TMDS261B Datasheet, PDF (28/48 Pages) Texas Instruments – TWO-PORT HDMI SWITCH

TMDS261B
SLLS987A – SEPTEMBER 2009 – REVISED JULY 2011
www.ti.com
OVS
RSCL
RSDA
T
TSCL
TSDA
R
B0344-01
Figure 40. I²C Drivers in the TMDS261B (R Side Is the HDMI Source Side, T Side Is the HDMI Sink Side)
When the T side is driven below 0.4 V by an external I²C driver, both drivers R and T are turned on. Driver R
drives 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
V_OL of driver T. Driver R turns off, because V_OL is above its 0.4-V V_IL 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 41.
VCC
TSCL/TSDA
t
PLH
0.5 V
5 V ±10%
RSCL/RSDA
VCC/2
Figure 41. Waveform of Driver T Turning Off
It is important that any external I²C driver on the T side is able to drive the bus below 0.4 V to achieve full
operation. If the T side cannot be driven below 0.4 V, driver R may not recognize and transmit the low value to
the R side.
DDC I²C Behavior
The typical application of the TMDS261B is as a 2×1 switch in a TV, connecting up to two HDMI input sources to
an HDMI receiver. The I²C repeater is 5-V tolerant, and no additional circuitry is required to translate between
3.3-V and 5-V bus voltages. In the following example, the system master is running on an R-side I²C-bus,
whereas 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.
V
Rdd
V _Tdd
R
Rup
Master
Driver T
R_Tup
Slave
C_SOURCE
C_I
C_O
C
CABLE
Driver R
C_slave
C_medium
Figure 42. Typical Application
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