Texas Instruments LM25119EVAL Manual de usuario

User's Guide

SNVA445B–August 2010–Revised April 2013

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

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).

All trademarks are the property of their respective owners.

SNVA445B–August 2010–Revised April 2013 AN-2066 LM25119 Evaluation Board

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

LM25119 DUAL BUCK

Powering and Loading Consideration

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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.

Figure 1. Typical Evaluation Setup

3.5 Quick Start-Up Procedure

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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Waveforms

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 0.5Ωon the 3.3V output, and 0.33Ωon the 1.8V output, respectively.

Conditions:

Input Voltage = 12VDC

0.5ΩLoad on 3.3V output

0.33ΩLoad 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

Figure 2. Start-up with Resistive Load

SNVA445B–August 2010–Revised April 2013 AN-2066 LM25119 Evaluation Board

Waveforms

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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

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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Waveforms

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

SNVA445B–August 2010–Revised April 2013 AN-2066 LM25119 Evaluation Board

Performance Characteristics

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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

0.5ΩLoad 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

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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Board Configuration

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 0Ωresistor 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

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.

SNVA445B–August 2010–Revised April 2013 AN-2066 LM25119 Evaluation Board

Board Configuration

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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).

Figure 9. Loop Response Measurement Setup

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Evaluation Board Schematic

7 Evaluation Board Schematic

SNVA445B–August 2010–Revised April 2013 AN-2066 LM25119 Evaluation Board

Evaluation Board Schematic

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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

10 AN-2066 LM25119 Evaluation Board SNVA445B–August 2010–Revised April 2013

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