BCM® Bus Converter
BCM48Bx040y200B00
S
®
US
C
C
NRTL
US
Isolated Fixed Ratio DC-DC Converter
Features & Benefits
Product Ratings
• 48VDC – 4VDC 200W Bus Converter
• High efficiency (>94%) reduces system
power consumption
• High power density (>681W/in3)
reduces power system footprint by >40%
•
VIN = 48V (38 – 55V)
POUT= up to 200W
VOUT = 4V (3.2 – 4.6V)
(no load)
K = 1/12
Description
Contains built-in protection features:
n Undervoltage
n Overvoltage Lockout
n Overcurrent Protection
n Short circuit Protection
n Overtemperature Protection
The VI Chip® bus converter is a high efficiency (>94%) Sine
Amplitude Converter™ (SAC™) operating from a 38 to 55VDC
primary bus to deliver an isolated, ratiometric output voltage from
3.2 to 4.6VDC. 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 BCM48Bx040y200B00 is 1/12, the capacitance value
can be reduced by a factor of 144x, resulting in savings of board
area, materials and total system cost.
• Provides enable/disable control,
internal temperature monitoring
• Can be paralleled to create multi-kW arrays
The BCM48BF040y200B00 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 BCM48Bx040y200B00 increases overall system
efficiency and lowers operating costs compared to conventional
approaches.
Typical Applications
• High End Computing Systems
• Automated Test Equipment
• High Density Power Supplies
Part Numbering
• Communications Systems
Product Number
BCM48Bx040y200B00
Package Style (x)
Product Grade (y)
F = J-Lead
T = -40° to 125°C
T = Through hole
M = -55° to 125°C
For Storage and Operating Temperatures see General Characteristics
Typical Application
enable / disable
switch
SW1
F1
PC
TM
L
O
A
D
BCM®
Bus Converter
+IN
+OUT
-IN
-OUT
VIN
BCM® Bus Converter
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Pin Configuration
4
3
2
1
A
A
+OUT
B
B
C
C
D
D
E
E
-OUT
F
G
H
H
J
J
+OUT
-OUT
+IN
K
K
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
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
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
Page 2 of 20
Rev 1.3
08/2016
Function
Temperature monitor, input side referenced signal
No connect
Enable and disable control, input side referenced signal
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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.
Parameter
Comments
+IN to –IN
VIN slew rate
Operational
Min
Max
Unit
-1
60
V
-1
1
V/µs
2250
V
-1
10
V
-3
75
A
-2
53
A
PC to –IN
-0.3
20
V
TM to –IN
-0.3
7
V
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
-40°C ≤ TCASE ≤ 100°C (T-Grade); all other specifications are at TCASE = 25ºC unless otherwise noted.
Attribute
Symbol
Conditions / Notes
Min
Typ
Max
Unit
38
55
V
38
55
V
0.5
1.0
mA
650
800
ms
Powertrain
Input voltage range, continuous
Input voltage range, transient
VIN_DC
VIN_TRANS
Quiescent current
IQ
VIN to VOUT time
TON1
Full current or power supported, 50ms max,
10% duty cycle max
Disabled, PC Low
VIN = 48V, PC floating
450
VIN = 48V, TCASE = 25ºC
No load power dissipation
PNL
5.0
1.5
VIN = 48V
VIN = 38V to 55V, TCASE = 25ºC
8
VIN = 38V to 55V
12
Inrush current peak
IINR_P
Worse case of: VIN = 55V, COUT = 9100μF,
RLOAD = 73mΩ
DC input current
IIN_DC
At POUT = 200W
Transformation ratio
K
Output power (average)
POUT_AVG
Output power (peak)
POUT_PK
Output current (average)
IOUT_AVG
Output current (peak)
IOUT_PK
Efficiency (ambient)
hAMB
6.3
11.0
10
K = VOUT / VIN, at no load
20
A
5
A
1/12
10ms max, POUT_AVG ≤ 200W
10ms max, IOUT_AVG ≤ 53A
VIN = 48V, IOUT = 50A; TCASE = 25°C
93.1
VIN = 38V to 55V, IOUT = 50A; TCASE = 25°C
90.2
VIN = 48V, IOUT = 25A; TCASE = 25°C
92.4
93.4
94.0
V/V
200
W
300
W
53
A
75
A
94.1
%
Efficiency (hot)
hHOT
VIN = 48V, IOUT = 50A; TCASE = 100°C
93.0
Efficiency (over load range)
h20%
10A < IOUT < 50A
80.5
ROUT_COLD
IOUT = 50A, TCASE = -40°C
1.5
2.0
2.6
ROUT_AMB
IOUT = 50A, TCASE = 25°C
1.8
2.4
3.0
ROUT_HOT
IOUT = 50A, TCASE = 100°C
Output resistance
W
%
%
mΩ
2.0
2.7
3.3
1.36
1.43
1.50
MHz
COUT = 0F, IOUT = 50A, VIN = 48V,
20MHz BW
216
350
mV
LOUT_PAR
Frequency up to 30MHz, Simulated J-lead model
600
pH
Output capacitance (internal)
COUT_INT
Effective value at 4VOUT
200
µF
Output capacitance (external)
COUT_EXT
Switching frequency
FSW
Output voltage ripple
VOUT_PP
Output inductance (parasitic)
BCM® Bus Converter
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9100
µF
BCM48Bx040y200B00
Electrical Specifications (Cont.)
Specifications apply over all line and load conditions, unless otherwise noted; boldface specifications apply over the temperature range of
-40°C ≤ TCASE ≤ 100°C (T-Grade); all other specifications are at TCASE = 25ºC unless otherwise noted.
Attribute
Symbol
Conditions / Notes
Min
Typ
Max
Unit
Protection
Input overvoltage lockout threshold
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
1.2
V
Overvoltage lockout response time
TOVLO
8
µs
TAUTO_RESTART
320
420
530
ms
Input undervoltage lockout
threshold
VIN_UVLO-
28.5
31.1
37.4
V
Input undervoltage recovery
threshold
VIN_UVLO+
28.5
33.7
37.4
V
Input undervoltage lockout
hysteresis
VIN_UVLO_HYST
1.6
V
TUVLO
8
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
TSCP
Output Power (W)
Thermal shutdown threshold
53
Effective internal RC filter
78
100
A
6.2
ms
100
A
1
µs
125
TJ_OTP
°C
350
120
300
100
250
80
200
60
150
40
100
20
50
0
2.99
3.17
3.35
3.52
3.70
3.88
4.05
4.23
4.40
Output Voltage (V)
P (ave)
P (pk), < 10ms
I (ave)
Figure 1 — Safe operating area
BCM® Bus Converter
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I (pk), < 10ms
4.58
4.76
Output Current (A)
Fault recovery time
BCM48Bx040y200B00
Signal Characteristics
Specifications apply over all line and load conditions, unless otherwise noted; boldface specifications apply over the temperature range of
-40°C ≤ TCASE ≤ 100°C (T-Grade); all other specifications are at TCASE = 25ºC unless otherwise noted.
Primary Control: PC
• The PC pin enables and disables the BCM. When held low, the BCM 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
DIGITAL
INPUT /
OUTPUT
ATTRIBUTE
SYMBOL
PC voltage
PC available current
MIN
TYP
MAX
UNIT
VPC
4.7
5.0
5.3
V
IPC_OP
2.0
3.5
5.0
mA
50
100
50
150
400
kΩ
1000
pF
PC source (current)
IPC_EN
PC resistance (internal)
RPC_INT
PC capacitance (internal)
CPC_INT
PC load resistance
RPC_S
Regular
Operation
PC enable threshold
VPC_EN
PC disable threshold
VPC_DIS
Standby
PC disable duration
TPC_DIS_T
Transition
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
Internal pull down resistor
To permit regular operation
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
INPUT /
OUTPUT
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 = 48V, IOUT = 50A
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 20
TYP
2.12
VTM
TM voltage reference
MIN
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mV/°C
200
mV
50
pF
10
µs
0
V
40
50
kΩ
BCM® Bus Converter
Page 7 of 20
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
BCM48Bx040y200B00
Timing Diagram
BCM48Bx040y200B00
Application Characteristics
The following values, typical of an application environment, are collected at TCASE = 25ºC unless otherwise noted. See associated figures for general trend data.
95
Full Load Efficiency (%)
Power Dissipa tion (W)
12
10
8
6
4
2
0
94
93
92
38
40
42
44
46
47
49
51
53
55
-40
-20
0
Input Voltage (V)
25°C
-40°C
TCASE:
100°C
V IN:
35
90
30
Power Dissipation (W)
Efficiency (%)
95
85
80
75
70
65
0
5
10
15
20
25
30
38V
38V
35
40
45
100
48V
55V
15
10
5
0
5
10
15
48V
20
25
30
35
40
45
50
45
50
Load Current (A)
VIN :
55V
38V
48V
55V
Figure 5 — Power dissipation at TCASE = -40°C
95
Power Dissipation (W)
35
90
Efficiency (%)
80
20
0
50
Figure 4 — Efficiency at TCASE = -40°C
85
80
75
70
60
25
Load Current (A)
VIN :
40
Figure 3 — Full load efficiency vs. temperature; Vin
Figure 2 — No load power dissipation vs. Vin
60
20
Case Temperature (°C)
28
21
14
7
0
0
5
10
15
20
25
30
35
40
45
50
0
5
10
VIN :
38 V
48 V
BCM® Bus Converter
Page 8 of 20
VIN :
55V
Figure 6 — Efficiency at TCASE = 25°C
15
20
25
30
35
38V
48V
Figure 7 — Power dissipation at TCASE = 25°C
Rev 1.3
08/2016
40
Load Current (A)
Load Current (A)
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BCM48Bx040y200B00
Application Characteristics (Cont.)
95
Power Dissipation (W)
35
Efficiency (%)
90
85
80
75
28
21
14
7
0
70
0
5
10
15
20
25
30
35
40
45
50
0
5
10
15
Load Current (A)
VIN :
38V
VIN :
55V
48V
Figure 8 — Efficiency at TCASE = 100°C
20
25
30
35
40
45
50
45
50
Load Current (A)
38V
48V
55V
Figure 9 — Power dissipation at TCASE = 100°C
3.5
250
225
Ripple (mV pk-pk)
ROUT (mΩ)
3.0
2.5
2.0
1.5
200
175
150
125
100
75
50
25
1.0
0
-40
-20
0
20
40
60
80
100
0
5
IOUT:
26.5A
BCM® Bus Converter
Page 9 of 20
Rev 1.3
08/2016
15
20
VIN:
53A
Figure 10 — ROUT vs. temperature; nominal input
10
25
30
35
40
Load Current (A)
Case Temperature (°C)
48V
Figure 11 — Vripple vs. Iout: No external Cout, board mounted
module, scope setting : 20MHz analog BW
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Application Characteristics (Cont.)
Figure 12 — Full load ripple, 330µF Cin: No external Cout, Board
mounted module, scope setting : 20MHz analog BW
Figure 13 — Start up from application of PC;
Vin pre-applied Cout = 9100µF
Figure 14 — 0A – 50A transient response: Cin = 330µF, Iin measured
prior to Cin , no external Cout
Figure 15 — 50A – 0A transient response: Cin = 330µF, Iin measured
prior to Cin, no external Cout
BCM® Bus Converter
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BCM48Bx040y200B00
General Characteristics
Specifications apply over all line and load conditions, unless otherwise noted; boldface specifications apply over the temperature range of
-40°C ≤ TCASE ≤ 100°C (T-Grade); All other specifications are at TCASE = 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
BCM48Bx040T200B00 (T-Grade)
-40
125
BCM48Bx040M200B00 (M-Grade)
-55
125
µm
Thermal
Operating temperature
TJ
Thermal resistance
fJC
Isothermal heatsink and
isothermal internal PCB
Thermal capacity
°C
1
°C/W
5
Ws/°C
Assembly
Peak compressive force
applied to case (Z-axis)
Storage
Temperature
Supported by J-lead only
TST
lbs
5.41
lbs/ in2
BCM48Bx040T200B00 (T-Grade)
-40
125
°C
BCM48Bx040M200B00 (M-Grade)
-65
125
°C
ESDHBM
Human Body Model,
“JEDEC JESD 22-A114D.01”Class 1D
1000
ESDCDM
Charge Device Model,
“JEDEC JESD 22-C101-D”
400
ESD Withstand
6
V
Soldering
Peak temperature during reflow
245
°C
Peak time above 217°C
MSL 4 (Datecode 1528 and later)
60
90
s
Peak heating rate during reflow
1.5
3
°C/s
Peak cooling rate post reflow
1.5
6
°C/s
60
VDC
Safety
Working voltage (IN – OUT)
VIN_OUT
Isolation voltage (hipot)
VHIPOT
Isolation capacitance
CIN_OUT
Unpowered unit
Isolation resistance
RIN_OUT
At 500VDC
MTBF
2,250
2500
VDC
3200
10
MIL-HDBK-217Plus Parts Count - 25°C
Ground Benign, Stationary, Indoors /
Computer Profile
5.01
MHrs
Telcordia Issue 2 - Method I Case III;
25°C Ground Benign, Controlled
8.68
MHrs
cURus
CE Marked for Low Voltage Directive and ROHS recast directive, as applicable.
BCM® Bus Converter
Page 11 of 20
pF
MΩ
cTUVus
Agency approvals / standards
3800
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BCM48Bx040y200B00
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
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Sine Amplitude Converter™ Point of Load Conversion
286pH
+
VinIN
V
Rout
2.4mΩ
ROUT
out
IIOUT
Lin = 5.7nH
RRcCin
IN
0.57mΩ
CIN
C
IN
2µF
IIQQ
+
+
–
100mA
K
+
RRC
cout
OUT
0.35Ω
V•I
1/12 • Iout
Lout = 600pH
130µΩ
1/12 • Vin
CCOUT
out
VVOUT
out
200µF
–
–
–
Figure 16 — 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
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 BCM48Bx040y200B00 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
VOUT = VIN • K
(1)
VVin
in
+
–
SAC™
SAC
K=
= 1/32
1/12
K
Vout
V
out
K represents the “turns ratio” of the SAC.
Rearranging Eq (1):
VOUT (2)
K =
VIN
Figure 17 — K = 1/12 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
Page 13 of 20
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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 secondary
side is 6.9mΩ, with K = 1/12.
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 18.
S
VVin
in
+
–
C
SAC™
SAC
K = 1/12
K = 1/32
VVout
out
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:
n No load power dissipation (PNL): defined as the power
used to power up the module with an enabled powertrain
at no load.
Figure 18 — 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:
n Resistive loss (PR
): refers to the power loss across
OUT
the BCM module modeled as pure resistive impedance.
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,
IC = IOUT • K
(8)
substituting Eq. (1) and (8) into Eq. (7) reveals:
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
IN
IN
= VIN • IIN – PNL – (IOUT)2 • ROUT
VIN • IIN
IOUT = C • dVOUT
K2 dt
(9)
= 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 = 1/12 as shown in Figure 18, C = 1µF would appear as
C = 144µF when viewed from the output.
BCM® Bus Converter
Page 14 of 20
Rev 1.3
08/2016
vicorpower.com
800 927.9474
(12)
BCM48Bx040y200B00
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:
COUT = CIN
K2
This enables a reduction in the size and number of capacitors used
in a typical system.
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.
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 14 and 15.
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 BCM48Bx040y200B00 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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