PCA9521DP118 Просмотр технического описания (PDF) - NXP Semiconductors.
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PCA9521DP118 Datasheet PDF : 23 Pages
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NXP Semiconductors
PCA9521
Fast dual bidirectional bus buffer
Peripheral cards (or FRU (Field Replaceable Units)) and backplanes operating at a range
of voltages can be interfaced together using a minimum of components. The PCA9521
can be teamed with the PCA9522 to achieve substantial noise margin gains across a
system.
Multiplexers such as the PCA9544A are simple analog switches which provide no
capacitive load isolation between connected branches. Figure 14 shows the PCA9521
enhancing an I2C-bus multiplexer application, by isolating the load capacitance of each
branch. Figure 15 and Figure 16 show alternate forms of bus multiplexing.
Similarly, the P82B715 I2C-bus extender, which is commonly used for line driver
applications, provides a ‘10 impedance transformation’ but does not isolate either side of
the buffer. Figure 13 shows the PCA9521 used to isolate the bus loading due to the
P82B715. This greatly simplifies calculation of the pull-ups, increases the total system
loading capability in extender applications, will meet the Fast-mode release requirement
(when PCA9521 and P82B715 VCC’s share a common supply), and ensures the 300 ns
rise time requirement can easily be met even if the cable bus rise is relatively slow.
Buffers are intended to extend total system capacitance above 400 pF, so anticipate high
capacitance on each side. When loading on one side is small, adding 47 pF is suggested
to avoid any waveform ripple, should it occur.
3.3 V
5V
R1
1.1 kΩ
SCL
SDA
isolated
I2C-bus
R2
1.1 kΩ
no pull-up
VCC
required
SA1
SA2
Sx
SB1
SB2
Sy
VCC
R3
Lx
Ly
PCA9521
P82B715
EN
U1
U2
R4
long
cable run
002aaf290
PCA9521 provides bus isolation and simplifies calculation of bus RC components.
Fig 13. PCA9521 isolating the Standard-mode I2C-bus from a P82B715 used as a
line driver
PCA9521
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 2 — 19 March 2013
© NXP B.V. 2013. All rights reserved.
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