TMDS341 Datasheet, PDF (18/25 Pages) Texas Instruments – 3-TO-1 DVI/HDMI SWITCH

TMDS341
SLLS660A – AUGUST 2005 – REVISED OCTOBER 2005
APPLICATION INFORMATION
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Supply Voltage
All V_CC pins can be tied to a single 3.3-V power source. A 0.01-µF capacitor is connected from each V_CC pin
directly to ground to filter supply noise.
TMDS Inputs
Standard TMDS terminations are integrated on all TMDS inputs. External terminations are not required. Each
input channel contains an 8-dB equalization circuit to compensate for cable losses. The voltage at the TMDS
input pins must be limited per the absolute maximum ratings. An unused input should not be connected to
ground as this would result in excessive current flow damaging the device.
TMDS Input Fail-Safe
TMDS input pins do not incorporate fail-safe circuits. An unused input channel can be externally biased to
prevent output oscillation. One pin can be left open with the other grounded through a 1-kΩ resistor as shown in
Figure 31.
V_CC
R_{INT RINT}
A
TMDS
Receiver
B
TMDS341
TMDS
Y
Driver
Z
R_T
AV_CC
R_T
Figure 31. TMDS Input Fail-Safe Recommendation
TMDS Outputs
A 1% precision resister, 4.64-kΩ, connected from VSADJ to ground is recommended to allow the differential
output swing to comply with TMDS signal levels. The differential output driver provides a typical 10-mA current
sink capability, which provides a typical 500-mV voltage drop across a 50-Ω termination resistor.
TMDS341
V_CC
TMDS
Driver
Z_O = R_T
Z_O = R_T
AV_CC
R_T
R_T
TMDS
Receiver
GND
Figure 32. TMDS Driver and Termination Circuit
As shown in Figure 32, if V_CC (TMDS341 supply) and AV_CC (sink termination supply) are powered, the TMDS
output signals are high impedance when OE is high. Normal operation is with both supplies active.
Also shown in Figure 32, if V_CC is on and AV_CC is off, the TMDS outputs source a typical 5-mA current through
each termination resistor to ground. The terminations consume a total of 10 mW of power independent of the OE
logical selection. When AV_CC is powered on, normal operation (OE controls output impedance) is resumed.
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