BCM® Bus Converter
MBCM270x450M270A00
S
®
US
C
C
NRTL
US
Isolated Fixed Ratio DC-DC Converter
Features & Benefits
Product Ratings
• 270VDC – 45.0VDC 270W Bus Converter
• MIL-STD-704E/F Compliant
• High efficiency (>96.0%) reduces
system power consumption
• High power density (>919 W/in3)
reduces power system footprint by >40%
VIN = 270V (230 – 330V)
POUT= up to 270W
VOUT = 45V (38.3 – 55.0V)
(no load)
K = 1/6
Description
• Contains built-in protection features against:
n Undervoltage
n Overvoltage
n Overcurrent
n Short Circuit
n Overtemperature
The MIL-COTS VI Chip® bus converter is a high efficiency (>96.0%)
Sine Amplitude Converter™ (SAC™) operating from a 230 to 330V
primary bus to deliver an isolated 38.3 – 55.0V secondary voltage.
The MBCM270F450M270A00 is provided in a VI Chip package
compatible with standard pick-and-place and surface mount
assembly processes.
• Provides enable/disable control,
internal temperature monitoring
Part Numbering
• Can be paralleled to create multi-kW arrays
Product Number
Package Style (x)
MBCM270x450M270A00
Typical Applications
F = J-Lead
T = Through hole
Product Grade
M = -55° to 125°C
For Storage and Operating Temperatures see General Characteristics.
• High Voltage 270V Aircraft Distributed Power
• Provides Interface for high power density PRM®
modules
• High Density Power Supplies
• Communications Systems
Typical Application
PRM
BCM
ENABLE
TM
ON/OFF
CONTROL
PC
SGND
NC
FUSE
+IN
IN
C
+OUT
I_BCM
–IN
PRI_GND
RAL
TRIM
VC
AL
VT
SHARE/
CONTROL NODE
VTM Start Up Pulse
VC
Adaptive Loop Temperature Feedback
TM
REF/
REF_EN
COUT
L
I_PRM
+IN
I_PRM
–OUT
PRIMARY
SGND
+OUT
VF: 20 V to 55 V
CIN_PRM
–IN
SGND
–OUT
SECONDARY
LO_PRM
+IN
CO_PRM
–IN
–OUT
SEC_GND
ISOLATION BOUNDRY
SGND
BCM® Bus Converter
Page 1 of 22
VOUT
+OUT
IFB
R
V
RTRIM
VTM
PC
VAUX
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MBCM270x450M270A00
Pin Configuration
4
3
2
+OUT
1
A
A
B
B
C
C
D
D
E
E
F
-OUT
G
H
H
J
J
K
K
+OUT
-OUT
+IN
L
L
M
M
N
N
P
P
R
R
TM
RSV
PC
-IN
T
T
Bottom View
Pin Descriptions
Pin Number
Signal Name
Type
Function
A1-E1, A2-E2
+IN
INPUT POWER
Positive input power terminal
L1-T1, L2-T2
–IN
INPUT POWER
RETURN
Negative input power terminal
H1, H2
TM
OUTPUT
J1, J2
RSV
NC
Temperature monitor, input side referenced signal
No connect
K1, K2
PC
OUTPUT/INPUT
A3-D3, A4-D4,
J3-M3, J4-M4
+OUT
OUTPUT POWER
Positive output power terminal
E3-H3, E4-H4,
N3-T3, N4-T4
–OUT
OUTPUT POWER
RETURN
Negative output power terminal
BCM® Bus Converter
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Rev 1.3
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Enable and disable control, input side referenced signal
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Absolute Maximum Voltage Ratings
The absolute maximum ratings below are stress ratings only. Operation at or beyond these maximum ratings can cause permanent damage to the device.
Parameter
Comments
Min
Max
Unit
-1
400
V
-1
1
V/µs
4242
V
-1
80
V
-3
12
A
-2
8
A
PC to –IN
-0.3
20
V
TM to –IN
-0.3
7
V
Operating IC junction temperature
-55
125
°C
Storage temperature
-65
125
°C
+IN to –IN
VIN slew rate
Operational
Isolation voltage, input to ouput
+OUT to –OUT
Output current transient
≤ 10ms, ≤ 10% DC
Output current average
BCM® Bus Converter
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Electrical Specifications
Specifications apply over all line and load conditions, unless otherwise noted; boldface specifications apply over the temperature range of
-55°C ≤ TJ ≤ 125°C (M-Grade); all other specifications are at TJ = 25ºC unless otherwise noted.
Attribute
Symbol
Conditions / Notes
Min
Typ
Max
Unit
230
330
V
200
350
V
0.65
1.00
mA
505
575
ms
7
10
Powertrain
Input voltage range, continuous
Input voltage range, transient
Quiescent current
VIN to VOUT time
VIN_DC
Full current or power supported, 75ms max,
10% duty cycle max
VIN_TRANS
IQ
Disabled, PC Low
TON1
VIN = 270V, PC floating
430
VIN = 270V, TCASE = 25ºC
No load power dissipation
4
VIN = 270V
PNL
VIN = 230V to 330V, TCASE = 25ºC
12
VIN = 230V to 330V
16
Inrush current peak
IINR_P
Worse case of: VIN = 330V, COUT = 50μF,
RLOAD = 7078mΩ
DC input current
IIN_DC
At POUT= 350W
Transformation ratio
K
POUT_AVG
Output power (average),
redcued temperature
POUT_AVG_RED_T
Output power (peak)
POUT_PK
Output current (average)
IOUT_AVG
Output current (average),
redcued temperature
IOUT_AVG_RED_T
Output current (peak)
IOUT_PK
Efficiency (ambient)
hAMB
2
K = VOUT/ VIN, at no load
Output power (average)
14
W
3
A
1.37
A
1/6
V/V
270
W
-55°C < TCASE < 85°C
350
W
10ms max, POUT_AVG ≤ 270W or
POUT_AVG_RED_T ≤ 350W
525
W
6.25
A
-55°C < TCASE < 85°C
8.00
A
10ms max, IOUT_AVG ≤ 6.25A or
IOUT_AVG_RED_T ≤ 8.00A
11.67
A
VIN = 270V, IOUT = 6.25A; TCASE = 25°C
94.5
VIN = 230V to 330V, IOUT = 6.25A; TCASE = 25°C
93.5
96.0
VIN = 270V, IOUT = 3.13A; TCASE = 25°C
93.5
95.2
95.6
%
Efficiency (hot)
hHOT
VIN = 270V, IOUT = 6.25A; TCASE = 100°C
94.0
Efficiency (over load range)
h20%
1.25A < IOUT < 6.25A
90.0
ROUT_COLD
IOUT = 6.25A, TCASE = -55°C
60.0
82.0
110
ROUT_AMB
IOUT = 6.25A, TCASE = 25°C
100
122
150
ROUT_HOT
IOUT = 6.25A, TCASE = 100°C
130
158
190
1.6
1.7
1.8
MHz
400
mV
Output resistance
%
%
mΩ
Switching frequency
FSW
Output voltage ripple
VOUT_PP
COUT = 0F, IOUT = 6.25A, VIN = 270V,
20MHz BW
190
Output inductance (parasitic)
LOUT_PAR
Frequency up to 30MHz, Simulated J-lead model
500
pH
Output capacitance (internal)
COUT_INT
Effective value at 45.0VOUT
4.8
µF
Output capacitance (external)
COUT_EXT
BCM® Bus Converter
Page 4 of 22
0
Rev 1.3
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50
µF
MBCM270x450M270A00
Electrical Specifications
Specifications apply over all line and load conditions, unless otherwise noted; boldface specifications apply over the temperature range of
-55°C ≤ TJ ≤ 125°C (M-Grade); all other specifications are at TJ = 25ºC unless otherwise noted.
Attribute
Symbol
Conditions / Notes
Min
Typ
Max
Unit
Protection
Input overvoltage lockout threshold
VIN_OVLO+
360
370
380
V
Input overvoltage recovery threshold
VIN_OVLO-
351
363
375
V
Input overvoltage lockout hysteresis
VIN_OVLO_HYST
Overvoltage lockout response time
7.9
TOVLO
V
50
µs
TAUTO_RESTART
255
300
355
ms
Input undervoltage lockout
threshold
VIN_UVLO-
160
168
176
V
Input undervoltage recovery
threshold
VIN_UVLO+
167
177
190
V
Input undervoltage lockout
hysteresis
VIN_UVLO_HYST
8.5
V
TUVLO
50
µs
Undervoltage lockout response time
Output overcurrent trip threshold
IOCP
Output overcurrent response time
constant
TOCP
Short circuit protection trip threshold
ISCP
Short circuit protection response time
Effective internal RC filter
11
12.5
A
5.0
ms
14
TSCP
Thermal shutdown threshold
Output Power (W)
8.5
A
1
µs
125
TJ_OTP
°C
600
12
550
11
500
10
450
9
400
8
350
7
300
6
250
5
200
4
150
3
2
100
38.0
41.5
45.0
48.5
52.0
55.5
Output Voltage (V)
P (ave)
P (ave), TC < 85°C
P (pk), < 10ms
I (ave)
Figure 1 — Safe operating area
BCM® Bus Converter
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I (ave), TC < 85°C
I (pk), < 10ms
Output Current (A)
Fault recovery time
MBCM270x450M270A00
Signal Characteristics
Specifications apply over all line and load conditions, unless otherwise noted; boldface specifications apply over the temperature range of
-55°C ≤ TJ ≤ 125°C (M-Grade); all other specifications are at TJ = 25ºC unless otherwise noted.
Primary Control: PC
• The PC pin enables and disables the BCM. When held low, the BCM module is disabled.
• In an array of BCM modules, PC pins should be interconnected to synchronize start up and permit start up into full load conditions.
• PC pin outputs 5V during normal operation. PC pin internal bias level drops to 2.5V during fault mode, provided VIN remains
in the valid range.
SIGNAL TYPE
STATE
Regular
Operation
ANALOG
OUTPUT
Standby
Transition
Start Up
Regular
Operation
DIGITAL
INPUT /
OUTPUT
Standby
Transition
ATTRIBUTE
SYMBOL
MIN
TYP
MAX
UNIT
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
PC resistance (internal)
RPC_INT
Internal pull down resistor
50
150
PC capacitance (internal)
CPC_INT
See Using Control Signals
PC voltage
PC load resistance
RPC_S
PC enable threshold
VPC_EN
PC disable threshold
VPC_DIS
PC disable duration
TPC_DIS_T
PC threshold hysteresis
VPC_HYSTER
PC enable to VOUT time
TON2
PC disable to standby time
TPC_DIS
PC fault response time
TFR_PC
CONDITIONS / NOTES
To permit regular operation
400
kΩ
1000
pF
60
2.0
Minimum time before attempting
re-enable
µA
kΩ
2.5
3.0
V
1.95
V
1
s
50
VIN = 48V for at least TON1 ms
50
From fault to PC = 2V
mV
100
150
µs
4
10
µs
100
µs
Temperature Monitor: TM
• The TM pin monitors the internal temperature of the controller IC within an accuracy of ±5°C.
• Can be used as a “Power Good” flag to verify that the BCM module is operating.
• Is used to drive the internal comparator for Overtemperature Shutdown.
SIGNAL TYPE
STATE
ATTRIBUTE
TM voltage range
ANALOG
OUTPUT
DIGITAL
OUTPUT
(FAULT FLAG)
Regular
Operation
Transition
Standby
SYMBOL
CONDITIONS / NOTES
VTM_AMB
TM available current
ITM
TM gain
ATM
TM voltage ripple
VTM_PP
TM capacitance (external)
CTM_EXT
TM fault response time
TFR_TM
TM voltage
VTM_DIS
TM pull down (internal)
RTM_INT
TJ controller = 27°C
CTM = 0pF, VIN = 270V, IOUT = 6.25A
3.00
120
From fault to TM = 1.5V
Internal pull down resistor
Reserved for factory use. No connection should be made to this pin.
Rev 1.3
08/2016
2.95
MAX
UNIT
4.04
V
3.05
V
100
µA
10
Reserved: RSV
BCM® Bus Converter
Page 6 of 22
TYP
2.12
VTM
TM voltage reference
MIN
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25
mV/°C
200
mV
50
pF
10
µs
0
V
40
50
kΩ
BCM® Bus Converter
Page 7 of 22
NL
5V
2.5 V
5V
3V
PC
VUVLO+
VUVLO–
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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
MBCM270x450M270A00
Timing Diagram
MBCM270x450M270A00
Application Characteristics
18
98
16
Full Load Efficiency (%)
No Load Power Dissipation (W)
The following values, typical of an application environment, are collected at TCASE = 25ºC unless otherwise noted. See associated figures for general trend data.
14
12
10
8
6
4
2
0
230
240
250
260
270
280
290
300
310
320
97
96
95
94
93
92
330
-55
Input Voltage (V)
25°C
-55°C
TCASE:
85°C
VIN :
100°C
25
45
65
85
105
230V
270V
330V
98
94
97
Efficiency (%)
Full Load Efficiency (%)
5
Figure 3 — Full load efficiency vs. full Tmax range
98
96
95
94
93
90
86
82
78
74
92
-55
-35
-15
5
25
45
65
Case Temperature (°C)
230V
VIN:
270V
85
70
0
1
330V
2
3
4
5
Load Current (A)
230V
VIN:
270V
6
7
8
7
8
330V
Figure 5 — Efficiency at TCASE = -55°C
Figure 4 — Full load efficiency vs. Tmax restricted
28
98
24
94
20
Efficiency (%)
Power Dissipation (W)
-15
Case Temperature (°C)
Figure 2 — No load power dissipation vs. Vin
16
12
8
4
0
-35
90
86
82
78
74
0
1
2
VIN:
3
4
5
6
Load Current (A)
230V
270V
330V
Figure 6 — Power dissipation at TCASE = -55°C
BCM® Bus Converter
Page 8 of 22
Rev 1.3
08/2016
7
8
70
0
1
2
VIN:
3
4
230V
Figure 7 — Efficiency at TCASE = 25°C
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Load Current (A)
270V
6
330V
MBCM270x450M270A00
28
98
24
94
20
Efficiency (%)
Power Dissipation (W)
Application Characteristics (Cont.)
16
12
8
4
0
86
82
78
74
0
1
2
3
4
5
6
Load Current (A)
230V
VIN:
270V
7
70
8
1
2
VIN:
24
94
20
90
Efficiency (%)
98
16
12
8
4
4
5
6
230V
270V
7
8
330V
86
82
78
74
0
1
2
3
4
5
6
Load Current (A)
230V
VIN:
270V
7
8
330V
70
0
1
VIN:
28
24
20
16
12
8
4
0
0
1
VIN:
2
3
4
Load Current (A)
230V
270V
5
6
330V
Figure 12 — Power dissipation at TCASE = 100°C
BCM® Bus Converter
Page 9 of 22
2
3
4
Load Current (A)
230V
270V
Figure 11 — Efficiency at TCASE = 100°C
Figure 10 — Power dissipation at TCASE = 85°C
Power Dissipation (W)
3
Load Current (A)
Figure 9 — Efficiency at TCASE = 85°C
28
0
0
330V
Figure 8 — Power dissipation at TCASE = 25°C
Power Dissipation (W)
90
Rev 1.3
08/2016
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5
330V
6
MBCM270x450M270A00
Application Characteristics (Cont.)
250
180
225
Ripple (mV pk-pk)
200
ROUT (mΩ)
160
140
120
100
80
60
200
175
150
125
100
75
50
25
40
0
-55
-35
-15
5
25
45
65
85
105
0
1
Case Temperature (°C)
I OUT :
4A
2
3
4
5
6
7
8
Load Current (A)
VIN :
8A
270V
Figure 13 — Rout vs. temperature; nominal input
Figure 14 — Vripple vs. Iout ; No external Cout. Board mounted
module, scope setting : 20MHz analog BW
Figure 15 — Full load ripple, 100µF Cin; No external Cout. Board
mounted module, scope setting : 20MHz analog BW
Figure 16 — Start up from application of PC; Vin pre-applied
Cout = 50µF
Figure 17 — 0A – 8.00A transient response:
Cin = 100µF, no external Cout
Figure 18 — 8.00A – 0A transient response:
Cin = 100µF, no external Cout
BCM® Bus Converter
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MBCM270x450M270A00
360
350
BCM OVLO
BCM Rated Transient Opera on
≤ 75ms, at ≤ 10% D.C.
340
330
320
Input Voltage (V)
310
MIL-STD-704 E/F for 270VDC system
“Limit for DC overvoltage”
300
290
280
270
MIL-STD-704 E/F for 270VDC system
“Envelope of Normal Voltage Transients”
BCM Rated DC Opera on Range
260
250
240
230
220
BCM Rated Transient Opera on
≤ 75ms, at ≤ 10% D.C.
210
200
190
0
10
20
30
40
BCM UVLO
50
60
Duration (ms)
Figure 19 — Envelope of normal voltage transient for 270Vdc system.
BCM® Bus Converter
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70
80
90
100
MBCM270x450M270A00
General Characteristics
Specifications apply over all line and load conditions, unless otherwise noted; boldface specifications apply over the temperature range of
-55°C ≤ TJ ≤ 125°C (M-Grade); all other specifications are at TJ = 25ºC unless otherwise noted.
Attribute
Symbol
Conditions / Notes
Min
Typ
Max
Unit
Mechanical
Length
L
32.25 / [1.270] 32.50 / [1.280] 32.75 / [1.289] mm / [in]
Width
W
21.75 / [0.856] 22.00 / [0.866] 22.25 / [0.876] mm / [in]
Height
H
6.48 / [0.255]
Volume
Vol
Weight
W
No heat sink
Lead Finish
6.73 / [0.265] 6.98 / [0.275]
mm / [in]
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
TJ
Thermal resistance
fJC
(T-Grade)
N/A
N/A
MBCM270F450M270A00 (M-Grade)
-55
125
Isothermal heatsink and
isothermal internal PCB
Thermal capacity
°C
1
°C/W
9
Ws/°C
Assembly
Peak compressive force
applied to case (Z-axis)
Storage
Temperature
Supported by J-lead only
6
lbs
5.41
lbs/ in2
(T-Grade)
N/A
N/A
°C
MBCM270F450M270A00 (M-Grade)
-65
125
°C
ESDHBM
Human Body Model,
“JEDEC JESD 22-A114C.01”Class 1C
1000
ESDCDM
Charge Device Model,
“JEDEC JESD 22-C101-C”
400
TST
ESD Withstand
V
Soldering
Peak temperature during reflow
MSL 4 (Datecode 1528 and later)
Peak time above 217°C
245
°C
150
s
Peak heating rate during reflow
1.5
2
°C/s
Peak cooling rate post reflow
2.5
3
°C/s
410
VDC
Safety
Working voltage (IN – OUT)
VIN_OUT
Isolation voltage (hipot)
VHIPOT
Isolation capacitance
CIN_OUT
Unpowered unit
500
Isolation resistance
RIN_OUT
At 500VDC
10
MTBF
4,242
VDC
600
MIL-HDBK-217Plus Parts Count - 25°C
Ground Benign, Stationary, Indoors /
Computer Profile
3.81
MHrs
Telcordia Issue 2 - Method I Case III;
25°C Ground Benign, Controlled
7.84
MHrs
cURus
CE Marked for Low Voltage Directive and ROHS recast directive, as applicable.
BCM® Bus Converter
Page 12 of 22
pF
MΩ
cTUVus
Agency approvals / standards
700
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MBCM270x450M270A00
Using the Control Signals PC, TM
Primary Control (PC) pin can be used to accomplish the following
functions:
n 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.
n Auxiliary voltage source: Once enabled in regular
operational conditions (no fault), each BCM module
PC provides a regulated 5V, 3.5mA voltage source.
n 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.
n Output disable: PC pin can be actively pulled down in order
to disable the module. Pull down impedance shall be lower
than 60Ω.
n Fault detection flag: The PC 5V voltage source is internally
turned off as soon as a fault is detected.
n 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:
n Monitor the control IC temperature: The temperature in
Kelvin is equal to the voltage on the TM pin scaled
by 100. (i.e. 3.0V = 300K = 27ºC). If a heat sink is applied,
TM can be used to protect the system thermally.
n 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
Page 13 of 22
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MBCM270x450M270A00
Sine Amplitude Converter™ Point of Load Conversion
1.7nH
Lout = 500pH
+
VIN
Rout
122mΩ
ROUT
Iout
IOUT
Lin = 5.7nH
R
RCCININ
9.2mΩ
CCINin
0.1µF
0.98Ω
V•I
1/6 • Iout
IIQq
26mA
+
+
–
–
K
+
RRCCOUT
OUT
310µΩ
1/6 • Vin
Cout
COUT
4.8µF
VOUT
–
–
Figure 20 — VI Chip® AC model
The Sine Amplitude Converter (SAC™) uses a high frequency
resonant tank to move energy from input to output. 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 MBCM270x450M270A00 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 = 0Ω and IQ = 0A, 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
+
–
TM
SAC
1/6
KK==1/32
Vout
V
out
K represents the “turns ratio” of the SAC.
Rearranging Eq (1):
VOUT (2)
K =
VIN
Figure 21 — K = 1/6 Sine Amplitude Converter™
with series input resistor
The relationship between VIN and VOUT becomes:
In the presence of load, VOUT is represented by:
VOUT = VIN • K – IOUT • ROUT (3)
VOUT = (VIN – IIN • R) • K
(5)
and IOUT is represented by:
Substituting the simplified version of Eq. (4)
(IQ is assumed = 0A) into Eq. (5) yields:
VOUT = VIN • K – IOUT • R • K2 (6)
IIN – IQ (4)
IOUT =
K
BCM® Bus Converter
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MBCM270x450M270A00
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 K 2 with
respect to the output.
Assuming that R = 1Ω, the effective R as seen from the output side
is 27.8mΩ, with K = 1/6 as shown in Figure 21.
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 22.
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.
S
VVin
in
+
–
C
The two main terms of power loss in the BCM module are:
SAC™
SAC
1/6
KK==1/32
Vout
V
out
n No load power dissipation (PNL): defined as the power
used to power up the module with an enabled powertrain
at no load.
n Resistive loss (PROUT): refers to the power loss across
the BCM module modeled as pure resistive impedance.
Figure 22 — 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:
PDISSIPATED = PNL + PR (10)
OUT
Therefore,
IC(t) = C
dVIN (7)
dt
Assume that with the capacitor charged to VIN, the switch is
opened and the capacitor is discharged through the idealized SAC.
In this case,
POUT = PIN – PDISSIPATED = PIN – PNL – PR (11)
OUT
The above relations can be combined to calculate the overall
module efficiency:
POUT PIN – PNL – PROUT
h =
=
P
P
IC = IOUT • K
(8)
IN
IN
substituting Eq. (1) and (8) into Eq. (7) reveals:
VIN • IIN – PNL – (IOUT)2 • ROUT
=
VIN • IIN
C dVOUT (9)
IOUT =
•
K2 dt
= 1 –
(PNL + (IOUT)2 • ROUT)
VIN • IIN
The equation in terms of the output has yielded a K 2 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 = 1/6 as shown in Figure 22, C = 1µF would appear as C = 36µF
when viewed from the output.
BCM® Bus Converter
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MBCM270x450M270A00
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 5MHz. The
connection of the bus converter module to its power
source should be implemented with minimal distribution
inductance. If the interconnect inductance exceeds
100nH, the input should be bypassed with a RC damper
to retain low source impedance and stable operation.
With an interconnect inductance of 200nH, the RC damper
may be as high as 1µF in series with 0.3Ω. 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 17 and 18.
Within this frequency range, capacitance at the input appears as
effective capacitance on the output per the relationship
defined in Eq. 13.
COUT = CIN
K2
This enables a reduction in the size and number of capacitors used
in a typical system.
Thermal Considerations
VI Chip® products are multi-chip modules whose temperature
distribution varies greatly for each part number as well as with the
input / output conditions, thermal management and environmental
conditions. Maintaining the top of the MBCM270x450M270A00
case to less than 100ºC will keep all junctions within the VI Chip
module below 125ºC for most applications.
The percent of total heat dissipated through the top surface
versus through the J-lead is entirely dependent on the particular
mechanical and thermal environment. The heat dissipated through
the top surface is typically 60%. The heat dissipated through the
J-lead onto the PCB surface is typically 40%. Use 100% top surface
dissipation when designing for a conservative cooling solution.
It is not recommended to use a VI Chip module for an extended
period of time at full load without proper heat sinking.
3. Protect the module from overvoltage transients imposed
by the system that would exceed maximum ratings and
cause failures:
The module input/output voltage ranges shall not be
exceeded. An internal overvoltage lockout function
prevents operation outside of the normal operating input
range. Even during this condition, the powertrain is
exposed to the applied voltage and power MOSFETs must
withstand it. A criterion for protection is the maximum
amount of energy that the input or output switches can
tolerate if avalanched.
Total load capacitance at the output of the BCM module shall not
exceed the specified maximum. Owing to the wide bandwidth
and low output impedance of the module, low-frequency bypass
capacitance and significant energy storage may be more densely
and efficiently provided by adding capacitance at the input of
the module. At frequencies
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