BCM® Bus Converter
BCM48Bx120y300A00
®
S
US
C
C
NRTL
US
Isolated Fixed Ratio DC-DC Converter
Features & Benefits
Product Ratings
• 48VDC – 12VDC 300W Bus Converter
• High efficiency (>96%) reduces system
power consumption
• High power density (>1022W/in3)
reduces power system footprint by >40%
VIN = 48V (38 – 55V)
POUT= up to 300W
VOUT = 12V (9.5 – 13.8V)
(no load)
K = 1/4
Description
• Contains built-in protection features:
Undervoltage
Overvoltage Lockout
Overcurrent Protection
Short circuit Protection
Overtemperature Protection
The VI Chip® bus converter is a high efficiency (>96%) Sine
Amplitude Converter™ (SAC™) operating from a 38 to 55VDC
primary bus to deliver an isolated, ratiometric output voltage from
9.5 to 13.8VDC. 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 BCM48Bx120y300A00 is 1/4, the capacitance value can
be reduced by a factor of 16x, 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 BCM48BF120y300A00 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 BCM48Bx120y300A00 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
• Communications Systems
Part Numbering
Product Number
BCM48Bx120y300A00
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
Page 1 of 21
Rev 1.9
01/2021
BCM48Bx120y300A00
Pin Configuration
4
3
2
1
A
A
+OUT
B
B
C
C
D
D
E
E
–OUT
F
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
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 21
Function
Temperature monitor, input side referenced signal
No connect
Enable and disable control, input side referenced signal
Rev 1.9
01/2021
BCM48Bx120y300A00
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
Isolation Voltage, Input to Ouput
2250
V
–1
16
V
–3
37.5
A
–2
30
A
PC to –IN
–0.3
20
V
TM to –IN
–0.3
7
V
+OUT to –OUT
Output Current Transient
≤ 10ms, ≤ 10% DC
Output Current Average
BCM® Bus Converter
Page 3 of 21
Rev 1.9
01/2021
BCM48Bx120y300A00
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 = 25°C unless otherwise noted.
Attribute
Symbol
Conditions / Notes
Min
Typ
Max
Unit
38
55
V
38
55
V
0.5
1.0
mA
450
620
ms
5.3
6.5
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, 50ms max,
10% duty cycle max
Disabled, PC Low
VIN = 48V, PC floating
340
VIN = 48V, TCASE = 25°C
No-Load Power Dissipation
PNL
3
VIN = 48V
VIN = 38 – 55V, TCASE = 25°C
9
VIN = 38 – 55V
17
Inrush Current Peak
IINR_P
Worse case of: VIN = 55V, COUT = 1000μF,
RLOAD = 391mΩ
DC Input Current
IIN_DC
At POUT = 300W
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)
ηAMB
15
10
K = VOUT / VIN, at no load
20
A
8.8
A
1/4
10ms max, POUT_AVG ≤ 300W
10ms max, IOUT_AVG ≤ 30A
VIN = 48V, IOUT = 25A; TCASE = 25°C
95.0
VIN = 38 – 55V, IOUT = 25A; TCASE = 25°C
93.5
VIN = 48V, IOUT = 12.5A; TCASE = 25°C
94.5
95.5
94.5
95.6
W
V/V
300
W
450
W
30
A
37.5
A
96.0
%
Efficiency (Hot)
ηHOT
VIN = 48V, IOUT = 25A; TCASE = 100°C
Efficiency (Over Load Range)
η20%
5A < IOUT < 25A
80
ROUT_COLD
IOUT = 25A, TCASE = –40°C
4.9
6.7
12.0
ROUT_AMB
IOUT = 25A, TCASE = 25°C
6.3
9.0
14.0
ROUT_HOT
IOUT = 25A, TCASE = 100°C
8.8
11.5
16.0
1.85
1.95
2.05
MHz
285
mV
Output Resistance
Switching Frequency
FSW
%
%
mΩ
Output Voltage Ripple
VOUT_PP
COUT = 0F, IOUT = 25A, VIN = 48V,
20MHz BW
150
Output Inductance (Parasitic)
LOUT_PAR
Frequency up to 30MHz, simulated J-lead model
600
pH
Output Capacitance (Internal)
COUT_INT
Effective value at 12VOUT
47
µF
Output Capacitance (External)
COUT_EXT
BCM® Bus Converter
Page 4 of 21
0
Rev 1.9
01/2021
1000
µF
BCM48Bx120y300A00
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 = 25°C 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
Fault Recovery Time
tAUTO_RESTART
240
300
380
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
Undervoltage Lockout
Response Time
tUVLO
8
µs
Output Overcurrent Trip Threshold
IOCP
Output Overcurrent Response
Time Constant
tOCP
Short Circuit Protection
Trip Threshold
ISCP
Short Circuit Protection
Response Time
tSCP
Effective internal RC filter
39
55
A
5.3
ms
30
A
1
µs
125
TJ_OTP
°C
375
50.00
350
43.75
325
37.50
300
31.25
275
25.00
250
18.75
225
12.50
200
6.25
8.70
9.23
9.76
10.29
10.82
11.36
11.89
12.42
12.95
Output Voltage (V)
P (ave)
P (pk), < 10ms
Figure 1 — Safe operating area
BCM® Bus Converter
Page 5 of 21
Rev 1.9
01/2021
I (ave)
I (pk), < 10ms
13.48
14.01
Output Current (A)
Output Power (W)
Thermal Shut-Down Threshold
30
BCM48Bx120y300A00
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 = 25°C 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
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
50
150
PC Capacitance (Internal)
CPC_INT
PC Voltage
Start Up
PC Load Resistance
Regular
Operation
PC Enable Threshold
VPC_EN
PC Disable Threshold
VPC_DIS
Standby
PC Disable Duration
tPC_DIS_T
Digital
Input /
Output
RPC_S
PC Threshold Hysteresis
Transition
Conditions / Notes
Internal pull down resistor
To permit regular operation
tON2
PC Disable to Standby Time
tPC_DIS
PC Fault Response Time
tFR_PC
kΩ
1000
pF
kΩ
2.5
3.0
V
1.95
V
1
VPC_HYSTER
PC Enable to VOUT Time
400
60
2.0
Minimum time before attempting
re-enable
µA
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 Shut Down.
Signal Type
State
Attribute
TM Voltage Range
TM Voltage Reference
Analog
Output
Digital
Input /
Output
Regular
Operation
Transition
Standby
Symbol
Conditions / Notes
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
3.00
Unit
4.04
V
3.05
V
100
CTM = 0pF, VIN = 48V, IOUT = 25A
120
From fault to TM = 1.5V
200
mV
50
pF
10
25
40
µA
mV/°C
µs
0
Internal pull down-resistor
Reserved for factory use. No connection should be made to this pin.
Rev 1.9
01/2021
2.95
Max
10
Reserved: RSV
BCM® Bus Converter
Page 6 of 21
Typ
2.12
VTM
VTM_AMB
Min
V
50
kΩ
BCM® Bus Converter
Page 7 of 21
NL
5V
2.5 V
5V
3V
PC
VUVLO+
VUVLO–
Rev 1.9
01/2021
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
0.4V
3V @ 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
BCM48Bx120y300A00
Timing Diagram
BCM48Bx120y300A00
Application Characteristics
The following values, typical of an application environment, are collected at TCASE = 25°C unless otherwise noted.
See associated figures for general trend data.
96.5
12
Full Load Efficiency (%)
Power Dissipation (W)
11
10
9
8
7
6
5
4
96.0
95.5
95.0
94.5
94.0
38
40
42
44
46
47
49
51
53
55
-40
-20
0
Input Voltage (V)
TCASE:
-40°C
25°C
100°C
V IN:
Figure 2 — No load power dissipation vs. Vin
Power Dissipation (W)
Efficiency (%)
60
80
100
38V
48V
55V
30
92
87
82
77
72
0
5
10
15
20
25
20
15
10
5
0
25
Load Current (A)
VIN:
38V
48V
0
5
10
15
20
25
Load Current (A)
VIN:
55V
Figure 4 — Efficiency at TCASE = –40°C
38V
48V
55V
Figure 5 — Power dissipation at TCASE = –40°C
98
24
Power Dissipation (W)
Efficiency (%)
40
Figure 3 — Full load efficiency vs. temperature; Vin
97
67
20
Case Temperature (°C)
93
88
83
78
18
12
6
0
0
5
VIN:
10
15
20
38V
48V
55V
Load Current (A)
Figure 6 — Efficiency at TCASE = 25°C
BCM® Bus Converter
Page 8 of 21
25
0
5
10
15
20
Load Current (A)
VIN:
38V
48V
Figure 7 — Power dissipation at TCASE = 25°C
Rev 1.9
01/2021
55V
25
BCM48Bx120y300A00
Application Characteristics (Cont.)
The following values, typical of an application environment, are collected at TCASE = 25°C unless otherwise noted.
See associated figures for general trend data.
24
Power Dissipation (W)
Efficiency (%)
98
93
88
83
78
0
5
10
15
20
18
12
6
0
25
0
5
Load Current (A)
38V
VIN:
48V
55V
VIN:
14
145
12
125
10
8
6
-40
-20
0
20
40
60
80
12.5A
25
38V
48V
55V
85
65
45
0
5
10
15
20
25
Load Current (A)
VIN:
25A
Figure 10 — ROUT vs. temperature; nominal input
BCM® Bus Converter
Page 9 of 21
20
105
25
100
Case Temperature (°C)
IOUT:
15
Figure 9 — Power dissipation at TCASE = 100°C
Ripple (mV pk-pk)
ROUT (mΩ)
Figure 8 — Efficiency at TCASE = 100°C
4
10
Load Current (A)
48V
Figure 11 — Vripple vs. Iout: no external Cout, board-mounted
module, scope setting: 20MHz analog BW
Rev 1.9
01/2021
BCM48Bx120y300A00
Application Characteristics (Cont.)
The following values, typical of an application environment, are collected at TCASE = 25°C unless otherwise noted.
See associated figures for general trend data.
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 = 1000µF
Figure 14 — 0 – 25A transient response: Cin = 330µF, Iin measured
prior to Cin , no external Cout
Figure 15 — 25 – 0A transient response: Cin = 330µF, Iin measured
prior to Cin, no external Cout
BCM® Bus Converter
Rev 1.9
Page 10 of 21 01/2021
BCM48Bx120y300A00
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 = 25°C 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]
6.48 [0.255]
6.73 [0.265]
6.98 [0.275]
Height
H
Volume
Vol
Weight
W
Lead Finish
No heat sink
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
BCM48Bx120T300A00 (T-Grade)
–40
125
BCM48Bx120M300A00 (M-Grade)
–55
125
µm
Thermal
Operating Temperature
TJ
Thermal Resistance
θJC
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
6
lbs
5.41
lbs / in2
BCM48Bx120T300A00 (T-Grade)
–40
125
°C
BCM48Bx120M300A00 (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
TST
ESD Withstand
V
Soldering
Peak Temperature During Reflow
RoHS
245
Non-RoHS
225
°C
Peak Time Above Liquidus
Requires AN:009 compliance
60
90
s
Peak Heating Rate During Reflow
Requires AN:009 compliance
1
1.5
3
°C/s
Peak Cooling Rate Post Reflow
Requires AN:009 compliance
1
1.5
6
°C/s
60
VDC
Safety
Working Voltage (IN – OUT)
VIN_OUT
2250
Isolation Voltage (Hipot)
VHIPOT
Isolation Capacitance
CIN_OUT
Unpowered unit
Isolation Resistance
RIN_OUT
At 500VDC
MTBF
2500
VDC
3200
10
pF
MΩ
MIL-HDBK-217Plus Parts Count - 25°C
Ground Benign, Stationary, Indoors /
Computer Profile
6.03
MHrs
Telcordia Issue 2 - Method I Case III;
25°C Ground Benign, Controlled
7.94
MHrs
cTÜVus
Agency Approvals / Standards
3800
cURus
CE Marked for Low Voltage Directive and ROHS recast directive, as applicable.
BCM® Bus Converter
Rev 1.9
Page 11 of 21 01/2021
BCM48Bx120y300A00
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.
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 = 27°C). 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
Rev 1.9
Page 12 of 21 01/2021
BCM48Bx120y300A00
Sine Amplitude Converter™ Point-of-Load Conversion
LIN
5.7nH
+
RC
IN
0.57mΩ
VIN
973pH
IOUT
CIN
2µF
IQ
109mA
+
+
–
–
K
LOUT
600pH
RC
OUT
430µΩ
3.13Ω
V•I
1/4 • IOUT
ROUT
9.0mΩ
1/4 • VIN
COUT
47µF
+
VOUT
–
–
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 use of DC voltage transformation provides additional
interesting attributes. Assuming that ROUT = 0Ω and IQ = 0A,
Equation 3 now becomes Equation 1 and is essentially load
independent, resistor R is now placed in series with VIN.
The BCM48Bx120y300A00 SAC can be simplified into the
preceeding model.
R
At no load:
VIN
VOUT = VIN • K
VOUT
VIN
(2)
The relationship between VIN and VOUT becomes:
VOUT = (VIN – IIN • R) • K
(3)
IIN – IQ
K
VOUT = VIN • K – IOUT • R • K2
(4)
ROUT represents the impedance of the SAC, and is a function of
the RDS_ON 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.
(5)
Substituting the simplified version of Equation 4
(IQ is assumed = 0A) into Equation 5 yields:
and IOUT is represented by:
IOUT =
VOUT
Figure 17 — K = 1/4 Sine Amplitude Converter with
series input resistor
In the presence of a load, VOUT is represented by:
VOUT = VIN • K – IOUT • ROUT
SAC™
K = 1/4
(1)
K represents the “turns ratio” of the SAC.
Rearranging Equation 1:
K=
+
–
(6)
This is similar in form to Equation 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 62.5mΩ, with K = 1/4.
BCM® Bus Converter
Rev 1.9
Page 13 of 21 01/2021
BCM48Bx120y300A00
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
VIN
+
–
C
SAC™
K = 1/4
VOUT
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.
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:
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
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.
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.
n
Resistive loss (PROUT): refers to the power loss across
the BCM modeled as pure resistive impedance.
PDISSIPATED = PNL + PR
(8)
Therefore,
POUT = PIN – PDISSIPATED = PIN – PNL – PR
OUT
substituting Equations 1 and 8 into Equation 7 reveals:
IOUT =
C
K2
•
dVOUT
dt
(10)
OUT
(9)
(11)
The above relations can be combined to calculate the overall
module efficiency:
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 = 1/4 as shown in Figure 18, C = 1µF would appear as
C = 16µF when viewed from the output.
η=
=
POUT
PIN
PIN – PNL – PR
PIN
OUT
VIN • IIN – PNL – (IOUT)2 • ROUT
=1–
BCM® Bus Converter
Rev 1.9
Page 14 of 21 01/2021
=
VIN • IIN
(PNL + (IOUT)2 • ROUT)
VIN • IIN
(12)
BCM48Bx120y300A00
Input and Output Filter Design
Thermal Considerations
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.
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 BCM48Bx120y300A00 case
to less than 100°C will keep all junctions within the VI Chip module
below 125°C for most applications.
This paradigm shift requires system design to carefully evaluate
external filters in order to:
n
Guarantee low source impedance:
To take full advantage of the BCM’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.
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.
n
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 14 and 15.
n
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 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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