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B048K120T10 Datasheet, PDF (12/16 Pages) Vicor Corporation – VI Chip - BCM Bus Converter Module | |||
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BCM Application Circuit
PRELIMINARY
Thermal Management
The high efficiency of the Vâ¢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 Vâ¢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 Vâ¢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
Vâ¢I Chips with the Pin Fin option. The total Junction-to-
Ambient thermal resistance, RθJA, of a surface mounted
Vâ¢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
temperature rise of 20°C allows the Vâ¢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 2âConduction to the PCB
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 Vâ¢I Chips, without a direct interface to
their case.
CASE 3âCombined direct convection to the air and
conduction to the PCB.
Parallel use of the Vâ¢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 Vâ¢I Chip
junction temperature and provides feedback and validation of
the thermal management of Vâ¢I Chips, as applied in diverse
power systems and environments.
210
180
150
120
90
The low thermal resistance Junction-to-BGA, RθJB, allows
use of the PCB to exchange heat from the Vâ¢I Chip,
including convection from the PCB to the ambient or
conduction to a cold plate.
For example, with a Vâ¢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 4 W dissipation at 100 W of
output power, a temperature rise of 26°C allows the Vâ¢I Chip to
operate at rated output power at up to 99°C ambient temperature.
60
30
0
-40
-20
0
20
40
60
80
100
Operating Junction Temperature
Figure 26â Thermal derating curve
120
140
BCM with 0.25'' optional Pin Fins
10
9
The thermal resistance of the PCB to the surrounding
8
environment in proximity to Vâ¢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 25âThermal resistance
45 Vicor Corporation
Tel: 800-735-6200
vicorpower.com
Figure 27âJunction-to-ambient thermal resistance of BCM
with 0.25" Pin Fins (Pin Fins available mounted to the Vâ¢I
Chip or as a separate item.)
Vâ¢I Chip Bus Converter
B048K120T10
Rev. 1.2
Page 12 of 16
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