PCA9601

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© NXP B.V. 2011. All rights reserved.

Product data sheet

Rev. 2 — 6 May 2011

21 of 32

NXP Semiconductors

PCA9601

Dual bidirectional bus buffer

10.2.1 Example with questions and answers

Question: On a falling edge of TX we measure undershoot at

−800 mV at the linked

TX, RX pins of the PCA9601 that is generating the LOW, but the PCA9601 data sheet

specifies minimum

−0.3 V. Does this mean that we violate the data sheet absolute

value?

Answer: For PCA9601 the

−0.3 V Absolute Maximum rating is not intended to apply to

transients, it is a DC rating. As shown in Figure 24, there is no theoretical reason for any

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 PCA9601 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

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.

Fig 24. Transients generated by the bus wiring

002aaf078

time (ns)

2

0

4

6

voltage

(V)

−2

horizontal scale = 62.5 ns/div

send

receive

5 V

RX

TX

SX

PCA9601

send

300

Ω

5 V

2 meter

cable

5 V

300

Ω

GND

receive