LM34910 Evaluation Board National Semiconductor Application Note

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LM34910 Evaluation Board National Semiconductor Application Note

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LM34910 Evaluation Board
LM34910 Evaluation Board
National Semiconductor Application Note 1349 Dennis Morgan November 2004
LM34910EVAL evaluation board provides design engineer with fully functional buck regulator, employing constant on-time (COT) operating principle. This evaluation board provides output from input range 36V. circuit provides load currents with current limit )1.3A board's specification are:
Input Voltage: Output Voltage: Maximum Continuous Output current: 1.0A Current Limit: 1.3A Measured Efficiency: (VIN IOUT Switching Frequency: )850 Size: 0.75 0.47
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FIGURE Evaluation Board Side
Theory Operation
Refer board's schematic Figure which contains simplified block diagram LM34910. When circuit regulation, buck switch each cycle time determined VIN. on-time this evaluation board will range from )775 )200 36V. on-time, feedback voltage above 2.5V, Minimum Off-Timer ensures buck switch least normal operation, off-time longer. During off-time, output capacitor (C6) discharges, when output voltage falls that voltage below 2.5V, comparator output switches initiate on-time. required datasheet, this circuit provides minimum mVp-p ripple pin. Refer LM34910 data sheet more detailed block diagram, complete description various functional blocks.
When operating high input voltage high load current, forced flow NECESSARY. LM34910, diode will touch when operating high input voltage high load current. CAUTION when probing circuit compact layout. maximum load current (1A), wire size length used connect load becomes important. Ensure there significant drop wires.
Board Connection/Start-up
input connections made connector. load normally connected OUT1 terminals connector. Ensure wires adequately sized intended load current. Before start-up voltmeter should connected input terminals, output terminals. load current should monitored with ammeter current probe. recommended that input voltage increased gradually which time output voltage will that indicates correctly, then proceed with evaluating circuit.
Board Layout Probing
pictorial Figure shows placement circuit components. following should kept mind when board powered:
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2004 National Semiconductor Corporation
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Ripple Output
ripple voltage OUT1 will range from mVp-p )160 mVp-p 36V). ripple output desired, connect load OUT2. ripple this output varies from mVp-p mVp-p over input voltage range. However, load regulation good OUT2 OUT1 presence
Increased Current Limit
evaluation board current limit activates load current )1.3A. desired increase current limit particular application, must added board. Refer data sheet determine appropriate value this resistor
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FIGURE Board Schematic
Bill Materials
Item Description Capacitor Capacitor Capacitor Capacitor Schottky diode Inductor Resistor Resistor Resistor Resistor Switching Regulator Mfg. Part C3225X7R1H225K C1608X7R1H104K C1608X7R1H223K C3216Y5V1A226Z Zetex ZLLS2000 SLF6028T-100M1R3 CRCW06033832F100 CRCW06032001F100 Panasonic ERJ6RQFR22V data sheet National Semi LM34910SD Package 1210 0603 0603 1206 SOT-23-6 0603 0603 0805 0805 LLP-10 Value 0.022 40V, 2.2A 1.3A 38.3 0.22, 1/8W
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FIGURE Efficiency Load Current
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FIGURE Efficiency
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Layout
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Board Silkscreen
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Board Layer
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Board Bottom Layer
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LM34910 Evaluation Board
Notes
National does assume responsibility circuitry described, circuit patent licenses implied National reserves right time without notice change said circuitry specifications. most current product information visit www.national.com. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT GENERAL COUNSEL NATIONAL SEMICONDUCTOR CORPORATION. used herein: Life support devices systems devices systems which, intended surgical implant into body, support sustain life, whose failure perform when properly used accordance with instructions provided labeling, reasonably expected result significant injury user. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that products packing materials meet provisions Customer Products Stewardship Specification (CSP-9-111C2) Banned Substances Materials Interest Specification (CSP-9-111S2) contain ``Banned Substances'' defined CSP-9-111S2. critical component component life support device system whose failure perform reasonably expected cause failure life support device system, affect safety effectiveness.
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LM34910 Evaluation Board National Semiconductor Application Note

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