BCM4414xD1E2663yzz
BCM in a VIA Package
IHI
ILO
RLO
+
+
V•I
K
K • ILO
K • VHI
+
–
+
–
VHI
VLO
IHI_Q
–
–
Figure 19 — BCM DC model (Forward Direction)
The BCM uses a high frequency resonant tank to move energy
from the high voltage side to the low voltage side and vice versa.
The resonant LC tank, operated at high frequency, is amplitude
modulated as a function of the HI side voltage and the LO side
current. A small amount of capacitance embedded in the high
voltage side and low voltage side stages of the module is sufficient
for full functionality and is key to achieving high power density.
The effective DC voltage transformer action provides additional
interesting attributes. Assuming that RLO = 0Ω and IHI_Q = 0A,
Equation 3 now becomes Equation 1 and is essentially load
independent, resistor R is now placed in series with VHI.
The BCM4414xD1E2663yzz can be simplified into the model shown
in Figure 19.
R
R
BCM
SAC
V
VLoOut
+
–
K = 1/16
At no load:
K = 1/32
Vin
VHI
VLO = VHI • K
(1)
K represents the “turns ratio” of the BCM.
Rearranging Eq (1):
Figure 20 — K = 1/16 BCM with series HI side resistor
VLO
K =
The relationship between VHI and VLO becomes:
(2)
VHI
V = V – I • R • K
(5)
(
)
LO
HI
HI
In the presence of a load, VLO is represented by:
Substituting the simplified version of Equation 4
(IHI_Q is assumed = 0A) into Equation 5 yields:
VLO = VHI • K – ILO • RLO
(3)
VLO = VHI • K – ILO • R • K2
(6)
and ILO is represented by:
This is similar in form to Equation 3, where RLO is used to represent
the characteristic impedance of the BCM. However, in this case a
real resistor, R, on the high voltage side of the BCM is effectively
scaled by K2 with respect to the low voltage side.
IHI – IHI_Q
(4)
ILO
=
K
RLO represents the impedance of the BCM and is a function of the
RDS_ON of the HI side and LO side MOSFETs, PC board resistance of
HI side and LO side boards and the winding resistance of the power
transformer. IHI_Q represents the HI side quiescent current of the
BCM controller, gate drive circuitry and core losses.
Assuming that R = 1Ω, the effective R as seen from the low voltage
side is 3.91mΩ, with K = 1/16.
BCM® in a VIA Package
Page 19 of 43
Rev 1.1
01/2018
VICOR [ VICOR CORPORATION ]
