NXP Semiconductors

PCA9601

Dual bidirectional bus buffer

- 1

5

3

1

7

VCC

(V)

time (ns)

0

900

002aac934

200

100

300 400 500 600 700 800

0

2

4

6

(1)

(2)

(1)

(2)

1. RX input.

2. SX output.

Figure 22. Propagation RX to SX (SX pull-up to 3.3 V; VCC = 3.3 V; RX pull-up to 4.6 V)

10.2 Negative undershoot below absolute minimum value

The reason why the IC pin reverse voltage on pins TX and RX in Table 5 is specified at

such a low value, -0.3 V, is

not that applying larger voltages is likely to cause damage

but that it is expected that, in normal applications, there is no reason why larger DC

voltages will be applied. This ‘absolute maximum’ specification is intended to be a DC

or continuous ratings and the nominal DC I2C-bus voltage LOW usually does not even

reach 0 V. Inside PCA9601 at every pin there is a large protective diode connected to

the GND pin and that diode will start to conduct when the pin voltage is more than about

-0.55 V with respect to GND at 25 °C ambient.

Figure 23 shows the measured characteristic for one of those diodes inside PCA9601.

The plot was made using a curve tracer that applies 50 Hz mains voltage via a series

resistor, so the pulse durations are long duration (several milliseconds) and are reaching

peaks of over 2 A when more than -1.5 V is applied. The IC becomes very hot during this

testing but it was not damaged. Whenever there is current flowing in any of these diodes

it is

possible that there can be faulty operation of any IC. For that reason we put a

specification on the negative voltage that is allowed to be applied. It is selected so that, at

the highest allowed junction temperature, there will be a big safety factor that guarantees

the diode will not conduct and then we do not need to make any 100 % production tests

to guarantee the published specification.

For the PCA9601, in specific applications, there will always be transient overshoot and

ringing on the wiring that can cause these diodes to conduct. Therefore we designed the

IC to withstand those transients and as a part of the qualification procedure we made

tests, using DC currents to more than twice the normal bus sink currents, to be sure

that the IC was not affected by those currents. For example, the TX/TY and RX/RY pins

were tested to at least -80 mA which, from Figure 23, would be more than -0.8 V. The

correct functioning of the PCA9601 is not affected even by those large currents. The

Absolute Maximum (DC) ratings are not intended to apply to transients but to steady

state conditions. This explains why you will never see any problems in practice even if,

during transients, more than -0.3 V is applied to the bus interface pins of PCA9601.

Figure 23 also explains how the general Absolute Maximum DC specification was

selected. The current at 25 °C is near zero at -0.55 V. The PCA9601 is allowed to

operate with +125 °C junction and that would cause this diode voltage to decrease by

PCA9601

All information provided in this document is subject to legal disclaimers.

© NXP B.V. 2022. All rights reserved.

Product data sheet

Rev. 3.1 — 4 January 2022

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