National Semiconductor Application Note 2066 Eric Lee September 28, 2010 Introduction ed 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. 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. 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 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. Refer to the LM25119 datasheet for complete design information. When applying power to the LM25119 evaluation board, certain precautions need to be followed. A misconnection can damage the assembly. 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. 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 connect- 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. Powering and Loading Consideration FIGURE 1. Typical Evaluation Setup © 2010 National Semiconductor Corporation 301261 www.national.com AN-2066 30126101 LM25119 Evaluation Board LM25119 Evaluation Board AN-2066 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. QUICK START-UP PROCEDURE STEP 1: Set the power supply current limit to at least 20A. Connect the power supply to J1 and J2. STEP 2: Connect one load with an 8A capacity between J3 and J4. Connect another load with an 8A capacity between J6 and J5. STEP 3: Set input voltage to 12V and turn it on. STEP 4: Measure the output voltages. CH1 should regulate at 3.3V and CH2 should regulate at 1.8V. 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 6.0V to 36V while monitoring the output voltages. The outputs should remain in regulation. Waveforms 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. 30126103 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 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. 30126102 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 FIGURE 2. Start-up with Resistive Load 30126104 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 www.national.com 2 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. 30126105 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 30126107 FIGURE 7. Typical Efficiency vs Load Current FIGURE 5. Clock Synchronization 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. 30126106 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 FIGURE 6. Shutdown 3 www.national.com AN-2066 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-2066 EXTERNAL VCC SUPPLY & 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. Board Configuration 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. 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. 30126108 FIGURE 8. Load Connection for Single Output 30126109 FIGURE 9. Loop Response Measurement Setup www.national.com 4 AN-2066 Evaluation Board Schematic 30126110 5 www.national.com AN-2066 TABLE 1. Bill of Materials Part Value Package Part Number Manufacturer C1,C2,C3,C4,C5,C32, C35,C36,C37,C38,C39 ,C40,C41,C42 2.2 µF, 50V, X7R 1210 C3225X7R1H225K TDK TDK C6,C7,C25,C29 1µF, 16V, X7R 0603 C1608X7R1C105K 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 CHEMICON 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, R36,R37 NU R6,R7 36.5k, 1% 0603 CRCW060336K5FKEA Vishay R8,R9, R23,R24,R29,R30, R31, R32 10 ohm, 5% 0805 CRCW080510R0JNEA Vishay 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 LLP32 LM25119 NSC 7693 Keystone 5002 Keystone 1040 Keystone U1 J1,J2,J3,J4,J5,J6 TP1,TP2,TP3 15A Φ10 TP5,TP6,TP7,TP8 www.national.com 6 AN-2066 PCB Layout 30126111 30126115 7 www.national.com AN-2066 30126112 30126113 www.national.com 8 AN-2066 30126114 30126116 9 www.national.com LM25119 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. 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