BCM6123xD1E5126yzz
Figure 23 shows a scenario where there is no bottom side cooling.
In this case, the heat flow path to the bottom is left open and the
equations now simplify to:
ZIN_EQ1
ZOUT_EQ1
BCM®1
R0_1
VPRI
VSEC
TINT – PD1 • ΦINT-TOP = TCASE_TOP
TINT – PD3 • ΦINT-LEADS = TLEADS
PDTOTAL = PD1+ PD3
ZOUT_EQ2
ZIN_EQ2
BCM®2
R0_2
+
Load
DC
Thermal Resistance Top
MAX INTERNAL TEMP
ΦINT-TOP
Thermal Resistance Bottom
Thermal Resistance Leads
ΦINT-BOTTOM
ΦINT-LEADS
ZOUT_EQn
BCM®n
R0_n
ZIN_EQn
+
–
T
CASE_BOTTOM(°C)
TLEADS(°C)
TCASE_TOP(°C)
Power Dissipation (W)
Figure 25 — BCM module array
Figure 24 — Top case thermal model
Figure 24 shows a scenario where there is no bottom side and
Fuse Selection
leads cooling. In this case, the heat flow paths to the bottom and
leads are left open and the equations now simplify to:
In order to provide flexibility in configuring power systems
ChiP modules are not internally fused. Input line fusing
of ChiP products is recommended at system level to provide
thermal protection in case of catastrophic failure.
TINT – PD1 • ΦINT-TOP = 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:
n■Current rating
(usually greater than maximum current of BCM module)
http://www.vicorpower.com/powerbench..
n■Maximum voltage rating
(usually greater than the maximum possible input voltage)
Current Sharing
n■Ambient temperature
n■Nominal 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.
n■Recommend fuse: See safety agency approvals.
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 the 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 BCM6123xD1E5126y0R and BCM6123xD1E5126y0P are both
qualified for continuous operation in reverse power condition. A
primary voltage of VPRI_DC > VPRI_UVLO+_R must be applied first to
allow the primary reference controller and power train to start.
Continuous operation in reverse is then possible after a
successful startup.
n■Dedicate common copper planes within the PCB
to deliver and return the current to the modules.
n■Provide as symmetric a PCB layout as possible among modules
n■An 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 27 of 30
Rev 1.1
01/2017
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