Datasheet

RSCL
RSDA
TSCL
TSDA
I2CEN
OVS
R
T
TSCL/TSDA
RSCL/RSDA
Vcc
0.5V
5V +
10%
Vcc/2
t
PLH
TMDS141
SLLS737D –JUNE 2006–REVISED SEPTEMBER 2011 www.ti.com
or not connected, V
OL
is typically 0.5 V. When OVS is connected to GND, V
OL
is typically 0.65 V. When OVS is
connected to V
CC
, V
OL
is typically 0.8 V. V
OL
is always higher than the driver R input threshold, V
IL
, which is
typically 0.4 V, preventing lockup of the repeater loop. The V
OL
value can be selected to improve or optimize
noise margins between V
OL
and the V
IL
of the repeater itself or the V
IL
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 19. I
2
C Drivers in TMDS141
When the T side is pulled below 0.4 V by an external I
2
C 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 I
2
C 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 I
2
C 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, since V
OL
is above its 0.4-V V
IL
threshold, releasing the R side. If no external
I
2
C 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 20.
Figure 20. Waveform of Turning Driver T Off
It is important that any external I
2
C 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.
I
2
C Enable
The I2CEN pin is active high with an internal pull-up to V
CC
. It can be used to isolate a badly behaved slave
during power up. It should never change state during an I
2
C operation because disabling during a bus operation
may hang the bus and enabling part way through a bus cycle could confuse the I
2
C parts being enabled.
I
2
C Behavior
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 I
2
C 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
I
2
C-bus while the slave is connected to a T-side bus. Both buses run at 100 kHz supporting standard-mode I
2
C
operation. Master devices can be placed on either bus.
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