BCM400P500T1K8A31 Datasheet, PDF (18/23 Pages) Vicor Corporation – Fixed Ratio DC-DC Converter

Sine Amplitude Converter™ Point of Load Conversion
L_{IN_LEADS} ^{= 6.7 nH}
+
R_CIN
21.5 mΩ
V^VIN_IN
C_IN
0.37
µF^CIN
L_{IN_INT} ^{= 0.56 µH}
–
RC_IN
I^I_Q^Q
25 mA
1/8 • I_OUT
I_O^IO_UU_TT
1.76 nH
V•I
++
138 mΩ
1/8 • V_IN
––
K
BCM400y500x1K8A31
R_OUT
2_R2_O.6_UTmΩ
C_OUT
L_{OUT_LEADS} ^{= 1.3 nH}
RR5_{CC1O0OUUµTTΩ}
C_OUT
25.6 µF
+
V^V_O^OU_U^T_T
–
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 BCM400y500x1K8A31 SAC can be simplified into the preceeding
model.
At no load:
V_OUT = V_IN ^• K
(1)
K represents the “turns ratio” of the SAC.
Rearranging Eq (1):
K = ^VOUT
(2)
V_IN
In the presence of load, V_OUT is represented by:
V_OUT = V_IN ^• K – I_OUT ^• R_OUT
(3)
and I_OUT is represented by:
I_OUT =
I_IN – I_Q
K
(4)
R_OUT represents the impedance of the SAC, and is a function of the
R_DSON of the input and output MOSFETs and the winding resistance of
the power transformer. I_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 R_OUT = 0 Ω and I_Q = 0 A, Eq. (3) now becomes
Eq. (1) and is essentially load independent, resistor R is now placed in
series with V_IN.
R_RIN
V^VIi^Nn
+
–
S^SA^AC^C™
K^K=⁼1¹/3^/82
V_VOoUuTt
Figure 17 — K = 1/8 Sine Amplitude Converter
with series input resistor
The relationship between V_IN and V_OUT becomes:
V_OUT = (V_IN – I_IN ^• R_IN) ^• K
(5)
Substituting the simplified version of Eq. (4)
(I_Q is assumed = 0 A) into Eq. (5) yields:
V_OUT = V_IN ^• K – I_OUT ^• R_IN ^• K²
(6)
BCM^® Bus Converter
Page 18 of 23
Rev 1.3
05/2015
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