BCM380Y475X1K2A31 Datasheet, PDF (21/23 Pages) Vicor Corporation – Fixed Ratio DC-DC Converter

Figure 20 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:
T_INT – PD₁ • 1.24 = T_{CASE_TOP}
T_INT – PD₃ • 7 = T_LEADS
PD_TOTAL = PD₁ + PD₃
Power Dissipation (W)
Thermal Resistance Top
1.24°C / W
Thermal Resistance Bottom
1.24°C / W
T_{CASE_BOTTOM}(°C)
MAX INTERNAL TEMP
Thermal Resistance Leads
7°C / W
T_LEADS(°C)
T_{CASE_TOP}(°C)
+
–
Vin
+ _DC
BCM380y475x1K2A31
Z_{IN_EQ1}
Z_{IN_EQ2}
BCM^®1
R_{0_1}
Z_{OUT_EQ1}
Vout
BCM^®2
R_{0_2}
Z_{OUT_EQ2}
Load
Z_{IN_EQn}
BCM^®n
R_{0_n}
Z_{OUT_EQn}
Figure 21 — One side cooling thermal model
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 left open and
the equations now simplify to:
T_INT – PD₁ • 1.24 = T_{CASE_TOP}
PD_TOTAL = 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:
http://www.vicorpower.com/powerbench.
Current Sharing
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.
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.
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.
Some general recommendations to achieve matched array impedances
include:
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.
Figure 22 — BCM module array
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.
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)
n Maximum voltage rating
(usually greater than the maximum possible input voltage)
n Ambient temperature
n Nominal melting I²t
n Recommend fuse: ≤ 5 A Bussmann PC-Tron
Reverse 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 V_IN • K. The module will
continue operation in this fashion for as long as no faults occur.
The BCM380y475x1K2A31 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.
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 10 ms, 10%
duty cycle is permitted and has been qualified to cover these cases.
BCM^® Bus Converter
Page 21 of 23
Rev 1.4
05/2015
vicorpower.com
800 927.9474