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TMDS171 Datasheet, PDF (43/62 Pages) Texas Instruments – 3.4 Gbps TMDS RETIMER
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TMDS171, TMDS171I
SLLSEN7A – OCTOBER 2015 – REVISED DECEMBER 2015
Application Information (continued)
T = k x RC
(2)
æ -t ö
V (t)
=
VDD
x
çççè1-eRC
÷
÷÷ø
(3)
Table 32. Value k upon Different Input Threshold Voltages
Vth-\Vth+
0.1 VCC
0.15 VCC
0.2 VCC
0.25 VCC
0.3 VCC
0.7 VCC
1.0986
1.0415
0.9808
0.9163
0.8473
0.65 VCC
0.9445
0.8873
0.8267
0.7621
0.6931
0.6 VCC
0.8109
0.7538
0.6931
0.6286
0.5596
0.55 VCC
0.6931
0.6360
0.5754
0.5108
0.4418
0.5 VCC
0.5878
0.5306
0.4700
0.4055
0.3365
0.45 VCC
0.4925
0.4353
0.3747
0.3102
0.2412
0.4 VCC
0.4055
0.3483
0.2877
0.2231
0.1542
0.35 VCC
0.3254
0.2683
0.2076
0.1431
0.0741
0.3 VCC
0.2513
0.1942
0.1335
0.0690
From Equation 1, Rup(min) = 5.5 V / 3 mA = 1.83 kΩ to operate the bus under a 5-V pull-up voltage and provide
less than 3 mA when the I2C device is driving the bus to a low state. If a higher sink current, for example 4 mA,
is allowed, Rup(min) can be as low as 1.375 kΩ.
If DDC working at standard mode of 100 Kbps, the maximum transition time T is fixed, 1 μs, and using the k
values from Table 32, the recommended maximum total resistance of the pull-up resistors on an I2C bus can be
calculated for different system setups. If DDC working at fast mode of 400 Kbps, the transition time should be set
at 300 ns according to I2C specification.
To support the maximum load capacitance specified in the HDMI spec, Ccable(max) = 700 pF/C(source) = 50 pF/Ci =
50 pF, R(max) can be calculated as shown in Table 33.
Vth-\Vth+
0.1 VCC
0.15 VCC
0.2 VCC
0.25 VCC
0.3 VCC
Table 33. Pull-Up Resistor Upon Different Threshold Voltages and 800-pF Loads
0.7 VCC
1.14
1.2
1.27
1.36
1.48
0.65 VCC
1.32
1.41
1.51
1.64
1.8
0.6 VCC
1.54
1.65
1.8
1.99
2.23
0.55 VCC
1.8
1.97
2.17
2.45
2.83
0.5 VCC
2.13
2.36
2.66
3.08
3.72
0.45 VCC
2.54
2.87
3.34
4.03
5.18
0.4 VCC
3.08
3.59
4.35
5.6
8.11
0.35 VCC
3.84
4.66
6.02
8.74
16.87
0.3 VCC
4.97
6.44
9.36
18.12
—
UNIT
KΩ
KΩ
KΩ
KΩ
KΩ
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