BCM Application Circuit
PRELIMINARY
Thermal Management
The PCB may also be coupled to a cold plate by low thermal
resistance standoff elements as a means of achieving effective
cooling for an array of V•I Chips, without a direct interface to
their case.
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. 25).
CASE 3—Combined direct convection to the air and
conduction to the PCB.
Parallel use of the V•I Chip internal thermal resistances
(including Junction-to-Case and Junction-to-BGA) in series
with external thermal resistances provides an efficient thermal
management strategy as it reduces total thermal resistance. This
may be readily estimated as the parallel network of two pairs of
series configured resistors.
CASE 1 Convection via optional Pin Fins to air (Pin Fins
available mounted to the V•I Chip or as a separate item.)
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 integral 0.25" Pin Fins is 5 °C/W in 300 LFM air
flow (Fig.27). At full rated output power of 100 W, the heat
generated by the BCM is approximately 4 W (Fig.6). Therefore,
the junction temperature rise to ambient is approximately 20°C.
Given a maximum junction temperature of 125°C, a
The TM (Temperature Monitor) port monitors the V•I Chip
junction temperature and provides feedback and validation of
the thermal management of V•I Chips, as applied in diverse
power systems and environments.
210
180
150
120
90
temperature rise of 20°C allows the V•I Chip to operate at rated
output power at up to 105°C ambient temperature. At 50 W of
output power, operating ambient temperature extends to 115°C.
CASE 2—Conduction to the PCB
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.
60
30
0
-40
-20
0
20
40
60
80
100
120
140
Operating Junction Temperature
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
Figure 26— Thermal derating curve
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 4 W dissipation at 100 W of
output power, a temperature rise of 26°C allows the V•I Chip to
operate at rated output power at up to 99°C ambient temperature.
BCM with 0.25'' optional Pin Fins
10
9
8
The thermal resistance of the PCB to the surrounding
environment in proximity to V•I Chips may be reduced by low
profile heat sinks surface mounted to the PCB.
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 27—Junction-to-ambient thermal resistance of BCM
with 0.25" Pin Fins (Pin Fins available mounted to the V•I
Chip or as a separate item.)
Figure 25—Thermal resistance
Vicor Corporation
Tel: 800-735-6200
vicorpower.com
V•I Chip Bus Converter
B048K120T10
Rev. 1.2
Page 12 of 16
45
VICOR [ VICOR CORPORATION ]
