organization
11801-016
1.
2.
3.
4.
Application Note
AN-1265
INTERRUPT AND TRIGGER ROUTING
Figure 32 shows the sinc filter interconnection with other
peripheral functions using interrupt and trigger signals. The
SINC_STAT interrupt is the single processor interrupt signal of
the sinc filter module. The TRU connects the other trigger signals
to the peripherals and processor interrupts of the sinc filter module.
Loading the trigger master address into the trigger slave registers in
the TRU connects the routing.
The TRU connects both of the sinc overload triggers to the
TR_T1 input of the PWM to enable overcurrent protection. The
TR_T0 input connects to the external trip signal only. The PWM,
as well as the TR_T0 and TR_T1 inputs, must be configured to
accept these triggers. There are two interrupt triggers produced by
an overload fault: the STAT interrupt, connected directly to the
CPU, and the TR_T1 interrupt, generated by the sinc overload
trigger.
Through a general-purpose timer, TMRx, the TRU synchronizes
the sinc filter modulator and decimation clocks with the PWM
frequency to meet the timing defined in Figure 15. The TRU
connects the sinc filter data transfer trigger to the control software
interrupt to start execution of the control algorithm.
SINC
TRU
SYNC0
TMRx
GENERAL-PURPOSE
TIMER TMRx
TMRx
STAT
CONTROL GROUP0
CONTROL GROUP1
CLK0
SYNC
OV0
OV1
TRIP
TR_T0
TR_T1
IRQ0
P0_OV
OV2
SEC2
P1_OV
OV3
SEC3
SINC0_D0
DMA
CPU
SEC0
SEC1
IV, IW
SRAM
Figure 32. Sinc Filter Trigger Routing
Rev. B | Page 15 of 20
PRIM0
PRIM1
D0
D1
PRIM2
PRIM3
11801-027
PWM0
AN-1265
Application Note
SINC_LEVEL1 register define the primary and secondary filter
order (PORD, SORD) and the primary filter scale (PSCALE).
The SINC_BIAS0 register and the SINC_BIAS1 register define
the primary filter data offset. The SINC_CLK register defines
the CLK0 and CLK1 modulator clock frequencies and can
enable synchronization with an external trigger. This register
also includes a means to adjust the clock phase if required.
PRIMARY AND SECONDARY FILTER
CONFIGURATIONS
Filter channels are organized in groups because it is typical for
two or three feedback signals to need the same filter parameters.
The sinc module has two groups of configuration registers. The
channels in any one group share the same clock and have common
filter parameters, such as filter order, decimation rate, scaling,
and bias. The exception is the overload limit and history registers,
which have a per channel organization. Enabling a filter channel
assigns it to a configuration group. The configuration registers
define the modulator clocks, filter parameters, DMA data
transfer, and overload detection.
Three registers per group support the primary DMA channels.
The SINC_PHEAD0 register and the SINC_PTAIL0 register define
the memory addresses for the Group 0 primary output data buffer.
The SINC_PPTRx register stores the pointer to the most recent
data in the buffer. The PCNT bits in the SINC_LEVELx register
set the software decimation rate by defining the number of data
transfers per data interrupt (PCNT + 1).
Figure 33 describes the assignment of filter and system parameters
to Group 0 registers. The organization of Group 1 registers is the
same. The SINC_CTL register enables each channel and assigns
the control group. The recommended process is to configure
the filter group before enabling the channels in the group. The
SINC_CTL register also masks the SINC_STAT interrupt. The
system status register, SINC_STAT, reports the fault and data
trigger count status.
Five registers per channel support the secondary overload
detection function. The SINC_LIMITx register defines the
maximum and minimum overload threshold, and the SINC_
PxSEC_HIST0 register, the SINC_PxSEC_HIST1 register, the
SINC_PxSEC_HIST2 register, and the SINC_PxSEC_HIST3
register store the last eight secondary filter outputs before an
overload trip. The SINC_LEVEL0 register and the SINC_
LEVEL1 register set the secondary filter glitch parameters (LWIN,
LCNT) for the channels in the associated group.
Three registers per group and the clock register define the primary
and secondary filter parameters. The SINC_RATE0 register and
the SINC_RATE1 register set the primary and secondary filter
decimation rates (PDEC, SDEC) and the primary filter phase
(typically 0°). The SINC_LEVEL0 register and the
CTL
STAT
CHANNEL 0
SINC_OUT_0_0
SINC_RATE0: PDEC
SINC_LEVEL0: PORD
SINC_LEVEL0: PSCALE
PRIMARY
SINC_D1
SINC_RATE0: SDEC
SINC_LEVEL0: SORD
÷2S
SINC_OUT_0_1
SINC_BIAS0
SINC_LIMIT0:
LMAX
SINC_LIMIT0:
LMIN
SINC_CLK
MODULATOR
CLOCK
SINC_D0
SINC_LEVEL0: LWIN
SINC_LEVEL0: CNT
SINC0_P1_OVLD
SINC_HIS_STAT
HISTORY BUFFER
CLOCK
SYNC0
DMA
SINC_PPTR0
SINC_PHEAD0
SINC_PTAIL0
SINC_LEVEL0: PCNT
GLITCH
FILTER
SECONDARY
STAT
CONTROL (0,1)
SINC_P0SEC_HIST0
SINC_P0SEC_HIST1
SINC_P0SEC_HIST2
SINC_P0SEC_HIST3
SYSCLK
Figure 33. Sinc Register Mapping
Rev. B | Page 16 of 20
11801-018
SINC_D0
Application Note
AN-1265
SINC FILTER SOFTWARE SUPPORT
The code segment that follows is an example of how to set up the
primary and secondary filters for two channels of current feedback.
The example was developed for the configuration in Table 3.
Table 3. Configuration of Software Example
Parameter
Core Clock
System Clock
Modulator Clock (1/tM)
Decimation Rate
Decimation Frequency
Software Decimation Rate
PWM Frequency (1/tSW)
Symbol
CCLK
SYSCLK
MCLK
PDEC
DCLK
SWDEC
PWM
Value
240
80
8
200
40.0
4
16.00
Unit
MHz
MHz
MHz
kHz
kHz
These code snippets are extracts from working code tested on a
closed-loop motor control evaluation platform. The main focus
of the code example is the setup and handling of the sinc filter,
but setting up the TRU is also required, and is included in the code.
The code example only relates to the sinc filter and cannot work on
its own. The code must be included in a complete software project.
The first block of code (Lines[1:18]) defines a number of parameter
constants. The next block of code (Lines[19:27]) defines prototype
functions and allocates memory for the sinc circular buffer. The
function defined on Line 24 implements a prototype for the
SINC_DATA0 interrupt service routine.
The external hardware trip connects to the TRIP0 input pin,
and the internal SINC_Px_OVLD triggers connect to the TRIP1
and TRIP2 trigger slaves.
The sinc setup code block (Lines[45:102]) is the main configuration block. Lines[48:68] set up various group parameters,
including order, decimation rate, modulator clock, registers
service function for data interrupt, and setup priority.
Lines[60:61] are the initial setting of the overload limits to their
full range to avoid a spurious trip when the filter starts. To set
the application specific overload limits, a defined sequence
must be followed. First, the filter is enabled (Lines[70:71]). To
let data propagate through the filter, a 10 µs delay is provided
(Lines[73:74]). At this point, the correct current levels have been
determined and the overload interrupt masks can be cleared
(Line 76). Finally, the application specific trip levels are set
(Lines[78:79]).
Startup and alignment of impulse response to PWM is handled
by Lines[90:101]. Utilizing triggers, a general-purpose timer is
used to generate the required interrupt. When the delay expires,
the general-purpose timer generates a trigger that starts the filter.
The final block of code (Lines[103:125]) includes the interrupt
service routine called when the data buffer has been transferred to
memory. The SincData0Handler function copies data from the
buffer to the motor control variables and calls the control function.
The TRU setup code block (Lines[28:44]) includes the setup of
the trigger routing. Among the triggers is overload detection.
Both the handling of overload and the shutdown of PWM is
handled by the PWM block. A code example for the PWM
setup is not included.
Rev. B | Page 17 of 20
AN-1265
Application Note
1. /****************************************
2. SINC FILTER SETUP CODE SNIPPETS
3. ****************************************/
4.
32. *pREG_TRU0_SSR12 = TRGM_SINC0_DATA0;
// Slave is TRU0_IRQ0 (12), master is
SINC0_DATA0
33.
5. /* SINC definitions */
34. // Setup TRU for GP timer enable. Slave
is TIMER0_TMR2, master is PWM0_SYNC
6. #define SINC_NUM_SAMPLES_HDR 4 /*
determines how often a data interrupt is
generated */
35. *pREG_TRU0_SSR4 = TRGM_PWM0_SYNC;
// Slave is TIMER0_TMR2 (4), master is
PWM0_SYNC
7. #define SINC_NUM_PAIRS
36. // Setup TRU for SINC enable. Slave is
SINC0 SYNC0, master is TIMER0_TMR2
2
8. #define CIRC_BUF_SIZE_HDR
(SINC_NUM_SAMPLES_HDR*2) /* size of the
circular buffer */
9. #define SINC_MODCLK
(8000000)
/* modulator clock frequency */
10. #define S_HDR
Primary scale */
23
/*
11. #define HDR
primary decimation */
200
/*
37. *pREG_TRU0_SSR57 = TRGM_TIMER0_TMR2;
// Slave is SINC0_SYNC0 (57), master is
TIMER0_TMR2
38.
39. // Setup TRU for SINC overload detection.
Slave is PWM0_TRIP_TRIGx, master is
SINC0_Px_OVLD
40. *pREG_TRU0_SSR49 = TRGM_SINC0_P0_OVLD; //
Slave is PWM0_TRIP_TRIG1 (49), master:
PWM0_TRIP_TRIG1
12. #define TRIP_DR
5
Decimation rate of TRIP filter */
/*
13. #define SINC_N
SINC order */
3
/*
14. #define LWIN
Glitch window */
4
/*
15. #define LCNT
Glitch count
4
/*
43. *pREG_TRU0_GCTL |= BITM_TRU_GCTL_EN;
Enable TRU
16. #define LMAX
Overload max limit */
124
/*
44. }
17. #define LMIN
Overload min limit */
1
/*
45. void SetupSINC(void){
41. *pREG_TRU0_SSR50 = TRGM_SINC0_P1_OVLD; //
Slave is PWM0_TRIP_TRIG2 (50), master:
PWM0_TRIP_TRIG2
42.
*/
//
46. uint8_t mdiv_temp;
18.
19. // Function prototypes
47. // Specify Group 0 Parameters for primary
and secondary filter
20. void SetupTRU(void);
21. void SetupSINC(void);
48. *pREG_SINC0_RATE0 =
(TRIP_DR<<BITP_SINC_RATE0_SDEC) | HDR;
22.
23. // SINC Data
24. void
SincData0Handler(uint32_t, void* );
49. *pREG_SINC0_LEVEL0 =
(0<<BITP_SINC_LEVEL0_PORD) |
(S_HDR<<BITP_SINC_LEVEL0_PSCALE)|
25. #pragma data_alignment = 2
// Make
sure buffer starts at an even address
(16-bit aligned)
50.
26. static int16_t
sincCircBuffer_HDR[CIRC_BUF_SIZE_HDR];
51.
(SINC_NUM_SAMPLES_HDR-1 <<
BITP_SINC_LEVEL0_PCNT) |
(0<<BITP_SINC_LEVEL0_SORD) |
(LCNT<<BITP_SINC_LEVEL0_LCNT) |
27. static int16_t ib_sinc_raw_HDR,
ic_sinc_raw_HDR;
52.
(LWIN<<BITP_SINC_LEVEL0_LWIN);
28. void SetupTRU(void){
29. *pREG_TRU0_GCTL |= BITM_TRU_GCTL_RESET;
// Reset the TRU
30.
31. // Setup TRU for SINC data interrupt.
Slave is TRU interrupt. Master is
SINC_DATAx
53. // Calculate bias as -DR^N/2. Offset
compensation due to drift is handled by
the application code
54. *pREG_SINC0_BIAS0 = -(HDR*HDR*HDR)/2;
Rev. B | Page 18 of 20
Application Note
AN-1265
55. // Set up head and tail address of result
buffers
56. *pREG_SINC0_PHEAD0 =
(uint32_t)&sincCircBuffer_HDR;
77. *pREG_SINC0_LIMIT0 =
(LMAX<<BITP_SINC_LIMIT0_LMAX) | LMIN; //
Limits for filter 0
78. *pREG_SINC0_LIMIT1 =
(LMAX<<BITP_SINC_LIMIT1_LMAX) | LMIN; //
Limits for filter 1
57. *pREG_SINC0_PTAIL0 =
(uint32_t)&sincCircBuffer_HDR + 2u *
(CIRC_BUF_SIZE_HDR-1);
58. // Reset overload amplitude detection
limits to 0 – FullScale
79. // SINC filter is now set up but not yet
started. We want to sync modulator clock
to PWM_SYNC
59. *pREG_SINC0_LIMIT0 =
(0xFFFF<<BITP_SINC_LIMIT0_LMAX) | 0x0000;
// Limits for filter 0
80. // To do so let PWM SYNC pulse start GP
timer. GP timer creates a phase shift
which is half
60. *pREG_SINC0_LIMIT1 =
(0xFFFF<<BITP_SINC_LIMIT1_LMAX) | 0x0000;
// Limits for filter 1
81. // the duration of the impulse response
of the filter. In that way the true
average of the
82. // motor current can be measured.
61. // Specify modulator clock frequency,
phase and start-up synchronization
83. // Set required phase shift in
TIMER0_TMRx_DLY register.
62. mdiv_temp =
(uint8_t)(fsysclk/SINC_MODCLK);
84. // Do not start timer here. PWM_SYNC
pulse starts timer through TRU.
63. // Scalers for MCLK and specify start
condition as "Enable and Commence on Next
Rising Edge"
85. // Enable timer slave (to start the
timer) and trigger master (to start SINC
mod clock)
64. *pREG_SINC0_CLK =
(mdiv_temp<<BITP_SINC_CLK_MDIV0) |
(3<<BITP_SINC_CLK_MCEN0);
86. // Note, to enable master trigger both
TRG_MSK register and valid IRQ mode must
be set or
87. // trigger won't happen.
65. //Install interrupt handler for data IRQ
and specify priority
88. // Disable Timer First
66. adi_int_InstallHandler((IRQn_Type)INTR_TR
U0_INT0, SincData0Handler, NULL, true);
89. *pREG_TIMER0_STOP_CFG_SET =
BITM_TIMER_STOP_CFG_TMR02;
67. NVIC_SetPriority((IRQn_Type)INTR_TRU0_INT
0, 0);
90. *pREG_TIMER0_RUN_CLR =
BITM_TIMER_RUN_SET_TMR02;
68. //Enable filters
69. *pREG_SINC0_CTL = (3<<BITP_SINC_CTL_EN3)
| (3<<BITP_SINC_CTL_EN2) |
91. *pREG_TIMER0_TMR2_CFG =
ENUM_TIMER_TMR_CFG_PWMSING_MODE |
ENUM_TIMER_TMR_CFG_IRQMODE1 |
70.
92.
(2<<BITP_SINC_CTL_EN1)
| (2<<BITP_SINC_CTL_EN0);
ENUM_TIMER_TMR_CFG_TRIGSTART |
ENUM_TIMER_TMR_CFG_POS_EDGE |
93.
71. // Wait 10 µs to let data propagate
through the filter before setting trip
limits.
ENUM_TIMER_TMR_CFG_PADOUT_EN
|ENUM_TIMER_TMR_CFG_EMU_CNT;
72. for (int i=0; i<500; i++)
73.
94. // Set timer delay to half an impulse
response: t_mod × (N × DR-2)/2
asm("nop;");
74. // Specify interrupt masks
75. *pREG_SINC0_CTL |= (BITM_SINC_CTL_EPCNT0
| BITM_SINC_CTL_EFOVF0 |
BITM_SINC_CTL_ELIM0);
76. // Now the correct trip limits can be set
95. *pREG_TIMER0_TMR2_DLY =
(uint32_t)((fsysclk/SINC_MODCLK) *
(SINC_N*HDR-2)/2);
96. // Width register just has to be greater
than delay register -> multiply with 2
97. *pREG_TIMER0_TMR2_WID =
*pREG_TIMER0_TMR2_DLY << 1;
Rev. B | Page 19 of 20
AN-1265
Application Note
98. // Enable trigger. On next PWM_SYNC pulse
TMR is started. When delay expires, SINC
is started
99. *pREG_TIMER0_TRG_MSK &=
~BITM_TIMER_TRG_MSK_TMR02;
106. // required, but makes handling of the
buffer easier.
107. // PPTR0 point at the latest data point.
Data are interleaved: pair0, pair1,...,
pairx.
100. *pREG_TIMER0_TRG_IE |=
BITM_TIMER_TRG_IE_TMR02;
108. static int16_t *pData;
101. }
110. PMSMctrl_U.ibc_sinc[0] = *(pData);
102. void SincData0Handler(uint32_t iid,
void* handlerArg){
111. PMSMctrl_U.ibc_sinc[1] = *(pData-1);
109. pData = (uint16_t*)*pREG_SINC0_PPTR0;
103. // Data is stored in a circular buffer
that wraps around every time it is full.
104. // By keeping the length of the buffer
and integer times the number of samples
per
105. // data irq, the buffer never wraps
around in the middle of a data set. This
is not
112. ib_sinc_raw_HDR =
PMSMctrl_U.ibc_sinc[0];
113. ic_sinc_raw_HDR =
PMSMctrl_U.ibc_sinc[1];
114. sMcAlgorithm();
code
// Call application
115. *pREG_SINC0_STAT |= (1u <<
BITP_SINC_STAT_PCNT0);
116. }
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AN11801-0-4/15(B)
Rev. B | Page 20 of 20