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TMDS181_16 Datasheet, PDF (46/59 Pages) Texas Instruments – 6 Gbps TMDS Retimer
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TMDS181, TMDS181I
SLASE75C – AUGUST 2015 – REVISED JULY 2016
www.ti.com
Vth–\Vth+
0.1VCC
0.15VCC
0.2VCC
0.25VCC
0.3VCC
0.7VCC
1.0986
1.0415
0.9808
0.9163
0.8473
Table 10. Value k upon Different Input Threshold Voltages
0.65VCC
0.9445
0.8873
0.8267
0.7621
0.6931
0.6VCC
0.8109
0.7538
0.6931
0.6286
0.5596
0.55VCC
0.6931
0.6360
0.5754
0.5108
0.4418
0.5VCC
0.5878
0.5306
0.4700
0.4055
0.3365
0.45VCC
0.4925
0.4353
0.3747
0.3102
0.2412
0.4VCC
0.4055
0.3483
0.2877
0.2231
0.1542
0.35VCC
0.3254
0.2683
0.2076
0.1431
0.0741
0.3VCC
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 pullup voltage and provide <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 10, the recommended maximum total resistance of the pullup
resistors on an I2C bus can be calculated for different system setups. If DDC working in 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 specification, calculate Ccable(max) = 700 pF / Csource = 50 pF / Ci = 50 pF,
R(max) as shown in Table 11.
Vth-\Vth+
0.1VCC
0.15VCC
0.2VCC
0.25VCC
0.3VCC
Table 11. Pullup Resistor Upon Different Threshold Voltages and 800 pF Loads
0.7VCC
1.14
1.2
1.27
1.36
1.48
0.65VCC
1.32
1.41
1.51
1.64
1.8
0.6VCC
1.54
1.66
1.8
1.99
2.23
0.55VCC
1.8
1.97
2.17
2.45
2.83
0.5VCC
2.13
2.36
2.66
3.08
3.72
0.45VCC
2.54
2.87
3.34
4.03
5.18
0.4VCC
3.08
3.59
4.35
5.6
8.11
0.35VCC
3.84
4.66
6.02
8.74
16.87
0.3VCC
4.97
6.44
9.36
18.12
—
UNIT
kΩ
kΩ
kΩ
kΩ
kΩ
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.
9.2.3.1.2 Compliance Testing
Compliance testing is very system design specific. Properly designing the system and configuring the TMDS181
can help pass compliance for a system. The following information is a starting point to help prepare for
compliance testing. As each system is different there are many features in the TMDS181 to help tune the circuit.
These include fixed RX equalization, adaptive RX equalization, VOD adjust by several methods, pre-emphasis/de-
emphasis, and source termination. Passing both HDMI2.0a and HDMI1.4b compliance is easier to accomplish
when using I2C as this provides more fine tuning capability.
9.2.3.1.2.1 Pin Strapping Configuration for HDMI2.0a and HDMI1.4b
• VSADJ Resistor = 7.06 kΩ: Note: This value may be changed in order to improve Intra-pair skew margin but
will increase output VOD so care must be taken to avoid VOD and VL compliance issues.
• PRE_SEL = L for -2 dB (For Intra-pair Skew)
• TX_TERM_CTL = NC for Auto Select.
9.2.3.1.2.2 I2C Control for HDMI2.0a and HDMI1.4b
• VSADJ Resistor = 7.06 kΩ: This value may be changed in order to improve Intra-pair skew but will increase
VOD so care must be taken to avoid VOD and VL compliance issues. The VOD can be increased or decreased
by using I2C Reg0Ch[7:2]
• PRE_SEL = Reg0Ch[1:0] = 01 for -2 dB (Labeled HDMI_TWPST)
• TX_TERM_CTL = NC for Auto Select.
– Reg0Bh[4:3] = 00 → No TX Term; HDMI1.4b < 2 Gbps (This may be best value for all HDMI1.4b)
– Reg0Bh[4:3] = 01 → 150 Ω to 300 Ω; HDMI1.4b > 2 Gbps
– Reg0Bh[4:3] = 11 → 75 Ω to 150 Ω; HDMI2.0a
46
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