TMDS261
www.ti.com ............................................................................................................................................................................................ SLLS953–DECEMBER 2008
Obviously, to accommodate the 3-mA drive current specification, a narrower threshold voltage range is required
to support a maximum 800-pF load capacitance for a standard-mode I2C bus.
When the input low- and high-level threshold voltages, Vth– and Vth+, are 0.7 V and 1.9 V, respectively, which is
0.15 VDD and 0.4 VDD, approximately. With VDD = 5 V from Table 5, the maximum pullup resistor is 3.59 kΩ. The
allowable pullup resistor is in the range of 1.83 kΩ and 3.59 kΩ.
HPD Pins
The HPD circuits are powered by the 3.3-V VCC supply. This provides maximum VOH = VCC and maximum VOL
=
0.4-V output signals to the SOURCE with a typical 1-kΩ output resistance. An external 1-kΩ resistor is not
needed here. The HPD output of the selected source port follows the logic level of the HPD_SINK input.
Unselected HPD outputs are kept low. When the device is in standby mode, all HPD outputs follow HPD_SINK.
If VOH greater than VCC is desired, then an external circuit as shown in Figure 33 can be used. In this case, the
max VOH can be equal to the 5 V coming from the HDMI source.
5V_Source (5 V coming from HDMI source)
VCC/5V_source
VCC
1 kW
1 kW
HPD_SOURCE
1 kW (internal
series resistor)
HPD_SINK
HPD[1:2]
10 kW
TMDS261
VCC
ON
HPD_SINK
HPD[1:2]
HPD_SOURCE
L
H
X
H
L
L
ON
H
H
OFF
Z
S0387-02
Figure 33. External Circuit to Drive 5-V VOH on HPD[1:2]
Layout Considerations
The high-speed differential TMDS inputs are the most critical paths for the TMDS261. 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 TMDS261.
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.
Using the TMDS261 in Systems with Different CEC Link Requirements
The TMDS261 supports a DTV with up to two HDMI inputs when used in conjunction with a signal-port HDMI
receiver. Figure 34 and Figure 35 through Figure 37 show simplified application block diagrams for the TMDS261
Copyright © 2008, Texas Instruments Incorporated
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