TMDS261B Datasheet, PDF (27/48 Pages) Texas Instruments – TWO-PORT HDMI SWITCH

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TMDS261B
SLLS987A – SEPTEMBER 2009 – REVISED JULY 2011
APPLICATION INFORMATION
Table 3. TMDS261B vs TMDS251 Pinout
PIN NUMBER I/O
TMDS251
Pins 32 and 33 I GPIO mode: S1 and S2 configured as
source selector pins
Pin 34
Pin 49
I EQ: TMDS input equalization control
select
EQ = High – 10-m 28 AWG HDMI cable
EQ = Low – HDMI 1.3 compliant cable
— VDD: HPD/DDC power supply
TMDS261B
GPIO mode: S1 and S2 configured as source selector pins (same as
TMDS251)
I²C mode: S1 and S2 configured as SCL and SDA for local slave I²C
communication
I2C_SEL: GPIO / local I²C control select
I2C_SEL = High – Device is configured by GPIO logic.
I2C_SEL= Low – Device is configured by I²C logic.
LP: Low-power mode-select bar
LP = High – Normal operational mode
LP = Low – Device goes into low-power state.
Based on the differences listed in Table 3, attention must be given to pin 34, which determines whether the
device uses I²C or GPIO control.
Supply Voltage
The TMDS261B is powered up with a single power source that is 3.3-V VCC for the TMDS circuitry for HPD,
DDC, and most of the control logic.
TMDS Input Fail-Safe
The TMDS261B incorporates clock-detect circuitry. If there is no valid TMDS clock from the connected HDMI/DVI
source, the TMDS261B does not switch on the terminations on the source-side data channels. Additionally, the
TMDS outputs are placed in the high-impedance state. This prevents the TMDS261B from turning on its outputs
if there is no valid incoming HDMI/DVI data.
TMDS Outputs
A 10% precision resistor, 4.02-kΩ, is recommended to control the output swing to the HDMI-supporting 800-mV
to 1200-mV range V_OD(pp) (1000 mV typical). The TMDS outputs are high-impedance under standby-mode
operation, S1 = H and S2 = L.
DDC I²C Function Description
The TMDS261B provides buffers on the DDC I²C lines on both input ports. This section explains the operation of
the buffer. For representation, the source side of the TMDS261B is represented by RSCL/RSDA, and the sink
side is represented by TSCL/TSDA. The buffers on the RSCL/RSDA and TSCL/TSDA pins are 5-V tolerant when
the device is powered off and high-impedance under low supply voltage, 1.5 V or below. If the device is powered
up, the driver T (see Figure 40) is turned on or off depending on the corresponding R-side voltage level.
When the R side is driven low below 1.5 V, the corresponding T-side driver turns on and drives the T side down
to a low level output voltage, V_OL. The value of V_OL and V_IL on the T side or the sink side of the TMDS261B
switch depends on the output-voltage select (OVS) control settings. OVS control can be changed by the slave
I²C, see Table 8. When the OVS1 setting is selected, V_OL is typically 0.7 V and V_IL is typically 0.4 V. When the
OVS2 setting is selected, V_OL is typically 0.6 V and V_IL is typically 0.4 V. When the OVS3 setting (default) is
selected, V_OL is typically 0.5 V and V_IL is typically 0.3 V. V_OL is always higher than the driver-R input threshold,
V_IL on the T side or the sink side, preventing lockup of the repeater loop. The TMDS261B is targeted primarily as
a switch in the HDTV market and is expected to be a companion chip to an HDMI receiver; thus, the OVS control
has been provided on the sink side, so that the requirement of V_IL to be less than 0.4 V can be met. The V_OL
value can be selected to improve or optimize noise margins between V_OL and V_IL of the repeater itself or 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.
Copyright © 2009–2011, Texas Instruments Incorporated
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