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AN10710
Features and applications of the P82B715 I
2
C-bus extender
Rev. 2 — 26 August 2010 Application note
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Keywords I2C-bus, twisted pair cables, Cat5e, Fast-mode, Fast-mode Plus, Fm+,
inter-IC, SDA, SCL, P82B715, P82B96, PCA9600, AdvancedTCA, IPMB,
SMBus, PMBus
Abstract The P82B715 allows extending I
2
C-bus systems over long cables and to a
total capacitance of about 3000 pF without compromising the important
features of the I
2
C-bus. It causes minimal changes to bus logic signal
levels and does not introduce any additional requirements on the levels of
the signals that it handles. That makes it compatible will all I
2
C-bus
devices and related buses and devices that use TTL switching levels
instead of I
2
C levels. It permits inclusion of all other classes of I
2
C-bus
buffers—even those that impose additional logic LOW level requirements
on the bus signals or that use static level or dynamic level offsets. The
slew control minimizes ringing and overshoot when driving I
2
C signals
over twisted pair communication cables that have a low characteristic
impedance (e.g., Category 5e and similar 4-pair cables, as typically used
for Ethernet communications, are around 100 ). A quick design method
is presented for cable design applications to 100 kHz and 30 m.
Application examples include driving 20 m cables to 400 kHz in
Fast-mode, a very large system for driving architectural LED displays that
could include more than 240 m of cabling, and an AdvancedTCA radial
IPMB distribution bus example driving 2800 pF.
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