BCM4414XD1E13A2YZZ Datasheet, PDF (19/42 Pages) Vicor Corporation – Isolated Fixed-Ratio DC-DC Converter

BCM in a VIA Package
BCM4414xD1E13A2yzz
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 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 BCM4414xD1E13A2yzz can be simplified into the model shown
in Figure 19.
At no load:
The effective DC voltage transformer action provides additional
interesting attributes. Assuming that R_LO = 0Ω and I_{HI_Q} = 0A,
Eq. (3) now becomes Eq. (1) 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/^/3³2²
V_Lo_Out
V_LO = V_HI • K
(1)
K represents the “turns ratio” of the BCM.
Rearranging Eq (1):
Figure 20 — K = 1/32 BCM with series HI side resistor
K = ^VLO
(2)
^VHI
In the presence of a 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 controller, 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
resistor, 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 1.0mΩ, with K = 1/32.
BCM^® in a VIA Package
Page 19 of 42
Rev 1.5
10/2016
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