TCA9617A Datasheet, PDF (2/17 Pages) Texas Instruments – LEVEL-TRANSLATING FM+ I2C BUS REPEATER

TCA9617A
SCPS244 – JUNE 2013
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
DESCRIPTION (CONTINUED)
The 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 70 mV or more below the output low level 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 TCA9617A 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 A-side drivers operate from 0.8 V to 5.5 V and drive more current. They do not require 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 pulldown 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 0.9 V.
The A side of two or more TCA9617As can be connected together to allow a start topography, 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 TCA9617As 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 TCA9617A has an active-high enable (EN) input with an internal pullup to V_CCB, which allows the user to
select when the repeater is active. This can be used to isolate a badly behaved slave on power-up reset. It
should never change state during an I²C operation, because disabling during a bus operation may hang the bus,
and enabling part way through the bus cycles could confuse the I²C parts being enabled. The EN input should
change state only when the global bus and repeater port are in the idle state, to prevent system failures.
The TCA9617A includes a power-up circuit that keeps the output drivers turned off until V_CCB is above 2.5 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 TCA9617A internal circuitry and all I/Os are powered by the V_CCB pin. V_CCB and V_CCA
can be applied in any sequence at power up. However, due to ESD protection requirements on the SCLA and
SDAA, it is recommended to power-up V_CCB prior to V_CCA.
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 0V before settling to approximately 0.5 V. When
the A-side rises above 0.3 V_CCA, the B-side pulldown driver is turned off and the external pullup 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 pulldown driver is turned off and the external pullup resistor
pulls the pin high.
As with the standard I²C system, pullup resistors are required to provide the logic-high levels on the buffered
bus. The TCA9617A has standard open-collector configuration of the I²C bus. The size of these pullup resistors
depends on the system, but each side of the repeater must have a pullup resistor. The device is designed to
work with Standard mode, Fast mode and Fast Mode+ I²C devices.
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