TDA2SA datasheet(373/427 Pages) TI2

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TDA2SX, TDA2SG, TDA2SA

TDA2HG, TDA2HV, TDA2HF, TDA2LF

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SPRS951F – DECEMBER 2015 – REVISED MAY 2019

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Applications, Implementation, and Layout

8.5.4.2

TMDS General Routing Guidelines

The TMDS signals are high speed differential pairs. Care must be taken in the PCB layout of these signals

to ensure good signal integrity.

The TMDS differential signal traces must be routed to achieve 100 Ohms (+/- 10%) differential impedance

and 60 ohms (+/-10%) single ended impedance. Single ended impedance control is required because

differential signals can’t be closely coupled on PCBs and therefore single ended impedance becomes

important.

These impedances are impacted by trace width, trace spacing, distance to reference planes, and dielectric

material. Verify with a PCB design tool that the trace geometry for both data signal pairs results in as

close to 60 ohms impedance traces as possible. For best accuracy, work with your PCB fabricator to

ensure this impedance is met.

In general, closely coupled differential signal traces are not an advantage on PCBs. When differential

signals are closely coupled, tight spacing and width control is necessary. Very small width and spacing

variations affect impedance dramatically, so tight impedance control can be more problematic to maintain

in production.

Loosely coupled PCB differential signals make impedance control much easier. Wider traces and spacing

make obstacle avoidance easier, and trace width variations don’t affect impedance as much, therefore it’s

easier to maintain accurate impedance over the length of the signal. The wider traces also show reduced

skin effect and therefore often result in better signal integrity.

Some general routing guidelines regarding TMDS:

•

Avoid crossing splits reference plane(s).

•

Shorter trace length is preferred.

•

Distance between common mode filter (CMF) and ESD protection device should be as short as

possible

•

Distance between ESD protection device and HDMI connector should be as short as possible.

Table 8-16 shows the routing specifications for the TMDS signals.

Table 8-16. TMDS Routing Specifications

PARAMETER

MIN

TYP

MAX

UNIT

Device balls to HDMI header trace length

4000

Mills

Skew within a differential pair

Mils

Number of stubs allowed on TMDS traces

stubs

TMDS pair differential impedance

100

110

TMDS single-ended impedance

Number of vias on each TMDS trace

Vias

TMDS differential pair to any other trace spacing (1) (2) (3)

2×DS

3xDS

Mils

Number of ground plane cuts allowed within HDMI routing region (except for specific

ground carving as explained in this document)

Cuts

Number of layers between HDMI routing region and reference ground plane

Layers

PCB trace width

4.4

Mils

(1) DS = differential spacing of the traces.

(2) Exceptions may be necessary in the SoC package BGA area.

(3) GND guard-bands may be closer, but should not be allowed to affect the impedance of the differential pair routing. GND guard-bands to

isolate HDMI differential pairs from all other signals is recommended.

Table 8-17. TDMS Routing Recommendations

Item

Description

Reason

ESD part number

TPD1E05U06

Minimize capacitance (0.42pF)

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