BCM352x125y300A00
Current Sharing
Fuse Selection
The performance of the SAC™ topology 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.
In order to provide flexibility in configuring power systems
VI Chip® modules are not internally fused. Input line fusing
of VI Chip products is recommended at system level to provide
thermal protection in case of catastrophic failure.
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.
n Current rating (usually greater than maximum current
of BCM module)
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.
n Maximum voltage rating (usually greater than the maximum
possible input voltage)
n Ambient temperature
n Nominal melting I2t
Some general recommendations to achieve matched array
impedances include:
n Recommend fuse: ≤ 2.5A Bussmann PC–Tron Fuse or ≤ 3.15A
SOC type 36CFA Fuse.
n Dedicate common copper planes within the PCB
to deliver and return the current to the modules.
Reverse Operation
n Provide as symmetric a PCB layout as possible among modules
n Apply same input / output filters (if present) to each unit.
BCM modules are capable of reverse power operation. Once the
unit is started, energy will be transferred from secondary back to
the primary whenever the secondary voltage exceeds VIN • K. The
module will continue operation in this fashion for as long as no
faults occur.
For further details see AN:016 Using BCM Bus Converters
in High Power Arrays.
The BCM352x125y300A00 has not been qualified for continuous
operation in a reverse power condition. Furthermore fault
protections which help protect the module in forward operation
will not fully protect the module in reverse operation.
ZIN_EQ1
ZOUT_EQ1
BCM®1
R0_1
VIN
VOUT
Transient operation in reverse is expected in cases where there is
significant energy storage on the output and transient voltages
appear on the input. Transient reverse power operation of less than
10ms, 10% duty cycle is permitted and has been qualified to cover
these cases.
ZOUT_EQ2
ZIN_EQ2
BCM®2
R0_2
+
Load
DC
ZOUT_EQn
BCM®n
R0_n
ZIN_EQn
Figure 21 — BCM module array
BCM® Bus Converter
Page 17 of 21
Rev 2.0
08/2016
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