Texas Instruments TUSB546-DCI in a DisplayPort Application Application notes

Brand: Texas Instruments

Model: TUSB546-DCI in a DisplayPort Application

Category: DisplayPort cables

Type: Application notes

Texas Instruments TUSB546-DCI in a DisplayPort Application**

The Texas Instruments TUSB546-DCI is a linear redriver that supports both USB3.1 Gen1 and DisplayPort 1.4 over a Type-C interface. It can also be used as a standalone redriver for DisplayPort applications. The TUSB546-DCI is ideal for use in DisplayPort applications because it is a linear redriver, which means that the output signal amplitude is a linear function of the input signal amplitude. This makes it transparent to link training, which is the process by which the DisplayPort source and sink determine the optimal settings for the link.

Texas Instruments TUSB546-DCI in a DisplayPort Application**

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TUSB546-DCI in a DisplayPort Application

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Application Report

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TUSB546-DCI in a DisplayPort Application

MikeCampbell

ABSTRACT

The TUSB546-DCI is a linear redriver that supports both USB3.1 Gen1 and DisplayPort 1.4 over a Type-C

interface. Even though the TUSB546-DCI is released for the Type-C market, the TUSB546-DCI can also

be used as a standalone redriver for DisplayPort applications. This application report describes how to use

the TUSB546-DCI in a DisplayPort application. The information in this document can also be applied to

the TUSB1046-DCI.

Contents

1 Introduction ................................................................................................................... 2

2 USB 3.1 Default ............................................................................................................. 2

3 Polarity Inversion............................................................................................................. 3

4 AUX Implementation ........................................................................................................ 4

5 HPD Implementation ........................................................................................................ 6

6 Example Software ........................................................................................................... 6

Appendix A Schematics .......................................................................................................... 8

List of Figures

1 PCB Trace Shortener Feature of a Linear Redriver .................................................................... 2

2 Method to Enable DisplayPort Mode When in GPIO Mode............................................................ 3

3 TX1 and RX1 Polarity Swap (FLIP = 0)................................................................................... 3

4 AUXP/N Connections When AUX Bypassed ............................................................................ 4

5 AUX Implementation in DisplayPort Sink Application................................................................... 5

6 AUX Implementation in DisplayPort Source Application................................................................ 6

7 TUSB546-DCI Schematic................................................................................................... 8

8 TUSB546-DCI Configuration Control...................................................................................... 9

9 DisplayPort Connectors..................................................................................................... 9

List of Tables

1 AUX Snoop Enable Control ................................................................................................ 4

2 HPD Connection Options................................................................................................... 6

Introduction

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1 Introduction

The TUSB546-DCI is a Type-C linear redriver mux intended for Type-C source applications. The

TUSB546-DCI multiplexes between four DP1.4 lanes and USB3.1 to a single Type-C receptacle. In a

DisplayPort only application only the TUSB546-DCI’s DisplayPort functionality is required. The USB3.1

functionality must be disabled and USB3.1 pins are left unconnected.

Before any video can be sent between source and sink, the DisplayPort source (DPTX) transmitter

settings, both voltage swing and pre-emphasis, must be optimized to provide for a robust communication

path to the sink (DPRX). These settings are determined during the link training phase. The DisplayPort

standard defines a minimum eye opening at the end of channel in which a compliant receiver must

operate. A redriver (limited or linear) is needed when the eye opening is no longer compliant. The purpose

of a redriver is to compensate for inter-symbol interference (ISI) caused by frequency-dependent channel

loss through a lossy medium like FR4 PCB trace. When the channel loss is properly compensated (or

equalized), the result is a compliant signal at the receiver. Without system knowledge of a limited redriver

presence, a limited redriver can have a negative impact on link training. But a linear redriver, like the

TUSB546-DCI, is transparent to link training.

A redriver is considered linear when the output signal amplitude is a linear function of the input signal

amplitude. A linear redriver can be thought of PCB trace shortener (electrical signal of long trace will look

like shorter trace). An example of shortening PCB trace is shown in Figure 1. The linear feature of the

TUSB546-DCI makes it ideal for DisplayPort applications. The DPTX’s voltage swing and pre-emphasis

levels presence at TUSB546-DCI receiver will be passed through to the DPRX.

Figure 1. PCB Trace Shortener Feature of a Linear Redriver

2 USB 3.1 Default

Because of USB Type-C requirements, the TUSB546-DCI will power-up in USB 3.1 mode. For a

DisplayPort application, the TUSB546-DCI must be taken out of USB 3.1 mode and into four Lane

DisplayPort mode. If the TUSB546-DCI is configured for I2C mode (I2C_EN pin != 0), then software must

program bits 1:0 of address 0x0A (General Registers) to a 2’b10. If the TUSB546-DCI is configured GPIO

mode (I2C_EN pin = 0), then the CTL0 pin must transition high and then back low. One method to create

the toggle on CTL0 pin is illustrated in Figure 2. The value chosen for C1 and R1 should result in a

discharge rate in which CTL0’s VIH level is held for at least 16 ms.

The TUSB546-DCI USB3.1 signals are not used in a DisplayPort application. The following pins can be

left unconnected: SSTXP/N, SSRXP/N, SSEQ1, EQ0 and EQ1. SSEQ0/A0 can be left unconnected if

TUSB546-DCI is configured for GPIO mode. If TUSB546-DCI is configured for I2C, then this pin selects

the TUSB546-DCI's 7-bit I2C slave address.

RX2P

RX2N

TX2P

TX2N

TX1N

TX1P

RX1N

RX1P

FLIP

DP0P

DP0N

DP1P

DP1N

DP2P

DP2N

DP3P

DP3N

TUSB546-DCI

100 nF

DP_ML0P

100 nF

SNK_DP0P

SNK_DP0N

SNK_DP1P

SNK_DP1N

SNK_DP2P

SNK_DP2N

SNK_DP3P

SNK_DP3N

POLARITY is

swapped

DP_ML0N

DP_ML1P

DP_ML1N

DP_ML2P

DP_ML2N

DP_ML3P

DP_ML3N

DisplayPort Sink

3.3V

C1 (1 F)

CTL0

CTL1

TUSB546-DCI

R1 (100 K)

I2C_EN

3.3V

10 K

1 K

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Polarity Inversion

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Figure 2. Method to Enable DisplayPort Mode When in GPIO Mode

3 Polarity Inversion

The USB Type-C receptacle has symmetrical placement of the differential pairs. The TUSB546-DCI pin-

out is targeted for easy routing to the Type-C receptacle. Because of this, the TUSB546-DCI’s pin-out will

produce an undesired polarity swap on RX1 and TX1 pins in DisplayPort applications. This polarity swap

must be handled on the PCB. Figure 3 shows the DisplayPort input to output routing along with the

polarity swap on TX1 and RX1. This figure assumes that FLIP orientation is set to zero.

Figure 3. TX1 and RX1 Polarity Swap (FLIP = 0)

AUX Implementation

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4 AUX Implementation

The TUSB546-DCI will snoop AUX transactions in order to enable and disable DisplayPort lanes to save

power. It does this by monitoring the AUX traffic passing over the AUXP/N pins. If the TUSB546-DCI is

configured for GPIO mode, AUX snoop feature is enabled when CAD_SNK pin is low and disabled when

CAD_SNK pin is high. If TUSB546-DCI is configured for I2C Mode, then AUX snoop feature control is

based on the state of bit 7 in register 13h. System AUX signals must be connected to TUSB546-DCI

AUXP/N pins anytime the AUX snoop feature is enabled.

If system designer desires to handle power saving through an alternative method, the snoop feature can

be disabled. If TUSB546-DCI snoop feature is disabled, then the DisplayPort AUXP/N signals can bypass

the TUSB546-DCI. When bypassing the TUSB546-DCI AUXP/N pins, the AUXN pin should be pulled up

to 3.3V through 100K resistor and the AUXP pin should be pulled down to GND through a 100K resistor

as depicted in Figure 4.

Table 1. AUX Snoop Enable Control

GPIO or I2C Mode AUX Snoop Enabled AUX Snoop Disabled

GPIO Mode (pin I2C_EN = 0) CAD_SNK (pin 29) = Low CAD_SNK (pin 29) = HIGH.

All four DisplayPort lanes are enabled.

I2C Mode (pin I2C_EN != 0) Clear bit 7 Reg13h Set bit 7 Reg13h

Figure 4. AUXP/N Connections When AUX Bypassed

4.1 Sink Application

The AUXP/N from DisplayPort receptacle should be routed directly to TUSB546-DCI and then to

DisplayPort sink through 100 nF AC capacitor. The TUSB546-DCI SBU1 and SBU2 pins should be left

unconnected. The Figure 5 illustrates the AUX implementation for a DisplayPort sink application when

AUX snoop is enabled.

AUXN

AUXP

DisplayPort Receptacle

AUXN

AUXP

SBU2

SBU1

TUSB546-DCI

100nF

DisplayPort Sink

3.3V +/- 10%

1 M

AUXN

AUXP

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AUX Implementation

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Figure 5. AUX Implementation in DisplayPort Sink Application

4.2 Source Application

The AUX implementation for a source is similar to the sink implementation. The AUXP/N signals are

routed to TUSB546-DCI AUXP/N signals through a 100nF AC coupling capacitor. The SBU1/2 pins should

be left unconnected. The AUXP should have a 100kΩ pull-down resistor and AUXN should have a 100K

ohm pull-up resistor. These 100KΩ resistors must be on the TUSB546-DCI side of the 100 nF capacitors.

The source application may have the added complexity of supporting dual mode DisplayPort (DP++).

When supporting DP++, the TUSB546-DCI configured in GPIO mode (I2C_EN = 0) the SNK_CAD pin

must be connected to the CONFIG1 pin on DisplayPort receptacle through a buffer like the

SN74AHC1G125. The buffer is required because the internal pulldown on CAD_SNK pin is too strong to

TUSB546-DCI in I2C mode, then system software must disable AUX snooping whenever the CONFIG1

pin is high.

Figure 6 illustrates an example AUX implementation of DisplayPort source application when TUSB546-

DCI is configured for GPIO mode (I2C_EN = 0).

AUXN

AUXP

DP_PWR (3.3V +/- 10%)

10 K ± 105 K

(100 K recommended)

10 K ± 105 K

(100 K recommended)

GPU

TUSB546-DCI

100nF

AUXP

2 K 2 K

3.3V +/- 10%

SDA

DDC_EN

SCL

DisplayPort Receptacle

AUXN

AUXP

CONFIG1

CAD

SNK_CAD

SBU1

SBU2

HPD

HPDIN

1 M

HPD Implementation

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Figure 6. AUX Implementation in DisplayPort Source Application

5 HPD Implementation

The TUSB546-DCI uses the HPDIN to enable and disable DisplayPort functionality to save power. The

HPD signal should be routed to either pin 23 or pin 32 based on the TUSB546-DCI GPIO/I2C Mode.

Table 2. HPD Connection Options

GPIO or I2C Mode HPD

GPIO Mode (pin I2C_EN = 0) Pin 32

I2C Mode (pin I2C_EN != 0) Pin 23

6 Example Software

TUSB546-DCI in I2C mode must be configured for DisplayPort only. The Aardvark script below shows

how to configure TUSB546-DCI for DisplayPort only mode. This script uses an arbitrary equalization value

for each lane’s receiver. Each receiver has 16 possible equalization settings. The actual value used

should be based on the channel insertion loss for each DisplayPort lane. This scripts slave address is set

to 0x0F which corresponds to both DPEQ0/A1 and SSEQ0/A0 pins being at a ‘1’ level. This slave address

should be changed to match DPEQ0/A1 and SSEQ0/A0 pins value in your system.

<i2c_bitrate khz="400"/>

===DP only and EQ override set====

<i2c_write addr="0x0F" count="1" radix="16"> 0A 12 </i2c_write> />

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Example Software

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===DP Lanes 0 and 1 EQ setting. 16 possible settings.====

===Lane 0 EQ: 0 Setting =====

===Lane 1 EQ: 1 Setting =====

<i2c_write addr="0x0F" count="1" radix="16"> 10 10 </i2c_write> />

===DP Lanes 2 and 3 EQ Settings. 16 possible settings.====

===Lane 2 EQ: 0 Setting =====

===Lane 3 EQ: 1 Setting =====

<i2c_write addr="0x0F" count="1" radix="16"> 11 10 </i2c_write> />

</aardvark>

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Appendix A

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Schematics

Figure 7. TUSB546-DCI Schematic

DisplayPort Source Connection

DisplayPort Sink Connection

Default is Short pins 2-3

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Appendix A

SLLA365–October 2016

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TUSB546-DCI in a DisplayPort Application

Figure 8. TUSB546-DCI Configuration Control

Figure 9. DisplayPort Connectors

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Texas Instruments TUSB546-DCI in a DisplayPort Application Application notes

Brand: Texas Instruments

Model: TUSB546-DCI in a DisplayPort Application

Category: DisplayPort cables

Type: Application notes

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Texas Instruments TUSB546-DCI in a DisplayPort Application Application notes

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