Not Recommended for New Designs
BCM® Bus Converter
B048x060y24A
S
C
NRTL
US
Unregulated DC-DC Converter
FEATURES
DESCRIPTION
The VI Chip® bus converter is a high efficiency (>95%) Sine
Amplitude Converter™ (SAC™) operating from a 38 to 55 Vdc
primary bus to deliver an isolated, unregulated 4.8 to 6.9
output. The Sine Amplitude Converter offers a low AC
impedance beyond the bandwidth of most downstream
regulators; therefore capacitance normally at the load can be
located at the input to the Sine Amplitude Converter. Since the
transformation ratio of the B048x060y24A is 1/8, the
capacitance value can be reduced by a factor of 64x, resulting
in savings of board area, materials and total system cost.
The B048x060y24A is provided in a VI Chip package
compatible with standard pick-and-place and surface mount
assembly processes. The co-molded VI Chip package provides
enhanced thermal management due to a large thermal
interface area and superior thermal conductivity. The high
conversion efficiency of the B048x060y24A increases overall
system efficiency and lowers operating costs compared to
conventional approaches.
• 48 Vdc – 6 Vdc 240 W Bus Converter
• High efficiency (>95%) reduces system
power consumption
• High power density (>817 W/in3)
reduces power system footprint by >40%
• Contains built-in protection features:
-
Undervoltage
Overvoltage Lockout
Overcurrent Protection
Short circuit Protection
Overtemperature Protection
• Provides enable/disable control,
internal temperature monitoring
• Can be paralleled to create multi-kW arrays
TYPICAL APPLICATIONS
PART NUMBERING
• High End Computing Systems
• Automated Test Equipment
• High Density Power Supplies
• Communications Systems
PART NUMBER
B048 x 060 y 24A
PACKAGE STYLE
F = J-Lead
T = Through hole
PC
TM
SW1
F1
T = -40° to 125°C
M = -55° to 125°C
For Storage and Operating Temperatures see Section 6.0 General Characteristics
TYPICAL APPLICATION
enable / disable
switch
PRODUCT GRADE
L
O
A
D
BCM®
Bus Converter
+In
+Out
-In
-Out
VIN
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 1 of 18
01/2014
800 927.9474
Not Recommended for New Designs
B048x060y24A
1.0 ABSOLUTE MAXIMUM RATINGS
The absolute maximum ratings below are stress ratings only. Operation at or beyond these maximum ratings can cause permanent
damage to the device.
MIN
MAX
+IN to –IN . . . . . . . . . . . . . . . . . . . . . . .
-1
60
V
VIN slew rate (operational) . . . . . . . . .
-1
1
V/µs
V
Isolation voltage, input to output . . . .
2250
+OUT to –OUT . . . . . . . . . . . . . . . . . . .
-1
12
UNIT
V
MIN
MAX
UNIT
-3
60
A
Output current average . . . . . . . . . . . .
-2
47
A
PC to –IN . . . . . . . . . . . . . . . . . . . . . . . .
-0.3
20
V
TM to –IN . . . . . . . . . . . . . . . . . . . . . . .
-0.3
7
V
Output current transient
(< = 10 ms, < = 10% DC) . . . . . . . . . . . .
2.0 ELECTRICAL CHARACTERISTICS
Specifications apply over all line and load conditions unless otherwise noted; Boldface specifications apply over the temperature
range of -40°C < TC < 100°C (T-Grade); All other specifications are at TC = 25ºC unless otherwise noted.
ATTRIBUTE
SYMBOL
CONDITIONS / NOTES
MIN
TYP
MAX
UNIT
38
55
V
38
55
V
POWERTRAIN
Input voltage range, continuous
Input voltage range, transient
Quiescent current
VIN to VOUT time
VIN_DC
VIN_TRANS
IQ
TON1
Full current or power supported, 50 ms max,
10% duty cycle max
Disabled, PC Low
VIN = 48 V, PC floating
550
VIN = 48 V, TC = 25ºC
No load power dissipation
PNL
Inrush current peak
IINR_P
DC input current
IIN_DC
Transformation ratio
Output power (average)
K
POUT_PK
Output current (average)
IOUT_AVG
Efficiency (ambient)
Efficiency (hot)
Efficiency (over load range)
Output resistance
Switching frequency
IOUT_PK
hAMB
hHOT
h20%
mA
ms
2.7
3.5
0.9
7.3
VIN = 38 V to 55 V, TC = 25ºC
6
VIN = 38 V to 55 V
8
Worse case of: VIN = 55 V, COUT = 4000 µF,
RLOAD = 122 mΩ
12
At POUT = 240 W
25
7
K = VOUT / VIN, at no load
1/8
10 ms max, POUT_AVG ≤ 240 W
10 ms max, IOUT_AVG ≤ 47 A
VIN = 48 V, IOUT = 40 A; Tc = 25°C
94.0
VIN = 38 V to 55 V, IOUT = 40 A; Tc = 25°C
90.0
VIN = 48 V, IOUT = 20 A; Tc = 25°C
94.8
95.6
VIN = 48 V, IOUT = 40 A; Tc = 100°C
92.8
94.5
W
A
A
V/V
240
W
360
W
47
A
60
A
94.7
%
%
8 A < IOUT < 40 A
87.5
ROUT_COLD
IOUT = 40 A, Tc = -40°C
2.5
ROUT_AMB
IOUT = 40 A, Tc = 25°C
3.8
5.8
7.1
mΩ
ROUT_HOT
IOUT = 40 A, TC = 100°C
4.5
6.5
9.0
mΩ
1.10
1.21
1.30
MHz
145
275
mV
FSW
Output voltage ripple
VOUT_PP
Output inductance (parasitic)
LOUT_PAR
Output capacitance (internal)
COUT_INT
COUT_EXT
Output capacitance (external)
1.0
940
POUT_AVG
Output power (peak)
Output current (peak)
VIN = 48 V
0.5
750
COUT = 0 F, IOUT = 40 A, VIN = 48 V,
20 MHz BW, Section 10
Frequency up to 30 MHz,
Simulated J-lead model
%
4.5
5.9
600
Effective value at 6 VOUT
pH
45
0
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 2 of 18
01/2014
800 927.9474
mΩ
µF
4000
µF
Not Recommended for New Designs
B048x060y24A
2.0 ELECTRICAL CHARACTERISTICS (CONT.)
ATTRIBUTE
SYMBOL
CONDITIONS / NOTES
MIN
TYP
MAX
UNIT
VIN_OVLO+
55.1
58.5
60
V
Input overvoltage recovery threshold
VIN_OVLO-
55.1
58.0
60
V
Input overvoltage lockout hysteresis
VIN_OVLO_HYST
PROTECTION
Input overvoltage lockout threshold
Overvoltage lockout response time
Fault recovery time
1.2
TOVLO
V
8
350
VIN_UVLOVIN_UVLO+
28.5
31.1
37.4
V
Input undervoltage recovery threshold
28.5
33.7
37.4
V
Input undervoltage lockout hysteresis
VIN_UVLO_HYST
1.6
V
Undervoltage lockout response time
TUVLO
8
µs
Input undervoltage lockout threshold
Output overcurrent trip threshold
IOCP
Output overcurrent response time constant
TOCP
Short circuit protection trip threshold
ISCP
Short circuit protection response time
TSCP
Thermal shutdown threshold
47
Effective internal RC filter
480
µs
TAUTO_RESTART
60
600
ms
80
A
7.7
ms
1
µs
80
TJ_OTP
A
ºC
125
Safe Operating Area Average & Peak
400
120
350
Output Power (W)
300
80
250
60
200
40
150
20
100
50
0
4.5
5.0
5.5
6.0
6.5
Output Voltage (V)
P (ave)
P (pk), < 10 ms
I (ave)
Figure 1 — Safe operating area
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 3 of 18
01/2014
800 927.9474
I (pk), < 10 ms
7.0
Output Current (A)
100
Not Recommended for New Designs
B048x060y24A
3.0 SIGNAL CHARACTERISTICS
Specifications apply over all line and load conditions unless otherwise noted; Boldface specifications apply over the temperature
range of -40°C < TC < 100°C (T-Grade); All other specifications are at TC = 25°C unless otherwise noted.
PRIMARY CONTROL : PC
• The PC pin enables and disables the BCM. When held low,
• PC pin outputs 5 V during normal operation. PC pin internal bias
the BCM is disabled.
level drops to 2.5 V during fault mode, provided VIN remains
in the valid range.
• In an array of BCM modules, PC pins should be interconnected
to synchronize start up and permit start up into full load conditions.
SIGNAL TYPE
STATE
Regular
Operation
ANALOG
OUTPUT
Standby
Transition
DIGITAL
INPUT / OUPUT
ATTRIBUTE
MIN
TYP
VPC
4.7
5.0
5.3
V
PC available current
IPC_OP
2.0
3.5
5.0
mA
PC source (current)
IPC_EN
50
100
50
150
PC voltage
PC resistance (internal)
PC capacitance (internal)
SYMBOL
CONDITIONS / NOTES
RPC_INT
CPC_INT
Internal pull down resistor
To permit regular operation
Section 7
MAX UNIT
µA
400
kΩ
1000
pF
Start Up
PC load resistance
RPC_S
Start Up
PC time to start
TON1
550
750
940
ms
VPC_EN
2.0
2.5
3.0
V
Regular
Operation
PC enable threshold
Standby
PC disable duration
PC threshold hysteresis
Transition
PC enable to VOUT time
TPC_DIS_T Minimum time before attempting re-enable
VPC_HYSTER
TON2
PC disable to standby time
TPC-DIS
PC fault response time
TFR_PC
VIN = 48 V for at least TON1 ms
60
kΩ
1
s
50
50
From fault to PC = 2 V
mV
100
150
µs
4
10
µs
100
µs
TEMPERATURE MONITOR : TM
• The TM pin monitors the internal temperature of the controller IC
• Can be used as a "Power Good" flag to verify that
within an accuracy of ±5°C.
the BCM module is operating.
• Is used to drive the internal comparator for Overtemperature Shutdown.
SIGNAL TYPE
STATE
ATTRIBUTE
TM voltage range
ANALOG
OUTPUT
Regular
Operation
Transition
Standby
CONDITIONS / NOTES
VTM
TM voltage reference
VTM_AMB
TM available current
ITM
TM gain
DIGITAL
OUTPUT
(FAULT FLAG)
SYMBOL
MIN
TJ controller = 27°C
2.95
VTM_PP
TM capacitance (external)
CTM_EXT
TM fault response time
TFR_TM
TM voltage
VTM_DIS
TM pull down (internal)
RTM_INT
MAX UNIT
4.04
3.00
3.05
100
ATM
TM voltage ripple
TYP
2.12
10
120
From fault to TM = 1.5 V
10
mV/°C
200
mV
50
pF
µs
0
RESERVED : RSV
Reserved for factory use. No connection should be made to this pin.
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 4 of 18
01/2014
800 927.9474
25
V
µA
CTM = 0 pF, VIN = 48 V, IOUT = 40 A
Internal pull down resistor
V
40
V
50
kΩ
NL
5V
2.5 V
5V
3V
PC
VUVLO+
VUVLO–
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 5 of 18
01/2014
800 927.9474
1
A
E: TON2
F: TOCP
G: TPC–DIS
H: TSCP**
B
D
1: Controller start
2: Controller turn off
3: PC release
C
*Min value switching off
**From detection of error to power train shut down
A: TON1
B: TOVLO*
C: TAUTO_RESTART
D:TUVLO
0.4 V
3 V @ 27°C
TM
LL • K
Vout
C
500mS
before retrial
3V
VIN
VOVLO+
VOVLO–
2
F
4: PC pulled low
5: PC released on output SC
6: SC removed
IOCP
ISSP
IOUT
E
3
G
4
Notes:
H
5
– Timing and signal amplitudes are not to scale
– Error pulse width is load dependent
6
Not Recommended for New Designs
B048x060y24A
4.0 TIMING DIAGRAM
Not Recommended for New Designs
B048x060y24A
5.0 APPLICATION CHARACTERISTICS
The following values, typical of an application environment, are collected at TC = 25ºC unless otherwise noted. See associated figures
for general trend data.
No Load Power Dissipation vs. Line
Full Load Efficiency (%)
7
6
5
4
3
2
1
95
94
93
38
40
42
44
46
47
49
51
53
-40
55
-20
0
-40 °C
TCASE:
100 °C
25 °C
VIN :
Efficiency & Power Dissipation -40 °C Case
15
87
10
82
5
PD
15
20
25
38 V
VIN:
48 V
55 V
30
35
40
0
20
15
87
10
82
77
PD
0
5
10
15
48 V
55 V
Efficiency & Power Dissipation 100 °C Case
38 V
6.5
25
6.0
20
15
87
10
82
5
PD
15
20
25
30
35
40
0
Rout (mΩ)
30
Power Dissipation (W)
Efficiency (%)
92
10
48 V
38 V
48 V
55 V
30
35
40
0
55 V
38 V
48 V
55 V
5.5
5.0
4.5
4.0
3.5
-40
-20
0
20
40
60
Case Temperature (°C)
38 V
48 V
ROUT vs. TCASE at VIN = 48 V
Load Current (A)
VIN:
25
Figure 5 — Efficiency and power dissipation at TC = 25°C
97
5
20
5
Load Current (A)
38 V
Figure 4 — Efficiency and power dissipation at TC = -40°C
0
55 V
92
VIN:
77
48 V
30
Load Current (A)
38 V
100
25
Efficiency (%)
20
10
80
97
Power Dissipation (W)
Efficiency (%)
25
92
5
60
Efficiency & Power Dissipation 25 °C Case
30
97
0
40
Figure 3 — Full load efficiency vs. temperature; VIN
Figure 2 — No load power dissipation vs. VIN
77
20
Case Temperature (°C)
Input Voltage (V)
Power Dissipation (W)
Power Dissipation (W)
8
0
Full Load Efficiency vs. TCASE
96
55 V
I OUT :
Figure 6 — Efficiency and power dissipation at TC = 100°C
Figure 7 — ROUT vs. temperature
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 6 of 18
01/2014
800 927.9474
47 A
80
100
Not Recommended for New Designs
B048x060y24A
Output Voltage Ripple vs. Load VIN = 48 V
250
Ripple (mV pk-pk)
225
200
175
150
125
100
75
50
25
0
0
5
10
15
20
25
30
35
40
Load Current (A)
Figure 8 — VRIPPLE vs. IOUT ; No external COUT. Board mounted
module, scope setting : 20 MHz analog BW
Figure 9 — Full load ripple, 330 µF CIN; No external COUT. Board
mounted module, scope setting : 20 MHz analog BW
Figure 10 — Start up from application of PC;
VIN pre-applied COUT = 4000 µF
Figure 11 — 0 A– 40 A transient response: CIN = 330 µF, IIN measured
prior to CIN , no external COUT
Figure 12 — 40 A – 0 A transient response:
CIN = 330 µF, IIN measured prior to CIN , no external COUT
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 7 of 18
01/2014
800 927.9474
Not Recommended for New Designs
B048x060y24A
6.0 GENERAL CHARACTERISTICS
Specifications apply over all line and load conditions unless otherwise noted; Boldface specifications apply over the temperature
range of -40ºC < TJ < 125ºC (T-Grade); All other specifications are at TJ = 25°C unless otherwise noted.
ATTRIBUTE
SYMBOL
CONDITIONS / NOTES
MIN
TYP
MAX
UNIT
mm/[in]
MECHANICAL
Length
L
32.25 / [1.270]
32.50 / [1.280]
32.75 / [1.289]
Width
W
21.75 / [0.856]
22.00 / [0.866]
22.25 / [0.876]
mm/[in]
Height
H
6.48 / [0.255]
6.73 / [0.265]
6.98 / [0.275]
mm/[in]
Volume
Vol
Weight
W
Lead finish
No heat sink
4.81 / [0.294]
cm3/[in3]
14.5 / [0.512]
g/[oz]
Nickel
0.51
2.03
Palladium
0.02
0.15
Gold
0.003
0.051
µm
THERMAL
Operating temperature
Thermal resistance
TJ
fJC
B048x060y24A (T-Grade)
-40
125
°C
BCM48BF060M240A00 (M-Grade)
Isothermal heatsink and
isothermal internal PCB
-55
125
°C
Thermal capacity
1
°C/W
5
Ws/°C
ASSEMBLY
Peak compressive force
applied to case (Z-axis)
Supported by J-lead only
Storage temperature
TST
Moisture sensitivity level
MSL
lbs
lbs / in2
B048x060y24A (T-Grade)
-40
125
°C
BCM48BF060M240A00 (M-Grade)
-65
125
°C
MSL 6, 4 hours out of bag maximum
ESDHBM
MSL 5
Human Body Model,
"JEDEC JESD 22-A114D.01"Class 1D
ESDCDM
Charge Device Model,
"JEDEC JESD 22-C101-D"
ESD withstand
6
5.41
1000
V
400
SOLDERING
Peak temperature during reflow
MSL 6, 4 hours out of bag maximum
245
°C
MSL 5
225
°C
Peak time above 217°C
60
90
s
Peak heating rate during reflow
1.5
3
°C/s
Peak cooling rate post reflow
1.5
6
°C/s
SAFETY
Working voltage (IN – OUT)
Isolation voltage (hipot)
VIN_OUT
60
VHIPOT
2,250
Isolation capacitance
CIN_OUT
Unpowered unit
Isolation resistance
RIN_OUT
At 500 Vdc
2500
MTBF
3200
10
MIL-HDBK-217Plus Parts Count - 25°C
Ground Benign, Stationary, Indoors /
Computer Profile
Telcordia Issue 2 - Method I Case III;
25°C Ground Benign, Controlled
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 8 of 18
01/2014
800 927.9474
3800
pF
MΩ
3.84
MHrs
7.60
MHrs
cTUVus
cURus
CE Marked for Low Voltage Directive and ROHS recast directive, as applicable.
Agency approvals / standards
VDC
VDC
Not Recommended for New Designs
7.0 USING THE CONTROL SIGNALS PC, TM
Primary Control (PC) pin can be used to accomplish the
following functions:
• Logic enable and disable for module: Once Ton1 time has
been satisfied, a PC voltage greater than Vpc_en will cause
the module to start. Bringing PC lower than Vpc_dis will
cause the module to enter standby.
• Auxiliary voltage source: Once enabled in regular
operational conditions (no fault), each BCM® module
PC provides a regulated 5 V, 3.5 mA voltage source.
• Synchronized start up: In an array of parallel modules, PC
pins should be connected to synchronize start up across
units. This permits the maximum load and capacitance
to scale by the number of paralleled modules.
• Output disable: PC pin can be actively pulled down in order
to disable the module. Pull down impedance shall be lower
than 60 Ω.
• Fault detection flag: The PC 5 V voltage source is internally
turned off as soon as a fault is detected.
• Note that PC can not sink significant current during a fault
condition. The PC pin of a faulted module will not cause
interconnected PC pins of other modules to be disabled.
Temperature Monitor (TM) pin provides a voltage
proportional to the absolute temperature of the converter
control IC.
It can be used to accomplish the following functions:
• Monitor the control IC temperature: The temperature in
Kelvin is equal to the voltage on the TM pin scaled
by 100. (i.e. 3.0 V = 300 K = 27ºC). If a heat sink is applied,
TM can be used to protect the system thermally.
• Fault detection flag: The TM voltage source is internally
turned off as soon as a fault is detected. For system
monitoring purposes microcontroller interface faults are
detected on falling edges of TM signal.
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 9 of 18
01/2014
800 927.9474
B048x060y24A
PC
-Vin
+Vin
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 10 of 18
01/2014
800 927.9474
1000 pF
3.1 V
Vcc
100 uA
150 K
2.5 V
PC Pull-Up
& Source
One shot
delay
Ton1
5 V, 2 mA min
18.5 V
“Wake-Up” Power
And Logic
Vin
Gate
Drive
supply
UVLO
OVLO
Adaptive
Soft Start
Vcc
Start up &
Fault logic
Enable
Modulator
V2
Primary
current
sensing
Q2
Overtemperature
Protection
Primary
Gate
Drive
Q1
Temp_Vref
Lr
Q4
Vref
Temperature
dependent voltage
source
Cr
Primary Stage &
Resonant Tank
Q3
Slow
current
limit
∫
Fast
current
Limit
Q6
40 K
Overcurrent
Protection
Secondary
Gate Drive
Power
Transformer
1K
Q5
0.01 F
Synchronous
Rectification
TM
-Vout
COUT
+Vout
Not Recommended for New Designs
B048x060y24A
8.0 B048X060Y24A BLOCK DIAGRAM
Not Recommended for New Designs
B048x060y24A
9.0 SINE AMPLITUDE CONVERTER™ POINT OF LOAD CONVERSION
810 pH
IOUT
IOUT
LIN = 600 nH
+
R
RCIN
CIN
0.57 mΩ
VIN
V
IN
2 µF
IIQQ
54 mA
+
+
–
–
LOUT = 600 pH
+
5.8 mΩ
0.8 Ω
V•I
1/8 • IOUT
CCININ
OUT
RROUT
RRCOUT
COUT
350 µΩ
1/8 • VIN
COUT
COUT
45 µF
OUT
VVOUT
K
–
–
Figure 13 — VI Chip® 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. See Section 8). 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
power density.
The B048x060y24A SAC can be simplified into the preceeding
model.
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.
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.
At no load:
R
R
VOUT = VIN • K
(1)
VVin
IN
+
–
SAC™
SAC
1/8
KK==1/32
Vout
V
OUT
K represents the “turns ratio” of the SAC.
Rearranging Eq (1):
V
K = OUT
VIN
(2)
The relationship between VIN and VOUT becomes:
VOUT = (VIN – IIN • R) • K
In the presence of load, VOUT is represented by:
VOUT = VIN • K – IOUT • ROUT
(3)
and IOUT is represented by:
IOUT =
Figure 14 — K = 1/8 Sine Amplitude Converter™
with series input resistor
Substituting the simplified version of Eq. (4)
(IQ is assumed = 0 A) into Eq. (5) yields:
VOUT = VIN • K – IOUT • R • K2
IIN – IQ
K
(5)
(4)
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 11 of 18
01/2014
800 927.9474
(6)
Not Recommended for New Designs
This is similar in form to Eq. (3), where ROUT is used to
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 K2 with respect to the output.
Assuming that R = 1 Ω, the effective R as seen from the secondary
side is 15.6 mΩ, with K = 1/8 .
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 VIN is added to the circuit. This is
depicted in Figure 15.
S
VVin
IN
+
–
C
SAC™
SAC
K = 1/8
K = 1/32
VVout
OUT
Figure 15 — Sine Amplitude Converter™ with input capacitor
A change in VIN with the switch closed would result in a
change in capacitor current according to the following
equation:
IC(t) = C
dVIN
dt
Low impedance is a key requirement for powering a highcurrent, 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:
- No load power dissipation (PNL): defined as the power
used to power up the module with an enabled powertrain
at no load.
- Resistive loss (ROUT): refers to the power loss across
the BCM module modeled as pure resistive impedance.
PDISSIPATED = PNL + PROUT
Assume that with the capacitor charged to VIN, the switch is
opened and the capacitor is discharged through the idealized
SAC. In this case,
(8)
POUT = PIN – PDISSIPATED = PIN – PNL – PROUT
C
K2
•
h =
=
dVOUT
dt
(9)
The equation in terms of the output has yielded a K2 scaling
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 = 1/8 as shown in Figure 15,
C=1 µF would appear as C=64 µF when viewed
from the output.
(11)
The above relations can be combined to calculate the overall
module efficiency:
substituting Eq. (1) and (8) into Eq. (7) reveals:
IOUT =
(10)
Therefore,
(7)
IC = IOUT • K
B048x060y24A
POUT = PIN – PNL – PROUT
PIN
PIN
VIN • IIN – PNL – (IOUT)2 • ROUT
VIN • IIN
= 1–
(
)
PNL + (IOUT)2 • ROUT
VIN • IIN
BCM® Bus Converter
Rev 1.0
vicorpower.com
Page 12 of 18
01/2014
800 927.9474
(12)
Not Recommended for New Designs
10.0 INPUT AND OUTPUT FILTER DESIGN
A major advantage of SAC™ systems versus conventional
PWM converters is that the transformers do not require large
functional filters. The resonant LC tank, operated at extreme
high frequency, is amplitude modulated as a function of input
voltage and output current and efficiently transfers charge
through the isolation transformer. A small amount of
capacitance embedded in the input and output stages of the
module is sufficient for full functionality and is key to achieve
power density.
This paradigm shift requires system design to carefully evaluate
external filters in order to:
1.Guarantee low source impedance:
To take full advantage of the BCM module’s dynamic
response, the impedance presented to its input terminals
must be low from DC to approximately 5 MHz. The
connection of the bus converter module to its power
source should be implemented with minimal distribution
inductance. If the interconnect inductance exceeds
100 nH, the input should be bypassed with a RC damper
to retain low source impedance and stable operation. With
an interconnect inductance of 200 nH, the RC damper
may be as high as 1 µF in series with 0.3 Ω. A single
electrolytic or equivalent low-Q capacitor may be used in
place of the series RC bypass.
2.Further reduce input and/or output voltage ripple without
sacrificing dynamic response:
Given the wide bandwidth of the module, the source
response is generally the limiting factor in the overall
system response. Anomalies in the response of the source
will appear at the output of the module multiplied by its
K factor. This is illustrated in Figures 11 and 12.
B048x060y24A
storage may be more densely and efficiently provided by
adding capacitance at the input of the module. At frequencies
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