FXMA2102 Datasheet, PDF (8/16 Pages) Fairchild Semiconductor – Dual Supply, 2-Bit Voltage Translator / Buffer / Repeater / Isolator for I2C Applications

I²C-Bus^® Isolation
The FXMA2102 supports I²C-Bus isolation for the
following conditions:
 Bus isolation if bus clear
 Bus isolation if either V_CC goes to ground
Bus Clear
Because the I²C specification defines the minimum SCL
frequency of DC, the SCL signal can be held LOW
forever; however, this condition shuts down the I²C bus.
The I²C specification refers to this condition as “Bus
Clear”. In Figure 7, if slave #2 holds down SCL forever,
the master and slave #1 are not able to communicate,
because the FXMA2102 passes the SCL stuck-LOW
condition from slave #2 to slave #1 as well as the
master. However, if the OE pin is pulled LOW
(disabled), both ports (A and B) are 3-stated. This
results in the FXMA2102 isolating slave #2 from the
master and slave #1, allowing full communication
between the master and slave #1.
Either V_CC to GND
If slave #2 is a camera that is suddenly removed from
the I²C bus, resulting in V_CCB transitioning from a valid
V_CC (1.65 V – 5.5 V) to 0 V, the FXMA2102
automatically forces SCL and SDA on both its A and B
ports into 3-state. Once V_CCB has reached 0V, full I²C
communication between the master and slave #1
remains undisturbed.
Figure 7. Bus Isolation
© 2010 Fairchild Semiconductor Corporation
FXMA2102 • Rev. 1.0.5
8
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