Datasheet

PCA9600 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 5 — 5 May 2011 18 of 31
NXP Semiconductors
PCA9600
Dual bidirectional bus buffer
10.2 Negative undershoot below absolute minimum value
The reason why the IC pin reverse voltage on pins TX and RX in Table 5 “Limiting values”
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 I
2
C-bus voltage LOW usually does not
even reach 0 V. Inside PCA9600 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 22
shows the measured characteristic for one of those diodes inside PCA9600.
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
(1) TX output.
(2) SX input.
(1) TX/RX output.
(2) SX input.
Fig 19. Propagation SX to TX with V
RX
=V
CC
=3.3V
(SX pull-up to 3.3 V; TX pull-up to 5.7 V)
Fig 20. Propagation SX to TX with RX tied to TX;
V
CC
= 3.3 V (SX pull-up to 3.3 V; TX pull-up to
5.7 V)
(1) RX input.
(2) SX output.
Fig 21. Propagation RX to SX (SX pull-up to 3.3 V; V
CC
= 3.3 V; RX pull-up to 4.6 V)
−1
5
3
1
7
V
CC
(V)
time (ns)
0 900
002aac932
200100 300 400 500 600 700 800
0
2
4
6
(1)
(2)
(1)
(2)
−1
5
3
1
7
V
CC
(V)
time (ns)
0 900
002aac933
200100 300 400 500 600 700 800
0
2
4
6
(1)
(2)
(1)
(2)
(2)
−1
5
3
1
7
V
CC
(V)
time (ns)
0 900
002aac934
200100 300 400 500 600 700 800
0
2
4
6
(1)
(2)
(1)
(2)