BCM3814X60E10A5YZZ Datasheet, PDF (18/39 Pages) Vicor Corporation – Isolated Fixed-Ratio DC-DC Converter

BCM in a VIA Package
BCM3814x60E10A5yzz
I_HI
+
V_HI
I_{HI_Q}
K • I_LO
–
I_LO
R_LO
+
V•I
++
K • V_HI
V_LO
––
K
–
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 BCM3814x60E10A5yzz can be simplified into the preceeding
model.
At no load:
V_LO = V_HI • K
(1)
K represents the “turns ratio” of the BCM.
Rearranging Eq (1):
The use of DC voltage transformation provides additional
interesting attributes. Assuming that R_LO = 0Ω and I_{HI_Q} = 0A,
Eq. (3) now becomes Eq. (3) and is essentially load independent,
resistor R is now placed in series with V_HI.
R^R
+
V_Vi_Hn_{I –}
S^BA^CC^M
K^K=⁼1¹/3^/62
V_Lo_Out
Figure 20 — K = 1/6 BCM with series HI side resistor
K = ^VLO
(2)
^VHI
In the presence of load, V_LO is represented by:
V_LO = V_HI • K – I_LO • R_LO
(3)
and I_LO is represented by:
I_LO = ^IHI

– I_{HI_Q}
K
(4)
R_LO represents the impedance of the BCM, and is a function of the
R_{DS_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. I_HI__Q represents the HI side quiescent current of the
BCM control, gate drive circuitry, and core losses.
The relationship between V_HI and V_LO becomes:
V_LO = (V_HI – I_HI ^• R) ^• K
(5)
Substituting the simplified version of Eq. (4)
(I_{HI_Q} is assumed = 0A) into Eq. (5) yields:
V_LO = V_HI ^• K – I_LO ^• R ^• K²
(6)
This is similar in form to Eq. (3), where R_LO 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.
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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