TMDS341 Datasheet, PDF (19/25 Pages) Texas Instruments – 3-TO-1 DVI/HDMI SWITCH

TMDS341
www.ti.com
SLLS660A – AUGUST 2005 – REVISED OCTOBER 2005
APPLICATION INFORMATION (continued)
When the power source of the device, V_CC, is off and the power source to termination, AV_CC, is on, the output
leakage current (I_o(off)) specification ensures leakage current is limited to 10-µA or less.
The PRE pin provides 3-dB de-emphasis, allowing output signal pre-conditioning to offset interconnect losses
from the TMDS341 outputs to a TMDS receiver. PRE is recommended to be low to the circuit design of a
stand-alone switch box.
HPD Pins
The input of the HPD_SINK is 5-V tolerant, allowing direct connection to 5-V signals. The HPD pin output
resistance is 35-Ω typically. A 1-kΩ 10% resistor is recommended to be connected from an HPD pin at the
TMDS341 to the HPD pin of the HDMI connector.
DDC Channels
The DDC channels are designed with a bi-directional pass gate, providing 5-V signal tolerance. The 5-V
tolerance allows direct connection to a standard I²C bus. The level shifter between 3.3 V and 5 V I²C interface
can be eliminated.
Configuring the TMDS341 as a 2:1 Switch
The TMDS341 can be configured as a 2-to-1 switch by pulling the source selector pin (S1, S2, S3) of the
non-active port low and leaving the corresponding TMDS inputs, SCL, SDA, and HPD pins open.
Layout Considerations
The high-speed TMDS inputs are the most critical paths for the TMDS341. 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 TMDS341
• 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
• Layout of the TMDS differential inputs should be with the shortest stubs from the connectors
Connecting Cables Longer Than 5 m
When using the TMDS341 with cables longer than 5 m, the impact to the TMDS signal path as well as the DDC
signal path must be considered.
TMDS Signal Path
The TMDS341 receiver equalization circuit provides the capability of compensating inter-symbol interference (ISI)
losses in a 5-m 28-AWG DVI cable. Typical cable measurements indicate that the TMDS341 can drive a 5-m
28-AWG HDMI cable and pass the eye mask at the output of a HDMI source (TP1) and a 10-m 28-AWG HDMI
cable and pass the eye mask at the input of a HDMI sink (TP2). Figure 33 through Figure 36 show the eye mask
measurement results.
Figure 33. Eye Diagram at Output 5-m 28-AWG Cable vs
TP1 Eye Mask
Figure 34. Eye Diagram Recovered by TMDS341 vs TP1
Eye Mask
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