ADuM140D/ADuM140E Data Sheet
Rev. 0 | Page 16 of 18
PROPAGATION DELAY RELATED PARAMETERS
Propagation delay is a parameter that describes the time it takes
a logic signal to propagate through a component. The propagation
delay to a Logic 0 output may differ from the propagation delay
to a Logic 1 output.
INPUT (V
Ix
)
OUTPUT (V
Ox
)
t
PLH
t
PHL
50%
50%
13119-011
Figure 13. Propagation Delay Parameters
Pulse width distortion is the maximum difference between these
two propagation delay values and is an indication of how
accurately the timing of the input signal is preserved.
Channel matching is the maximum amount the propagation delay
differs between channels within a single ADuM140D/
ADuM140E component.
Propagation delay skew is the maximum amount the
propagation delay differs between multiple ADuM140D/
ADuM140E components operating under the same conditions
JITTER MEASUREMENT
Figure 14 shows the eye diagram for the ADuM140D/ADuM140E.
The measurement was taken using an Agilent 81110A pulse
pattern generator at 150 Mbps with pseudorandom bit sequences
(PRBS) 2(n − 1), n = 14, for 5 V supplies. Jitter was measured
with the Tektronix Model 5104B oscilloscope, 1 GHz, 10 GS/sec
with the DPOJET jitter and eye diagram analysis tools. The result
shows a typical measurement on the ADuM140D/ADuM140E
with 490 ps p-p jitter.
105
0
1
2
3
4
V
LTAGE (V)
5
0
TIME (ns)
–5–10
13119-012
Figure 14. ADuM140D/ADuM140E Eye Diagram
INSULATION LIFETIME
All insulation structures eventually break down when subjected
to voltage stress over a sufficiently long period. The rate of
insulation degradation is dependent on the characteristics of the
voltage waveform applied across the insulation as well as on the
materials and material interfaces.
The two types of insulation degradation of primary interest are
breakdown along surfaces exposed to the air and insulation
wear out. Surface breakdown is the phenomenon of surface
tracking, and the primary determinant of surface creepage
requirements in system level standards. Insulation wear out is the
phenomenon where charge injection or displacement currents
inside the insulation material cause long-term insulation
degradation.
Surface Tracking
Surface tracking is addressed in electrical safety standards by
setting a minimum surface creepage based on the working voltage,
the environmental conditions, and the properties of the insulation
material. Safety agencies perform characterization testing on the
surface insulation of components that allows the components to be
categorized in different material groups. Lower material group
ratings are more resistant to surface tracking and, therefore, can
provide adequate lifetime with smaller creepage. The minimum
creepage for a given working voltage and material group is in each
system level standard and is based on the total rms voltage
across the isolation, pollution degree, and material group.
The material group and creepage for the ADuM140D/ADuM140E
isolators are presented in Table 9.
Insulation Wear Out
The lifetime of insulation caused by wear out is determined by
its thickness, material properties, and the voltage stress applied.
It is important to verify that the product lifetime is adequate at
the application working voltage. The working voltage supported
by an isolator for wear out may not be the same as the working
voltage supported for tracking. It is the working voltage
applicable to tracking that is specified in most standards.
Testing and modeling have shown that the primary driver of long-
term degradation is displacement current in the polyimide
insulation causing incremental damage. The stress on the
insulation can be broken down into broad categories, such as:
dc stress, which causes very little wear out because there is no
displacement current, and an ac component time varying
voltage stress, which causes wear out.
The ratings in certification documents are usually based on
60 Hz sinusoidal stress because this reflects isolation from line
voltage. However, many practical applications have combinations
of 60 Hz ac and dc across the barrier as shown in Equation 1.
Because only the ac portion of the stress causes wear out, the
equation can be rearranged to solve for the ac rms voltage, as is
shown in Equation 2. For insulation wear out with the
polyimide materials used in these products, the ac rms voltage
determines the product lifetime.
