Datasheet
PCA9646 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 1 — 1 March 2011 12 of 22
NXP Semiconductors
PCA9646
Buffered 4-channel 2-wire bus switch
Figure 16 shows how PCA9646 can be used to combine or extend existing long cable
systems using P82B715 I
2
C-bus extenders when they have reached their maximum
capacitance limit. P82B715 alone provides a ‘10 impedance transformation’ (Ref. 2
) but
no isolation of the loadings on either side. P82B715 systems have a finite capacitance
limit and its system calculations can be relatively complex. The buffering action of
PCA9646 simplifies calculations and allows the isolated bus rise time to meet the
Fast-mode requirement even when that is not possible on the long cable section.
Of course it is possible to create a much larger system by connecting existing long
P82B715 cable systems to each of the four channels and driving all of them from one
isolated Master.
PCA9646 provides bus isolation and simplifies calculation of bus RC components.
Fig 16. PCA9646 isolating the standard I
2
C-bus from a P82B715 used as a line driver
002aaf377
SCL
SDA
SCL
SDA
PCA9646
V
DD
SC0
SC1
U1
RESET
5 V
R1
1.8 kΩ
R2
1.8 kΩ
A[2:0]
SD0
SD1
SC2
SC3
SD2
SD3
P82B715
U2
V
CC
SX
SY
R4R3
3
LX
LY
long cable runisolated I
2
C-bus
no pull-up
required