TMDS181I datasheet(46/58 Pages) TI1

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TMDS181, TMDS181I

SLASE75A – AUGUST 2015 – REVISED OCTOBER 2015

www.ti.com

Table 10. Value k upon Different Input Threshold Voltages

Vth–\Vth+

0.7VCC

0.65VCC

0.6VCC

0.55VCC

0.5VCC

0.45VCC

0.4VCC

0.35VCC

0.3VCC

0.1VCC

1.0986

0.9445

0.8109

0.6931

0.5878

0.4925

0.4055

0.3254

0.2513

0.15VCC

1.0415

0.8873

0.7538

0.6360

0.5306

0.4353

0.3483

0.2683

0.1942

0.2VCC

0.9808

0.8267

0.6931

0.5754

0.4700

0.3747

0.2877

0.2076

0.1335

0.25VCC

0.9163

0.7621

0.6286

0.5108

0.4055

0.3102

0.2231

0.1431

0.0690

0.3VCC

0.8473

0.6931

0.5596

0.4418

0.3365

0.2412

0.1542

0.0741

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.

Table 11. Pullup Resistor Upon Different Threshold Voltages and 800 pF Loads

Vth-\Vth+

0.7VCC

0.65VCC

0.6VCC

0.55VCC

0.5VCC

0.45VCC

0.4VCC

0.35VCC

0.3VCC

UNIT

0.1VCC

1.14

1.32

1.54

1.8

2.13

2.54

3.08

3.84

4.97

Ω

0.15VCC

1.2

1.41

1.66

1.97

2.36

2.87

3.59

4.66

6.44

Ω

0.2VCC

1.27

1.51

1.8

2.17

2.66

3.34

4.35

6.02

9.36

Ω

0.25VCC

1.36

1.64

1.99

2.45

3.08

4.03

5.6

8.74

18.12

Ω

0.3VCC

1.48

1.8

2.23

2.83

3.72

5.18

8.11

16.87

—

Ω

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 k

Ω: 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

2C Control for HDMI2.0a and HDMI1.4b

•

VSADJ Resistor = 7.06 k

Ω: 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

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