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TMDS Outputs

HPD Pins

DDC Channels

RupSource

VDDSource

Source

Sink

Ron

SCL_SINK

SDA_SINK

SCL

SDA

Driver(Source)

I to-Sink

I to-Source

VDDSink

RupSink

VCCRx

RupRx

Driver(Sink)

Ito

* Sink +

dd * Vol(Sink)max

upSource ø RupSink

(1)

lto

* Sink +

upSource ø RupSink

(2)

ith(Source)min u lto * Sink

Ron ) Vol(Sink)max

(3)

upSink w

Ron

upSource

ith(Source)min * Vol(Sink)max)

upSource * Vdd

Ron

(4)

TMDS351

SLLS840 – MAY 2007

APPLICATION INFORMATION (continued)

A 10% precision resistor, 4.02-k

Ω, is recommended to control the output swing to the HDMI compliant 400 mV

to 600 mV range (500 mV typical). The TMDS outputs are high impedance under standby mode operation, S1 =

H and S2 = L.

The HPD circuits are powered by the 5-V supply. They provide 5-V TTL output signals to the SOURCE with a

typical 1-k

Ω output resistance. An external 1-kΩ resistor is not needed here. The HPD output of the selected

source port follows the logic level of the HPD_SINK input. Unselected HPD outputs are kept low. When the

device is in standby mode, all HPD outputs follow HPD_SINK. A 1-k

Ω resistor to ground keeps all HPD outputs

low in standby mode if a fixed low state is preferred.

The DDC circuits (SDA, SCL) are powered by a 5-V supply. The I/O pins can connect to the 5-V termination

voltages directly. A 47-k

Ω pull-up resistor to the 5 V is recommended on the SCL1, SCL2, and SCL3 pins. There

is no pull-up resistor on the SDA pins. The pull-up resistor can be replaced with a different value.

Figure 17. Simplified Electrical Circuit Model for DDC Channel

In Figure 17, when the Driver (Sink) pulls the bus low, the highest voltage level is Vol(Sink)max. The current flow

through the pass-gate resistor can be presented as:

where the Vddsource = Vddsink = Vdd

To simplify the equation, Vol(Sink)max is set equal to 0 V to reach equation (2):

The voltage at the input of the SINK is Ito - Sink

× Ron + V

ol(Sink)max, which should be lower than the minimum

input low threshold voltage of the Driver (Source), Vith(Source)min to keep the bus in correct interoperations.

By combining equations (2) and (3), the minimum pull-up resistor at the Sink input is:

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