TCA9617B Datasheet, PDF (9/24 Pages) Texas Instruments – Level-Translating FM+ I2C Bus Repeater

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9 Detailed Description
TCA9617B
SCPS259A – DECEMBER 2014 – REVISED DECEMBER 2014
9.1 Overview
The TCA9617B is a BiCMOS dual bidirectional buffer intended for I²C bus and SMBus systems. As with the
standard I²C system, pull-up resistors are required to provide the logic high levels on the buffered bus. The
TCA9617B has standard open-drain configuration of the I²C bus. The size of these pull-up resistors depends on
the system, but each side of the repeater must have a pull-up resistor. The device is designed to work with
Standard mode, Fast mode and Fast Mode+ I²C devices. The SCL and SDA lines shall be at high-impedance
when either one of the supplies is powered off.
The TCA9617B B-side drivers operate from 2.2 V to 5.5 V. The output low level for this internal buffer is
approximately 0.5 V, but the input voltage must be below V_IL when the output is externally driven low. The
higher-voltage low signal is called a buffered low. When the B-side I/O is driven low internally, the low is not
recognized as a low by the input. This feature prevents a lockup condition from occurring when the input low
condition is released. This type of design on the B side prevents it from being used in series with another
TCA9617B B-side or other buffers that incorporate a static or dynamic offset voltage. This is because these
devices do not recognize buffered low signals as a valid low and do not propagate it as a buffered low again.
The TCA9617B A-side drivers operate from 0.8 V to 5.5 V and do not have the buffered low feature (or the static
offset voltage). This means that a low signal on the B side translates to a nearly 0-V low on the A side, which
accommodates smaller voltage swings of low-voltage logic. The output pull-down on the A side drives a hard low,
and the input level is set to 0.3 V_CCA to accommodate the need for a lower low level in systems where the low-
voltage-side supply voltage is as low as 0.8 V.
The A side of two or more TCA9617Bs can be connected together to allow a star topology, with the A side on the
common bus. Also, the A side can be connected directly to any other buffer with static or dynamic offset voltage.
Multiple TCA9617Bs can be connected in series, A side to B side, with no buildup in offset voltage with only
time-of-flight delays to consider.
The TCA9617B includes a power-up circuit that keeps the output drivers turned off until V_CCB is above 2.0 V and
V_CCA is above 0.7 V. V_CCA is only used to provide references for the A-side input comparators and the power-
good-detect circuit. The TCA9617B internal circuitry and all I/Os are powered by the V_CCB pin.
After power up and with the EN high, the A side falling below 0.7 V_CCA turns on the corresponding B-side driver
(either SDA or SCL) and drives the B-side down momentarily to 0 V before settling to approximately 0.5 V. When
the A-side rises above 0.3 V_CCA, the B-side pull-down driver is turned off and the external pull-up resistor pulls
the pin high. If the B side falls first and goes below 0.7 V_CCB, the A-side driver is turned on and drives the A-side
to 0 V. When the B-side rises above 0.45 V, the A-side pull-down driver is turned off and the external pull-up
resistor pulls the pin high.
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