BCM4414xG0F4440yzz
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.
R
R
The BCM4414xG0F4440yzz can be simplified into the model
shown in Figure 19.
BCM
SAC
V
VLoOut
+
–
K = 1/16
K = 1/32
Vin
VHI
At no load:
VLO = VHI • K
(1)
Figure 20 — K = 1/16 BCM with series HI-side resistor
The relationship between VHI and VLO becomes:
V = V – I • R • K
K represents the “turns ratio” of the BCM.
Rearranging Equation 1:
VLO
K =
(2)
(5)
(
)
LO
HI
HI
VHI
Substituting the simplified version of Equation 4
(IHI_Q is assumed = 0A) into Equation 5 yields:
In the presence of a load, VLO is represented by:
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
Assuming that R = 1Ω, the effective R as seen from the low-voltage
side is 3.9mΩ, with K = 1/16.
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.
BCM® in a VIA™ Package
Page 20 of 44
Rev 1.7
10/2020
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