Application Note
Parallel Operation
Input Impedance Recommendations
The BCM™ bus converter will inherently current share when operated
in an array. Arrays may be used for higher power or redundancy in an
application.
To take full advantage of the BCM™ bus converter capabilities, the
impedance presented to its input terminals must be low from DC to
approximately 5 MHz. The source should exhibit low inductance and
should have a critically damped response. If the interconnect inductance
is excessive, the module input pins should be bypassed with an RC
damper (e.g., 47 µF in series with 0.3 ohm) to retain low source
impedance and proper operation. Given the wide bandwidth of the
module, the source response is generally the limiting factor in the
overall system response.
Current sharing accuracy is maximized when the source and load
impedance presented to each bus converter within an array are equal.
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.
Anomalies in the response of the source will appear at the output of
the module multiplied by its K factor. The DC resistance of the source
should be kept as low as possible to minimize voltage deviations. This is
especially important if the module is operated near low or high line as
the overvoltage/undervoltage detection circuitry could be activated.
The bus converter power train and control architecture allow bi-
directional power transfer, including reverse power processing from the
module output to its input. Reverse power transfer is enabled if the
module input is within its operating range and the module is otherwise
enabled. The bus converter’s ability to process power in reverse
improves the module’s transient response to an output load dump.
Input Fuse Recommendations
•
V I Chip modules are not internally fused in order to provide flexibility
in configuring power systems. However, input line fusing of the
modules must always be incorporated within the power system. A fast
acting fuse should be placed in series with the +In port.
Thermal Considerations
•
V I Chip™ products are multi-chip modules whose temperature
distribution varies greatly for each part number as well as with the
input/output conditions, thermal management and environmental
conditions. Maintaining the top of the B048F240T30 case to less than
100°C will keep all junctions within the module below 125°C for most
applications. The percent of total heat dissipated through the top
surface versus through the J-lead is entirely dependent on the particular
mechanical and thermal environment. The heat dissipated through the
top surface is typically 60%. The heat dissipated through the J-lead
onto the PCB board surface is typically 40%. Use 100% top surface
dissipation when designing for a conservative cooling solution.
It is not recommended to use a module for an extended period of time
at full load without proper heat sinking.
Application Notes
For application notes on soldering, thermal management, board layout,
and system design click on the link below:
http://www.vicorpower.com/technical_library/application_information/chips/
vicorpower.com
800-735-6200
BCM™ Bus Converter
B048F240T30
Rev. 2.8
Page 10 of 12
VICOR [ VICOR CORPORATION ]
