NSC LM5119_1

National Semiconductor
Application Note 2065
Eric Lee
September 28, 2010
Introduction
choose the correct connector and wire size when attaching
the source power supply and the load.
The LM5119EVAL evaluation board provides the design engineer with a fully functional dual output buck converter, employing the LM5119 Dual Emulated Current Mode Synchronous Buck Controller. The evaluation board is designed
to provide both 10V and 5V outputs over an input range of
14V to 55V. Also the evaluation board can be easily configured for a single 10V, 8A regulator.
Performance of the Evaluation
Board
•
•
•
•
•
•
•
•
Input Voltage Range: 14V to 55V
Output Voltage: 10V (CH1), 5V (CH2)
Output Current: 4A (CH1), 8A (CH2)
Nominal Switching Frequency: 230 KHz
Synchronous Buck Operation: Yes
Diode Emulation Mode: Yes
Hiccup Mode Overload Protection: Yes
External VCC Sourcing: Yes
Powering and Loading
Consideration
When applying power to the LM5119 evaluation board, certain precautions need to be followed. A misconnection can
damage the assembly.
PROPER BOARD CONNECTION
The input connections are made to the J1 (VIN) and J2 (RTN/
GND) connectors. The CH1 load is connected to the J3
(OUT1+) and J4 (OUT1-/GND) and the CH2 load is connected to the J6 (OUT2+) and J5 (OUT2-/GND). Be sure to
SOURCE POWER
The power supply and cabling must present low impedance
to the evaluation board. Insufficient cabling or a high
impedance power supply will droop during power supply application with the evaluation board inrush current. If large
enough, this droop will cause a chattering condition during
power up. During power down, insufficient cabling or a high
impedance power supply will overshoot. This overshoot will
cause a non-monotonic decay on the output.
An additional external bulk input capacitor may be required
unless the output voltage droop/overshoot of the source power is less than 0.7V. In this board design, UVLO setting is
conservative while UVLO hysteresis setting is aggressive.
Minimum input voltage can goes down with an aggressive
design. Minimum operating input voltage depends on the output voltage droop/overshoot of the source power supply and
the forced off-time of the LM5119. Refer to the LM5119
datasheet for complete design information.
LOADING
When using an electronic load, it is strongly recommended to
power up the evaluation board at light load and then slowly
increase the load. If it is desired to power up the evaluation
board at maximum load, resistor banks must be used. In general, electronic loads are best suited for monitoring steady
state waveforms.
AIR FLOW
Prolonged operation with high input voltage at full power will
cause the MOSFETs to overheat. A fan with a minimum of
200LFM should be always provided.
FIGURE 1. Typical Evaluation Setup
301260
www.national.com
AN-2065
30126006
© 2010 National Semiconductor Corporation
LM5119 Evaluation Board
LM5119 Evaluation Board
AN-2065
LOAD TRANSIENT
Figure 3 shows the transient response for a load of change
from 2A to 6A on 5V output. The upper waveform shows output voltage droop and overshoot during the sudden change
in output current shown by the lower waveform.
QUICK START-UP PROCEDURE
STEP 1: Set the power supply current limit to at least 16A.
Connect the power supply to J1 and J2.
STEP 2: Connect one load with a 4A capacity between J3 and
J4. Connect another load with an 8A capacity between J6 and
J5.
STEP 3: Set input voltage to 24V and turn it on.
STEP 4: Measure the output voltages. CH1 should regulate
at 10V and CH2 should regulate at 5V.
STEP 5: Slowly increase the load current while monitoring the
output voltages. The outputs should remain in regulation up
to full load current.
STEP 6: Slowly sweep the input voltage from 14V to 55V
while monitoring the output voltages. The outputs should remain in regulation.
Waveforms
SOFT START
When applying power to the LM5119 evaluation board a certain sequence of events occurs. Soft-start capacitors and
other components allow for a linear increase in output voltages. The soft-start time of each output can be controlled
independently. Figure 2 shows the output voltage during a
typical start-up with a load of 3Ω on the 10V output, and 1Ω
on the 5V output, respectively.
30126008
Conditions:
Input Voltage = 24VDC
Output Current 2A to 6A
Traces:
Top Trace: 5V Output Voltage, Volt/div = 100mV, AC coupled
Bottom Trace: Output Current, Amp/div = 2A
Horizontal Resolution = 0.5 ms/div
FIGURE 3. Load Transient Response
OVERLOAD PROTECTION
The evaluation board is configured with hiccup mode overload protection. The restart time can be programmed by C11.
Figure 4 shows hiccup mode operation in the event of an output short on CH2 output. One channel may operate in the
normal mode while the other is in hiccup mode overload protection.
30126007
Conditions:
Input Voltage = 24VDC
3Ω Load on 10V output
1Ω Load on 5V output
Traces:
Top Trace: 10V Output Voltage, Volt/div = 5V
Bottom Trace: 5V Output Voltage, Volt/div = 5V
Horizontal Resolution = 1 ms/div
FIGURE 2. Start-Up with Resistive Load
30126009
Conditions:
Input Voltage = 24VDC
Output Short on 5V
Traces:
Top Trace: SW Voltage on CH2, Volt/div = 20V
Bottom Trace: Inductor Current, Amp/div = 10A
Horizontal Resolution = 20 ms/div
FIGURE 4. Short Circuit
www.national.com
2
Performance Characteristics
Figure 7 shows the efficiency curves. The efficiency of the
power converter is 96% at 24V with full load current. Monitor
the current into and out of the evaluation board. Monitor the
voltage directly at the input and output terminals of the evaluation board.
30126010
Conditions:
Input Voltage = 24VDC
4A on 10V Output
8A on 5V Output
Traces:
Top Trace: SYNC pulse, Volt/div = 5V
Middle Trace: SW voltage on CH1, Volt/div = 10V
Bottom Trace: SW voltage on CH2, Volt/div = 10V
Horizontal Resolution = 1 µs/div
30126019
FIGURE 7. Typical Efficiency vs Load Current
Board Configuration
FIGURE 5. Clock Synchronization
INTERLEAVED BUCK OPERATION FOR SINGLE 10V 8A
OUTPUT
The evaluation board is designed to be easily converted to a
10V, 8A single output regulator with the interleaved operation.
Proper electronic load connection is shown in Figure 8. Connecting the electronic load at the center of shorting bar is
recommended to prevent a voltage difference between CH1
and CH2 output. In order to produce a single 10V output with
8A maximum output current, populate R21 and R22 with 0Ω
resistor and open R6, C15 and C14. The electronic load
should have over 8A capability to test the interleaved operation.
SHUTDOWN
Figure 6 shows the shutdown procedure by powering off the
source power. When UVLO pin voltage is less than 1.26V, the
switching stops and soft-start capacitors are discharged by
internal switches.
30126018
Conditions:
Input Voltage = 24VDC
1Ω Load on 5V Output
Traces:
Top Trace: Input Voltage, Volt/div = 20V
Middle Trace1: 5V Output, Volt/div = 2V
Middle Trace2: VCC, Volt/div = 5V
Bottom Trace: SS Voltage, Volt/div = 5V
Horizontal Resolution = 20 ms/div
30126020
FIGURE 8. Load Connection for Single Output
FIGURE 6. Shutdown
3
www.national.com
AN-2065
EXTERNAL CLOCK SYNCHRONIZATION
A TP1 (SYNC) test point has been provided on the evaluation
board in order to synchronize the internal oscillator to an external clock.Figure 5 shows the synchronized switching operation. Each channel operates 180 degrees out of phase
from the other.
AN-2065
EXTERNAL VCC SUPPLY & VCC DISABLE
External VCC supply helps to reduce the temperature and the
power loss of the LM5119 at high input voltage. By populating
D3 and D4, VCC can be supplied from an external power
supply. Use TP3 as an input of the external VCC supply with
0.1A current limit. R36, R35 and C45 should be populated
with proper value when the voltage of the external VCC is
smaller than 7V. The voltage at the VCCDIS pin can be monitored at TP2. To prevent a reverse current flow from VCC to
VIN through the internal diode, the external VCC voltage
should always be lower than VIN. In this LM5119 evaluation
board, VCC1 and VCC2 are supplied from the 10V output to
achieve high efficiency.
LOOP RESPONSE
TP5 and TP6 (TP7 and TP8) have been provided in order to
measure the loop transfer function of CH1 (CH2). Refer to
AN-1889 for detail information about the loop transfer function
measurement.
30126022
FIGURE 10. Loop Response Measurement Setup
30126021
FIGURE 9. Efficiency Comparison at 48V with External
VCC vs Without External VCC
www.national.com
4
AN-2065
Evaluation Board Schematic
30126023
5
www.national.com
AN-2065
Bill of Materials
Part
Value
Package
Part Number
Manufacturer
C1, C2, C3, C4,C5,
C32, C35,C36, C37,
C38, C39, C40, C41,
C42
2.2µF, 100V, X7R
1210
C3225X7R2A225K
TDK
TDK
C6, C7, C25,C29
1µF, 16V, X7R
0603
C1608X7R1C105K
C8, C10, C14, C16
100pF, 50V, C0G
0603
C1608C0G1H101J
TDK
C9
0.47µF, 100V, X7R
0805
GRM21BR72A474KA73
Murata
C11, C18, C19
0.47µF, 25V, X7R
0603
GRM188R71E474KA12
Murata
C12,C13
0.047µF, 16V, X7R
0603
C1608X7R1C473K
TDK
C15,C17
6800pF, 25V, C0G
0603
C1608C0G1E682J
TDK
C20,C21
820pF, 50V, C0G
0603
C1608C0G1H821J
TDK
C22,C26
470µF, 16V
PCG1C471MCL1GS
Nichicon
C23,C24,C27,C28
22µF,16V, X7R
Φ10
1210
C3225X7R1C226K
TDK
C30,C31
1000pF, 50V, X7R
0603
C1608X7R1H102K
TDK
C33,C34
1000pF,100V, C0G
0805
C2012C0G2A102J
TDK
C43,C44,C45,C46,C47
NU
R1
3.9 ohm, 5%
0805
CRCW08053R90JNEA
Vishay
R2
60.4k, 1%
0805
CRCW080560K4FKEA
Vishay
R3
6.19k, 1%
0603
CRCW06036K19FKEA
Vishay
R4
22.1k, 1%
0603
CRCW060322K1FKEA
Vishay
R5,R16,R21,R22,R35,
R36
NU
R6,R7
36.5k, 1%
0603
CRCW060336K5FKEA
Vishay
R8,R9,R23,R24,R31,
R32
10 ohm, 5%
0805
CRCW080510R0JNEA
Vishay
R10,R12
6.98k, 1%
0805
CRCW08056K98FKEA
Vishay
R11
604 ohm, 1%
0805
MCR10EZHF6040
Rohm
R13
1.33k, 1%
0805
MCR10EZHF1331
Rohm
R14,R15
73.2k, 1%
0603
CRCW060373K2FKEA
Vishay
R17,R37
0 ohm
0603
MCR03EZPJ000
Rohm
R18,R20
0.01 ohm, 1W, 1%
0815
RL3720WT-R010-F
Susumu
R25,R26
5.1 ohm, 1W, 1%
2512
ERJ-1TRQF5R1U
Panasonic — ECG
Rohm
R27,R28,R29,R30
0 ohm
0805
MCR10EZPJ000
D1,D2
60V, 1A
SOD123F
PMEG6010CEH
NXP
D3,D4
20V, 1A
PowerDI323
PD3S120L
Diodes
L1,L2
15µH, 14A
18.2x18.3
74435571500
WE
Q1,Q3, Q2,Q4
60V, 100A
LFPAK SO-8
PSMN5R5-60YS
NXP
LLP32
LM5119
NSC
7693
Keystone
5002
Keystone
1040
Keystone
U1
J1,J2,J3,J4,J5,J6
15A
Φ0.1
TP1,TP2,TP3
TP5,TP6,TP7,TP8
www.national.com
6
AN-2065
PCB Layout
30126011
30126012
7
www.national.com
AN-2065
30126013
30126014
www.national.com
8
AN-2065
30126015
30126016
9
www.national.com
LM5119 Evaluation Board
Notes
For more National Semiconductor product information and proven design tools, visit the following Web sites at:
www.national.com
Products
Design Support
Amplifiers
www.national.com/amplifiers
WEBENCH® Tools
www.national.com/webench
Audio
www.national.com/audio
App Notes
www.national.com/appnotes
Clock and Timing
www.national.com/timing
Reference Designs
www.national.com/refdesigns
Data Converters
www.national.com/adc
Samples
www.national.com/samples
Interface
www.national.com/interface
Eval Boards
www.national.com/evalboards
LVDS
www.national.com/lvds
Packaging
www.national.com/packaging
Power Management
www.national.com/power
Green Compliance
www.national.com/quality/green
Switching Regulators
www.national.com/switchers
Distributors
www.national.com/contacts
LDOs
www.national.com/ldo
Quality and Reliability
www.national.com/quality
LED Lighting
www.national.com/led
Feedback/Support
www.national.com/feedback
Voltage References
www.national.com/vref
Design Made Easy
www.national.com/easy
www.national.com/powerwise
Applications & Markets
www.national.com/solutions
Mil/Aero
www.national.com/milaero
PowerWise® Solutions
Serial Digital Interface (SDI) www.national.com/sdi
Temperature Sensors
www.national.com/tempsensors SolarMagic™
www.national.com/solarmagic
PLL/VCO
www.national.com/wireless
www.national.com/training
PowerWise® Design
University
THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION
(“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY
OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO
SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS,
IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS
DOCUMENT.
TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT
NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL
PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR
APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND
APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE
NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS.
EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO
LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE
AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR
PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY
RIGHT.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR
SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and
whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected
to result in a significant injury to the user. A critical component is any component in a life support device or system whose failure to perform
can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness.
National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other
brand or product names may be trademarks or registered trademarks of their respective holders.
AN-2065
Copyright© 2010 National Semiconductor Corporation
For the most current product information visit us at www.national.com
National Semiconductor
Americas Technical
Support Center
Email: [email protected]
Tel: 1-800-272-9959
www.national.com
National Semiconductor Europe
Technical Support Center
Email: [email protected]
National Semiconductor Asia
Pacific Technical Support Center
Email: [email protected]
National Semiconductor Japan
Technical Support Center
Email: [email protected]