Texas Instruments | AN-2126 LM5046 Based Eighth Brick Reference Design (Rev. B) | Application notes | Texas Instruments AN-2126 LM5046 Based Eighth Brick Reference Design (Rev. B) Application notes

Texas Instruments AN-2126 LM5046 Based Eighth Brick Reference Design (Rev. B) Application notes
User's Guide
SNVA474B – March 2011 – Revised May 2013
AN-2126 LM5046 Based Eighth Brick Reference Design
1
Introduction
The LM5046 reference board is designed in the telecom industry standard one-eighth brick footprint based
on the phase-shifted full-bridge topology. This board is for reference only and is intended to demonstrate
the capability of the LM5046. Hardware is not provided for evaluation. Please refer to AN-2115 LM5046
Evaluation Board (SNVA470) for more information.
The performance of the reference board is as follows:
• Input operating range: 36V to 75V
• Output voltage: 12V
• Measured efficiency at 48V: 92% @ 10A
• Frequency of operation: 420kHz
• Board size: 2.28 x 0.89 x 0.4 inches
• Load Regulation: 0.2%
• Line Regulation: 0.1%
• Line UVLO (34V/32V on/off)
• Hiccup Mode Current Limit
The printed circuit board consists of 10 layers; 2 ounce copper outer layers and 3 ounce copper inner
layers on FR4 material with a total thickness of 0.12 inches. The unit is designed for continuous operation
at rated load at <40°C and a minimum airflow of 300 LFM at full load.
2
Theory of Operation
The Phase-Shifted Full-Bridge (PSFB) topology is a derivative of the classic full-bridge topology. When
tuned appropriately the PSFB topology achieves zero voltage switching (ZVS) of the primary FETs while
maintaining constant switching frequency. The ZVS feature is highly desirable as it reduces both the
switching losses and EMI emissions. Figure 1 illustrates the circuit arrangement for the PSFB topology.
The power transfer mode of the PSFB topology is similar to the hard switching full-bridge i.e., when the
FETs in the diagonal of the bridge are turned-on (Q1 & Q3 or Q2 & Q4), a power transfer cycle is initiated.
At the end of the power transfer cycle, PWM turns off the switch Q3 or Q4 depending on the phase with a
pulse width determined by the input and output voltages and the transformer turns ratio. In the freewheel
mode, unlike the classic full-bridge where all the four primary FETs are off, in the PSFB topology the
primary of the power transformer is shorted by activating either both the top FETs (Q1 and Q4) or both the
bottom FETs (Q2 and Q3) alternatively. In a PSFB topology, the primary switches are turned on
alternatively energizing the windings in such a way that the flux swings back and forth in the first and the
third quadrants of the B-H curve. The use of two quadrants allows better utilization of the core resulting in
a smaller core volume compared to the single-ended topologies.
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1
Theory of Operation
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Vin
T1
Q1
Vout
Q4
T1
VCC
VCC
Q2
HO1 BST1
HS1
LO1
SLOPE
Q3
CS
LO2
HS2 BST2
HO2
VIN
VCC
SR2
COMP
OVP
RT
SR1
PHASE-SHIFTED FULL-BRIDGE
CONTROLLER WITH
INTEGRATED GATE DRIVERS
UVLO
RES
SS SS SR
RD1
RD2
REF
PGND
GATE
DRIVE
ISOLATION
ISOLATED
FEEDBACK
AGND
Figure 1. Simplified Phase-Shifted Full-Bridge Converter
Figure 2. LM5046 Based Eighth Brick Reference Board
The secondary side employs synchronous rectification scheme, which is controlled by the LM5046. In
addition to the basic soft-start already described, the LM5046 contains a second soft-start function that
gradually turns on the synchronous rectifiers to their steady-state duty cycle. This function keeps the
synchronous rectifiers off until the error amplifier on the secondary side soft-starts, allowing a linear startup of the output voltage even into pre-biased loads. Then the SR output duty cycle is gradually increased
to prevent output voltage disturbances due to the difference in the voltage drop between the body diode
and the channel resistance of the synchronous MOSFETs. Feedback from the output is processed by an
amplifier and reference, generating an error voltage, which is coupled back to the primary side control
through an opto-coupler. The LM5046 evaluation board employs peak current mode control and a
standard “type II” network is used for the compensator.
2
AN-2126 LM5046 Based Eighth Brick Reference Design
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Performance Characteristics
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3
Performance Characteristics
Once the circuit is powered up and running normally, the output voltage is regulated to 12V with the
accuracy determined by the feedback resistors and the voltage reference. The frequency of operation is
selected to be 420 kHz, which is a good comprise between board size and efficiency. Please refer to the
Figure 3 for efficiency curves.
100
EFFICIENCY (%)
90
80
70
60
50
0
3
6
9
LOAD CURRENT (A)
12
Figure 3. Reference Board Efficiency
Figure 4 shows the output voltage during a typical start-up with a 48V input and a load of 12A. There is no
overshoot during start-up.
Conditions: Input Voltage=48V
Output Current=12A
Trace 1: Output Voltage Volts/div=5V
Horizontal Resolution =1.0 ms/div
Figure 4. Soft-Start
Figure 5 shows typical transient response on the reference board when the load current is switched from
5A to 10A and back to 5A. There is minimal output voltage droop and overshoot during the sudden
change in output current shown by the lower trace.
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Performance Characteristics
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Conditions: Input Voltage=48V
Output Current=5A to 10A to 5A
Upper Trace: Output Voltage Volts/div=500mV
Horizontal Resolution=200 µs/div
Figure 5. Transient Response
Figure 6 shows typical output ripple seen directly across the output capacitor, for an input voltage of 48V
and a load of 12A. This waveform is typical of most loads and input voltages.
Conditions: Input Voltage=48V
Output Current=12A
Bandwidth Limit=20 MHz
Trace 1: Output Voltage 100 mV/div
Horizontal Resolution=2 µs/div
Figure 6. Output Ripple
Figure 7 and Figure 8 show the typical SW node voltage waveforms with a 25A load. Figure 7 shows an
input voltage represents an input voltage of 48V and Figure 8 represents an input voltage of 75V.
Conditions: Input Voltage=48V
Output Current=10A
Trace 1: SW1 Node Q2 Drain Voltage Volts/div=20V
Trace 2: SW2 Node Q3 Drain Voltage Volts/div=20V
Horizontal Resolution=1 µs/div
Figure 7. 48V Switch Node Waveforms
4
AN-2126 LM5046 Based Eighth Brick Reference Design
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Performance Characteristics
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Conditions: Input Voltage=75V
Output Current=10A
Trace 1: SW1 Node Q2 Drain Voltage Volts/div=20V
Trace 2: SW2 Node Q3 Drain Voltage Volts/div=20V
Horizontal Resolution=1 µs/div
Figure 8. 75V Switch Node Waveforms
Figure 9 shows a typical startup of the LM5045 into a 6V pre-biased load.
Conditions: Input Voltage=48V, Output Pre-Bias=6V
Trace 1 (Channel 1): Output Voltage Volts/div=5V
Trace 2 (Channel 2): SR gate Volage Volts/Div=5V
Trace 3 (Channel 3): Output Current Amps/div=200mA
Horizontal Resolution=2.0 ms/div
Figure 9. Soft-Start into a 6V Pre-Biased Output
Figure 10 shows the output current de-rating on the reference board at 48V input.
LOAD CURRENT (A)
12
9
6
3
0
0
50
100
150
200
250
300
AIR FLOW (LFM)
Figure 10. Load Current vs. Air Flow
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Performance Characteristics
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Figure 11. LM5046 Based Eight Brick Reference Board Schematic
6
AN-2126 LM5046 Based Eighth Brick Reference Design
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Bill of Materials
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4
Bill of Materials
Designator
Description
Manufacturer
Part Number
C1, C2, C3
Ceramic, 2.2uF, X7R, 100V,
10%
MuRata
GRM32ER72A225KA35L
C4, C40
Ceramic, 100pF,C0G/NP0,
50V, 5%
TDK
C1608C0G1H101J
C5
Ceramic, 2.2uF, X7R, 16V,
10%
MuRata
GRM21BR71C225KA12L
C6, C13
CAP, CERM, 3300pF, 250V,
+/-10%, X7R, 0603
MuRata
GRM188R72A332MA01D
C7, C9
Ceramic, 1uF, X7R, 50V, 10%
MuRata
GRM21BR71H105KA12L
C11
Ceramic,1uF, X7R, 16V, 10%
TDK
C1608X7R1C105K
C12, C15, C21, C32
Ceramic, 0.1uF,X7R, 25V, 10% AVX
06033C104KAT2A
C14
CAP, CERM, 0.1uF, 100V, +/10%, X7R, 0603
MuRata
GRM18872A104KA
C17
CAP, TANT, 150uF, 16V, +/10%, 0.085 ohm, 7343-31
SMD
Kemet
T495D157K016ATE085
C18, C19
Ceramic, 47uF,X5R, 16V, 20%
MuRata
GRM32ER61C476ME15L
C22
CAP, CERM, 0.022uF, 16V, +/- TDK
10%, X7R, 0402
C1005X7R1C223K
C24
Ceramic, 0.1uF, X5R, 6.3V,
10%
TDK
C1005X5R0J104K
C25, C33, C37
CAP, CERM, 0.01uF, 16V, +/10%, X7R, 0402
TDK
C1005X7R1C103K
C26
CAP, CERM, 1uF, 16V, +/20%, X7R, 0805
MuRata
GRM21BR71C105MA01L
C27, C35
CAP, CERM, 1uF, 16V, +/10%, X7R, 0603
MuRata
GRM188R71C105KA12D
C29
CAP, CERM, 47pF, 50V, +/5%, C0G/NP0, 0402
MuRata
GRM1555C1H470JZ01
C31
CAP CER 33000PF 16V X7R
0402
TDK
C1005X7R1C333K
C34, C36
Ceramic, 1000pF, C0G/NP0,
25V, 5%
TDK
C1005C0G1E102J
C38
CAP CER .47uF 6.3V X5R
0402
TDK
C1005X5R0J474M
D1
Diode, Ultrafast, 100V, 0.25A,
SOD-323
NXP Semiconductor
BAS316,115
D2
Diode, Zener, 8.2V, 500mW,
SOD-123
Central Semiconductor
CMHZ4694
D3, D7
Diode Switching Array 90V
SOT363
NXP
BAV756S,115
D5
Diode, Zener, 5.1V, 500mW,
SOD-123
Central Semiconductor
CMHZ4689
D8, D12
Vr = 100V, Io = 1A, Vf = 0.77V
Diodes Inc.
DFLS1100-7
D11
11V SMT Zener Diode
Central Semiconductor
CMHZ4698
D16
Diode, Schottky, 45V, 0.1A,
SOD-523
Diodes Inc.
SDM10U45-7-F
D17
Diode, Zener, 4.7V, 200mW,
SOD-323
Central Semiconductor
CMDZ4L7
L2
Inductor, Flat Wire, Ferrite,
3.0uH, 12A, 0.0048 ohm, SMD
Epcos Inc
B82559A0302A013
P1, P2, P3
PCB Pin
Mill-Max
3104-2-00-34-00-00-08-0
P4, P7
Conn Pin Nail-Head L =.610"
GOLD
Mill-Max
6142-0-00-15-00-00-33-0
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Bill of Materials
8
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Q1, Q3
NPN, 1A, 45V, Transistor,
NPN, 45V, 1A, SOT-89
Diodes Inc.
FCX690BTA
Q2
PNP, 0.2A, 40V
Central Semiconductor
CMPT3906
Q4, Q10
MOSFET N-CH D-S 100V 8SOIC
Vishay
SIR882DP-T1-GE3
Q6, Q7, Q8, Q9
MOSFET, N-CH, 100V, 28A,
PG-TSDSON-8
Infineon Technologies
BSZ160N10NS3 G
R1, R4
RES 0805, 5.1k, 5%, 0.125W
Panasonic
ERJ-6GEYJ512V
R2, R24, R33, R36
RES 0402, 10k,1%, 0.063W
Vishay-Dale
CRCW040210k0FKED
R5
RES, 1.00k ohm, 1%, 0.1W,
0603
Vishay-Dale
CRCW06031K00FKEA
R6
RES 100k, 1%, 0.125W
Vishay-Dale
CRCW0805100KFKEA
R7
RES, 2.61k ohm, 1%, 0.063W,
0402
Vishay-Dale
CRCW04022K61FKED
R8
RES 20 ohm, 0805, 5%,
0.125W
Panasonic
ERJ-6GEYJ200V
R9
RES, 1.65k ohm, 1%, 0.063W,
0402
Vishay-Dale
CRCW04021K65FKED
R13
RES, 6.04k ohm, 1%, 0.063W,
0402
Vishay-Dale
CRCW04026K04FKED
R14
RES 24k, 5%, 0.063W
Vishay-Dale
CRCW040224k0JNED
R15
RES, 30.1k ohm, 1%, 0.063W,
0402
Vishay-Dale
CRCW040230K1FKED
R16, R18
RES, 499 ohm, 1%, 0.063W,
0402
Vishay-Dale
CRCW0402499RFKED
R37
RES 0 ohm 5%, 0.063W
Vishay-Dale
CRCW04020000Z0ED
R23
RES, 17.4ohm, 1%, 0.063W,
0402
Vishay-Dale
CRCW040217R4FKED
R27
RES, 47 ohm, 5%, 0.25W,
0603
Vishay-Dale
CRCW060347R0JNEA
R28
RES, 7.5k ohm, 5%, 0.063W,
0402
Vishay-Dale
CRCW04027K50JNED
R30
RES 1.82k ohm, 1%, 0.063W
Vishay-Dale
CRCW04021k82FKED
R32
RES 100 ohm, 1%, 0.063W
Vishay-Dale
CRCW0402100RFKED
R22
RES 30.1k ohm, 1%, 0.063W
Vishay-Dale
CRCW040230k1FKED
R29
RES 7.87k ohm, 1%, 0.063W
Vishay-Dale
CRCW04027k87FKED
R21
RES 1.0k ohm, 1%, 0.063W
Vishay-Dale
CRCW04021k00FKED
T2
Current Sense Transformer
Ice Components
CT02-150
U1
100V Full-Bridge PWM
Controller with Integrated
MOSFET Drivers
Texas Instruments
LM5046
U2
Dual 5A Compound Gate
Driver with Negative Output
Voltage Capability
Texas Instruments
LM5110
U3
Low Input Current, High CTR
Photocoupler
NEC
PS2811-1-M-A
U4
RRIO, High Output Current &
Texas Instruments
Unlimited Cap Load Op Amp in
SOT23-5
LM8261
U5
Precision Micropower Shunt
Voltage Reference
Texas Instruments
LM4040
U6
ISOPro Low-Power DualChannel Digital Isolator
Silicon Laboratories
Si8420BB-D-IS
AN-2126 LM5046 Based Eighth Brick Reference Design
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PCB Layouts
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5
PCB Layouts
Figure 12. Top Layer Assembly
Figure 13. Bottom Layer Assembly
Figure 14. Top Layer (Layer 1)
Figure 15. Layer 2
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PCB Layouts
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Figure 16. Layer 3
Figure 17. Layer 4
Figure 18. Layer 5
Figure 19. Layer 6
10
AN-2126 LM5046 Based Eighth Brick Reference Design
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Figure 20. Layer 7
Figure 21. Layer 8
Figure 22. Layer 9
Figure 23. Bottom Layer (Layer 10)
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11
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