BCM6123xD1E5126yzz
Sine Amplitude Converter™ Point of Load Conversion
RSEC
1.77nH
24.2mΩ
= 1.3nH
IOISUECT
ROUT
lSEC_OUT_LEADS
= 6.7nH
lPRI_IN_LEADS
+
+
CPRI_INT_ESR
21.5mΩ
R
CSEC_INT_ESR
510µΩ
COUT
R
139mΩ
CIN
V•I
K
1/8 • ISEC
1/8 • VPRI
+
–
CPRI_INT
0.37µF
+
–
CSEC_INT
25.6µF
CIN
COUT
VSEC
VOUT
V
I
V
PRI
PRII_QQ
IN
25.8mA
LPRI_INT = 1.20µH
–
–
Figure 19 — BCM module AC model
The Sine Amplitude Converter (SAC™) 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 primary voltage and
secondary current. A small amount of capacitance embedded in
Eq. (3) now becomes Eq. (1) and is essentially load independent,
resistor R is now placed in series with VPRI
.
the primary and secondary stages of the module is sufficient for full
functionality and is key to achieving high power density.
R
R
SAC™
K = 1/8
K = 1/32
SAC
Vout
VSEC
+
–
Vin
VPRI
The BCM6123xD1E5126yzz SAC can be simplified into the
preceeding model.
At no load:
(1)
VSEC = VPRI • K
Figure 20 — K = 1/8 Sine Amplitude Converter
with series primary resistor
K represents the “turns ratio” of the SAC.
Rearranging Eq (1):
The relationship between VPRI and VSEC becomes:
VSEC
(2)
(3)
(4)
VSEC = VPRI – IPRI • R • K
(5)
K =
VPRI
(
)
Substituting the simplified version of Eq. (4)
(IPRI_Q is assumed = 0A) into Eq. (5) yields:
In the presence of load, VSEC is represented by:
VSEC = VPRI • K – ISEC • RSEC
2
(6)
VSEC = VPRI • K – ISEC • R • K
and ISEC is represented by:
This is similar in form to Eq. (3), where RSEC is used to represent the
characteristic impedance of the SAC™. However, in this case a real
R on the primary side of the SAC is effectively scaled by K2 with
respect to the secondary.
IPRI – IPRI_Q
ISEC
=
K
Assuming that R = 1Ω, the effective R as seen from the secondary
side is 16mΩ, with K = 1/8.
RSEC represents the impedance of the SAC, and is a function of
the RDSON of the primary and secondary MOSFETs and the winding
resistance of the power transformer. IPRI_Q represents the quiescent
current of the SAC control, gate drive circuitry, and core losses.
The use of DC voltage transformation provides additional
interesting attributes. Assuming that RSEC = 0Ω and IPRI_Q = 0A,
BCM® Bus Converter
Page 24 of 30
Rev 1.1
01/2017
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