STDVE001A Datasheet, PDF (17/49 Pages) STMicroelectronics – Adaptive single 3.4 Gbps TMDS/HDMI signal equalizer

STDVE001A
Functional description
3.5
I²C DDC line repeater
The device contains two identical bi-directional open-drain, non-inverting buffer circuits that
enable I²C DDC bus lines to be extended without degradation in system performance. The
STDVE001A buffers both the serial data (DDC SDA) and serial clock (DDC SCL) on the I²C
bus, while retaining all the operating modes and features of the I²C system. This enables
two buses of 400 pF bus capacitance to be connected in an I²C application. These buffers
are operational from a supply V of 3.0 V to 3.6 V.
The I²C bus capacitance limit of 400 pF restricts the number of devices and bus length. The
STDVE001A enables the system designer to isolate the two halves of a bus,
accommodating more I²C devices or longer trace lengths. It can also be used to run two
buses, one at 5 V and the other at 3.3 V or a 400 kHz and 100 kHz bus, where the 100 kHz
bus is isolated when 400 kHz operation of the other bus is required. The STDVE001A can
be used to run the I²C bus at both 5 V and 3.3 V interface levels.
The DDC_EN acts as the enable for the DDC buffer. The DDC_EN line should not change
state during an I²C operation, because disabling during bus operation hangs the bus and
enabling port may through a bus cycle could confuse the I²C ports being enabled. The
DDC_EN input should change state only when the global bus and repeater port are in idle
state, to prevent system failures.
The output low levels for each internal buffer are approximately 0.5 V, but the input voltage
of each internal buffer must be 70 mV or more below the output low level, when the output
internally is driven low. This prevents a lock-up condition from occurring when the input low
condition is released.
As with the standard I²C system, pull up resistors are required to provide the logic high
levels on the buffered bus. The STDVE001A has standard open collector configuration of
the I²C bus. The size of the pull up resistors depends on the system, but each side of the
repeater must have a pull up resistor.
This part is designed to work with standard mode and fast mode I²C devices. Standard
mode I²C devices only specify 3 mA output drive, this limits the termination current to 3 mA
in a generic I²C system where standard mode devices and multiple masters are possible.
Under certain conditions, higher termination currents can be used.
3.6
Power-down condition
The OE_N pin can be used to disable the device. Also there is no ESD protection dode to
supply on any of the IOs. This prevents a reverse current flow condition when the main box
is switched off while the TV is switched on.
The OE_N is used to disable most of the internal circuitry of STDVE001A that puts the
device in a low power mode of operation.
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