PCA9600DP-T NXP Semiconductors, PCA9600DP-T Datasheet - Page 21

• Manufacturer Part Number: PCA9600DP-T
• Manufacturer: NXP Semiconductors

Specifications of PCA9600DP-T

• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Package Type: TSSOP
• Pin Count: 8
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

NXP Semiconductors
PCA9600_4
Product data sheet
Fig 24. Wiring transients limited by the diodes in PCA9600
Question: We have 2 meters of cable in a bus that joins the TX/RX sides of two
PCA9600 devices. When one TX drives LOW the other PCA9600 TX/RX is driven to
undershoot?
Answer: Because the cable joining the two PCA9600s is a ‘transmission line’ that will
have a characteristic impedance around 100
resistors that are larger than that characteristic impedance there will always be negative
undershoot generated. The duration of the undershoot is a function of the cable length
and the input impedance of the connected IC. As shown in
undershoot will be limited, by the diodes inside PCA9600, to around 0.8 V and that will
not cause problems for PCA9600. Those transients will not be passed inside the IC to
the SX/SY side of the IC.
Question: If we input 800 mV undershoot at TX, RX pins, what kind of problem is
expected?
Answer: When that undershoot is generated by another PCA9600 and is simply the
result of the system wiring, then there will be no problems.
Question: Will we have any functional problem or reliability problem?
Answer: No.
0.8 V for over 50 ns. What is the expected value and the theoretically allowed value of
voltage
Rev. 04 — 11 November 2009
(V)
SX
6
4
2
0
2
5 V
horizontal scale = 62.5 ns/div
RX
PCA9600
TX
send
send
5 V
300
2 meter
cable
receive
and it will be terminated by pull-up
5 V
300
receive
GND
time (ns)
Dual bidirectional bus buffer
Figure
RX
TX
002aaf082
5 V
SX
24, the transient
PCA9600
© NXP B.V. 2009. All rights reserved.
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