BCM3814x60E10A5yzz
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 in a VIA package uses a high frequency resonant tank
to move energy from high voltage side to low voltage side and
vice versa. The resonant LC tank, operated at high frequency, is
amplitude modulated as a function of HI side voltage and 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 use of DC voltage transformation provides additional
interesting attributes. Assuming that RLO = 0Ω and IHI_Q = 0A,
Eq. (3) now becomes Eq. (3) and is essentially load independent,
resistor R is now placed in series with VHI.
The BCM3814x60E10A5yzz can be simplified into the preceeding
model.
R
R
BCM
SAC
V
VLoOut
+
–
K = 1/6
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 = 1/6 BCM with series HI side resistor
VLO
K =
(2)
(3)
(4)
The relationship between VHI and VLO becomes:
VHI
In the presence of load, VLO is represented by:
•
•
K
VLO = (VHI – IHI R)
(5)
VLO = VHI • K – ILO • RLO
and ILO is represented by:
IHI – IHI_Q
Substituting the simplified version of Eq. (4)
(IHI_Q is assumed = 0A) into Eq. (5) yields:
2
•
•
•
R K
VLO = VHI K – ILO
(6)
ILO
=
K
This is similar in form to Eq. (3), where RLO is used to represent the
characteristic impedance of the BCM. However, in this case a real R
on the high voltage side of the BCM is effectively scaled by K2 with
respect to the low voltage side.
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 control, gate drive circuitry, and core losses.
Assuming that R = 1Ω, the effective R as seen from the low voltage
side is 28mΩ, with K = 1/6.
BCM® in a VIA Package
Page 18 of 39
Rev 1.4
09/2016
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