Data Sheet
March 27, 2008
QBK025A0B DC-DC Power Modules:
36-55Vdc Input; 12Vdc Output Voltage; 25A Output Current
LINEAGE POWER 9
Feature Description (continued)
Forced Load Sharing (Parallel Operation with
– P option)
For additional power requirements, the power module
can be configured for parallel operation with active
load current sharing. Good layout techniques should
be observed for noise immunity when using multiple
modules in parallel. To implement active load sharing,
the following recommendations must be followed:
• The parallel pins of all units in parallel must be
connected together. The path of these
connections should be as direct as possible, but
should not pass beneath the perimeter of the
module body, except immediately adjacent to the
parallel pin location.
• Parallel modules must use the same 48V source.
The V
IN
(-) input pin is the return path for the
active current share signal of the parallel pin.
Separate 48V sources will prevent the active
current share return signal from being connected
to other modules.
• The V
IN
(-) input connection should never be
disconnected from any of the parallel modules,
while another of the parallel modules is operating,
unless the V
IN
(+) pin, or the parallel pin is also
disconnected. The V
IN
(-) input provides the
internal logic ground and for the module’s primary
circuits, including the active current share circuit;
and there are sneak paths through the module’s
internal control ICs, when the V
IN
(-) pin is
disconnected (allowing the internal logic circuit to
float), while the parallel pin and V
IN
(+) pin are
connected to other operating modules. These
sneak paths do not cause permanent damage,
but do create false conditions that can affect the
module’s internal logic configuration.
• The on/off pins of all modules should also be tied
together to the same external control circuitry, so
that the modules are turned on and off at the
same time, unless all parallel modules’ on/off pins
are tied to the input pins for automatic start upon
application of input voltage.
• When modules in parallel applications contain the
auto-restart (4) option, it is required that the total
maximum load current value be less than 90% of
[n-1] times the individual module output current
rating, where n is the number of modules in
parallel. For example, if the application is using
three modules rated at 25A, then the maximum
total load shall be less than 0.9 x (3-1) x 25A =
0.9 x 2 x 25A = 45A. This insures that a single
module can shutdown without causing the total
load to exceed the capability of the remaining
operating module(s). The shutdown module can
then automatically restart, and assume its share
of the total load.
• In all parallel applications (including applications
meeting the [n-1] sizing criteria discussed earlier),
if it is expected that a protective shutdown event
could cause more than one parallel module to
shutdown (for example, over temperature due to
a common fan failure, or gross over current
affecting two or more modules simultaneously),
then the use of the auto-restart (4) option is not
recommended. The auto-restart interval of these
modules is not synchronized to other modules,
nor is it precise. There will not be a successful
restart following multiple module shutdowns,
because the individual module’s restart timings
will be different. There will not be sufficient
module capacity to prevent the first module which
restarts from experiencing an over current, and
then again shutting down before the slowest
module has restarted. Meanwhile, the slowest
module will then restart, and then shutdown
during the interval the fastest module is waiting
for its next restart. And so on and so on. In these
cases, only latching shutdown modules should be
used; and either toggling the V
in
source or the
on/off pin to simultaneously restart the modules,
following a shutdown, is advised.
When not using the parallel feature, leave the share
pin open.
