PCA9600D NXP [NXP Semiconductors], PCA9600D Datasheet - Page 20

• Manufacturer Part Number: PCA9600D
• Description: Dual bidirectional bus buffer
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCA9600_4
Product data sheet
10.2.1 Example with questions and answers
Fig 23. Transients generated by the bus wiring
Question: On a falling edge of TX we measure undershoot at 800 mV at the linked TX,
RX pins of the PCA9600 that is generating the LOW, but the PCA9600 data sheet
specifies minimum 0.3 V. Does this mean that we violate the data sheet absolute
value?
Answer: For PCA9600 the 0.3 V Absolute Maximum rating is not intended to apply to
transients, it is a DC rating. As shown in
undershoot at the IC that is driving the bus LOW and no significant undershoot should
be observed when using reasonable care with the ground connection of the ‘scope. It is
more likely that undershoot observed at a driving PCA9600 is caused by local stray
inductance and capacitance in the circuit and by the oscilloscope connections. As
shown, undershoot will be generated by PCB traces, wiring, or cables driven by a
PCA9600 because the allowed value of the I
than that required to correctly terminate the wiring. In this example, with no IC
connected at the end of the wiring, the undershoot is about 2 V.
voltage
Rev. 04 — 11 November 2009
(V)
6
4
2
0
2
horizontal scale = 62.5 ns/div
SX
5 V
RX
PCA9600
TX
send
send
5 V
Figure
300
2 meter
2
cable
C-bus pull-up resistor generally is larger
receive
23, there is no theoretical reason for any
time (ns)
5 V
002aaf081
300
receive
GND
Dual bidirectional bus buffer
PCA9600
© NXP B.V. 2009. All rights reserved.
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