LM25037 Evaluation Board National Semiconductor Application Note
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LM25037 Evaluation Board
LM25037 Evaluation Board
National Semiconductor Application Note 1861 Ajay Hari July 2008
LM25037 evaluation board designed provide design engineer with fully functional power converter based push-pull topology evaluate LM25037 controller. performance evaluation board follows: Input Operating Range: Output Voltage: 5.0V Output Current: Measured Efficiency: Load Input Frequency Operation: Board Size: 3.5x2.25x0.05 inches Load Regulation: Line UVLO (14V rising falling) printed circuit board consists layers copper material, with thickness 0.050 unit designed continuous operation rated load <40°C minimum airflow CFM.
Theory Operation
Push-Pull topology consists MOSFETs primary side driven degrees phase. When either MOSFET turned voltage equal "Vin-Vds(on)", applied across half power transformer's primary. Where, Vds(on) drain source voltage across MOSFET when turned
center-tapped secondary transformer turns each winding, resulting step-down voltage applied across primary. transformer secondary voltage then rectified filtered with filter provide output voltage. push-pull topology, primary MOSFETS turned alternatively energizing windings such that flux swings back forth first third quadrants curve. quadrants allows better utilization core resulting smaller core volume compared single-ended topologies such forward converter. feedback resistors that desired output voltage, voltage feedback equal internal reference voltage (1.25V). LM25037 been configured current mode control. Current mode control inherently provides line voltage feed-forward, cycle-by-cycle current limiting ease loop compensation removes additional pole output inductor. Hence, standard "type network used compensation. this particular evaluation board, output inductor only smoothes output voltage waveform, also generates auxiliary voltage means secondary winding). This feature reduces power dissipation within thereby increasing reliability efficiency. evaluation board synchronized external clock with recommended frequency range kHz.
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Typical Push-Pull Circuit
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Powering Loading Considerations
When applying power LM25037 evaluation board certain precautions should followed. misconnection damage assembly. PROPER CONNECTIONS When operated input voltages evaluation board draw current full load. Ensure that input supply suficient current capability. maximum rated output current 10A. sure choose correct connector wire size when attaching source supply load. Monitor current into evaluation board. Monitor voltage directly output terminals evaluation board. voltage drop across load connecting wires will give inaccurate measurements. This especially true accurate efficiency measurements. SOURCE POWER evaluation board viewed constant power load. input line voltage (16V) input current reach 3.75A typically steady state, while high input line voltage (32V) input current will approximately 1.9A. Therefore, fully test LM25037 evaluation board power supply capable least required. power supply must have adjustments both voltage current. power supply cabling must present impedance evaluation board. Insufficient cabling high impedance power supply will droop during power supply application with evaluation board inrush current. large enough, this droop will cause chattering condition upon power This chattering condition interaction with evaluation board under-voltage lockout, cabling impedance inrush current. LOADING When using electronic load, strongly recommended power evaluation board light load then slowly increase load. This necessary most electronic loads draw current till power supply output voltage reaches internally point; this result soft-
start function work desired trip current sense comparator. Electronic loads, general, best suited monitoring steady state waveforms. desired power evaluation board maximum load, resistor banks used. This will ensure soft-start evaluation board will perform desired. high output current requires thick cables! resistor banks used there certain precautions taken. resistance maximum load 0.5. wattage current ratings must adequate 10A, supply. Monitor both current voltage times. Ensure there sufficient cooling provided load. FLOW Full power loading should never attempted without providing specified flow over evaluation board. stand-alone should provided. POWERING suggested current limit source supply provide about times wattage load. most common occurrence, that will prove unnerving, when current limit source supply insufficient load. result similar having high source impedance referred earlier. interaction source supply folding back evaluation board going into under-voltage shutdown will start oscillation, chatter, that have undesirable consequences. quick efficiency check best confirm that everything operating properly. something amiss reasonably sure that will affect efficiency adversely. parameters incorrect switching power supply without creating losses potentially damaging heat. OVER CURRENT PROTECTION evaluation board configured with hiccup over-current protection. event output overload (approximately 14A@16V Input) unit will discharge soft-start capacitor, which disables power stage. After delay softstart released. shutdown, delay slow recharge time soft-start capacitor protects unit, especially during short circuit event where stress highest.
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Typical Evaluation Setup
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Performance Characteristics
Once circuit powered running normally, output voltage regulated 5.0V, with accuracy determined feedback resistors bandgap reference voltage inside When load current varied from 10A, regulator output should vary less than frequency operation selected kHz, which good compromise between board size efficiency. efficiency power converter measured 10A. Please refer figure below efficiency curves.
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Conditions: Input Voltage 24VDC Output Current Trace: Output Voltage, Volts/div Horizontal Resolution ms/div
FIGURE Soft Start Figure shows typical output ripple seen directly across output capacitor, input voltage load 10A. This waveform typical most loads input voltages.
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FIGURE Efficiency Output Current
Waveforms
When power applied LM25037 evaluation board certain sequence events occurs. Soft-start capacitor values other components ensure linear increase output voltage short time until feedback loop stabilize without overshoot. Figure shows output voltage during typical start-up with input load 10A. There overshoot during startup. strongly recommended resistor load instead electronic load, while capturing soft-start data electronic loads tend have small idiosyncrasies such providing load resistance till output reaches certain voltage. This occasionally causes transient during start-up.
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Conditions: Input Voltage 24VDC Output Current Bandwidth Limit Trace: Output Ripple, Volts/div Horizontal Resolution µs/div
FIGURE Output Ripple
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Figure shows transient response load change from 10A. upper trace shows minimal output voltage droop overshoot during sudden change output current shown lower trace.
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Conditions: Input Voltage 32VDC Output Current Trace: drain source voltage, Volts/div Horizontal Resolution µs/div
Conditions: Input Voltage 24VDC Output Current Bandwidth Limit Traces: Bottom Trace: Output Current Amps/div Trace: Output Voltage response Volts/div Horizontal Resolution µs/div
FIGURE Drain Waveform Figure shows soft-stop. This achieved seeting UVLO voltage between 0.4V 1.25V.
FIGURE Transient Response Figures show drain voltage with load. Figure represents drain voltage input voltage Figure represents drain voltage input voltage 32V. Drain sees twice input voltage when during dead-time exactly sees input voltage.
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Conditions: Input Voltage 24VDC Trace: Output Voltage, Volts/div Horizontal Resolution ms/div
FIGURE Soft Stop
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Conditions: Input Voltage 24VDC Output Current Trace: drain source voltage, Volts/div Horizontal Resolution µs/div
FIGURE Drain Waveform
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Typical Application Circuit
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Layout
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Bottom Layer
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Bottom Layer Silk Screen
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Layer-1
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Layer-2
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Layer
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Layer Silk Screen
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Bill Materials Part C14, C17, Value 1500 2200 0.68 10,000 Schottky Schottky Common Cathode Diode MAIN XFMR Channel,100 MOSFET 49.9 150k 100k 9.76k 23.2k 41.2k Package C1210 C0603 C0805 C0603 C0603 C0603 C0805 C0603 C0603 C0603 C0603 C1206 Part Number GCM32ER71475KA55L GRM188R71H152KA01D GRM21BR71H104KA01L GRM188R71C105KA12D GRM188R71H104KA93D GRM188R71H222KA01D GRM219R71C684KC01D ECT-ZEB1H221K GRM033R71AQ103KA01D GRM188R71H471KA01D 12061A471KAT2A Manufacturer Murata Murata Murata Murata Murata Murata Murata Murata Murata Murata Corporation NIPPON CHEMICON Murata Murata Central Semiconductor Description CERAMIC 1210 CERAMIC 1500 0603 CERAMIC 0805 CERAMIC 0603 CERAMIC 0603 CERAMIC 2200 0603 CERAMIC 0805 CERAMIC 0603 3300 0603 CERAMIC 0603 CERAMIC 100V 1206 CAPSM, ALUM ELECT, 0.26X0.31 CERAMIC 6.3V 1210 CERAMIC 0805 Schottky Diode
CAPSM_AL_ APXE6R3ARA331MF80G 26x31 C1210 C0805 C0603 SOD-123F D2PAK GCM32ER70J476KE19L GRM219R71C104KA01D CMMSH1-20 MBRB3030CTL CMPD2838
Semiconductor DIODE SCHOTTKY D2PAK Central Semiconductor Bourns Coil Craft Coil Craft Vishay/Siliconix Rohm Rohm Rohm Rohm Rohm Rohm Dual Common Cathode Ultra High Speed Diode Inductor, Bourns Filter Inductor XFMR, PL140-100L, SCHEMATIC 100V, N_channel MOSFET, 49.9 1/8W 0805 1/8W 0805 1/8W 0805 9.76 1/10W 0603 23.2 1/10W 0603 41.2 1/10W 0603
Inductor SRU1048-3ROY EFD20-10 GA-3382-BL PLANAR PL140-100L PowerPak SO-8 R0805 R0805 R0805 R0603 R0603 R0603 SI7456DP MCR10EZHF49R9 MCR10EZPF1503 MCR10EZHF1003 MCR03EZPFX9761 MCR03EZPFX2322 MCR03EZPFX4122
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Part R12, R16, J1-J4
Value 4.22k 4.02k 12.1k 10.0 0.027 10.0 10.0 10.0 National Controller Terminal Screw,
Package R0603 R0603 R0603 R0603 R0603 R0805 R0830 R0603 R2010 R1206 R0805 TSSOP16
Part Number MCR03EZPFX4990 MCR03EZPFX4221 MCR03EZPFX4021 MCR03EZPFX1212 MCR10EZHJ100 RL7520WT-R027-F MCR03EZPFX10R0 CRCW201010R0FKEF MCR18EZHF10R0 LM25037 7693
Manufacturer Rohm Rohm Rohm Rohm Rohm SUSUMU Rohm Vishay/Dale Rohm National Semiconductor Keystone Electronics
Description 1/10W 0603 4.22 1/10W 0603 4.02 1/10W 0603 12.1 1/10W 0603 1/8W 0805 Series, Resistor 10.0 1/10W 0603 10.0 1/2W 2010 10.0 1/4W 1206 Dual Mode controller Terminal Screw,
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LM25037 Evaluation Board
Notes
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