BCM3814x60E15A3yzz
ZIN_EQ1
ZOUT_EQ1
BCM®1
R0_1
VLO
VHI
ΦINT
+ TC_BOT
s
ZOUT_EQ2
ZIN_EQ2
BCM®2
R0_2
PDISS
+
Load
DC
s
Figure 23 — Single-sided cooling VIA thermal model
ZOUT_EQn
BCM®n
R0_n
ZIN_EQn
ꢀnDouble side cooling: while this option might bring limited
advantage to the module internal components (given the
surface-to-surface coupling provided), it might be appealing
in cases where the external thermal system requires allocating
power to two different elements, such as heatsinks with
independent airflows or a combination of chassis/air cooling.
Figure 24 — BCM module array
Fuse Selection
Current Sharing
In order to provide flexibility in configuring power systems, BCM in
a VIA package modules are not internally fused. Input line fusing
of BCM products is recommended at the system level to provide
thermal protection in case of catastrophic failure.
The performance of the BCM is based on efficient transfer
of energy through a transformer without the need of closed
loop control. For this reason, the transfer characteristic can be
approximated by an ideal transformer with a positive temperature
coefficient series resistance.
The fuse shall be selected by closely matching system
requirements with the following characteristics:
This type of characteristic is close to the impedance characteristic
of a DC power distribution system both in dynamic (AC) behavior
and for steady state (DC) operation.
ꢀnCurrent rating
(usually greater than maximum current of BCM module)
ꢀnMaximum voltage rating
(usually greater than the maximum possible input voltage)
When multiple BCM modules of a given part number are
connected in an array, they will inherently share the load current
according to the equivalent impedance divider that the system
implements from the power source to the point of load. Ensuring
equal current sharing among modules requires that BCM array
impedances be matched.
ꢀnAmbient temperature
ꢀnNominal melting I2t
ꢀnRecommend fuse: ≤40A Littlefuse 456 Series (HI side)
Some general recommendations to achieve matched array
impedances include:
Reverse Operation
BCM modules are capable of reverse power operation. Once the
unit is started, energy will be transferred from the low voltage
side back to the high voltage side whenever the low side voltage
exceeds VHI • K. The module will continue operation in this fashion
as long as no faults occur.
ꢀnDedicate common copper planes/wires within the PCB/Chassis to
deliver and return the current to the modules.
ꢀnProvide as symmetric a PCB/Wiring layout as possible among
modules
For further details see AN:016 Using BCM Bus Converters
in High Power Arrays.
The BCM3814x60E15A3yzz has not been qualified for continuous
operation in a reverse power condition. However, fault protections
that help to protect the module in forward operation will also
protect the module in reverse operation.
Transient operation in reverse is expected in cases where there is
significant energy storage on the low voltage side and transient
voltages appear on the high voltage side.
BCM® in a VIA Package
Page 22 of 41
Rev 2.0
02/2018
VICOR [ VICOR CORPORATION ]
