bcm48bf120t300a00 Vicor Corporation, bcm48bf120t300a00 Datasheet - Page 12

• Manufacturer Part Number: bcm48bf120t300a00
• Description: Bcm™ Bus Converter
• Manufacturer: Vicor Corporation

PRELIMINARY DATASHEET
This is similar in form to Eq. (3), where R
represent the characteristic impedance of the SAC™. However,
in this case a real R on the input side of the SAC is effectively
scaled by K
Assuming that R = 1 Ω, the effective R as seen from the secondary
side is 62.5 mΩ, with K = 1/4 .
A similar exercise should be performed with the additon of a
capacitor or shunt impedance at the input to the SAC.
A switch in series with V
depicted in Figure 15.
A change in V
change in capacitor current according to the following
equation:
Assume that with the capacitor charged to V
opened and the capacitor is discharged through the idealized
SAC. In this case,
substituting Eq. (1) and (8) into Eq. (7) reveals:
The equation in terms of the output has yielded a K
factor for C, specified in the denominator of the equation.
A K factor less than unity results in an effectively larger
capacitance on the output when expressed in terms of the
input. With a K = 1/4 as shown in Figure 15,
C=1 µF would appear as C=16 µF when viewed
from the output.
Figure 15 — Sine Amplitude Converter™ with input capacitor
v i c o r p o w e r. c o m
I
I
I
C
C
OUT
V
(t) = C
= I
Vin
IN
OUT
=
K
C
+
–
2
•
2
dV
K
•
S
dt
S
with respect to the output.
IN
IN
dV
dt
with the switch closed would result in a
OUT
C
C
IN
V•I CHIP CORP. (A VICOR COMPANY) 25 FRONTAGE RD. ANDOVER, MA 01810 800-735-6200
is added to the circuit. This is
K = 1/32
K = 1/4
SAC™
SAC
OUT
is used to
IN
, the switch is
2
scaling
V
Vout
OUT
(7)
(8)
(9)
Low impedance is a key requirement for powering a high-
current, low-voltage load efficiently. A switching regulation
stage should have minimal impedance while simultaneously
providing appropriate filtering for any switched current. The
use of a SAC between the regulation stage and the point of
load provides a dual benefit of scaling down series impedance
leading back to the source and scaling up shunt capacitance or
energy storage as a function of its K factor squared. However,
the benefits are not useful if the series impedance of the SAC
is too high. The impedance of the SAC must be low, i.e. well
beyond the crossover frequency of the system.
A solution for keeping the impedance of the SAC low involves
switching at a high frequency. This enables small magnetic
components because magnetizing currents remain low. Small
magnetics mean small path lengths for turns. Use of low loss
core material at high frequencies also reduces core losses.
The two main terms of power loss in the BCM™ module are:
Therefore,
The above relations can be combined to calculate the overall
module efficiency:
- No load power dissipation (P
- Resistive loss (R
P
P
η =
used to power up the module with an enabled powertrain
at no load.
the BCM module modeled as pure resistive impedance.
DISSIPATED
OUT
=
= 1 –
= P
P
V
OUT
P
IN
IN
IN
(
•
P
= P
– P
I
= P
NL
IN
DISSIPATED
– P
+ (I
NL
IN
V
V
+ P
OUT
NL
IN
– P
OUT
IN
BCM
•
– (I
R OUT
•
): refers to the power loss across
NL
P
)
I
2 •
IN
I
IN
IN
OUT
– P
= P
R
OUT
R OUT
)
IN
2 •
48
– P
)
R
NL
B
OUT
NL
): defined as the power
– P
x 120
R OUT
y
300A00
Page 12 of 18
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Rev. 1.2
7/2011