Texas Instruments | TPS254x Eye Diagram Performance Test | Application notes | Texas Instruments TPS254x Eye Diagram Performance Test Application notes

Texas Instruments TPS254x Eye Diagram Performance Test Application notes
Application Report
SLVA913 – July 2017
TPS254x Eye Diagram Performance Test
Benjamin Zhao, Yongqiang Sun
ABSTRACT
An eye diagram is an important parameter in automotive applications. Good eye performance is beneficial
for applications like CarPlay™, Android Auto™, and CarLife™. This application report discusses the
influence of the TPS254x series devices on eye performance in automotive systems, and how to improve
the eye performance.
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Contents
Introduction ...................................................................................................................
Impact of TPS254x on System Eye Performance .......................................................................
Improving Eye Diagram Performance .....................................................................................
References ...................................................................................................................
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3
5
9
List of Figures
1
TPS254x Typical Application Circuit ...................................................................................... 2
2
Eye Diagram Without TPS254900......................................................................................... 3
3
Eye Diagram With TPS254900 ............................................................................................ 3
4
TPS2549 Source Impact (Lower Amplitude) ............................................................................. 5
5
TPS2549 Source Impact Eye Diagram (Lower Amplitude)
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7
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10
11
12
13
14
............................................................
TPS2549 Source Impact (Higher Amplitude) ............................................................................
TPS2549 Source Impact Eye Diagram (Higher Amplitude) ............................................................
Connect Inductor in Data Lines ............................................................................................
Eye Diagram With and Without LC Network .............................................................................
Bypass DP_IN and DM_IN .................................................................................................
Bypass DP_OUT and DM_OUT ...........................................................................................
TPS254900 Connected .....................................................................................................
TPS254900 Bypassed ......................................................................................................
Eye Diagram With and Without TUSB211 ................................................................................
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5
5
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List of Tables
1
TPS254x Device Bandwidth ................................................................................................ 4
2
Eye Diagram Test Results of TPS2546, TPS2549, and TPS254900 ................................................. 4
3
TPS254900 Eye Diagram Connected and Bypassed ................................................................... 8
Trademarks
CarPlay is a trademark of Apple.
CarLife is a trademark of Baidu.
Android Auto is a trademark of Google, Inc.
All other trademarks are the property of their respective owners.
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1
Introduction
1
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Introduction
The TPS254x series devices are host controllers that support USB2.0 communication, while providing
overcurrent protection, overtemperature protection, cable compensation, short-to-battery protection, and
more. Figure 1 shows a typical application of TPS254X devices in an automotive system.
DC/DC
USB
Connector
TPS254x
IN
OUT
VBUS
SOC
D-
DM_OUT
DM_IN
D-
D+
DP_OUT
DP_IN
D+
GND
Figure 1. TPS254x Typical Application Circuit
2
TPS254x Eye Diagram Performance Test
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Impact of TPS254x on System Eye Performance
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2
Impact of TPS254x on System Eye Performance
Being interconnected, the TPS254x device impacts the eye performance of the system, due to the
parasitic resistance and capacitance of internal circuits in the TPS254x. Figure 2 and Figure 3 show a
comparison of one system before and after connecting the TPS254900 device. From the eye diagram test
results, we see that the rising edge rate becomes slightly slower after connecting the TPS254900 device.
Figure 2. Eye Diagram Without TPS254900
Figure 3. Eye Diagram With TPS254900
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Impact of TPS254x on System Eye Performance
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The higher the bandwidth of the TPS254x, the lower the impact on eye performance. The TPS2546 device
has the highest bandwidth in the TPS254x series products; TPS254900 has a higher bandwidth than
TPS2549. Table 1 lists the –3 dB bandwidth of the TPS254x series products.
Table 1. TPS254x Device Bandwidth
Part Number
Bandwidth (GHz)
TPS2546
2.6
TPS254900
0.940
TPS2549
0.925
Table 2 lists the eye diagram test results of the TPS2546, TPS254900, and TPS2549 devices. From the
test results, we know that the TPS2546 device has the best eye performance, due to its highest
bandwidth.
Table 2. Eye Diagram Test Results of TPS2546, TPS2549, and TPS254900
Part Number
4
Eye Diagram
Rising Edge Rate
Falling Edge Rate
TPS2546
877.77 V / µs
874.51 V / µs
TPS254900
832.88 V / µs
830.53 V / µs
TPS2549
785.57 V / µs
783.08 V / µs
TPS254x Eye Diagram Performance Test
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Improving Eye Diagram Performance
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3
Improving Eye Diagram Performance
3.1
Improving Source Drive Capability
Figure 4 to Figure 7 show the impact of the source amplitude on the TPS2549 eye diagram. A higher
amplitude source signal results in a more open eye. In actual applications, customers can configure the
registers of the host controller to adjust the signal amplitude.
Figure 4. TPS2549 Source Impact (Lower Amplitude)
Figure 5. TPS2549 Source Impact Eye Diagram
(Lower Amplitude)
Figure 6. TPS2549 Source Impact (Higher Amplitude)
Figure 7. TPS2549 Source Impact Eye Diagram
(Higher Amplitude)
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Improving Eye Diagram Performance
3.2
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Using Inductors and Capacitors to Improve Eye Performance
Figure 8 shows the LC network diagram used to improve the system eye performance. Figure 9 shows the
test results before and after connecting the LC network.
DC/DC
USB
Connector
TPS254x
OUT
IN
VBUS
SOC
D-
DM_OUT
DM_IN
D-
D+
DP_OUT
DP_IN
D+
GND
Figure 8. Connect Inductor in Data Lines
Figure 9. Eye Diagram With and Without LC Network
6
TPS254x Eye Diagram Performance Test
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3.3
Bypassing TPS254x to Improve Eye Performance
Figure 10 and Figure 11 show two ways to bypass the TPS254x device. In these methods, the TPS254x
only implements BC1.2 primary detection and secondary detection. The eye performance will be improved
because the TPS254x device is not connected in the data lines.
DC/DC
USB
Connector
TPS254x
IN
VBUS
OUT
SOC
D-
DM_OUT
DM_IN
D-
D+
DP_OUT
DP_IN
D+
GND
Figure 10. Bypass DP_IN and DM_IN
DC/DC
USB
Connector
TPS254x
IN
VBUS
OUT
SOC
D-
DM_OUT
DM_IN
D-
D+
DP_OUT
DP_IN
D+
GND
Figure 11. Bypass DP_OUT and DM_OUT
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Improving Eye Diagram Performance
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Table 3 shows a comparison of the TPS254900 eye diagram when connected and bypassed.
Table 3. TPS254900 Eye Diagram Connected and Bypassed
TPS254900 Status
Rising Edge Rate
Falling Edge Rate
Connected
862.90 V / µs
915.84 V / µs
Bypassed
902.54 V / µs
900.24 V / µs
Figure 12 and Figure 13 show the eye diagrams of the TPS254900 in connected and bypassed states.
Figure 12. TPS254900 Connected
Figure 13. TPS254900 Bypassed
8
TPS254x Eye Diagram Performance Test
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3.4
Using Redrivers to Improve Eye Performance
Another effective way to improve eye performance is to add a redriver. The TUSB211 device is a USB,
high-speed signal conditioner designed to compensate for ISI signal loss in a transmission channel.
Figure 14 shows the test results of the TPS2549 eye diagram before and after connecting the TUSB211,
based on the real PCB of the customer.
Figure 14. Eye Diagram With and Without TUSB211
However, eye diagram performance is a system-level parameter. Eye diagram performance can be
influenced by the host controller, PCB routes, cables, USB connectors, common chokes, TVS, and so on.
Any negligence of these factors will result in bad eye performance. Some recommendations when
designing a system follow:
• Route D+ and D– as differential pairs according to the USB2.0 specification.
• The differential impedance from D+ and D– routes to ground must be 90 Ω.
• Ensure the ground plane is not split, to ensure continuity of differential impedance.
• Route the D+ and D– lines as short as possible to minimize the voltage drop and parasitic inductance.
• Minimize the use of vias in the D+ and D– data lines.
• Use certified cables and USB connectors.
4
References
•
•
•
•
Texas Instruments, TPS2549 USB Charging Port Controller and Power Switch With Cable
Compensation, data sheet
Texas Instruments, TPS254900-Q1 Automotive USB Host Charger With Short-to-VBATT Protection,
data sheet
Texas Instruments, TUSB211 USB 2.0 High Speed Signal Conditioner, data sheet
Texas Instruments, TPS254xEVM-064, user's guide
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