BCM6123E60E15A3T00 Datasheet, PDF (24/28 Pages) Vicor Corporation – BCM® Bus Converter

Input and Output Filter Design
A major advantage of SAC™ systems versus conventional PWM
converters is that the transformer based SAC does not require
external filtering to function properly. The resonant LC tank,
operated at extreme high frequency, is amplitude modulated as a
function of primary voltage and secondary current and efficiently
transfers charge through the isolation transformer. A small amount
of capacitance embedded in the primary and secondary stages of
the module is sufficient for full functionality and is key to achieving
power density.
This paradigm shift requires system design to carefully evaluate
external filters in order to:
n Guarantee low source impedance:
To take full advantage of the BCM module’s dynamic
response, the impedance presented to its primary terminals
must be low from DC to approximately 5MHz. The
connection of the bus converter module to its power
source should be implemented with minimal distribution
inductance. If the interconnect inductance exceeds
100nH, the primary should be bypassed with a RC damper
to retain low source impedance and stable operation. With
an interconnect inductance of 200nH, the RC damper
may be as high as 1µF in series with 0.3Ω. A single
electrolytic or equivalent low-Q capacitor may be used in
place of the series RC bypass.
n Further reduce primary and/or secondary 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 primary
source will appear at the secondary of the module multiplied by
its K factor.
n Protect the module from overvoltage transients imposed
by the system that would exceed maximum ratings and
induce stresses:
The module primary/secondary voltage ranges shall not be
exceeded. An internal overvoltage lockout function
prevents operation outside of the normal operating primary
range. Even when disabled, the powertrain is exposed
to the applied voltage and power MOSFETs must
withstand it.
Total load capacitance at the secondary of the BCM module shall
not exceed the specified maximum. Owing to the wide bandwidth
and low secondary impedance of the module, low-frequency
bypass capacitance and significant energy storage may be more
densely and efficiently provided by adding capacitance at the
primary of the module. At frequencies <500kHz the module
appears as an impedance of R_SEC between the source and load.
Within this frequency range, capacitance at the primary appears as
effective capacitance on the secondary per the relationship
defined in Eq. (13).
C_{SEC_EXT} =
C_{PRI_EXT}
(13)
K²
This enables a reduction in the size and number of capacitors used
in a typical system.
BCM^® Bus Converter
Page 24 of 28
Rev 1.2
07/2016
BCM6123x60E15A3yzz
Thermal Considerations
The ChiP package provides a high degree of flexibility in that it
presents three pathways to remove heat from internal power
dissipating components. Heat may be removed from the top
surface, the bottom surface and the leads. The extent to which
these three surfaces are cooled is a key component for determining
the maximum power that is available from a ChiP, as can be seen
from Figure 1.
Since the ChiP has a maximum internal temperature rating, it is
necessary to estimate this internal temperature based on a real
thermal solution. Given that there are three pathways to remove
heat from the ChiP, it is helpful to simplify the thermal solution into
a roughly equivalent circuit where power dissipation is modeled as
a current source, isothermal surface temperatures are represented
as voltage sources and the thermal resistances are represented as
resistors. Figure 19 shows the “thermal circuit” for a VI Chip^® BCM
module 6123 in an application where the top, bottom, and leads
are cooled. In this case, the BCM power dissipation is PD_TOTAL and
the three surface temperatures are represented as T_{CASE_TOP}, T_{CASE_}
BOTTOM^{, and T}LEADS^{. This thermal system can now be very easily}
analyzed using a SPICE simulator with simple resistors, voltage
sources, and a current source. The results of the simulation would
provide an estimate of heat flow through the various pathways as
well as internal temperature.
Power Dissipation (W)
Thermal Resistance Top
ΦINT-TOP
MAX INTERNAL TEMP
Thermal Resistance Bottom
ΦINT-BOTTOM
T_{CASE_BOTTOM}(°C)
+
–
Thermal Resistance Leads
ΦINT-LEADS
T (°C) +
LEADS
–
T_{CASE_TOP}(°C)
+
–
Figure 19 — Top case, Bottom case and leads thermal model
Alternatively, equations can be written around this circuit and
analyzed algebraically:
T_INT – PD₁ • Φ_INT-TOP = T_{CASE_TOP}
T_INT – PD₂ • Φ_INT-BOTTOM = T_{CASE_BOTTOM}
T_INT – PD₃ • Φ_INT-LEADS = T_LEADS
PD_TOTAL = PD₁+ PD₂+ PD₃
Where T_INT represents the internal temperature and PD₁, PD₂, and
PD₃ represent the heat flow through the top side, bottom side, and
leads respectively.
Power Dissipation (W)
Thermal Resistance Top
ΦINT-TOP
Thermal Resistance Bottom
ΦINT-BOTTOM
T_{CASE_BOTTOM}(°C)
MAX INTERNAL TEMP
Thermal Resistance Leads
ΦINT-LEADS
T_LEADS(°C)
+
–
T_{CASE_TOP}(°C)
+
–
Figure 20 — Top case and leads thermal model
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