TMDS261B Datasheet, PDF (31/48 Pages) Texas Instruments – TWO-PORT HDMI SWITCH

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5V_Source (5V coming from HDMI source)
HPD_SOURCE
1 kW
VCC
1 kW (internal
series resistor)
HPD[1:2]
TMDS261B
TMDS261B
SLLS987A – SEPTEMBER 2009 – REVISED JULY 2011
VCC/5V_source
1 kW
10 kW
HPD_SINK
VCC
ON
ON
OFF
HPD_SINK
L
H
X
HPD[1:2]
H
L
Z
HPD_SOURCE
L
H
H
Figure 45. External Circuit to Drive 5-V V_OH on HPD[1:2]
S0387-07
Layout Considerations
The high-speed differential TMDS inputs are the most critical paths for the TMDS261B. There are several
considerations to minimize discontinuities on these transmission lines between the connectors and the device:
• Maintain 100-Ω differential transmission-line impedance into and out of the TMDS261B.
• Keep an uninterrupted ground plane beneath the high-speed I/Os.
• Keep the ground-path vias to the device as close as possible to allow the shortest return current path.
• Keep the trace lengths of the TMDS signals between connector and device as short as possible.
• Keep intra-pair skew (trace length) between the positive and negative TMDS inputs matched to within 5 mils
(0.005 inches or 0.127 mm).
Using the TMDS261B in Systems with Different CEC Link Requirements
The TMDS261B supports a DTV with up to two HDMI inputs when used in conjunction with a signal-port HDMI
receiver. Figure 46 and Figure 47 through Figure 49 show simplified application block diagrams for the
TMDS261B in different DTVs with different consumer electronic control (CEC) requirements. The CEC is an
optional feature of the HDMI interface for centralizing and simplifying user control instructions from multiple
audio/video products in an interconnected system, even when all the audio/video products are from different
manufacturers. This feature minimizes the number of remote controls in a system, as well as reducing the
number of times buttons must be pressed.
A DTV Supporting a Passive CEC Link
In Figure 46, the DTV does not have the capability of handling CEC signals, but allows CEC signals to pass over
the CEC bus. The source selection is done by the control command of the DTV. The user cannot force the
command from any audio/video product on the CEC bus. The selected source reads the E-EDID data after
receiving an asserted HPD signal. The microcontroller loads different CEC physical addresses while changing
the source by means of the S1 and S2 pins.
Copyright © 2009–2011, Texas Instruments Incorporated
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