BCM6123XD1E1368YZZ Datasheet, PDF (24/30 Pages) Vicor Corporation – Isolated Fixed-Ratio DC-DC Converter

BCM in a ChiP
L_{PRI_IN_LEADS} ^{= 7nH}
+
VV_PRINI
C_{PRI_INT_ESR}
31.8mΩ
C_{0.P2R5I_CµINFINT}
RC_IN
I IPRI__QQ
24mA
–
L_{PRI_INT} = 0.56µH
Figure 19 — BCM AC model
1/32 • I_SEC
BCM6123xD1E1368yzz
I_O^IS_UEC_T
0.124nH
V•I
++
122mΩ
1/32 • V_PRI
––
K
R_SEC
R²_O^.3_U^m_T^Ω
C_OUT
L_{SEC_OUT_LEADS} ^{= 0.64nH}
RCC_{SEOC_UINTT_ESR}
106µΩ
C_{SEC_INT}
104µF
+
V^V_O^SE_U^C_T
–
The BCM uses a high frequency resonant tank to move energy
from primary to secondary and vice versa. The resonant LC tank,
operated at high frequency, is amplitude modulated as a function
of the primary voltage and the secondary current. A small amount
of capacitance embedded in the primary and secondary stages of
the module is sufficient for full functionality and is key to achieving
high power density.
The BCM6123xD1E1368yzz can be simplified into the model
shown in Figure 19.
At no load:
V_SEC = V_PRI • K
(1)
K represents the “turns ratio” of the BCM.
Rearranging Eq (1):
K=
V_SEC
V_PRI
(2)
In the presence of a load, V_SEC is represented by:
V_SEC = V_PRI • K – I_SEC • R_SEC
(3)
and I_SEC is represented by:
I_SEC
=
I_PRI – I_{PRI_Q}
K
(4)
R_SEC represents the impedance of the BCM, and is a function of the
R_{DS_ON} of the primary and secondary MOSFETs and the winding
resistance of the power transformer. I_{PRI_Q} represents the quiescent
current of the BCM controller, gate drive circuitry and core losses.
The effective DC voltage transformer action provides additional
interesting attributes. Assuming that R_SEC = 0Ω and I_{PRI_Q} = 0A,
Eq. (3) now becomes Eq. (1) and is essentially load independent,
resistor R is now placed in series with V_PRI.
R
+
V^V_Pⁱ_Rⁿ_{I –}
S^BA^CC^M
K^K=⁼ 1¹/^/3³2²
V_So_Eu_C t
Figure 20 — K = 1/32 BCM with series primary resistor
The relationship between V_PRI and V_SEC becomes:
( ) ^V_SEC ^{= V}_PRI ^{– I}_PRI ^{• R • K}
(5)
Substituting the simplified version of Eq. (4)
(I_{PRI_Q} is assumed = 0A) into Eq. (5) yields:
V_SEC = V_PRI • K – I_SEC • R • K²
(6)
This is similar in form to Eq. (3), where R_SEC is used to represent the
characteristic impedance of the BCM. However, in this case a real
resistor, R, on the primary side of the BCM is effectively scaled by
K² with respect to the secondary.
Assuming that R = 1Ω, the effective R as seen from the secondary
side is 0.98mΩ, with K = 1/32.
BCM^® Bus Converter
Page 24 of 30
Rev 1.1
04/2017
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