BCM380y475x800A31
Sine Amplitude Converter™ Point of Load Conversion
ROUT
1.76 nH
35 mΩ
ROUT
= 1.3 nH
IOIOUUTT
LOUT_LEADS
= 6.7 nH
LIN_LEADS
+
+
RCIN
R
R COUT
COUT
R
138 mΩ
1/8 • VIN
CIN
1020 µΩ
31.8 mΩ
CIN
V•I
K
1/8 • IOUT
COUT
+
–
+
–
CIN
COUT
VOUT
VOUT
0.25 µF
VIN
VIN
IQ
12.8 µF
IQ
23.4 mA
= 0.56 µH
LIN_INT
–
–
Figure 16 — BCM module AC model
The Sine Amplitude Converter (SAC™) uses a high frequency resonant
tank to move energy from input to output. (The resonant tank is
formed by Cr and leakage inductance Lr in the power transformer
windings as shown in the BCM module Block Diagram). The resonant
LC tank, operated at high frequency, is amplitude modulated as a
function of input voltage and output current. A small amount of
capacitance embedded in the input and output 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 ROUT = 0 Ω and IQ = 0 A, Eq. (3) now becomes
Eq. (1) and is essentially load independent, resistor R is now placed in
series with VIN
.
RIN
R
SAC™
The BCM380y475x800A31 SAC can be simplified into the preceeding
model.
SAC
VOUT
Vout
+
K = 1/8
V
ViINn
–
K = 1/32
At no load:
•
VOUT = VIN
K
(1)
(2)
Figure 17 — K = 1/8 Sine Amplitude Converter
with series input resistor
K represents the “turns ratio” of the SAC.
Rearranging Eq (1):
The relationship between VIN and VOUT becomes:
VOUT
K =
•
•
K
VOUT = (VIN – IIN RIN)
(5)
VIN
Substituting the simplified version of Eq. (4)
(IQ is assumed = 0 A) into Eq. (5) yields:
In the presence of load, VOUT is represented by:
•
•
2
VOUT = VIN K – IOUT ROUT
(3)
(4)
•
•
•
VOUT = VIN K – IOUT RIN K
(6)
and IOUT is represented by:
I
IN – IQ
K
IOUT
=
ROUT represents the impedance of the SAC, and is a function of the
RDSON of the input and output MOSFETs and the winding resistance of
the power transformer. IQ represents the quiescent current of the SAC
control, gate drive circuitry, and core losses.
BCM® Bus Converter
Page 18 of 23
Rev 1.3
05/2015
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