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RSCL

RSDA

TSCL

TSDA

I2CEN

OVS

TSCL/TSDA

RSCL/RSDA

Vcc

0.5V

5V +

10%

Vcc/2

PLH

I2C Enable

I2C Behavior

TMDS141

SLLS737B – JUNE 2006 – REVISED APRIL 2007

APPLICATION INFORMATION (continued)

or not connected, VOL is typically 0.5 V. When OVS is connected to GND, VOL is typically 0.65 V. When OVS is

connected to VCC, VOL is typically 0.8 V. VOL is always higher than the driver R input threshold, VIL, which is

typically 0.4 V, preventing lockup of the repeater loop. The VOL value can be selected to improve or optimize

noise margins between VOL and the VIL of the repeater itself or the VIL of some external device connected on the

T side.

When the R side is pulled up, above 1.5 V, the T side driver turns off and the T side pin is high impedance.

Figure 18. I2C Drivers in TMDS141

When the T side is pulled below 0.4 V by an external I2C driver, both drivers R and T are turned on. Driver R

pulls the R side to near 0 V, and driver T is on, but is overridden by the external I2C driver. If driver T is already

on, due to a low on the R side, driver R just turns on.

When the T side is released by the external I2C driver, driver T is still on, so the T side is only able to rise to the

VOL of driver T. Driver R turns off, since VOL is above its 0.4-V VIL threshold, releasing the R side. If no external

I2C driver is keeping the R side low, the R side rises, and driver T turns off once the R side rises above 1.5 V,

see Figure 19.

Figure 19. Waveform of Turning Driver T Off

It is important that any external I2C driver on the T side is able to pull the bus below 0.4 V to ensure full

operation. If the T side cannot be pulled below 0.4 V, driver R may not recognize and transmit the low value to

the R side.

The I2CEN pin is active high with an internal pull-up to VCC. It can be used to isolate a badly behaved slave

during power up. It should never change state during an I2C operation because disabling during a bus operation

may hang the bus and enabling part way through a bus cycle could confuse the I2C parts being enabled.

The typical application of the TMDS141 is as a repeater in a TV connecting the HDMI input connector and an

internal HDMI Rx through flat cables. The I2C repeater is 5-V tolerant, and no additional circuitry is required to

translate between 3.3-V to 5-V bus voltages. In the following example, the system master is running on an

R-side I2C-bus while the slave is connected to a T-side bus. Both buses run at 100 kHz supporting

standard-mode I2C operation. Master devices can be placed on either bus.

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