LM26001 Evaluation Board National Semiconductor Application Note

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LM26001 Evaluation Board National Semiconductor Application Note

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LM26001 Evaluation Board
LM26001 Evaluation Board
National Semiconductor Application Note 1454 Allan Fisher August 2006
LM26001 evaluation board designed demonstrate capabilities LM26001 switching regulator. LM26001 board, schematic shown Figure configured provide output 3.3V 1.5A from input range 3.5V minimum 4.5V required startup). nominal operating frequency synchronized from +30% -20% nominal using SYNC connection post. evaluation board designed operate ambient temperatures 75°C. Typical evaluation board waveforms performance curves shown Figures through Figures show trace layout. design evaluation dc/dc buck converters based LM26001 regulator, evaluation board re-configured different output voltages operating frequencies. Test points also provided enable easy connection monitoring critical signals. Table shows second example circuit 1.5V output switching frequency. This design operates from input voltage 3.5V enters pulse skipping mode approximately 24Vin, depending loading. more information about device function circuit design, refer LM26001 datasheet.
Output voltage frequency easily adjustable with single resistors, respectively. However, large changes default settings require other changes inductor, output capacitor, compensation network. Several optional component pads have been provided application flexibility. provided additional ceramic output capacitor. This capacitor used lower total output. blocks reverse current input supply during input voltage light load conditions. This diode necessary applications replaced with jumper. phase lead capacitor which installed increase phase gain margin. compensation section datasheet more detailed information.
Powering
Before powering LM26001 evaluation board, external connections should verified. power supply input must turned connected with proper polarity posts. load should connected between VOUT post post. Both VOUT connections should post closest post. Output voltage monitored with oscilloscope VOUT post. second post, close provided primarily small signal measurements, such soft-start voltage, PGOOD. This post should also used when applying optional external signals such SYNC. Once connections have been verified, input power applied. input voltage must between 4.5V 38V. load startup. post left open, output voltage will ramp when applied
Jumper Settings
FPWM jumper used disable sleep mode function. normal operation, select `off', which connects FPWM GND. FPWM operation (sleep mode disabled), select `on'. Vbias jumper connects VBIAS Vout. When Vout greater than VBIAS function will activated improved efficiency. disable VBIAS, Vout less than jumper `GND'.
Optional Components
Before changing default components, please refer product datasheet information regarding component selection.
AN-1454
2006 National Semiconductor Corporation
AN201871
www.national.com
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20187101
FIGURE Evaluation Board Schematic
TABLE LM26001 Bill Materials 3.3V, 1.5A, 305kHz
Value 3.3µF ceramic 47µF electrolytic 10µF ceramic 0.1µF ceramic 10nF ceramic 100µF 12mohm installed 4.7nF ceramic 47pF ceramic installed NSQ03A06 EC21QS06 22µH 3.5A SLF12565T-220M3R5 120k 200k 0603 0603 0603 0603 0603 0603 1206 0603 0603 0603 1206 1206 0603 Footprint 1210 Supplier Panasonic Murata Murata Murata Panasonic Murata Murata NIEC NIEC
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Performance Characteristics
Unless otherwise specified, 12V, 25°C.
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FIGURE Start-Up Waveforms (IOUT
FIGURE Load Transient Response (IOUT 0.25A 1.5A step)
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FIGURE Waveforms (IOUT
FIGURE Efficiency IOUT (VBIAS VOUT)
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FIGURE Sleep Mode Waveforms (IOUT 25mA)
20187107
FIGURE Sleep Mode Threshold Load Current Input Voltage
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Layout Diagram(s)
20187108
FIGURE Side Layout
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Layout Diagram(s)
(Continued)
20187109
FIGURE Bottom Side Layout
TABLE LM26001 Bill Materials 1.5V, 1.5A, 480kHz
Value 3.3µF ceramic 47µF electrolytic 10µF ceramic 0.1µF ceramic 10nF ceramic 100µF 12mohm 10µF 6.3V ceramic 6.8nF ceramic 68pF ceramic installed NSQ03A06 EC21QS06 3.3µH 4.1A RLF7030T-3R3M4R1 8.2k 200k 0603 0603 0603 0603 0603 0603 1206 0603 0603 0603 1206 1206 0603 Footprint 1210 Supplier Panasonic Murata Murata Murata Panasonic Murata Murata Murata NIEC NIEC
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LM26001 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 follows provisions Product Stewardship Guide Customers (CSP-9-111C2) Banned Substances Materials Interest Specification (CSP-9-111S2) regulatory environmental compliance. Details found www.national.com/quality/green. Lead free products RoHS compliant. critical component component life support device system whose failure perform reasonably expected cause failure life support device system, affect safety effectiveness.
AN-1454
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LM26001 Evaluation Board National Semiconductor Application Note

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