BCM6123XD1E5126YZZ Datasheet, PDF (27/30 Pages) Vicor Corporation – Isolated Fixed-Ratio DC-DC Converter

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:
T_INT – PD₁ • Φ_INT-TOP = T_{CASE_TOP}
T_INT – PD₃ • Φ_INT-LEADS = T_LEADS
PD_TOTAL = PD₁+ PD₃
Power Dissipation (W)
Thermal Resistance Top
ΦINT-TOP
Thermal Resistance Bottom
ΦINT-BOTTOM
T
(°C)
CASE_BOTTOM
MAX INTERNAL TEMP
Thermal Resistance Leads
ΦINT-LEADS
T_LEADS(°C)
T
(°C) +
CASE_TOP
–
V_PRI
+ _DC
BCM6123xD1E5126yzz
Z_{IN_EQ1}
Z_{IN_EQ2}
BCM^®1
R_{0_1}
Z_{OUT_EQ1}
V_SEC
BCM^®2
R_{0_2}
Z_{OUT_EQ2}
Load
Z_{IN_EQn}
BCM^®n
R_{0_n}
Z_{OUT_EQn}
Figure 24 — Top case thermal model
Figure 24 shows a scenario where there is no bottom side and
leads cooling. In this case, the heat flow paths to the bottom and
leads are left open and the equations now simplify to:
T_INT – PD₁ • Φ_INT-TOP = 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:
nnDedicate common copper planes within the PCB
to deliver and return the current to the modules.
nnProvide as symmetric a PCB layout as possible among modules
nnAn 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
Figure 25 — BCM module array
Fuse Selection
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.
The fuse shall be selected by closely matching system
requirements with the following characteristics:
nnCurrent rating
(usually greater than maximum current of BCM module)
nnMaximum voltage rating
(usually greater than the maximum possible input voltage)
nnAmbient temperature
nnNominal melting I²t
nnRecommend fuse: See safety agency approvals.
Reverse 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 V_PRI • K.
The module will continue operation in this fashion for as long as
no faults occur.
Transient operation in reverse is expected in cases where there is
significant energy storage on the output and transient voltages
appear on the input.
The BCM6123xD1E5126y0R and BCM6123xD1E5126y0P are both
qualified for continuous operation in reverse power condition. A
primary voltage of V_{PRI_DC} > V_{PRI_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.
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