Datasheet

PCA9616 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 2 — 10 March 2014 7 of 32
NXP Semiconductors
PCA9616
3-channel multipoint Fm+ dI
2
C-bus buffer with hot-swap logic
7.2.1 Noise rejection
Impulse noise coupled into the I
2
C-bus/SMBus signals can prevent the I
2
C-bus/SMBus
bus from operating reliably. The hostile signals may appear on the SCL line, SDA line, or
both. Impulse noise may also enter the common ground connection, or be caused by
current in the ground path caused by DC power supplies, or other signals sharing the
common ground return path. This problem is removed by using a differential transmission
line, in place of the I
2
C-bus/SMBus signal path. The dI
2
C-bus receiver (at each dI
2
C-bus
node) subtracts the signals on the two differential lines (D+ and D), and eliminates any
common-mode noise that is coupled into the dI
2
C-bus. The receiver amplifies the signals
which are also attenuated by the bulk resistance of the transmission line cable
connection, and does not rely on a common ground connection at each node.
7.2.2 Rejection of ground offset voltage
Hostile signals interfere with the I
2
C-bus/SMBus bus through the common ground
connection between each node. Current in this ground path will cause an offset that may
cause false data or push the I
2
C-bus/SMBus signals outside of an acceptable range.
Unwanted ground offset can be caused by heavy DC current in the ground path, or
injection of ground current from AC signals, either of which may show up as false signals.
Because the dI
2
C-bus node’s receiver responds only to the difference between the two
dI
2
C-bus transmission lines, common-mode signals are ignored. There is no need to have
a ground connection between each of the nodes, which may be powered locally. Nodes
may also be powered by extra conductors (for V
DD
and ground) run with the dI
2
C-bus
signals. Voltage offsets caused by DC current in these additional wires will be ignored by
the dI
2
C-bus receiver, which subtracts the two differential signals (D+ and D).
7.2.3 Interrupt channel
The PCA9616 has a third channel identical to the SCL or SDA channel that can be used
as a side band for interrupt or reset.
If unused, the INT pin should be held LOW and the DINTM and DINTP are left ‘not
connected’.
Fig 5. dI
2
C-bus terminations
DxxxP
DxxxM
aaa-011061
twisted-pair cable
DxxxP
DxxxM