V048K020T080 Datasheet, PDF (10/15 Pages) Vicor Corporation – VI Chip - VTM Voltage Transformation Module

Configuration Options (Cont.)
PRELIMINARY
F1
7A
Fuse
Input reflected ripple
measurement point
C1
100 µF
Al electrolytic
C2
0.47 µF
ceramic
14 V ^+–
Figure 16—VTM test circuit
+Out
+In
-Out
TM
VC
VTM
PC
+Out
K
Ro ^-In
-Out
+
Temperature Monitor
–
+
C3
100 µF
15 mΩ
Load
–
Notes:
C3 should be placed close to the load
Application Note
Parallel Operation
In applications requiring higher current or redundancy, VTMs
can be operated in parallel without adding control circuitry or
signal lines. To maximize current sharing accuracy, it is imperative
that the source and load impedance on each VTM in a parallel
array be equal. If VTMs are being fed by an upstream PRM, the
VC nodes of all VTMs must be connectd to the PRM VC.
To achieve matched impedances, dedicated power planes
within the PC board should be used for the output and output
return paths to the array of paralleled VTMs. This technique is
preferable to using traces of varying size and length.
The VTM power train and control architecture allow bi-directional
power transfer when the VTM is operating within its specified
ranges. Bi-directional power processing improves transient
response in the event of an output load dump. The VTM may
operate in reverse, returning output power back to the input
source. It does so efficiently.
Thermal Management
The high efficiency of the VTM results in low power
dissipation minimizing temperature rise, even at full output
current. The heat generated within the internal semiconductor
junctions is coupled through very low thermal resistances, RθJC
and RθJB (see Figure 17), to the PC board allowing flexible
thermal management.
CASE 1 Convection via optional heatsink to air
In an environment with forced convection over the surface
of a PCB with 0.4" of headroom, a VTM with a 0.25 heat sink
offers a simple thermal management option. The total
Junction toAmbient thermal resistance of a surface mounted
V048K020T080 with a heat sink attached is 4.8 ºC/W in
300 LFMairflow, (see Figure 18).
At 2 Vout and full rated current (80A), the VTM dissipates
approximately 12 W per Figure 4. This results in a temperature
rise of approximately 56 ºC, allowing operation in an air
temperature of 69 ºC without exceeding the 125 ºC max
junction temperature.
CASE 2 Conduction via the PC board to air
The low Junction to BGA thermal resistance allows the use
of the PC board as a means of removing heat from the VTM.
Convection from the PC board to ambient, or conduction to a
cold plate, enable flexible thermal management options.
With a VTM mounted on a 2.0 in² area of a multi-layer PC
board with appropriate power planes resulting in 8 oz of
effective copper weight, the Junction-to-BGA thermal
resistance, RθJA, is 6.5 ºC/W in 300 LFM of air. With a
maximum junction temperature of 125 ºC and 12 W of
dissipation at full current of 80 A, the resulting temperature
rise of 76 ºC allows the VTM to operate at full rated current
up to a 49 ºC ambient temperature. See thermal resistances
on page 9 for additional details on this thermal management option.
Adding low-profile heat sinks to the PC board can lower the
thermal resistance of the PC board surrounding the VTM.
Additional cooling may be added by coupling a cold plate to
the PC board with low thermal resistance stand offs.
CASE 3 Combined direct convection to the air and conduction
to the PC board.
A combination of cooling techniques that utilize the power
planes and dissipation to the air will also reduce the total
thermal impedance. This is the most effective cooling
method. To estimate the total effect of the combination, treat
each cooling branch as one leg of a parallel resistor network.
Vicor Corporation
Tel: [phone]
vicorpower.com
V•I Chip Voltage Transformation Module V048K020T080 Rev. 1.2 Page 10 of 15