Evaluation LM26480 Dual DC/DC Buck Regulators with Dual LowNoise Linea
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Evaluation LM26480 Dual DC/DC Buck Regulators with Dual Low-Noise Linear Regulators
Evaluation LM26480 Dual DC/DC Buck Regulators with Dual LowNoise Linear Regulators
LM26480 OVERVIEW LM26480 multi-function, programmable Power Management Unit, optimized power digital applications. This device integrates highly efficient 1.5A step-down converters Linear Regulators. LM26480 offered tiny 24-pin package.
National Semiconductor Application Note 1800 John Woodward September 2008
EVALUATION OVERVIEW LM26480 Evaluation comes preassembled with VOUT Buck1 1.8V, VOUT Buck2 3.3V, VOUT LDO1 1.0V, VOUT LDO2 1.2V. These what user would like their evaluation, possible change regulator outputs adjusting feedback network. Details this document. LM26480 Evaluation allows user effectively utilize functions LM26480. evaluation consists LM26480 evaluation board LM26480 datasheet Evaluation Manual (this document)
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FIGURE LM26480 Evaluation Board
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Evaluation Setup
Please protection prevent unwanted damaging events!
user LM26480 Evaluation Board leave regulator outputs change them time. order change them, remove existing feedback network reconfigure using optimal resistors capacitors designated output voltage which chosen from Table Table
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FIGURE Feedback Network Locations
Cautionary Notes
Turrets placed somewhat close together board. careful short adjacent pins each other!
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Getting Started
When LM26480 evaluation board configured needed, been properly cleaned, supply board with power through AVDD pins. (See Figure
should able regulators supply desired voltage.
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FIGURE Board Power Pins
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Using Evaluation Board
ENABLING LM26480 BOARD LM26480 evaluation board allows user enable regulators through jumper, applying voltage regulator's enable pin. mark jumpers enabling Buck1 Buck2, respectively. When jumpers lower position, shorts
enable GND. Inversely, when jumpers upper position, enable shorted VDD. mark jumpers enabling LDO2 LDO1, respectively. When jumpers lower position, shorts enable GND. Inversely, when jumpers upper position, enable shorted VDD. enabling regulators applying voltage turret, make sure remove jumper that specific regulator.
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FIGURE Regulator Enables COMPONENT SELECTION Table shows ideal resistor values establish buck voltages from 0.8V 3.5V along with common resistor values establish these voltages. Common resistors always produce target value; error given delta column. addition resistor feedback, capacitor feedback always required, depending output voltage capacitor also required. Figure below.
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Table Component Values Ideal Resistor Values Target VOUT R1(K) Common Values Actual VOUT Com/R R2(K) 0.803 0.905 1.31 1.393 1.505 1.605 1.713 1.803 1.902 2.01 2.083 2.202 2.282 2.415 2.51 2.61 2.71 2.82 2.875 2.995 3.115 3.18 3.31 3.38 3.52 Actual VOUT Delta from Target 0.002 0.005 0.01 -0.008 0.005 0.005 0.013 0.003 0.002 0.01 -0.017 0.002 -0.018 0.015 0.01 0.01 0.01 0.02 -0.025 -0.005 0.015 -0.02 0.01 -0.02 0.02 Feedback Capacitors C1(pF) C2(pF) none none none none none none none none none none none none none none none none none none none Buck Only Buck Buck Buck Only
R2(K) R1(K)
output voltages bucks LM26480 established feedback resistor dividers shown Figure equation determining VOUT
VOUT R2)/R2 where voltage Buck pin. buck control loop will force 0.50V
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COMPONENT SELECTION LDO1 LDO2 Table shows ideal resistor values establish voltages from along with common resistor values
tablish these voltages. Common resistors always produce target value; error given final column.
Table Component Values LDO1 LDO2 Target VOUT Ideal Resistor Values 1000 1040 1080 1120 1160 1200 1100 1150 1210 1000 1000 1000 1210 1210 1210 Common Values 1.31 1.393 1.505 1.605 1.711 1.802 1.905 2.01 2.118 2.203 2.283 2.412 2.505 2.614 2.709 2.809 2.873 3.118 3.174 3.314 3.381 3.525 Actual VOUT W/Com/R
output voltages LDOs LM26480 established feedback resistor dividers shown Figure
equation determining VOUT VOUT (R1+R2)/R2, where voltage LDO_FBX pin. control loop will force 0.50V ±3%.
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FIGURE Feedback Network Bucks LDOs corresponds feedback caps bucks, refers bottom feedback caps C10. more detailed diagram evaluation board, please refer Figure schematic below.
seen Figure above, refers resistor which corresponds bucks, LDOs. Similarly, bottom resistor which corresponds bucks, LDOs.
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LM26480 Hardware Block Description
LM26480 evaluation board designed allow user test blocks independently well system. Jumpers described Jumper table allow path each blocks separated from rest blocks. look each blocks, follow instructions below: Start with jumpers connected. Remove connecting jumpers (JP3, JP6, JP9, JP10) based jumper table isolate power ground planes block under test.
Connect power supply (VOUT 0.3V) input desired block referenced corresponding ground. Enable block proceed with normal testing. output voltage dropout regulators accessed `Turrets' (LDO1 LDO2) referenced GND_M. These marked silkscreen evaluation board. output voltage buck regulators accessed `Turrets' BUCK1, BUCK2 referenced GND1, GND2. External power supplies attached AVDD referenced GND_C. voltage supplied system must between range 2.8V 5.5V.
Table Jumper Settings JUMPER 1,3,6,9,10 PURPOSE These jumpers connect different VINs system (AVDD): connects VINLDO1 AVDD connects VIN1 AVDD connects VIN2 AVDD connects VINLDO1 AVDDM JP10 connects VINLDO2 AVDD These jumpers enables each regulator VDD: Buck1 Buck2 JP7- LDO2 LDO1 This jumper connects SYNC GND. NOTE allow bucks powered from system power. JP10 allow LDOs powered from system power. powers internal bias error amplifiers from system power. voltage applied AVDD VINLDO12 should range 5.5V. When connected, these jumpers enable regulators. disconnected, regulator will power off.
4,5,7,8
SYNC default OFF. Please contact National Sales Office wish this feature.
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FIGURE LM26480 Evaluation Board Schematic
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Gerber Files
LM26480 four layer board. Below Gerber files board, constructed Altium Designer.
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Layer
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Bottom Layer
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Plane
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Plane
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Layout Considerations
evaluation board layers from bottom are: Top, component side Ground plane signal section Bottom, solder side good performance circuit, essential place input output capacitors very close circuit wide routing traces allowing high currents. Sensitive components should placed from those components with high pulsating current. Decoupling capacitors should close circuit's pins. Digital analog ground should routed separately connected together star connection. It's good practice minimize high current switching current paths. DROP REGULATORS Place filter capacitors very close input output pins. large trace width high current carrying traces returns ground. BUCK REGULATORS Place supply bypass, filter capacitor, inductor close together keep traces short. traces between these components carry relatively high switching current antennas. Following these rules reduces radiated noise.
Arrange components that switching current loops curl same direction. Connect buck ground ground capacitors together using generous component-side copper fill pseudo-ground plane. Then connect this back general board system ground plane single point. Place pseudo-ground plane below these components then have tied system ground output capacitor outside current loops. This prevents switched current from injecting noise into system ground. These components along with inductor output should placed same side circuit board, their connections should made same layer. Route noise sensitive traces such voltage feedback path away from inductor. This done routing bottom layer adding grounded copper area between switching node feedback path. reduce noisy traces between power components, keep digital lines away from this section. Keep Feedback node small possible that ground ground traces will shield from buck output. wide traces between power components power connections DC-DC converter circuit reduce voltage errors caused resistive losses. sense lines, make sure Kelvin contact connection.
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Table List Main Components LM26480 Evaluation Board Reference Designator C11,C14 C12, R1,R2 R11, S1,S2 L1,L2 package 1sat 4x4mm package Value, Size, Tolerance 1uF, 16V, X7R, 0805 10uF, 16V, X7R, 1206 0.47uF, 25V, X7R, 0805 1/10W 0603 0603 Description C2012X7R1C105K C3216X7R1C106M C2012X7R1E474K MCR03EZPFX2202 Rohm MCR03EZPJ000 Connector 131-1701-206 Coil inductor NP04SZB 2R2N Power management Rohm Emerson TaiyoYuden National Semiconductor LM26480 Vendor/Type
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Evaluation LM26480 Dual DC/DC Buck Regulators with Dual Low-Noise Linear Regulators
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