BCM® Bus Converter
BCM384x480y325Bzz
S
®
US
C
C
NRTL
US
Isolated Fixed Ratio DC-DC Converter
Features & Benefits
Product Ratings
• 384VDC – 48VDC 325W Bus Converter
VIN = 384V (360 – 400V)
POUT = up to 325W
• High efficiency (95%) reduces system
power consumption
VOUT = 48V (45 – 50V)
(no load)
K = 1/8
• High power density (1106W/in3)
reduces power system footprint by >40%
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 (95%) Sine
Amplitude Converter™ (SAC™) operating from a 360 to 400VDC
primary bus to deliver an isolated, ratiometric output voltage from
45 to 50VDC. 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 BCM384x480y325Bzz 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.
• Provides enable/disable control,
internal temperature monitoring
• Can be paralleled to create multi-kW arrays
The BCM384F480y325Bzz 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 BCM384x480y325Bzz 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
Typical Application
BCM
TM
PC
SW1
enable/disable
switch
F1
VIN
+IN
+OUT
–IN
–OUT
COUT
CIN
GND
PRIMARY
SECONDARY
ISOLATION BOUNDRY
BCM® Bus Converter
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BCM384x480y325Bzz
Typical Application
PRM
BCM
ENABLE
enable/disable
switch
TM
PC
SGND
enable/disable
switch
R
FUSE
V
C
IN
+IN
+OUT
–IN
–OUT
I_BCM_ELEC
PRIMARY
SOURCE_RTN
VAUX
R
R
TRIM_PRM
VTM
REF/
REF_EN
TRIM
AL
VT
SHARE/
CONTROL NODE
VC
AL_PRM
TM
VTM Start Up Pulse
+OUT
PC
C
R
O_PRM_DAMP
SGND
I_PRM_FLT
R
+IN
+OUT
–IN
–OUT
L
I_PRM_CER
SGND
LOAD
O_VTM_CER
+IN
O_PRM_FLT
C
O_PRM_CER
–IN
–OUT
PRIMARY
SECONDARY
SECONDARY
LOAD_RTN
ISOLATION BOUNDRY
ISOLATION BOUNDRY
SGND
BCM384x480y325Bzz + PRM + VTM, Adaptive Loop Configuration
V
TM
enable/disable
switch
VAUX/SER-IN
FUSE
VIN
SOURCE_RTN
C
I_BCM_ELEC
+IN
+OUT
–IN
–OUT
VT
SHARE/
CONTROL NODE
VC
IFB
I_PRM_DAMP
L
I_PRM_FLT
PRIMARY
AL
SGND
R
IN
Voltage Sense and Error Amplifier
(Differential)
GND
VTM
SGND
VTM Start up Pulse
V+
+IN
+OUT
–IN
–OUT
SGND
External Current Sense
I_PRM_ELEC
SGND
R
L
C
O_PRM_DAMP
+IN
O_PRM_FLT
C
O_PRM_CER
–IN
–OUT
PRIMARY
SECONDARY
SECONDARY
ISOLATION BOUNDRY
ISOLATION BOUNDRY
SGND
BCM384x480y325Bzz + PRM + VTM, Remote Sense Configuration
BCM® Bus Converter
Page 2 of 22
VC
PC
V–
VOUT
–IN
+OUT
TM
Voltage Reference with Soft Start
+IN
C
SGND
OUT
REF/
REF_EN
TRIM
SGND
REF 3312
VAUX
ENABLE
enable/disable
switch
PC
REF
SGND
PRM
Rev 1.1
10/2016
Voltage Sense
BCM
OUT
VC
IFB
I_PRM_DAMP
L
V
Adaptive Loop Temperature Feedback
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O_VTM_CER
LOAD
BCM384x480y325Bzz
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
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
Page 3 of 22
Rev 1.1
10/2016
Enable and disable control, input side referenced signal
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BCM384x480y325Bzz
Part Ordering Information
Device
Input Voltage Range
Package Type
Output Voltage x 10
Temperature Grade
BCM
384
x
480
y
BCM = BCM
384 = 360 – 400V
F = Full VIC SMD
Output Power Revision
325
B
325 = 325W
B
T = -40 – 125ºC
zz
00 = standard
480 = 48V
T = Full VIC TH
Version
M = -55 – 125ºC
>00 = Customer
specific version
Standard Models
Part Number
BCM384F480T325B00
BCM384F480M325B00
BCM384T480T325B00
BCM384T480M325B00
VIN
Package Type
VOUT
Temperature
360 – 400V
Full VIC SMD
48V
(45 – 50V)
-40 – 125ºC
360 – 400V
Full VIC TH
48V
(45 – 50V)
-40 – 125ºC
-55 – 125ºC
-55 – 125ºC
Power
Version
325W
00 = standard
325W
00 = standard
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
Min
Max
-1
440
V
1
V / µs
4242
V
60
V
10.5
A
7.05
A
Operational
Isolation voltage, input to ouput
+OUT to –OUT
Output current transient
-1
≤ 1ms, ≤ 10% DC
Output current average
Unit
PC to –IN
-0.3
20
V
TM to –IN
-0.3
7
V
Operating IC junction temperature
T–Grade
-40
125
ºC
Storage temperature
T–Grade
-40
125
ºC
BCM® Bus Converter
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Rev 1.1
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BCM384x480y325Bzz
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
400
V
1.2
mA
620
ms
Powertrain
Input voltage range, continuous
360
VIN_DC
Quiescent current
IQ
VIN to VOUT time
TON1
Disabled, PC Low
1
VIN = 384V, PC floating
VIN = 384V, TCASE = 25ºC
No load power dissipation
PNL
7.2
3
VIN = 384V
12
VIN = 360V to 400V
15
Inrush current peak
IINR_P
DC input current
IIN_DC
At POUT = 325W
K
18
VIN = 360V to 400V, TCASE = 25ºC
Worse case of: VIN = 400V, COUT = 100μF,
RLOAD = 7Ω
Transformation ratio
10
2
K = VOUT / VIN, at no load
W
4
A
0.9
A
1/8
V/V
Output power (average)
POUT_AVG
IOUT_AVG ≤ 7.05A
325
W
Output power (peak)
POUT_PK
1ms max, POUT_AVG ≤ 325W
450
W
Output current (average)
IOUT_AVG
POUT_AVG ≤ 325W
7.05
A
Output current (peak)
IOUT_PK
1ms max, IOUT_AVG ≤ 7.05A
10.5
A
VIN = 384V, IOUT = 7.05A; TCASE = 25°C
Efficiency (ambient)
hAMB
95.0
VIN = 360V to 400V, IOUT = 7.05A; TCASE = 25°C
94.9
VIN = 384V, IOUT = 3.53A; TCASE = 25°C
93.5
94.9
95.4
Efficiency (hot)
hHOT
VIN = 384V, IOUT = 7.05A; TCASE = 100°C
94.3
Efficiency (over load range)
h20%
1.41A < IOUT < 7.05A
80.0
Output resistance
96.0
%
%
%
ROUT_COLD
IOUT = 7.05A, TCASE = -40°C
60
100
130
ROUT_AMB
IOUT = 7.05A, TCASE = 25°C
110
135
150
ROUT_HOT
IOUT = 7.05A, TCASE = 100°C
130
165
260
1.56
1.65
1.73
MHz
400
mV
mΩ
Switching frequency
FSW
Output voltage ripple
VOUT_PP
COUT = 0F, IOUT = 7.05A, VIN = 384V,
20MHz BW
200
Input inductance (parasitic)
LIN_PAR
Simulated J-lead model
5.6
nH
Frequency up to 30MHz, Simulated J-lead model
600
pH
CIN_INT
Effective value at 384VIN
0.1
µF
Output capacitance (internal)
COUT_INT
Effective value at 48VOUT
5.6
µF
Output capacitance (external)
COUT_EXT
Output inductance (parasitic)
LOUT_PAR
Input capacitance (internal)
BCM® Bus Converter
Page 5 of 22
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Rev 1.1
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100
µF
BCM384x480y325Bzz
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
VIN_OVLO+
410
429
440
V
401
420
435
V
Protection
Input overvoltage lockout threshold
Input overvoltage recovery threshold
VIN_OVLO-
Input overvoltage lockout hysteresis
VIN_OVLO_HYST
9
V
Overvoltage lockout response time
TOVLO
47
µs
TAUTO_RESTART
460
540
620
ms
Input undervoltage lockout
threshold
VIN_UVLO-
270
293
315
V
Input undervoltage recovery
threshold
VIN_UVLO+
285
308
330
V
Input undervoltage lockout
hysteresis
VIN_UVLO_HYST
15
V
TUVLO
47
µs
Fault recovery time
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
Thermal shutdown threshold
7.3
Effective internal RC filter
11
14
A
4.0
ms
14
A
1
µs
125
TJ_OTP
°C
12
500
450
Output Power (W)
350
8
300
6
250
200
4
150
100
2
50
0
0
43.3
44.1
45.0
45.8
46.6
47.5
48.3
49.2
Output Voltage (V)
P (ave)
I (ave)
p (pk), ≤ 1ms
I (pk), ≤ 1ms
Figure 1 — Safe operating area
BCM® Bus Converter
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50.0
50.8
Output Current (A)
10
400
BCM384x480y325Bzz
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
SYMBOL
TYP
MAX
UNIT
VPC
4.7
5.0
5.3
V
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
To permit regular operation
60
RPC_S
Start Up
PC time to start
TON1
Transition
MIN
IPC_OP
PC load resistance
Standby
CONDITIONS / NOTES
PC available current
PC voltage
Start Up
Regular
Operation
DIGITAL
INPUT /
OUTPUT
ATTRIBUTE
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
µA
400
1000
2.0
Minimum time before attempting
re-enable
2.5
620
ms
3.0
V
1.95
V
1
50
From fault to PC = 2V
pF
kΩ
s
50
VIN = 384V for at least TON1 ms
kΩ
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
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 = 352V, IOUT = 28.5A
120
From fault to TM = 1.5V
200
mV
50
pF
10
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25
40
µA
mV/°C
µs
0
Internal pull down resistor
Reserved for factory use. No connection should be made to this pin.
Rev 1.1
10/2016
2.95
MAX
10
Reserved: RSV
BCM® Bus Converter
Page 7 of 22
TYP
2.12
VTM
VTM_AMB
MIN
V
50
kΩ
BCM® Bus Converter
Page 8 of 22
NL
5V
2.5 V
5V
3V
PC
VUVLO+
VUVLO–
Rev 1.1
10/2016
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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
BCM384x480y325Bzz
Timing Diagram
BCM384x480y325Bzz
Application Characteristics
14
97.0
13
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.
12
11
10
9
8
7
6
5
4
360
364
368
372
376
380
384
388
392
396
96.5
96.0
95.5
95.0
94.5
94.0
-55
400
-35
-15
Input Voltage (V)
TCASE:
-40ºC
25ºC
VIN_DC:
100ºC
Figure 2 — No load power dissipation vs. Vin
18
Power Dissipation (W)
20
97
Efficiency (%)
94
91
88
85
82
79
76
73
0.0
0.8
1.6
2.4
3.2
4.0
4.8
360V
5.6
6.4
7.2
384V
4
2
0.0
0.8
1.6
Power Dissipation (W)
Efficiency (%)
85
82
79
76
73
4.8
5.6
6.4
4.8
5.6
6.4
360V
384V
7.2
8.0
7.2
8.0
400V
7.2
8.0
14
12
10
8
6
4
2
0
0.0
0.8
1.6
384V
2.4
3.2
4.0
4.8
5.6
6.4
Output Current (A)
400V
Figure 6 — Efficiency at TCASE = 25°C
BCM® Bus Converter
Page 9 of 22
4.0
16
Output Current (A)
360V
3.2
Figure 5 — Power dissipation at TCASE = -40°C
88
VIN_DC:
2.4
VIN_DC:
400V
91
4.0
400V
6
18
3.2
384V
Output Current (A)
94
2.4
360V
8
20
1.6
105
10
97
0.8
85
12
100
0.0
65
14
0
8.0
Figure 4 — Efficiency at TCASE = -40°C
70
45
16
Output Current (A)
VIN_DC:
25
Figure 3 — Full load efficiency vs. temperature; Vin
100
70
5
Case Temperature (ºC)
VIN_DC:
360V
384V
Figure 7 — Power dissipation at TCASE = 25°C
Rev 1.1
10/2016
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800 927.9474
400V
BCM384x480y325Bzz
Application Characteristics (Cont.)
20
97
18
Power Dissipation (W)
100
Efficiency (%)
94
91
88
85
82
79
76
73
70
0.0
0.8
1.6
2.4
3.2
4.0
4.8
5.6
6.4
7.2
16
14
12
10
8
6
4
2
0
8.0
0.0
0.8
1.6
360V
384V
VIN_DC:
400V
Figure 8 — Efficiency at TCASE = 100°C
4.8
5.6
6.4
7.2
8.0
360V
384V
400V
250
225
Ripple (mVPK-PK)
200
180
ROUT (mΩ)
4.0
Figure 9 — Power dissipation at TCASE = 100°C
220
160
140
120
200
175
150
125
100
75
50
25
100
80
3.2
Output Current (A)
Output Current (A)
VIN_DC:
2.4
0
-40
-20
0
20
40
60
80
100
0.0
0.8
BCM® Bus Converter
Page 10 of 22
Rev 1.1
10/2016
3.2
VIN_DC:
7.05A
Figure 10 — ROUT vs. temperature; nominal input
2.4
4.0
4.8
5.6
6.4
7.2
8.0
Output Current (A)
Case Temperature (°C)
IOUT_DC:
1.6
384V
Figure 11 — Vripple vs. Iout: No external Cout, board mounted
module, scope setting : 20MHz analog BW
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BCM384x480y325Bzz
Application Characteristics (Cont.)
Figure 12 — Full load ripple, 2.2µF Cin: No external Cout, Board
mounted module, scope setting : 20MHz analog BW
Figure 13 — Start up from application of PC;
Vin pre-applied Cout = 100µF, 100% IOUT R-load
Figure 14 — 0A – 7.05A transient response: Cin = 2.2µF,
Iin measured prior to Cin , no external Cout
Figure 15 — 7.05A – 0A transient response: Cin = 2.2µF,
Iin measured prior to Cin, no external Cout
BCM® Bus Converter
Page 11 of 22
Rev 1.1
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BCM384x480y325Bzz
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
BCM384x480T325B00 (T-Grade)
-40
125
BCM384x480M325B00 (M-Grade)
-55
125
µm
Thermal
Operating temperature
TJ
Thermal resistance
fJC
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
TST
lbs
5.41
lbs/ in2
BCM384x480T325B00 (T-Grade)
-40
125
°C
BCM384x480M325B00 (M-Grade)
-55
125
°C
ESDHBM
Human Body Model,
“JEDEC JESD 22-A114C.01”Class 1C
2000
ESDCDM
Charge Device Model,
“JEDEC JESD 22-C101-D”
500
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
500
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
4242
VDC
660
MIL-HDBK-217Plus Parts Count - 25°C
Ground Benign, Stationary, Indoors /
Computer Profile
3.2
MHrs
Telcordia Issue 2 - Method I Case III;
25°C Ground Benign, Controlled
7.2
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
800
Rev 1.1
10/2016
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BCM384x480y325Bzz
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
Rev 1.1
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Sine Amplitude Converter™ Point of Load Conversion
1.94nH
+
VinIN
V
Rout
125mΩ
ROUT
out
IIOUT
Lin = 5.6nH
RRcCin
IN
9.2mΩ
CIN
C
IN
0.1µF
IIQQ
20.0mA
+
+
–
–
K
RRC
cout
OUT
110mΩ
V•I
1/8 • Iout
Lout = 600pH
+
550µΩ
1/8 • Vin
CCOUT
out
VVOUT
out
5.6µF
–
–
Figure 17 — 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 BCM384x480y325Bzz 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
1/8
KK==1/32
Vout
V
out
K represents the “turns ratio” of the SAC.
Rearranging Eq (1):
VOUT (2)
K =
VIN
Figure 18 — K = 1/8 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 – IIN • R) • K
VOUT = VIN • K – IOUT • ROUT (3)
and IOUT is represented by:
IIN – IQ (4)
IOUT =
K
BCM® Bus Converter
Page 14 of 22
Rev 1.1
10/2016
(5)
Substituting the simplified version of Eq. (4)
(IQ is assumed = 0A) into Eq. (5) yields:
VOUT = VIN • K – IOUT • R • K2 (6)
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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 15.6mΩ, 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 19.
S
VVin
in
+
–
C
SAC™
SAC
K = 1/8
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 19 — 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 = 1/8 as shown in Figure 19, C = 1µF would appear
as C = 64µF when viewed from the output.
BCM® Bus Converter
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BCM384x480y325Bzz
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.
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 15 and 16.
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 BCM384x480y325Bzz 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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