AM3892 datasheet(228/299 Pages) TI

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TD0+

TD0-

TD1+

TD1-

TD2+

TD2-

TD0

Shld

TD1

Shld

TD2

Shld

TCLK

Shld

CEC

SDA

SCL

DDC

Gnd

Rpullup

(A)

DVDD_3P3

HDMI_TMDSDP0

HDMI_TMDSDN0

HDMI_TMDSDP1

HDMI_TMDSDN1

HDMI_TMDSDN2

HDMI_TMDSDP2

HDMI_TMDSCLKP

HDMI_TMDSCLKN

HDMI_CEC

HDMI_SDA

HDMI_SCL

HDMI Connector

Device

TCLK+

TCLK

TPD12S521

or other

ESD Protection

w/I2C-Level

Translation

AM3894

AM3892

SPRS681A – OCTOBER 2010 – REVISED MARCH 2011

www.ti.com

5K-10K

Ω pullup resistors are required if not integrated in the ESD protection chip.

Figure 8-67. HDMI Interface High-Level Schematic

8.9.1.2

TMDS Routing

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

Ω (±10%) differential impedance and

Ω (±10%) single-ended impedance. Single-ended impedance control is required because differential

signals are extremely difficult to closely couple 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

Ω 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 do not affect impedance as much; therefore, it

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

reduced skin effect and, therefore, often result in better signal integrity.

Table 8-62 shows the routing specifications for the TMDS signals.

228

Peripheral Information and Timings

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