Not Recommended for New Designs
B048x096y24A
10.0 INPUT AND OUTPUT FILTER DESIGN
storage may be more densely and efficiently provided by
adding capacitance at the input of the module. At frequencies
<500 kHz the module appears as an impedance of ROUT
between the source and load.
A major advantage of SAC™ systems versus conventional
PWM converters is that the transformers do not require large
functional filters. The resonant LC tank, operated at extreme
high frequency, is amplitude modulated as a function of input
voltage and output current and efficiently transfers charge
through the isolation transformer. A small amount of
capacitance embedded in the input and output stages of the
module is sufficient for full functionality and is key to achieve
power density.
Within this frequency range, capacitance at the input appears
as effective capacitance on the output per the relationship
defined in Eq. 5.
CIN
K2
COUT
=
Eq. 6
This paradigm shift requires system design to carefully evaluate
external filters in order to:
This enables a reduction in the size and number of capacitors
used in a typical system.
1.Guarantee low source impedance:
To take full advantage of the BCM module’s dynamic
response, the impedance presented to its input terminals
must be low from DC to approximately 5 MHz. The
connection of the bus converter module to its power
source should be implemented with minimal distribution
inductance. If the interconnect inductance exceeds
100 nH, the input should be bypassed with a RC damper
to retain low source impedance and stable operation. With
an interconnect inductance of 200 nH, the RC damper
may be as high as 1 µF in series with 0.3 Ω. A single
electrolytic or equivalent low-Q capacitor may be used in
place of the series RC bypass.
11.0 THERMAL CONSIDERATIONS
VI 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
B048x096y24A case to less than 100ºC will keep all junctions
within the VI Chip module below 125ºC 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 surface is typically
40%. Use 100% top surface dissipation when designing for a
conservative cooling solution.
2.Further reduce input and/or output voltage ripple without
sacrificing dynamic response:
Given the wide bandwidth of the module, the source
response is generally the limiting factor in the overall
system response. Anomalies in the response of the source
will appear at the output of the module multiplied by its
K factor. This is illustrated in Figures 11 and 12.
It is not recommended to use a VI Chip module for an
extended period of time at full load without proper
heat sinking.
3.Protect the module from overvoltage transients imposed
by the system that would exceed maximum ratings and
cause failures:
The module input/output voltage ranges shall not be
exceeded. An internal overvoltage lockout function
prevents operation outside of the normal operating input
range. Even during this condition, the powertrain is exposed
to the applied voltage and power MOSFETs must withstand
it. A criterion for protection is the maximum amount of
energy that the input or output switches can tolerate if
avalanched.
Total load capacitance at the output of the BCM module shall
not exceed the specified maximum. Owing to the wide
bandwidth and low output impedance of the module,
low-frequency bypass capacitance and significant energy
BCM® Bus Converter
Page 13 of 18
Rev 1.1
vicorpower.com
800 927.9474
08/2014
VICOR [ VICOR CORPORATION ]
