B048K120T15 Datasheet, PDF (12/16 Pages) Vicor Corporation – VI Chip - BCM Bus Converter Module

BCM Application Circuit
PRELIMINARY
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. 25).
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 150 W, the heat
generated by the BCM is approximately 6 W (Fig.6). Therefore,
the junction temperature rise to ambient is approximately 30°C.
Given a maximum junction temperature of 125°C, a
temperature rise of 30°C allows the V•I Chip to operate at rated
output power at up to 95°C ambient temperature. At 75 W of
output power, operating ambient temperature extends to 105°C.
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.
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.
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
CASE 2—Conduction to the PCB
90
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.
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 6 W dissipation at 150 W of
output power, a temperature rise of 39°C allows the V•I Chip to
operate at rated output power at up to 86°C ambient temperature.
60
30
0
-40
-20
0
20
40
60
80
100
Operating Junction Temperature
120
140
Figure 26— Thermal derating curve
BCM with 0.25'' optional Pin Fins
10
9
The thermal resistance of the PCB to the surrounding
8
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
4
θJB = 2.1 °C/W
3
0
100
200
300
400
500
600
Airflow (LFM)
Figure 25—Thermal resistance
45 Vicor Corporation
Tel: [phone]
vicorpower.com
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.)
V•I Chip Bus Converter
B048K120T15
Rev. 1.2
Page 12 of 16