SB3231 D

RHYTHM SB3231
Pre-configured DSP System
for Hearing Aids
Description
Features
•
•
•
•
•
•
•
•
•
FrontWave Static Directional
Adaptive Noise Reduction
Adaptive Feedback Cancellation
WDRC Compression with Choice of 1, 2 or 4 Channels of
Compression
Auto Telecoil with Programmable Delay
EVOKE LITEt Acoustic Indicators
Noise Generator for Tinnitus Treatment or In−situ Audiometry
Frequency Response Shaping with Graphic EQ
Trimmer Compatibility – Four Three−Terminal
Trimmers with Configurable Assignments of Control
Parameters
© Semiconductor Components Industries, LLC, 2014
November, 2014 − Rev. 4
1
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25 PAD
HYBRID
CASE 127DN
PAD CONNECTION
17
18
VIN1
1
VREG
TIN
16
19
TR4
2
MGND
DAI
15
20
TR3
3
GND
VC
14
21
TR2
4
PGND
D_VC
13
22
TR1
5
OUT+
SDA
12
23
N/C
6
OUT−
CLK
11
7
VBP
MS1
10
25
24
N/C
VIN2
N/C
O N S e m i c o n d u c t o r ’s R H Y T H M t S B 3 2 3 1 h y b r i d i s
a trimmer−configurable DSP system based on a four−channel
compression circuit featuring Adaptive Feedback Cancellation,
Adaptive Noise Reduction, and FrontWave static directionality.
Based on a phase cancellation method, Rhythm SB3231’s Adaptive
Feedback Reduction algorithm provides added stable gain to enable
extra gain and user comfort. It features rapid adjustment for dynamic
feedback situations and resistance to tonal inputs.
Rhythm SB3231’s Adaptive Noise Reduction monitors noise levels
independently in 64 individual bands and employs advanced
psychoacoustic models to provide user comfort.
The FrontWave directional system utilizes a pair of microphones to
create a fully customizable static polar pattern, such as bidirectional,
cardiod, hyper−cardiod and super−cardiod.
In addition to these adaptive algorithms, Rhythm SB3231 also
supports the following features: up to four channel WDRC,
low−distortion compression limiting, cross fading between audio
paths for click−free memory changes, eight−band graphic equalizer,
eight configurable generic biquad filters, programming speed
enhancements, in−channel squelch to attenuate microphone and
circuit noise in quiet environments, optional peak clipping, flexible
compression adjustments, volume control, rocker switch, noise
generation for Tinnitus treatment, and industry−leading security
features to avoid cloning and software piracy.
A trimmer interface supports manual circuit configuration. It
continuously monitors trimmer positions and translates them into the
hearing−aid parameters of choice. A Serial Data or I2C Interface
provides full programmability at the factory and in the field.
The Rhythm SB3231 hybrid contains a 256 kbit EEPROM intended
for programmable and trimmer based devices.
9
8
VB
MS2
(Bottom View)
MARKING DIAGRAM
SB3231−E1
XXXXXX
SB3231 = Specific Device Code
E1
= RoHS Compliant Hybrid
XXXXXX = Work Order Number
ORDERING INFORMATION
See detailed ordering and shipping information on page 14 of
this data sheet.
Publication Order Number:
SB3231/D
RHYTHM SB3231
• I2C and SDA Programming
• Rocker Switch Support for Memory Change and/or
• 96 dB Input Dynamic Range with HRXt Headroom
•
Volume Control Adjustment
• Support for Active Hi or Active Lo Switching
• Analog or Digital Volume Control with Programmable
•
•
•
•
•
•
•
•
•
•
•
•
Range
High Quality 20−bit Audio Processing
High Power/High Gain Capability
SOUNDFIT® Fitting Software
Configurable Low Battery Indicator
Eight Biquadratic Filters
16 kHz or 8 kHz Bandwidth
Four Fully Configurable Memories with Audible
Memory Change Indicator
•
Extension
128−bit Fingerprint Security System and Other Security
Features to Protect against Device Cloning and
Software Piracy
High Fidelity Audio CODEC
Soft Acoustic Fade between Memory Changes
Drives Zero−Bias Two−Terminal Receivers
E1 RoHS−compliant Hybrid
Hybrid Typical Dimensions:
0.220 x 0.125 x 0.060 in
(5.59 x 3.18 x 1.52 mm)
These Devices are Pb−Free and are RoHS Compliant
BLOCK DIAGRAM
MS2
MS1
9
SDA
VB
CLK
12
10
11
8
PROGRAMMING
INTERFACE
VREG
1
REGULATOR
FEEDBACK
CANCELLER
TONE
GENERATOR
MIC1
18
MIC2
17
TIN
16
DAI
15
MGND
2
A/D
A/D
PRE BIQUAD FILTERS
1−4
+
POST BIQUAD FILTERS
3&4
1, 2 or 4 CHANNEL
WDRC, EQ, ANR
AGC−O
POST BIQUAD FILTERS
1&2
VC GAIN
WIDEBAND GAIN
MIC / TELECOIL
COMPENSATION
CROSS
FADER
D/A
HBRIDGE
PEAK
CLIPPING
EVOKE
NOISE GENERATOR
TRIMMER/VC INTERFACE
BIQUAD 1−4
SB3231
13
14
22
21
20
19
3
D_VC
VC
TR1
TR2
TR3
TR4
GND
Figure 1. Hybrid Block Diagram
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2
7
VBP
5
OUT+
6
OUT −
4
PGND
RHYTHM SB3231
SPECIFICATIONS
Table 1. ABSOLUTE MAXIMUM RATINGS
Parameter
Value
Units
0 to 40
°C
−20 to +70
°C
25
mW
Maximum Operating Supply Voltage
1.65
VDC
Absolute Maximum Supply Voltage
1.8
VDC
Operating Temperature Range
Storage Temperature Range
Absolute Maximum Power Dissipation
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
WARNING: Electrostatic Sensitive Device − Do not open packages or handle except at a static−free workstation.
WARNING:
Moisture Sensitive Device − RoHS Compliant; Level 4 MSL. Do not open packages except under controlled conditions.
Table 2. ELECTRICAL CHARACTERISTICS (Supply Voltage VB = 1.25 V; Temperature = 25°C)
Parameter
Hybrid Current
Symbol
Conditions
Min
Typ
Max
Units
IAMP
All functions, 32 kHz sampling rate
−
770
−
mA
All functions, 16 kHz sampling rate
−
600
−
Ramp down, audio path
0.93
0.95
0.97
Ramp down, control logic
0.77
0.80
0.83
VBON
Ramp up
1.06
1.10
1.16
V
EEPROM Burn Cycles
−
−
100 k
−
−
cycles
Low Frequency System Limit
−
−
−
125
−
Hz
Minimum Operating Supply Voltage
Supply Voltage Turn On Threshold
High Frequency System Limit
VBOFF
V
−
−
−
16
−
kHz
THD
VIN = −40 dBV
−
−
1
%
THDM
VIN = −15 dBV, HRX − ON
−
−
3
%
fCLK
−
3.973
4.096
4.218
MHz
−
8 kHz bandwidth
−
4.2
−
ms
−
16 kHz bandwidth
−
4.0
−
−
SB3231
−
1600
−
ms
VREG
−
0.87
0.90
0.93
V
PSRRSYS
1 kHz, Input referred, HRX enabled
−
70
−
dB
Input Referred Noise
IRN
Bandwidth 100 Hz − 8 kHz, HRX on
−
−108
−106
dBV
Input Impedance
Total Harmonic Distortion
THD at Maximum Input
Clock Frequency
Audio Path Latency
System Power On Time (Note 1)
REGULATOR
Regulator Voltage
System PSRR
INPUT
ZIN
1 kHz
−
3
−
MW
Anti−aliasing Filter Rejection
−
f = fCLK/2 − 8 kHz, VIN = −40 dBV
−
80
−
dB
Crosstalk
−
Between both A/D and Mux
−
60
−
dB
Maximum Input Level
−
−
−15
−13
−
dBV
VAN_IN
VIN1, VIN2, Al
0
−
800
mV
VAN_TIN
TIN
−100
−
800
−
HRX − ON Bandwidth
100 Hz − 8 kHz
−
95
96
Analogue Input Voltage Range
Input Dynamic Range
1. Times do not include additional programmable startup delay.
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3
dB
RHYTHM SB3231
Table 2. ELECTRICAL CHARACTERISTICS (Supply Voltage VB = 1.25 V; Temperature = 25°C)
Parameter
Symbol
Conditions
Min
Typ
Max
Units
−
100 Hz − 8 kHz
−
88
−
dB
ZOUT
−
−
10
13
W
Resolution (monotonic)
−
−
7
−
−
bits
Zero Scale Level
−
−
−
0
−
V
Full Scale Level
−
−
−
VREG
−
V
RVC
Three−terminal connection
100
−
360
kW
−
−
−
−
42
dB
Logic 0 Voltage
−
−
0
−
0.3
V
Logic 1 Voltage
−
−
1
−
1.25
V
Stand−by Pull Up Current
−
Creftrim = 6
3
5
6.5
mA
Sync Pull Up Current
−
Creftrim = 6
748
880
1020
mA
Max Sync Pull Up Current
−
Creftrim = 15
−
1380
−
mA
Min Sync Pull Up Current
−
Creftrim = 0
−
550
−
mA
Logic 0 Current (Pull Down)
−
Creftrim = 6
374
440
506
mA
Logic 1 Current (Pull Up)
−
Creftrim = 6
374
440
506
mA
TSYNC
Baud = 0
237
250
263
ms
Baud = 1
118
125
132
OUTPUT
D/A Dynamic Range
Output Impedance
CONTROL A/D
VOLUME CONTROL
Volume Control Resistance
Volume Control Range
PC_SDA INPUT
PC_SDA OUTPUT
Synchronization Time
(Synchronization Pulse Width)
Baud = 2
59
62.5
66
Baud = 3
29.76
31.25
32.81
Baud = 4
14.88
15.63
16.41
Baud = 5
7.44
7.81
8.20
Baud = 6
3.72
3.91
4.10
Baud = 7
1.86
1.95
2.05
1. Times do not include additional programmable startup delay.
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4
RHYTHM SB3231
Table 3. I2C TIMING
Standard Mode
Fast Mode
Symbol
Min
Max
Min
Max
Units
Clock Frequency
fPC_CLK
0
100
0
400
kHz
Hold time (repeated) START condition. After this
period, the first clock pulse is generated.
tHD;STA
4.0
−
0.6
−
msec
LOW Period of the PC_CLK Clock
tLOW
4.7
−
−
−
msec
HIGH Period of the PC_CLK Clock
tHIGH
4.0
−
−
−
msec
Set−up time for a repeated START condition
tSU;STA
4.7
−
−
−
msec
Data Hold Time:
for CBUS Compatible Masters
for I2C−bus Devices
tHD;DAT
5.0
0
(Note 1)
−
3.45
(Note 2)
−
0
(Note 1)
−
0.9
(Note 2)
Data set−up time
tSU;DAT
250
−
100
−
nsec
Rise time of both PC_SDA and PC_CLK signals
tr
−
1000
20 + 0.1 Cb
(Note 4)
300
nsec
Fall time of both PC_SDA and PC_CLK signals
tf
−
300
20 + 0.1 Cb
(Note 4)
300
nsec
tSU;STO
4.0
−
0.6
−
nsec
tBUF
4.7
−
1.3
−
msec
Output fall time from VIHmin to VILmax with a bus
capacitance from 10 pF to 400 pF
tof
−
250
20 + 0.1 Cb
(Note 4)
250
nsec
Pulse width of spikes which must be suppressed by
the input filter
tSP
n/a
n/a
0
50
nsec
Capacitive load for each bus line
Cb
−
400
−
400
pF
Parameter
Set−up time for STOP condition
Bus free time between a STOP and START condition
msec
1. A device must internally provide a hold time of at least 300 ns for the PC_SDA signal to bridge the undefined region of the falling edge of PC_CLK.
2. The maximum tHD;DAT has only to be met if the device does not stretch the LOW period (tLOW) of the PC_CLK signal.
3. A Fast−mode I2C−bus device can be used in a Standard−mode I2C−bus system, but the requirement tSU;DAT P250ns must then be met.
This will automatically be the case if the device does not stretch the LOW period of the PC_CLK signal. If such a device does stretch the
LOW period of the PC_CLK signal, it must output the next data bit to the PC_SDA line tr max + tSU;DAT = 1000 + 250 = 1250 ns (according
to the Standard−mode I2C−bus specification) before the PC_CLK line is released.
4. Cb = total capacitance of one bus line in pF.
TYPICAL APPLICATIONS
VB
9
10
12
11
8
PROGRAMMING
INTERFACE
1
REGULATOR
FEEDBACK
CANCELLER
TONE
GENERATOR
3k9
A/D
18
PRE BIQUAD FILTERS
1−4
+
3k9
CROSS
FADER
17
A/D
16
1, 2 or 4 CHANNEL
WDRC, EQ, ANR
AGC−O
POST BIQUAD FILTERS
1&2
VC GAIN
WIDEBAND GAIN
MIC / TELECOIL
COMPENSATION
7
OUT
POST BIQUAD FILTERS
3&4
D/A
HBRIDGE
PEAK
CLIPPING
15
2
NOISE GENERATOR
TRIMMER/VC INTERFACE
BIQUAD 1−4
SB3231
13
14
22
21
20
3
19
Note: All resistors in ohms and all capacitors in farads, unless otherwise stated.
Figure 2. Test Circuit
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5
LP FILTER
6
4
EVOKE
1k
5
RHYTHM SB3231
TYPICAL APPLICATIONS (continued)
VB
MS2
MS1
To Programming box
9
12
10
11
8
PROGRAMMING
INTERFACE
REGULATOR
1
FEEDBACK
CANCELLER
TONE
GENERATOR
A/D
18
PRE BIQUAD FILTERS
1−4
+
CROSS
FADER
17
A/D
16
1, 2 or 4 CHANNEL
WDRC, EQ, ANR
MIC / TELECOIL
COMPENSATION
7
POST BIQUAD FILTERS
3&4
5
D/A
HBRIDGE
PEAK
CLIPPING
6
AGC−O
4
EVOKE
15
POST BIQUAD FILTERS
1&2
VC GAIN
WIDEBAND GAIN
2
NOISE GENERATOR
TRIMMER/VC INTERFACE
BIQUAD 1−4
SB3231
14
13
21
22
20
19
3
VC
200 k
Note: All resistors in ohms and all capacitors in farads, unless otherwise stated.
Figure 3. Typical Programmable Application Circuit
VB
Reed Switch
For Autotcoil
22
MS1
47μ
9
12
10
11
8
PROGRAMMING
INTERFACE
1
REGULATOR
FEEDBACK
CANCELLER
TONE
GENERATOR
18
A/D
PRE BIQUAD FILTERS
1−4
+
POST BIQUAD FILTERS
3&4
CROSS
FADER
17
A/D
16
1, 2 or 4 CHANNEL
WDRC, EQ, ANR
MIC / TELECOIL
COMPENSATION
7
D/A
HBRIDGE
PEAK
CLIPPING
POST BIQUAD FILTERS
1&2
4
VC GAIN
WIDEBAND GAIN
2
NOISE GENERATOR
TRIMMER/VC INTERFACE
BIQUAD 1−4
SB3231
13
14
21
22
VC
TR1
20
TR2 TR3
3
19
TR4
Note: All resistors in ohms and all capacitors in farads, unless otherwise stated.
Figure 4. Typical Trimmer Application Circuit
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6
6
AGC−O
EVOKE
15
5
RHYTHM SB3231
RHYTHM SB3231 OVERVIEW
directionality, compression, wideband gain, and volume
control. The Adaptive Feedback Canceller reduces acoustic
feedback while offering robust performance against pure
tones.
The Rhythm SB3231 contains a 256 kbit EEPROM and
can be used for both programmable and trimmer based
applications. It is compatible with ON Semiconductor’s
ARK tools and SOUNDFIT fitting software.
During trimmer mode operation, a low−speed A/D circuit
monitors the positions of up to four manual trimmers and
a VC potentiometer. Trimmer position changes are
immediately interpreted and translated into new circuit
parameter values, which are then used to update the signal
path.
Rhythm SB3231 is a DSP system implemented on
ON Semiconductor’s WOLVERINEt hardware platform.
Wolverine is the hearing industry’s first 90 nm
Silicon−on−Chip
platform
enabling
design
of
highly−efficient and flexible hearing aid solutions. The
device is packaged for easy integration into a wide range of
applications from CIC to BTE. Rhythm SB3231 can be used
as a programmable or trimmer adjustable device. It may be
configured as one, two or four channels with linear or
WDRC processing. Configuration data stored in
non−volatile memory defines hearing−aid parameters.
Rhythm SB3231 can be programmed via the SDA or I2C
programming interfaces.
The DSP core implements Adaptive Feedback
Cancellation, Adaptive Noise Reduction, FrontWave
FUNCTIONAL BLOCK DESCRIPTION
A/D and D/A Converter
Analog input signals should be ground referenced to
MGND. (Microphones, telecoils, DAI). MGND is
internally connected to GND to minimize noise, and should
not be connected to any external ground point.
The system’s A/D converter is a 2nd−order sigma−delta
modulator operating at a 2.048 MHz sample rate.
The system’s input is pre−conditioned with anti−alias
filtering and a programmable gain pre−amplifier. The
analog output is oversampled and modulated to produce
a 1−bit pulse density modulated (PDM) data stream. The
digital PDM data is then decimated down to pulse−code
modulated (PCM) digital words at the system’s sampling
rate of 32 kHz.
The D/A is comprised of a digital 3rd−order sigma−delta
modulator and an H−bridge. The modulator accepts PCM
audio data from the DSP path and converts it into a 64−times
oversampled, 1−bit PDM data stream, which is then
supplied to the H−bridge. The H−bridge is a specialized
CMOS output driver used to convert the 1−bit data stream
into a low−impedance, differential output voltage
waveform suitable for driving zero−biased hearing aid
receivers.
Channel Processing
Figure 5 represents the I/O characteristic of independent
AGC channel processing. The I/O curve can be divided into
four main regions:
• Low input level expansion (squelch) region
• Low input level linear region
• Compression region
• High input level linear region (return to linear)
0
High Level
Gain
OUTPUT LEVEL (dBV)
−10
Analog Inputs
Rhythm SB3231 provides for up to four analog inputs,
Microphone 1 (MIC1), Microphone 2 (MIC2), Telecoil
(TCOIL) and Direct Audio Input (DAI) with the following
configurable front end modes:
• 1 Mic Omni
• 1 Mic Omni (Rear channel only)
• FrontWave Directional
• 2 Mic Omni (MIC1 + MIC2)
• DAI
• TCOIL
• 1 Mic Omni + TCOIL
• 1 Mic Omni + DAI
−20
−30 Low Level
−40 Gain
−50
Compression
Ratio
Lower
Threshold
Upper
Threshold
−60
−70
−80
Squelch
Threshold
−90
−100
−120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20
INPUT LEVEL (dBV)
Figure 5. Independent Channel I/O Curve Flexibility
Channel I/O processing is specified by the Squelch
threshold (SQUELCHTH) and any four of the following
five parameters (only four of the five properties are
independent):
• Low level gain (LLGAIN)
• Lower threshold (LTH)
Attenuation can be applied to the input when mixing with
either TCOIL or DAI inputs.
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7
RHYTHM SB3231
• High level gain (HLGAIN)
• Upper threshold (UTH)
• Compression ratio (CR)
1. Added stable gain will vary based on hearing aid style and
acoustic setup. Please refer to the Adaptive Feedback
Cancellation Information note for more details.
During the Parameter Map creation, constraints are
applied to the compression parameters to ensure that the I/O
characteristics are continuous. Parameter adjustments
support two popular styles of compression ratio adjustment:
• The compression region of the I/O curve pivots about
the upper threshold. As the compression ratio trimmer
is adjusted, high−level gain remains constant while the
low−level gain changes.
• The compression region of the I/O curve pivots about
the lower threshold. Low−level gain remains constant
as the compression ratio trimmer is adjusted.
Feedback path
+
−
Σ
H
G
H’
Estimated feedback
Figure 6. Adaptive Feedback Canceller (AFC)
Block Diagram
The squelch region within each channel implements a low
level noise reduction scheme (1:3 expansion) for listener
comfort. This scheme operates in quiet listening
environments (programmable threshold) to reduce the gain
at very low levels.
Feedback Path Measurement Tool
The Feedback Path Measurement Tool uses the onboard
feedback cancellation algorithm and noise generator to
measure the acoustic feedback path of the device. The noise
generator is used to create an acoustic output signal from the
hearing aid, some of which leaks back to the microphone via
the feedback path. The feedback canceller algorithm
automatically calculates the feedback path impulse response
by analyzing the input and output signals. Following
a suitable adaptation period, the feedback canceller
coefficients can be read out of the device and used as an
estimate of the feedback−path impulse response.
Automatic Telecoil
The automatic telecoil feature in Rhythm SB3231 is to be
used with memory D programmed with the telecoil or
MIC + TCOIL front end configuration. The feature enables
the part to transition to memory D upon the closing of
a switch connected to MS2. With the feature enabled and
a reed switch connected to MS2, the static magnetic field of
a telephone handset will close the switch whenever the
handset is brought close to the device, causing the hybrid to
change to memory D. The part will transition back to the
initial memory once the switch is deemed opened after
proper debouncing.
A debounce algorithm with a programmable debounce
period is used to prevent needless switching in and out of
memory D due to physical switch bounces when MS2 is
configured for automatic telecoil. Upon detecting a close to
open switch transition, the debounce algorithm monitors the
switch status. The debounce algorithm switches the device
out of memory D only once the switch signal has been
continuously sampled open over the specified debounce
period.
Adaptive Noise Reduction
The noise reduction algorithm is built upon a high
resolution 64−band filter bank (32 bands at 16 kHz
sampling) enabling precise removal of noise. The algorithm
monitors the signal and noise activities in these bands, and
imposes a carefully calculated attenuation gain
independently in each of the 64 bands.
The noise reduction gain applied to a given band is
determined by a combination of three factors:
• Signal−to−Noise Ratio (SNR)
• Masking threshold
• Dynamics of the SNR per band
Adaptive Feedback Canceller
The SNR in each band determines the maximum amount
of attenuation to be applied to the band − the poorer the SNR,
the greater the amount of attenuation. Simultaneously, in
each band, the masking threshold variations resulting from
the energy in other adjacent bands is taken into account.
Finally, the noise reduction gain is also adjusted to take
advantage of the natural masking of ‘noisy’ bands by speech
bands over time.
Based on this approach, only enough attenuation is
applied to bring the energy in each ‘noisy’ band to just below
the masking threshold. This prevents excessive amounts of
attenuation from being applied and thereby reduces
unwanted artifacts and audio distortion. The Noise
The Adaptive Feedback Canceller (AFC) reduces
acoustic feedback by forming an estimate of the hearing aid
feedback signal and then subtracting this estimate from the
hearing aid input. The forward path of the hearing aid is not
affected. Unlike adaptive notch filter approaches, Rhythm
SB3231’s AFC does not reduce the hearing aid’s gain. The
AFC is based on a time−domain model of the feedback path.
The third−generation AFC (see Figure 6) allows for an
increase in the stable gain1 of the hearing instrument while
minimizing artefacts for music and tonal input signals. As
with previous products, the feedback canceller provides
completely automatic operation.
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RHYTHM SB3231
Volume Control, Trimmers and Switches
Reduction algorithm efficiently removes a wide variety of
types of noise, while retaining natural speech quality and
level. The level of noise reduction (aggressiveness) is
configurable to 3, 6, 9 and 12 dB of reduction.
External Volume Control
The volume of the device can either be set statically via
software or controlled externally via a physical interface.
Rhythm SB3231 supports both analog and digital volume
control functionality, although only one can be enabled at
a time. Digital control is supported with either a momentary
switch or a rocker switch. In the latter case, the rocker switch
can also be used to control memory selects.
FrontWave Directional Microphones
The FrontWave feature is implemented in two front−end
modes on Rhythm SB3231: static directional and
two−microphone omnidirectional. Both these front−end
modes are designed to operate using two closely spaced
omnidirectional microphones connected to the VIN1 and
VIN2 inputs.
In static directional mode, FrontWave synthesizes
a directional response pattern by delaying the
rear−microphone signal and subtracting it from the front
microphone signal. Various microphone response patterns
can be obtained by adjusting the rear−microphone time
delay.
In two−microphone omnidirectional mode, FrontWave
synthesizes a secondary omnidirectional response pattern
by delaying the front microphone signal and adding it to the
rear microphone signal. The resulting omnidirectional
microphone signal possesses a noise floor that is
approximately 3 dB lower than that provided by a single
microphone (assuming both microphones have similar noise
floors).
The FrontWave feature includes three parameters that can
be set via external software: time delay, rear−microphone
compensation filter and a low−frequency boost filter
intended for static directional mode. Time delay can be
configured using IDS software. It determines the polar
patter in static directional mode and accounts for
microphone spacing in two−microphone omnidirectional
mode. The rear−microphone compensation filter provides
a means to adjust the rear−microphone sensitivity so that it
can better match the front microphone. It is controlled
automatically through Cal/Config software. The
low−frequency boost filter compensates for the 6 dB/octave
roll−off in frequency response that occurs in directional
mode. The amount of low frequency equalization is
programmable through IDS.
NOTE: For optimum FrontWave operation,
ON Semiconductor recommends using matched
microphone pairs.
The time delay implemented using FrontWave is not
explicitly limited within the system. Optimum accuracy is
obtained, however, for smaller time delays. For example, in
32 kHz operation, a time delay of 81.5 microseconds can be
achieved with a maximum deviation of 5% over a bandwidth
of 0 to 4 kHz. This allows a microphone port spacing of
approximately 28 mm. For 16 kHz operation, a similar
accuracy is observed for a time delay of 78.1 microseconds,
corresponding to a port spacing of approximately 26.8 mm.
Smaller time delays can be implemented with improved
accuracy.
Analog Volume Control
Both the external (analog) volume control and trimmers
work with a three−terminal 100 kW − 360 kW variable
resistor. The volume control can have either a log or linear
taper, which is selectable via IDS. It is possible to use a VC
with up to 1 MW of resistance, but this could result in a slight
decrease in the resolution of the taper.
Trimmers
The trimmer interface provides the ability to control up to
19 hearing aid parameters through up to four trimmers.
A single trimmer parameter can have up to 16 values and
a single trimmer can control multiple parameters (e.g.,
Trimmer 1 can control compression ratio in all four channels
simultaneously). The trimmer must be three−terminal
100 kW to 360 kW variable resistors and have a linear taper.
Parameters that can be assigned to trimmers include Noise
Reduction, Low Cut, High Cut, Compression Ratio,
Wideband Gain, Tinnitus Noise Level, Crossover
Frequency, Lower Threshold, Upper Threshold, EQ Gain,
Squelch Threshold, High Level Gain, Low Level Gain,
AGC−O Threshold, Static Volume Control and Peak Clipper
Threshold.
NOTE: There may be limitations to which parameters
can be used together.
Digital Volume Control
The digital volume control makes use of two pins for
volume control adjustment, VC and D_VC, with
momentary switches connected to each. Closure of the
switch to the VC pin indicates a gain increase while closure
to the D_VC pin indicates a gain decrease. Figure 7 shows
how to wire the digital volume control to Rhythm SB3231.
GND
VC
D_VC
Figure 7. Wiring for Digital Volume Control
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9
RHYTHM SB3231
Memory Select Switches
The behavior of the MS switches is controlled by two
main parameters in IDS:
MSSmode: this mode determines whether a
connected switch is momentary or static.
Donly: this parameter determines whether the MS2
switch is dedicated to the last memory position
There are four basic MS switch modes of operation as
shown in Table 4 below.
One or two, two−pole Memory Select (MS) switches can
be used with Rhythm SB3231. This enables user s
tremendous flexibility in switching between configurations.
Up to four memories can be configured and selected by the
MS switches on Rhythm SB3231. Memory A must always
be valid. The MS switches are either momentary or static
and are fully configurable through IDS in the IDS setting
tab.
Table 4. MS SWITCH MODES
MS Switch Mode
MS1 Switch
MS2 Switch
Max # of Valid
Memories
Donly
MSSMode
Use
Mode 1
Momentary
None
4
Off
Momentary
Simplest configuration
Mode 2
Momentary
Static
4
On
Momentary
Jump to last memory
Mode 3
Static
Static
4
Off
Static
Binary selection of memory
Mode 4
Static
Static
3
On
Static
Jump to last memory
The flexibility of the MS switches is further increased by
allowing the MS switches to be wired to GND or VBAT,
corresponding to an active low or active high logic level on
the MS pins. This option is configured with the
MSPullUpDown/MS2PullUpDown setting in the IDS
settings tab as shown in Table 5 below.
Table 5. MS SWITCH LOGIC LEVELS VS. IDS PULLUPDOWN SETTINGS
“PullUpDown” Setting in IDS
MS Switch State
MS Input Logic Level
Switch Connection
Pulldown
CLOSED
HI
To VBAT
Pulldown
OPEN
LOW
To VBAT
Pullup
CLOSED
LOW
To GND
Pullup
OPEN
HI
To GND
If the static switch on MS2 is OPEN, the part starts in
memory A and is controlled by the momentary switch on
MS1 as described in section Momentary Switch on MS1,
with the exception that memory D is not used. If the static
switch on MS2 is set to CLOSED, the part automatically
jumps to memory D (occurs on startup or during normal
operation). In this setup, the state of the momentary switch
on MS1 is ignored. When MS2 is set to OPEN, the part loads
in the memory that was active prior to jumping to memory
D.
The possible memory selection sequences are:
If MS2 = OPEN and there are four valid memories, MS1
selects: ABCABCA…
If MS2 = OPEN and there are three valid memories, MS1
selects: ABABA…
If MS2 = OPEN and there is one valid memory: A
If MS2 = CLOSED: D
In the following mode descriptions, it is assumed that the
PullUpDown setting has been properly configured for the
MS switch wiring so that a CLOSED switch state is at the
correct input logic level.
Mode 1: Momentary Switch on MS1
This mode uses a single momentary switch on MS1 input
to change memories. Using this mode causes the part to start
in memory A, and whenever the button is pressed, the next
valid memory is loaded. When the user is in the last valid
memory, a button press causes memory A to be loaded.
Thus, the possible selection sequences are:
• If 4 valid memories: ABCDABCDA…
• If 3 valid memories: ABCABCA…
• If 2 valid memories: ABABA…
• If 1 valid memory: AAA…
Mode 2: Momentary Switch on MS1, Static Switch on
MS2 (D−only, Jump to Last Memory)
Mode 3: Static Switch on MS1 and MS2
This mode uses a static switch on MS2 and a momentary
switch on MS1 to change memories. It can be used to support
the Automatic Telecoil feature, see section Automatic
Telecoil.
This mode uses two static switches to change memories.
In this mode, it is possible to jump from any memory to any
other memory by changing the state of both switches. If the
two switches are changed one after the other, the part
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10
RHYTHM SB3231
transitions to an intermediate memory before reaching the
final memory. The part starts in whatever memory the
switches are selecting. If a memory is invalid, the part
defaults to memory A.
advance to the next higher numbered memory and “down”
switch closures indicates a program retreat to the next lower
numbered memory. In this mode, volume control is only
available through software control.
In Mixed Mode, operation of the switch as a volume
control or memory select is governed by the time duration
of the switch closure: either short or long. The
discrimination of short and long pulses is set by
a programmable, time−threshold value, from 1 s to 5 s in 1 s
increments. An additional programmable parameter
determines whether the short pulses refer to volume−control
operation or memory−select operation.
If long pulses control memory select operation, the
memory change is initiated once the switch is held for the
long pulse period without requiring the switch to be
released. In Digital VC mode or Momentary Memory Select
mode, the action takes place after the switch is released.
Table 6. STATIC SWITCH TRUTH TABLE:
D−ONLY DISABLED
State (MS1/MS2)
Selected Memory
OPEN OPEN
Memory A
CLOSED OPEN
Memory B
OPEN CLOSED
Memory C
CLOSED CLOSED
Memory D
Mode 4: Static Switch on MS1, Static Switch on MS2
(D−Only, Jump to Last Memory)
This mode uses two static switches to change memories.
Similar to the behaviour described in the Static Switch on
MS1 and MS2 section, this mode will switch to memory D
if the static switch on MS2 is HIGH (the state of the switch
on MS1 is ignored). The mode, however, supports
a maximum of three memories (even if four valid memories
are programmed). This mode can be used to support the
Automatic Telecoil feature (see the Automatic Telecoil
section).
In this mode, it is possible to jump from any memory to
any other memory by changing the state of both switches. If
the two switches are changed one after the other, the part
transitions to an intermediate memory before reaching the
final memory.
The part starts in whatever memory the switches are
selecting. If a memory is invalid, the part defaults to
memory A.
AGC−O
The AGC−O module is an output limiting circuit with
a fixed compression ratio of ∞ : 1. The limiting level is
programmable as a level measured in dB from full scale. The
maximum output of the device is 0 dBFS.
The AGC−O module has its own level detector, with
programmable attack and release time constants.
Graphic Equalizer
Rhythm SB3231 has a 8−band graphic equalizer. Each
band provides up to 31 dB of gain adjustment in 1 dB
increments.
Biquadratic Filters
Additional frequency shaping can be achieved by
configuring generic biquad filters. The transfer function for
each of the biquad filters is as follows:
Table 7. STATIC SWITCH TRUTH TABLE:
D−ONLY ENABLED; (EXAMPLE WITH THREE VALID
MEMORIES)
State (MS1/MS2)
Selected Memory
OPEN OPEN
Memory A
CLOSED OPEN
Memory B
X CLOSED
Memory D
H(z) + b0 ) b1
1 ) a1
z *1 ) b2
z *1 ) a2
z *2
z *2
NOTE: The a0 coefficient is hard−wired to always be
‘1’. The coefficients are each 16 bits in length
and formatted as one sign bit, one integer bit and
14 fractional bits. This maps onto a decimal
range of −2.0 to 2.0 before quantization (−32767
to 32767 after quantization).
Thus, before quantization, the floating−point coefficients
must be in the range −2.0 ≤ x < 2.0 and quantized with the
function:
Rocker Switch Support
The device supports connection of a rocker switch to the
digital volume control interface that can perform volume
control (VC) adjustments and/or memory selection (MS).
There are three modes of operation:
• Digital Volume Control Mode
• Momentary Memory Select Mode
• Mixed Mode (VC and MS)
round(x
2 14)
After designing a filter, the quantized coefficients can be
entered into the PreBiquads or PostBiquads tab in the
Interactive Data Sheet. The coefficients b0, b1, b2, a1, and
a2 are as defined in the transfer function above. The
parameters meta0 and meta1 do not have any effect on the
signal processing, but can be used to store additional
information related to the associated biquad.
In Digital VC mode, the rocker switch provides the digital
volume control functionality described in this section.
In Momentary Memory Select mode, the rocker switch
allows cycling through the memory profiles in both
directions. An “up” switch closure indicates a program
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11
RHYTHM SB3231
The underlying code in the product components
automatically checks all of the filters in the system for
stability (i.e., the poles have to be within the unit circle)
before updating the graphs on the screen or programming
the coefficients into the hybrid. If the Interactive Data Sheet
receives an exception from the underlying stability checking
code, it automatically disables the biquad being modified
and displays a warning message. When the filter is made
stable again, it can be re−enabled.
Also note that in some configurations, some of these
filters may be used by the product component for
microphone/telecoil compensation, low−frequency EQ, etc.
If this is the case, the coefficients entered by the user into
IDS are ignored and the filter designed by the software is
programmed instead. For more information on filter design
refer to the Biquad Filters In PARAGON® Digital Hybrid
information note.
• Volume Up and Volume Down
• Volume Max and Volume Min
• Low Battery
Tinnitus Treatment Noise
Power On Reset Delay
The Tinnitus Treatment noise is generated using white
noise generator hardware and shaping the generated noise
using four 2nd order biquadratic filters. The filter parameters
are the same coefficients as those presented in the
Biquadratic Filters section.
The Tinnitus Treatment noise can be added into the signal
path at two possible locations: before the VC (before the
AGC−O, but compensated for the Wideband Gain) or after
the VC (between the last generic biquad and the Cross
Fader).
If the noise is injected before the VC and the audio path
is also enabled, the device can be set up to either have both
the audio path and noise adjust via the VC, or to have only
the noise adjust via the VC (see Table 8). If the noise in
injected after the VC, it is not affected by VC changes.
The programmable POR delay controls the amount of
time between power being connected to the hybrid and the
audio output being enabled. This gives the user time to
properly insert the hearing aid before the audio starts,
avoiding the temporary feedback that can occur while the
device is being inserted. During the delay period,
momentary button presses are ignored.
Each Acoustic Indicator is made up of up to four faded
tones. A faded tone exhibits a nominal 32 ms fade−in and
fade−out transition time. The duration of an Acoustic
Indicator is configurable, with a maximum value of 6.35
seconds.
EVOKE Lite Acoustic Indicators can be programmed as
output referred or input referred (prior to the filter bank).
Power Management
Rhythm SB3231 has three user−selectable power
management schemes to ensure the hearing aid turns off
gracefully at the end of battery life. Shallow reset, Deep reset
and Advanced Reset mode. It also contains a programmable
power on reset delay function.
Power Management Functionality
As the voltage on the hearing aid battery decreases, an
audible warning is given to the user indicating the battery
life is low. In addition to this audible warning, the hearing
aid takes other steps to ensure proper operation given the
weak supply. The exact hearing aid behaviour in low supply
conditions depends on the selected POR mode. The hearing
aid has three POR modes:
• Shallow Reset Mode
• Deep Reset Mode
• Advanced Mode
Table 8. NOISE INSERTION MODES
Noise Insertion Modes
Off
VC Controls
Noise Injected
Audio
Off
Pre VC
Audio + Noise
Pre VC
Post VC
Audio
Post VC
Noise only Pre VC
Noise
Pre VC
Noise only Post VC
−
Post VC
Pre VC with Noise
Noise
Pre VC
Shallow Reset Mode
In Shallow Reset mode, the hearing aid will operate
normally when the battery is above 0.95 V. Once the supply
voltage drops below 0.95 V the audio will be muted and
remain in that state until the supply voltage rises above
1.1 V. Once the supply voltage drops below the control logic
ramp down voltage, the device will undergo a hardware
reset. At this point, the device will remain off until the supply
voltage returns to 1.1 V. When the supply voltage is below
the control logic voltage, but above 0.6 V and rises above the
1.1 V turn on threshold, the device will activate its output
and operate from the memory that was active prior to reset.
If the supply voltage drops below 0.6 V, and rises above the
1.1 V turn on threshold, the device will reinitialize, activate
its output and operate from memory A.
8.14 EVOKE Lite Acoustic Indicators
Ten Acoustic Indicators are available for indicating
events. Each indicator is fixed to a particular event. Any
event can have its assigned indicator enabled or disabled
although not always independently. Individual
enable/disable control is provided for the following event or
group of events:
• Power on reset (POR)
• Four memory selects
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12
RHYTHM SB3231
Deep Reset Mode
a hardware reset. When it turns back on because the voltage
has risen above the turn−on threshold, it will behave the
same as it would in shallow reset mode.
In Deep Reset mode, the hearing aid will operate normally
when the battery is above 0.95 V. Once the supply voltage
drops below 0.95 V the audio will be muted. The device
remains in this state until the supply voltage drops below the
hardware reset voltage of 0.6 V. When this occurs, the
device will load memory A and operate normally after the
supply voltage goes above 1.1 V.
Low Battery Notification
Notification of the low battery condition via an acoustic
indicator is optionally performed when the battery voltage
drops below a configurable low battery notification
threshold. The low battery indicator is repeated every five
minutes until the device shuts down.
Advanced Reset Mode
Advanced Reset Mode on Rhythm SB3231 is a more
sophisticated power management scheme than shallow and
deep reset modes. This mode attempts to maximize the
device’s usable battery life by reducing the gain to stabilize
the supply based on the instantaneous and average supply
voltage levels. Instantaneous supply fluctuations below
0.95 V can trigger up to two 3 dB, instantaneous gain
reductions. Average supply drops below 0.95 V can trigger
up to eighteen, 1 dB average gain reductions.
While the average supply voltage is above 0.95 V, an
instantaneous supply voltage fluctuation below 0.95 V will
trigger an immediate 3 dB gain reduction. After the 3 dB
gain reduction has been applied, the advanced reset model
holds off checking the instantaneous voltage level for
a monitoring period of 30 second in order to allow the
voltage level to stabilize. If after the stabilization time the
instantaneous voltage drops a second time below 0.95 V
during the next monitoring period, the gain will be reduced
an additional 3 dB for a 6 dB total reduction and a 30 second
stabilization time is activated. The advanced reset mode
continues to monitor the instantaneous voltage levels over
30 second monitoring periods. If the instantaneous voltage
remains above 1.1 V during that monitoring period, the gain
will be restored to the original setting regardless of whether
one or two gain reductions are applied. If two gain
reductions are applied and the instantaneous voltage level
remains above 1.0 V for a monitoring period, the gain will
be restored to a 3 dB reduction.
Should the average supply voltage drop below 0.95 V, the
device will then reduce the gain by 1 dB every 10 seconds
until either the average supply voltage rises above 0.95 V or
a total of 18 average gain reductions have been applied, at
which point the audio path will be muted. If the average
supply voltage returns to a level above 1.1 V, the audio path
will first be un−muted, if required. The gain will then be
increased by 1 dB every 10 seconds until either the average
supply voltage drops below 1.1 V, or all average gain
reductions have been removed. No action is taken while the
average supply voltage resides between 0.95 V and 1.1 V.
NOTE: Instantaneous and average gain reductions are
adjusted independently.
When the instantaneous voltage falls below the hardware
shutdown voltage of 0.6 V, the device will undergo
SDA and I2C Communication
Rhythm SB3231 can be programmed using the SDA or
I2C protocol. During parameter changes, the main audio
signal path of the hybrid is temporarily muted using the
memory switch fader to avoid the generation of disturbing
audio transients. Once the changes are complete, the main
audio path is reactivated. Any changes made during
programming are lost at power−off unless they are explicitly
burned to EEPROM memory.
Improvements have been made to the ARK software,
resulting in improved communication speed. Certain
parameters in ARKonline® can be selected to reduce the
number of pages that need to be read out. In SDA mode,
Rhythm SB3231 is programmed via the SDA pin using
industry standard programming boxes. I2C mode is
a two−wire interface which uses the SDA pin for
bidirectional data and CLK as the interface clock input. I2C
programming support is available on the HiPro (serial or
USB versions) and ON Semiconductor’s
DSP
Programmer 3.0.
Input Connection and Layout Considerations
It is recommended to connect unused audio input pins
directly to MGND to minimize the possibility of noise
pickup. Inputs are internally AC coupled, so there is no
additional leakage current when inputs are connected
directly to ground.
In order to further minimize noise at the inputs the following
guidelines are recommended:
• MGND is used as reference ground plane for input
signals. All input components should be grounded to
MGND. This ground plane should be isolated from all
other ground connections in the system.
• Keep the input traces as short as possible and avoid
routing traces near high noise sources such as the
OUT+ and OUT− pins
• Star ground input component grounds to the MGND
connection.
Unused trimmer inputs should also be connected to GND.
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13
RHYTHM SB3231
ORDERING INFORMATION
Package
Shipping†
SB3231−E1
25 Pad Hybrid
Case 127DN
25 Units / Bubble Pack
SB3231−E1−T
25 Pad Hybrid
Case 127DN
250 Units / Tape & Reel
Device
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
Hybrid Jig Ordering Information
To order a Hybrid Jig Evaluation Board for Rhythm SB3231 contact your Sales Account Manager or FAE and use part
number SA3405GEVB.
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14
RHYTHM SB3231
PAD LOCATIONS
Table 9. PAD POSITION AND DIMENSIONS
Pad Position
Pad Dimensions
Pad No.
X
Y
Xdim (mil)
Ydim (mil)
1
0
0
20
33
2
−27
0
20
33
3
−54
−5
20
23
4
−81
−5
20
23
5
−108
−5
20
23
6
−135
−5
20
23
7
−162
−5
20
23
8
−189
0
20
33
9
−189
42
20
23
10
−189
85
20
23
11
−162
85
20
23
12
−135
85
20
23
13
−108
85
20
23
14
−81
85
20
23
15
−54
85
20
23
16
−27
85
20
23
17
0
85
20
23
18
0
42
20
23
19
−27
42
20
23
20
−54
42
20
23
21
−81
42
20
23
22
−108
42
20
23
23
−135
42
20
23
24
−162
26.5
18
12
25
−162
53.5
18
12
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15
RHYTHM SB3231
Table 9. PAD POSITION AND DIMENSIONS
Pad No.
X
Y
Xdim (mm)
Ydim (mm)
1
0
0
0.508
0.838
2
−0.686
0
0.508
0.838
3
−1.372
−0.127
0.508
0.584
4
−2.057
−0.127
0.508
0.584
5
−2.743
−0.127
0.508
0.584
6
−3.429
−0.127
0.508
0.584
7
−4.115
−0.127
0.508
0.584
8
−4.801
0
0.508
0.838
9
−4.801
1.067
0.508
0.584
10
−4.801
2.159
0.508
0.584
11
−4.115
2.159
0.508
0.584
12
−3.429
2.159
0.508
0.584
13
−2.743
2.159
0.508
0.584
14
−2.057
2.159
0.508
0.584
15
−1.372
2.159
0.508
0.584
16
−0.686
2.159
0.508
0.584
17
0
2.159
0.508
0.584
18
0
1.067
0.508
0.584
19
−0.686
1.067
0.508
0.584
20
−1.372
1.067
0.508
0.584
21
−2.057
1.067
0.508
0.584
22
−2.743
1.067
0.508
0.584
23
−3.429
1.067
0.508
0.584
24
−4.115
0.673
0.457
0.305
25
−4.115
1.359
0.457
0.305
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16
RHYTHM SB3231
PACKAGE DIMENSIONS
SIP25, 5.59x3.18
CASE 127DN
ISSUE O
E
NOTES:
1. DIMENSIONING AND TOLERANCING PER
ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. COPLANARITY APPLIES TO THE SPHERICAL
CROWNS OF THE PADS.
A B
D
PIN A1
INDICATOR
0.13 C
2X
0.13 C
2X
e
ÈÈÈ
ÈÈÈ
3X
L2
20X
2X
TOP VIEW
L
L3
A2
2X
b1
0.13 C
DETAIL A
A
0.05 C
A1
NOTE 3
C
SIDE VIEW
DIM
A
A1
A2
b
b1
D
E
e
e1
e2
e3
L
L2
L3
MILLIMETERS
MIN
MAX
−−−
1.83
0.08
0.18
−−−
1.65
0.478
0.538
0.427
0.487
3.18 BSC
5.59 BSC
0.686 BSC
0.051 BSC
1.067 BSC
1.092 BSC
0.554
0.614
0.808
0.868
0.275
0.335
SEATING
PLANE
e
e/2
e2
A
e
e/2
B
e1
C
e3
1
2
3
4
5
6
7
8
23X
b
0.05
0.03
BOTTOM VIEW
C A
C
B
RECOMMENDED
SOLDERING FOOTPRINT*
NOTE 4
23X
0.538
0.686
1.092
20X
1.067
0.614
2X
2X
0.487
0.335
0.051
3X
0.686
0.868
A1
DETAIL B
0.686
PITCH
DETAIL B
DIMENSIONS: MILLIMETERS
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
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17
RHYTHM SB3231
RHYTHM, HRX, WOLVERINE and EVOKE LITE are trademarks of Semiconductor Components Industries, LLC.
FRONTWAVE, PARAGON and ARKonline are registered trademarks of Semiconductor Components Industries, LLC.
ON Semiconductor and the
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries.
SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed
at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation
or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and
specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets
and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each
customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended,
or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which
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