Texas Instruments | TPA3140D2 Design Considerations for EMC | Application notes | Texas Instruments TPA3140D2 Design Considerations for EMC Application notes

Texas Instruments TPA3140D2 Design Considerations for EMC Application notes
Application Report
SLOA216 – February 2015
TPA3140D2 Design Considerations for EMC
ABSTRACT
The TPA3140D2 Class D audio power amplifier is the latest TI analog input amplifier that uses advanced
PWM switching techniques for reducing electromagnetic interference (EMI) without degrading audio
performance. This application note describes the system design and printed circuit board (PCB) guidelines
used to maximize the technology employed in the TPA3140D2 device. These techniques include the EMI
suppression without the need for expensive inductor filters and the reduction of external component count.
1
2
3
4
Contents
General Overview ............................................................................................................
Advanced Emission Suppression .........................................................................................
2.1
Spread Spectrum Modulation ....................................................................................
2.2
Dephase and Edge Rate Control ................................................................................
Printed Circuit Board Design for EMC ....................................................................................
3.1
Printed Circuit Board Layout ......................................................................................
3.2
Ferrite Bead Filter...................................................................................................
3.3
Power Supply and Speaker Wires ................................................................................
TPA3140D2 EVM EMI Results.............................................................................................
4.1
EN55013 Radiated Emission Results ...........................................................................
4.2
EN55022 Conducted Emission Results ..........................................................................
4.3
Conclusions..........................................................................................................
2
2
2
4
4
4
5
5
5
5
6
7
List of Figures
1
Class D Audio Amplifier ..................................................................................................... 2
2
Fixed-Frequency Mode Modulation
3
Spread Spectrum Mode Modulation ....................................................................................... 3
4
Comparison of FFM and SSM Modulation
5
6
7
8
.......................................................................................
...............................................................................
Radiated Emission – Horizontal Pre-Scan ...............................................................................
Radiated Emission – Vertical Pre-Scan...................................................................................
Conducted Emission – Line Pre-Scan ....................................................................................
Conducted Emission – Neutral Pre-Scan .................................................................................
3
4
5
6
6
7
List of Tables
1
Radiated Emission Margins – Horizontal ................................................................................. 5
2
Radiated Emission Margins – Vertical .................................................................................... 6
3
Conducted Emission Margins – Line ...................................................................................... 7
4
Conducted Emission Margins – Neutral .................................................................................. 7
SLOA216 – February 2015
Submit Documentation Feedback
TPA3140D2 Design Considerations for EMC
Copyright © 2015, Texas Instruments Incorporated
1
General Overview
1
www.ti.com
General Overview
The emphasis on green technologies and sleek looking electronics (such as the flat panel TV) has lead
manufacturers to produce space-efficient and attractive products without sacrificing performance. The
TPA3140D2 mono/stereo Class D audio power amplifier provides Class AB audio performance using only
the PC board as heat sink due to its high efficiency. In addition, the TPA3140D2 device has advanced
PWM modulation and switching schemes that help reduce EMI while eliminating the need for the
traditional Class D output filter. PWM filtering requires only smaller and less expensive RF filter
components. No external heat sink and less RF filtering result directly in PC board size reduction.
Discussions in the following sections explain the PC board layout practice and external components
selection in order to achieve optimal audio performance and pass electromagnetic compatibility (EMC)
specification EN55022.
• Section 2 describes the advanced emission suppression techniques used to combat EMI.
• Section 3 discusses the PC board design guidelines for audio quality and EMC.
• Section 4 shows the EMC results for TPA3140D2 EVM.
2
Advanced Emission Suppression
2.1
Spread Spectrum Modulation
EMI is electromagnetic radiation emitted by electrical systems with fast changing signals that are common
to the outputs of a class D audio power amplifier. EMI encompasses two aspects: emission and
susceptibility. Emission refers to the generation of unwanted electromagnetic energy by the equipment.
Susceptibility, by contrast, refers to the degree in which the equipment is affected by the electromagnetic
disturbances. EMC is achieved by addressing both emission and susceptibility issues. The TPA3140D2
device has advanced emission suppression technology which enables the device to run without an LC
filter with speaker wires up to one meter long and still meet the EMI regulatory standards such as
EN55022, CISPR 22, or FCC Part 15 Class B.
The TPA3140D2 device features an advanced spread spectrum modulation mode with low EMI emission
to lower the overall system cost. This reduced system cost is achieved by replacing large expensive LC
output filters with small, low-cost ferrite beads filters. The spread spectrum modulation scheme exhibits
less EMI by flattening the wideband spectral components from the speaker cables and still retains the
high-efficiency feature of a traditional class D amplifier such as the TPA3110D2 device.
Figure 1 shows the topology of a conventional (nonspread-spectrum) BD modulation class D amplifier.
The BD switching technique uses an internally generated triangular waveform with a fixed frequency and a
complementary signal pair at the input stage. The output PWM changes the duty cycle to generate a
moving average of the signal that correspond to the input analog signal. The advantages of PWM
switching topology is high efficiency, which provides low power consumption and small thermal design.
+
Output A
±
+
Output B
±
Figure 1. Class D Audio Amplifier
2
TPA3140D2 Design Considerations for EMC
Copyright © 2015, Texas Instruments Incorporated
SLOA216 – February 2015
Submit Documentation Feedback
Advanced Emission Suppression
www.ti.com
VIN ±
VIN +
OUTP
OUTN
Figure 2. Fixed-Frequency Mode Modulation
The TPA3140D2 device features two modulation modes: fixed-frequency modulation mode (FFM) and
spread spectrum modulation (SSM) mode. In the conventional FFM mode (Figure 1) the frequency of the
triangular waveform is fixed as shown in Figure 2. In SSM mode, the frequency of the triangular waveform
frequency varies by ±10% cycle-to-cycle with a center frequency at about 310 kHz. SSM mode improves
EMI emissions radiated by the speaker wires by spreading the energy over a larger bandwidth and
reducing the wideband spectral content. On the other hand, FFM produces larger amounts of spectral
energy at multiples of the PWM switching frequency. The cycle-to-cycle variation of the switching
frequency does not affect the efficiency of the audio amplifier. Figure 3 shows the effects of the frequency
variation on the triangular waveform.
VIN ±
VIN +
OUTP
OUTN
Figure 3. Spread Spectrum Mode Modulation
Compared to traditional FFM class D amplifier, the spread spectrum scheme has reduced the peak energy
of the switching frequency and lessens harmonics. shows a comparison of FFM and SSM modulation.
SLOA216 – February 2015
Submit Documentation Feedback
TPA3140D2 Design Considerations for EMC
Copyright © 2015, Texas Instruments Incorporated
3
Advanced Emission Suppression
www.ti.com
FFM Modulation
SSM Modulation
Figure 4. Comparison of FFM and SSM Modulation
2.2
Dephase and Edge Rate Control
In addition to the spread spectrum technology, the TPA3140D2 device employs edge rate control and
dephase circuits to further reduce electromagnetic emission without degrading audio performance.
The edge rate control circuit reduces emission by controlling the PWM output FET switching transitions
near the rails with as little impact to the efficiency as possible. In this mode, the edge rate is optimized and
fixed.
The dephase circuit improves EMI and noise performance by interleaving the switching timing between the
two audio channels. This improved EMI and noise performance reduces conducted emission on the PVCC
line because the output ripple current of the two audio channels will be out of phase, and the ripple peak
current from the PVCC line will thus be reduced to half value.
3
Printed Circuit Board Design for EMC
3.1
Printed Circuit Board Layout
It is necessary to follow recommended PC board guidelines for EMC success. Proper PC board floor
planning, component selection, component placement, and routing are all essential to counter EMI.
Emissions are exacerbated by improper layout, components, and output trace length causing antenna
effect. Practical PC board design guidelines for achieving EMC include:
• Place the high-frequency decoupling capacitors as close to the power pin and ground pin of the device
as possible to reduce the parasitic inductance of the trace. To ensure low AC impedance over a wide
frequency range for noise reduction, use good quality, low-ESR, 1-nF ceramic capacitors. For midfrequency noise due to PWM transients, use another good quality 0.1 µF ceramic capacitor placed as
close as possible to the PVCC leads.
• Use a continuous ground plane and avoid voltage offset on the ground planes whenever possible.
• Low impedance routing back to source (return signal).
• Power planes should be away from the edges of the PC board.
• Proper filtering of the PC board connectors.
• Place EMC snubbers and ferrite bead filters as close as possible to the IC. Minimize unfiltered loops
and trace length as well as stray inductance.
• Keep amplifier output traces to the speaker as short as possible. PC board traces and the speaker wire
are the largest sources of emission.
4
TPA3140D2 Design Considerations for EMC
Copyright © 2015, Texas Instruments Incorporated
SLOA216 – February 2015
Submit Documentation Feedback
Printed Circuit Board Design for EMC
www.ti.com
3.2
Ferrite Bead Filter
Low-cost ferrite bead filters are used to suppress EMI. They are placed close to the amplifier output to
minimize loop antennas. At low frequencies, ferrite beads act as 0 Ω resistors with no DC drop. However,
the impedance of ferrite bead increases significantly at frequencies above 1 MHz to suppress radiation.
Ferrite beads also play a significant role on the THD+N of the system. Examples of ferrite beads which
have been tested and worked well with the TPA3140D2 device include the NFZ2MSM series from Murata.
If other ferrite beads are used, the EMC testing must be repeated to ensure compliance.
3.3
Power Supply and Speaker Wires
When performing the conducted emission test, it is essential to keep the AC power cable away from the
speaker cables. This prevents stray signals from coupling to power source and other potential unintended
radiators or conductors.
4
TPA3140D2 EVM EMI Results
The following sections show the EMI test results from a certified third-party vendor (National Technical
Systems) in Plano, TX. The passing margins are greater than 10 dBuV in most cases.
The radiated EMI plots below are taken with standard EVM configuration and BOM components.
The conducted EMI plots are taken using the same EVM configuration but with a TV power supply. The
TV is currently available on US consumer market (2015).
4.1
EN55013 Radiated Emission Results
TPA3140D2 EVM, PVCC = 12 V, 8-Ω load, up to 1-meter speaker cable, Spread Spectrum enabled, Po =
1.25 W
Figure 5. Radiated Emission – Horizontal Pre-Scan
Table 1. Radiated Emission Margins – Horizontal
Frequency
MHz
Limit
dBuV/m
Peaks
dBuV/m
Q-Peak
dBuV/m
Margin
dB
166.246
40.457
21.781
21.975
237.372
47.457
29.330
29.186
SLOA216 – February 2015
Submit Documentation Feedback
Turn Table
Degrees
Tower
cm
–18.482
44.9
100
–18.271
326.9
100
TPA3140D2 Design Considerations for EMC
Copyright © 2015, Texas Instruments Incorporated
5
TPA3140D2 EVM EMI Results
www.ti.com
Figure 6. Radiated Emission – Vertical Pre-Scan
Table 2. Radiated Emission Margins – Vertical
4.2
Frequency
MHz
Limit
dBuV/m
Peaks
dBuV/m
Q-Peak
dBuV/m
Margin
dB
Turn Table
Degrees
Tower
cm
56.841
40.457
26.213
27.058
241.9
47.457
19.429
20.430
–13.399
54
100
–27.027
–0.1
100
EN55022 Conducted Emission Results
TV (40-inch) from the major TV manufacturer, TPA3140D2 EVM, PVCC = 12 V, 8-Ω speakers, Spread
Spectrum enabled, Po = 1.25 W
Figure 7. Conducted Emission – Line Pre-Scan
6
TPA3140D2 Design Considerations for EMC
Copyright © 2015, Texas Instruments Incorporated
SLOA216 – February 2015
Submit Documentation Feedback
TPA3140D2 EVM EMI Results
www.ti.com
Table 3. Conducted Emission Margins – Line
Frequency
MHz
QP Limit
dBuV
AVE Limit
dBuV
AVE Readings
dBuV
AVE Margin
dB
QP Readings
dBuV
QP Margin
dB
0.156
65.83
55.83
33.774
–22.056
45.956
–19.873
0.552
56
46
28.872
–17.128
39.164
–16.836
0.806
56
46
21.341
–24.659
29.585
–26.415
0.95
56
46
22.678
–23.322
31.471
–24.529
1.485
56
46
22.622
–23.378
31.082
–24.918
1.976
56
46
20.952
–25.048
29.849
–26.151
Figure 8. Conducted Emission – Neutral Pre-Scan
Table 4. Conducted Emission Margins – Neutral
4.3
Frequency
MHz
QP Limit
dBuV
AVE Limit
dBuV
AVE Readings
dBuV
AVE Margin
dB
QP Readings
dBuV
QP Margin
dB
0.158
65.785
55.785
34.022
–21.763
45.398
–20.387
0.554
56
46
29.574
–16.426
40.485
–15.515
0.735
56
46
22.652
–23.348
32.52
–23.48
0.918
56
46
22.699
–23.301
31.849
–24.151
1.402
56
46
23.264
–22.736
32.173
–23.827
7.806
60
50
28.006
–21.994
35.214
–24.786
Conclusions
The TPA3140D2 device has the proven advanced RF emission suppression technology that helps to
design an EMI-compliant audio system without compromising cost and performance. The EVM User’s
Guide (SLOU405) provides the details of the schematic and BOM. By adhering to the guidelines
discussed in this report, EMI requirements are met and costly PC board rework is avoided.
For further questions and discussions on this topic, go to the TI E2E Forums (http://e2e.ti.com/).
SLOA216 – February 2015
Submit Documentation Feedback
TPA3140D2 Design Considerations for EMC
Copyright © 2015, Texas Instruments Incorporated
7
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation
www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom
www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2015, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertising