Datasheet

V
N
R
IN
C
IN
R
ISO
C
ISO
SystemGround (GND1)
BusReturn(GND2)
16 V
A,B, Y, orZ
1
16
GND2 ISO
ISO
N
ISO IN
IN
1
v C
1 1
= = = = 0.94
1 1 C
v
+ 1 +
1 +
C C
C
´
9
GN D2 ISO
9 4
N ISO IN
v R 10
= =
v R + R
10 + 6 10
ISO
GND2 N
ISO IN
Z
v = v
Z + Z
ISO1176T
SLLSE28F –OCTOBER 2010–REVISED OCTOBER 2012 www.ti.com
APPLICATION INFORMATION
REFERENCE DESIGN
ISO1176T Reference Design (SLUU471) is available to provide complete isolated data and power solution.
TRANSIENT VOLTAGES
Isolation of a circuit insulates it from other circuits and earth so that noise develops across the insulation rather
than circuit components. The most common noise threat to data-line circuits is voltage surges or electrical fast
transients that occur after installation and the transient ratings of ISO1176T are sufficient for all but the most
severe installations. However, some equipment manufacturers use their ESD generators to test transient
susceptibility of their equipment and can exceed insulation ratings. ESD generators simulate static discharges
that may occur during device or equipment handling with low-energy but high voltage transients.
Figure 31 models the ISO1176T bus IO connected to a noise generator. C
IN
and R
IN
is the device and any other
stray or added capacitance or resistance across the A or B pin to GND2, C
ISO
and R
ISO
is the capacitance and
resistance between GND1 and GND2 of ISO1176T plus those of any other insulation (transformer, etc.), and we
assume stray inductance negligible. From this model, the voltage at the isolated bus return is
and will always be less than 16 V from V
N
. If ISO1176T is tested as a stand-alone device,
R
IN
= 6 × 10
4
Ω, C
IN
= 16 × 10
-12
F, R
ISO
= 10
9
Ω and C
ISO
= 10
-12
F.
SPACER
Note from Figure 31 that the resistor ratio determines
the voltage ratio at low frequency and it is the inverse
capacitance ratio at high frequency. In the stand-
alone case and for low frequency,
or essentially all of noise appears across the barrier.
At high frequency,
and 94% of V
N
appears across the barrier. As long as
R
ISO
is greater than R
IN
and C
ISO
is less than C
IN
,
most of transient noise appears across the isolation
Figure 31. Noise Model
barrier, as it should.
We recommend the reader not test equipment
transient susceptibility with ESD generators or
consider product claims of ESD ratings above the
barrier transient ratings of an isolated interface. ESD
is best managed through recessing or covering
connector pins in a conductive connector shell and
installer training.
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