Application Note
Parallel Operation
rated output power at up to 80°C ambient temperature. At 100 W
of output power, operating ambient temperature extends to
105°C.
The BCM will inherently current share when properly
configured in an array of BCMs. Arrays may be used for
higher power or redundancy in an application.
CASE 2—Conduction to the PCB
Current sharing accuracy is maximized when the source and
load impedance presented to each BCM within an array are equal.
The low thermal resistance Junction-to-BGA, RθJB, allows
use of the PCB to exchange heat from the V•I Chip,
including convection from the PCB to the ambient or
conduction to a cold plate.
The recommended method to achieve matched impedances is to
dedicate common copper planes within the PCB to deliver and
return the current to the array, rather than rely upon traces of
varying lengths. In typical applications the current being
delivered to the load is larger than that sourced from the input,
allowing traces to be utilized on the input side if necessary. The
use of dedicated power planes is, however, preferable.
For example, with a V•I Chip surface mounted on a 2" x 2"
area of a multi-layer PCB, with an aggregate 8 oz of effective
copper weight, the total Junction-to-Ambient thermal
resistance, RθJA, is 6.5°C/W in 300 LFM air flow (see
Thermal Resistance section, page 1). Given a maximum
junction temperature of 125°C and 9 W dissipation at 240 W of
output power, a temperature rise of 60°C allows the V•I Chip to
operate at rated output power at up to 65°C ambient temperature.
The BCM power train and control architecture allow
bi-directional power transfer, including reverse power
processing from the BCM output to its input. Reverse power
transfer is enabled if the BCM input is within its operating
range and the BCM is otherwise enabled. The BCM’s ability to
process power in reverse improves the BCM transient response
to an output load dump.
240
210
180
150
120
90
Thermal Management
The high efficiency of the V•I Chip results in relatively low
power dissipation and correspondingly low generation of heat.
The heat generated within internal semiconductor junctions is
coupled with low effective thermal resistances, RθJC and RθJB,
to the V•I Chip case and its Ball Grid Array allowing thermal
management flexibility to adapt to specific application
requirements (Fig.23).
60
30
0
-40
-20
0
20
40
60
80
100
120
140
Operating Junction Temperature
CASE 1 Convection via optional Pin Fins to air.
Figure 24— Thermal derating curve
If the application is in a typical environment with forced
convection over the surface of the PCB and greater than 0.4"
headroom, a simple thermal management strategy is to procure
V•I Chips with the Pin Fin option. The total Junction-to-
Ambient thermal resistance, RθJA, of a surface mounted
V•I Chip with optional 0.25" Pin Fins is 5°C/W in 300 LFM air
flow (Fig.25). At full rated output power of 240 W, the heat
generated by the BCM is approximately 9 W (Fig.6). Therefore,
the junction temperature rise to ambient is approximately
45°C. Given a maximum junction temperature of 125°C, a
temperature rise of 45°C allows the V•I Chip to operate at
BCM with 0.25'' optional Pin Fins
10
9
8
7
6
5
θJC = 1.1°C/W
θJB = 2.1°C/W
4
3
0
100
200
300
400
500
600
Airflow (LFM)
Figure 25—Junction-to-ambient thermal resistance of BCM
with 0.25" Pin Fins (Pin Fins available as a separate item.)
Figure 23—Thermal resistance
Vicor Corporation
Tel: 800-735-6200
vicorpower.com
V•I Chip Bus Converter
B048K096T24
Rev. 1.9
Page 12 of 16
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