BCM400x500y1K8A3z
Figure 20 shows a scenario where there is no bottom side cooling. In
this case, the heat flow path to the bottom is leꢀ open and the
equations now simplify to:
ZIN_EQ1
ZOUT_EQ1
BCM®1
R0_1
VPRI
VSEC
TINT – PD1 • 1.24 = TCASE_TOP
TINT – PD3 • 7 = TLEADS
PDTOTAL = PD1 + PD3
ZOUT_EQ2
ZIN_EQ2
BCM®2
R0_2
+
Load
DC
Thermal Resistance Top
MAX INTERNAL TEMP
1.33°C / W
Thermal Resistance Bottom
Thermal Resistance Leads
1.29°C / W
5.64°C / W
+
–
TCASE_BOTTOM(°C)
TLEADS(°C)
TCASE_TOP(°C)
Power Dissipation (W)
ZOUT_EQn
BCM®n
R0_n
ZIN_EQn
Figure 21 — Top case thermal model
Figure 22 — BCM module array
Figure 21 shows a scenario where there is no bottom side and leads
cooling. In this case, the heat flow path to the bottom is leꢀ open and
the equations now simplify to:
Fuse Selection
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.
TINT – PD1 • 1.24 = TCASE_TOP
PDTOTAL = PD1
Please note that Vicor has a suite of online tools, including a simulator
and thermal estimator which greatly simplify the task of determining
whether or not a BCM thermal configuration is valid for a given
condition. These tools can be found at:
The fuse shall be selected by closely matching system
requirements with the following characteristics:
nCurrent rating
http://www.vicorpower.com/powerbench.
(usually greater than maximum current of BCM module)
nMaximum voltage rating
Current Sharing
(usually greater than the maximum possible input voltage)
nAmbient temperature
nNominal melting I2t
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.
nRecommend fuse: ≤ 5 A Bussmann PC-Tron
Reverse Operation
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.
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 VPRI • K. The module will
continue operation in this fashion for as long as no faults occur.
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.
Transient operation in reverse is expected in cases where there is
significant energy storage on the output and transient voltages appear
on the input.
Some general recommendations to achieve matched array impedances
include:
The BCM400T500P1K8A3R and BCM400M500P1K8A3R are both
qualified for continuous operation in reverse power condition. A
primary voltage of VPRI_DC > VPRI_UVLO+_R must be applied first allowing
primary reference controller and power train to start. Continuous
operation in reverse is then possible aꢀer a successful startup.
nDedicate common copper planes within the PCB
to deliver and return the current to the modules.
nProvide as symmetric a PCB layout as possible among modules
nAn input filter is required for an array of BCMs in order to
prevent circulating currents.
For further details see AN:016 Using BCM Bus Converters
in High Power Arrays.
BCM® Bus Converter
Page 22 of 25
Rev 1.4
07/2015
vicorpower.com
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