AN-2066 LM25119 Evaluation Board
1 Introduction
The LM25119EVAL evaluation board provides the design engineer with a fully functional dual output buck
converter, employing the LM25119 Dual Emulated Current Mode Synchronous Buck Controller. The
evaluation board is designed to provide both 3.3V and 1.8V outputs over an input range of 6.0V to 36V.
Also the evaluation board can be easily configured for a single 3.3V, 16A regulator.
2 Performance of the Evaluation Board
• Input Voltage Range: 6.0V to 36V
• Output Voltage: 3.3V (CH1), 1.8V (CH2)
• Output Current: 8A (CH1), 8A (CH2)
• Nominal Switching Frequency: 230 KHz
• Synchronous Buck Operation: Yes
• Diode Emulation Mode: Yes
• Hiccup Mode Overload Protection: Yes
• External VCC Sourcing: No
User's Guide
SNVA445B–August 2010–Revised April 2013
3 Powering and Loading Consideration
When applying power to the LM25119 evaluation board, certain precautions need to be followed. A
misconnection can damage the assembly.
3.1 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 choose the correct connector and wire size when attaching the source power
supply and the load.
3.2 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 0.5V. 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 LM25119. For complete design information, see the
LM25119/LM25119Q Wide Input Range Dual Synchronous Buck Controller Data Sheet (SNVS680).
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Volt-meter
Current-meter
VIN
RTN(GND)
OUT1+(3.3V)
OUT1-(GND)
OUT2-(GND)
OUT2+(1.8V)
+ Electric Load
With Current Meter
- 0A-8A
- Electric Load
With Current Meter
+ 0A-8A
0-36V, 20A
DC Power
Supply
Volt-meter
Volt-meter
Scope
J1
J2
J6
J5
J4
J3
LM25119 DUAL BUCK
Powering and Loading Consideration
3.3 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.
3.4 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.
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3.5 Quick Start-Up Procedure
Figure 1. Typical Evaluation Setup
1. Set the power supply current limit to at least 20A. Connect the power supply to J1 and J2.
2. Connect one load with an 8A capacity between J3 and J4. Connect another load with an 8A capacity
between J6 and J5.
3. Set input voltage to 12V and turn it on.
4. Measure the output voltages. CH1 should regulate at 3.3V and CH2 should regulate at 1.8V.
5. Slowly increase the load current while monitoring the output voltages. The outputs should remain in
regulation up to full load current.
6. Slowly sweep the input voltage from 6.0V to 36V while monitoring the output voltages. The outputs
should remain in regulation.
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4 Waveforms
4.1 Soft Start
When applying power to the LM25119 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 0.5Ω on the 3.3V output, and 0.33Ω on the 1.8V output, respectively.
Conditions:
Input Voltage = 12VDC
0.5Ω Load on 3.3V output
0.33Ω Load on 1.8V output
Traces:
Top Trace: 3.3V Output Voltage, Volt/div = 1V
Bottom Trace: 1.8V Output Voltage, Volt/div = 1V
Horizontal Resolution = 1 ms/div
Waveforms
Figure 2. Start-up with Resistive Load
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Waveforms
4.2 Load Transient
Figure 3 shows the transient response for a load of change from 2A to 6A on 3.3V output. The upper
waveform shows output voltage droop and overshoot during the sudden change in output current shown
by the lower waveform.
Conditions:
Input Voltage = 12VDC
Output Current 2A to 6A
Traces:
Top Trace: 3.3V Output Voltage, Volt/div = 100mV, AC coupled
Bottom Trace: Output Current Amp/Div = 2A
Horizontal Resolution = 0.5 ms/div
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Figure 3. Load Transient Response
4.3 Over Load 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 CH1
output. One channel may operate in the normal mode while the other is in hiccup mode overload
protection.
Conditions:
Input Voltage = 12VDC
Output Short on 3.3V
Traces:
Top Trace: SW voltage on CH1, Volt/div = 10V
Bottom Trace: Inductor Current Amp/div = 10A
Horizontal Resolution = 20 ms/div
Figure 4. Short Circuit
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4.4 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° out of phase from the other.
Conditions:
Input Voltage = 12VDC
8A on 3.3V output
8A on 1.8V 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
Figure 5. Clock Synchronization
Waveforms
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Performance Characteristics
4.5 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.
Conditions:
Input Voltage = 12VDC
0.5Ω Load on 3.3v output
Traces:
Top Trace: Input Voltage, Volt/div = 10V
Middle Trace1: 3.3V Output, Volt/div = 2V
Middle Trace2: VCC, Volt/div = 5V
Bottom Trace: SS voltage, Volt/div = 5V
Horizontal Resolution = 20 ms/div
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Figure 6. Shutdown
5 Performance Characteristics
Figure 7 shows the efficiency curves. The efficiency of the power converter is 90% at 12V 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.
Figure 7. Typical Efficiency vs Load Current
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6 Board Configuration
6.1 Interleaved Buck Operation for Single 3.3V 16A Output
The evaluation board is designed to be easily converted to a 3.3V, 16A 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 3.3V output with 16A maximum output current, populate R21 and R22
with 0Ω resistor and open R6, C15 and C14. The electronic load should have over 16A capability to test
the interleaved operation.
Figure 8. Load Connection for Single Output
Board Configuration
6.2 External VCC Supply and VCC Disable
External VCC supply helps to reduce the temperature and the power loss of the LM25119 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.
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Board Configuration
6.3 Loop Response
TP5 and TP6 (TP7 and TP8) have been provided in order to measure the loop transfer function of CH1
(CH2). For detail information about the loop transfer function measurement, see AN-1889 How to Measure
the Loop Transfer Function of Power Supplies (SNVA364).
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Figure 9. Loop Response Measurement Setup
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7 Evaluation Board Schematic
Evaluation Board Schematic
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Evaluation Board Schematic
Table 1. Bill of Materials (BOM)
Part Value Package Part Number Manufacturer
C1,C2,C3,C4,C5,C32,C3 2.2 µF, 50V, X7R 1210 C3225X7R1H225K TDK
5,C36,C37,C38,C39,C40
,C41,C42
C6,C7,C25,C29 1µF, 16V, X7R 0603 C1608X7R1C105K TDK
C8,C10,C14,C16 100pF, 50V, C0G 0603 C1608C0G1H101J TDK
C9 0.47µF, 50V, X7R 0805 UMK212B7474KG Taiyo Yuden
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 680µF, 6.3V Φ10 APXA6R3ARA681MJC0G NIPPON CHEMI-CON
C23,C24,C27,C28 22µF,10V, X7R 1210 C1210C226K8RAC Kemet
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 52.3k, 1% 0805 MCR10EZHF5232 Rohm
R3 15k, 1% 0603 MCR03EZPFX1502 Rohm
R4 22.1k, 1% 0603 CRCW060322K1FKEA Vishay
R5,R16,R21,R22,R35,R NU
36,R37
R6,R7 36.5k, 1% 0603 CRCW060336K5FKEA Vishay
R8,R9, 10 ohm, 5% 0805 CRCW080510R0JNEA Vishay
R23,R24,R29,R30, R31,
R32
R10,R12 6.98k, 1% 0805 CRCW08056K98FKEA Vishay
R11 2.21k, 1% 0805 MCR10EZHF2211 Rohm
R13 5.49k, 1% 0805 MCR10EZHF5491 Rohm
R14,R15 34k, 1% 0603 CRCW060334K0FKEA Vishay
R17 0 ohm 0603 MCR03EZPJ000 Rohm
R18,R20 0.008 ohm, 1W, 1% 0815 RL3720WT-R008-F Susumu
R25,R26 5.1 ohm, 1W, 1% 2512 ERJ-1TRQF5R1U Panasonic-ECG
R27,R28 0 ohm, 5% 0805 MCR10EZPJ000 Rohm
D1,D2 60V, 1A SOD123F PMEG6010CEH NXP
D3,D4 NU
L1,L2 6.8µH, 18.5A 18.2x18.3 7443556680 WE
Q1,Q2,Q3,Q4 40V, 58A PowerPAK SO-8 SI7884BDP Vishay
U1 WQFN32 LM25119 TI
J1,J2,J3,J4,J5,J6 15A 7693 Keystone
TP1,TP2,TP3 Φ10 5002 Keystone
TP5,TP6,TP7,TP8 1040 Keystone
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8 PCB Layout
PCB Layout
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PCB Layout
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PCB Layout
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