Data Sheet
QBK020A Series Power Modules; DC-DC Converters
36 – 55 Vdc Input; 12Vdc Output; 20A Output Current
March 27, 2008
•
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 Vin source or the on/off
pin to simultaneously restart the modules, following
a shutdown, is advised.
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 VIN (-) 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 VIN (-) input connection should never be
disconnected from any of the parallel modules, while
another of the parallel modules is operating, unless
the VIN (+) pin, or the parallel pin is also
When not using the parallel feature, leave the share pin
open.
disconnected. The VIN (-) 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 VIN (-) pin is disconnected
(allowing the internal logic circuit to float), while the
parallel pin and VIN (+) 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 20A, then the maximum total load shall be
less than 0.9 x (3-1) x 20A = 0.9 x 2 x 20A = 36A.
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.
10
LINEAGE POWER
LINEAGEPOWER [ LINEAGE POWER CORPORATION ]
