TMDS341APFC datasheet(21/27 Pages) TI

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DDC Signal Path

TMDS341A

SLLS702B – MAY 2006 – REVISED MARCH 2007

APPLICATION INFORMATION (continued)

Figure 38. Eye Diagram at Output 10-m 28-AWG Cable

Figure 39. Eye Diagram Recovered by TMDS341A vs TP2

vs TP2 Eye Mask

Eye Mask

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) = VDD(1 – e

–t/RC)

(1)

Where:

t is the time since the charging started

VDD 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 VIH = 0.7 VDD, and the low-level

threshold voltage is VIL = 0.3 VDD.

From equation (1), the times to charge from a bus voltage of 0 V to the VIH and VIL levels are:

tIH = 1.204 × RC

tIL = 0.357 × RC

The bus rise time (from 0.3 VDD to 0.7 VDD) is then given by equation (2):

tr(30-70) = tIH– tIL = 0.847 × RC

(2)

The TMDS341A 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 40 shows the TMDS341A being used as a stand-alone switch. Both pull-up resistors are decided by the

source and sink equipment. A 1.5-k

Ω resistor at the source and a 47-kΩ resistor at the sink are recommended.

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