TMDS341 Datasheet, PDF (20/25 Pages) Texas Instruments – 3-TO-1 DVI/HDMI SWITCH

TMDS341
SLLS660A – AUGUST 2005 – REVISED OCTOBER 2005
APPLICATION INFORMATION (continued)
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Figure 35. Eye Diagram at Output 10-m 28-AWG Cable vs
TP2 Eye Mask
Figure 36. Eye Diagram Recovered by TMDS341 vs TP2
Eye Mask
DDC Signal Path
Observed I²C bus voltage is dependent on bus resistance, capacitance, and time. The transient bus voltage,
when charging from a low state to a high state, can be calculated using equation (1).
V(t) = V_DD(1 – e^–t/RC)
(1)
Where:
t is the time since the charging started
V_DD is the pull-up termination voltage
R is the total resistance on the I²C link
C is the total capacitance on the I²C link
In the I²C bus specification, version 2.1, the high-level threshold voltage is V_IH = 0.7 V_DD, and the low-level
threshold voltage is V_IL = 0.3 V_DD.
From equation (1), the times to charge from a bus voltage of 0 V to the V_IH and V_IL levels are:
t_IH = 1.204 × RC
t_IL = 0.357 × RC
The bus rise time (from 0.3 V_DD to 0.7 V_DD) is then given by equation (2):
t_r(30-70) = t_IH– t_IL = 0.847 × RC
(2)
The TMDS341 can be easily applied in stand-alone switch boxes and digital displays. The following sections
show the bus lengths that can be supported in each case.
Maximum Bus Lengths for Switch Applications
Figure 37 shows the TMDS341 being used as a stand-alone switch. Both pull-up resistors are decided by the
source and sink equipment. A 1.5-kΩ resistor at the source and a 47-kΩ resistor at the sink are recommended.
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