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PCA9600DP/S911,118

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P32
PCA9600 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 6 — 25 September 2015 19 of 32
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)
PCA9600 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 6 — 25 September 2015 20 of 32
NXP Semiconductors
PCA9600
Dual bidirectional bus buffer
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 PCA9600, 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 22
, would be more than 0.8 V. The correct
functioning of the PCA9600 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 PCA9600.
Figure 22 “
Diode characteristic curve” also explains how the general Absolute Maximum
DC specification was selected. The current at 25 C is near zero at 0.55 V. The
PCA9600 is allowed to operate with +125 C junction and that would cause this diode
voltage to decrease by 100 2 mV = 200 mV. So for zero current we need to specify
0.35 V and we publish 0.3 V just to have some extra margin.
Remark: You should not be concerned about the transients generated on the wiring by a
PCA9600 in normal applications and that is input to the TX/RX or TY/RY pins of another
PCA9600. Because not all ICs that may be driven by PCA9600 are designed to tolerate
negative transients, in Section 10.2.1 “
Example with questions and answers” we show
they can be managed if required.
Fig 22. Diode characteristic curve
002aaf063
voltage (V)
−2.0 0−0.5−1.5 −1.0
−10
−10
3
−10
2
−10
−1
−1
0
−10
4
diode current
(mA)
PCA9600 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2015. All rights reserved.
Product data sheet Rev. 6 — 25 September 2015 21 of 32
NXP Semiconductors
PCA9600
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 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 Figure 23
, 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 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
2
C-bus pull-up resistor generally is larger
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 23. Transients generated by the bus wiring
002aaf081
time (ns)
2
0
4
6
voltage
(V)
−2
horizontal scale = 62.5 ns/div
send
receive
5 V
RX
TX
SX
PCA9600
send
300 Ω
5 V
2 meter
cable
5 V
300 Ω
GND
receive
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PCA9600DP/S911,118

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Manufacturer:
NXP Semiconductors
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IC REDRIVER I2C 1CH 8TSSOP
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