Data Sheet
ADuM5401W/ADuM5402W/ADuM5403W
RATED PEAK VOLTAGE
Symptom
0V
The VISO output voltage restarts to an incorrect voltage between
3.4 V and 4.7 V when power is removed at VDD1 and then reapplied
between 250 ms and 3 sec later. The error occurs only on restart; it
does not occur at initial power-up. If the part initializes incorrectly,
power must be removed for an extended time to allow internal
nodes to discharge and reset. The amount of time required can
be several minutes at low temperature; therefore, it is critical to
avoid allowing the device to initialize improperly.
Figure 28. Bipolar AC Waveform
RATED PEAK VOLTAGE
0V
Figure 29. DC Waveform
Cause
The secondary side band gap reference does not initialize to the
proper voltage due to a slow slew rate on VISO after the internal
nodes are precharged during the previous power cycle. The
secondary side band gap sets the output voltage of the regulator.
RATED PEAK VOLTAGE
0V
NOTES
Solution
1. THE VOLTAGE IS SHOWN AS SINUSOIDAL FOR ILLUSTRATION
PURPOSES ONLY. IT IS MEANT TO REPRESENT ANY VOLTAGE
WAVEFORM VARYING BETWEEN 0V AND SOME LIMITING VALUE.
THE LIMITINGVALUE CAN BE POSITIVE OR NEGATIVE, BUT THE
VOLTAGE CANNOT CROSS 0V.
The slew rate of VISO is determined by the resistive and capacitive
load present on the output. Designs that attempt to reduce ripple
by adding capacitance to the VISO output can slow the slew rate
enough to cause start-up errors. Choose values for bulk capacitance
based on the effective dc load. Calculate the dc load as the resistive
equivalent to the current drawn from the VISO line. Determine
the range of allowable capacitance for the VISO output from
Figure 31. Choose the bulk capacitance for VISO to achieve the
application required ripple, unless the value is in the disallowed
combinations area; then the value must be reduced to avoid
restart issues.
Figure 30. Unipolar AC Waveform
VISO START-UP ISSUES
An issue with reliable startup was identified in the ADuM5401W/
ADuM5402W/ADuM5403W components. This issue has been
addressed in the ADuM5401W-1/ADuM5402W-1/ADuM5403W-
1 for the current silicon. The ADuM5401W-1/ADuM5402W-1/
ADuM5403W-1 devices are recommended for all new designs.
The following description applies only to the original released
version of these devices. Production of the original release of
the devices is being continued for existing customers, but it is
not recommended for new designs.
100k
10k
DISALLOWED
COMBINATIONS
The start-up issue in the original release of the ADuM5401W/
ADuM5402W/ADuM5403W is related to initialization of the
band gap voltage references on the primary (power input) and
secondary (power output) sides of the isoPower device and are
being addressed in future revisions of the silicon. For current
versions of the silicon, the user must follow these design guide-
lines to guarantee proper operation of the device.
1k
100
10
The band gap voltage references are vulnerable to slow power-up
slew rate. The susceptibility to power-up errors is process sensitive;
therefore, not all devices display these behaviors. These recommen-
dations should be implemented for all designs until the corrections
are made to the silicon. The symptoms and corrective actions
required for issues with the primary and secondary side startup
are different.
1
1
10
100
1k
C
(µF)
VISO
Figure 31. Maximum Capacitive Load for Proper Restart
Rev. D | Page 23 of 24
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