lm25117psqx National Semiconductor Corporation, lm25117psqx Datasheet

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lm25117psqx

Manufacturer Part Number
lm25117psqx
Description
Wide Input Range Synchronous Buck Controller With Analog Current Monitor
Manufacturer
National Semiconductor Corporation
Datasheet

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Part Number:
LM25117PSQX
Manufacturer:
TI/德州仪器
Quantity:
20 000
© 2011 National Semiconductor Corporation
Wide Input Range Synchronous Buck Controller with
Analog Current Monitor
General Description
The LM25117 is a synchronous buck controller intended for
step-down regulator applications from a high voltage or widely
varying input supply. The control method is based upon cur-
rent mode control utilizing an emulated current ramp. Current
mode control provides inherent line feed-forward, cycle-by-
cycle current limiting and ease of loop compensation. The use
of an emulated control ramp reduces noise sensitivity of the
pulse-width modulation circuit, allowing reliable control of
very small duty cycles necessary in high input voltage appli-
cations.
The operating frequency is programmable from 50 kHz to 750
kHz. The LM25117 drives external high-side and low-side
NMOS power switches with adaptive dead-time control. A us-
er-selectable diode emulation mode enables discontinuous
mode operation for improved efficiency at light load condi-
tions. A high voltage bias regulator that allows external bias
supply further improves efficiency. The LM25117’s unique
analog telemetry feature provides average output current in-
formation. Additional features include thermal shutdown, fre-
quency synchronization, hiccup mode current limit and
adjustable line under-voltage lockout.
Typical Application
301550
LM25117
Features
Packages
Emulated peak current mode control
Wide operating range from 4.5V to 42V
Robust 3.3A peak gate drives
Adaptive dead-time output driver control
Free-run or synchronizable clock up to 750kHz
Optional diode emulation mode
Programmable output from 0.8V
Precision 1.5% voltage reference
Analog current monitor
Programmable current limit
Hiccup mode over current protection
Programmable soft-start and tracking
Programmable line under-voltage lockout
Programmable switch-over to external bias supply
Thermal shutdown
TSSOP-20EP (Thermally enhanced)
LLP-24 (4mmx4mm)
30155001
www.national.com
May 25, 2011

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lm25117psqx Summary of contents

Page 1

... Additional features include thermal shutdown, fre- quency synchronization, hiccup mode current limit and adjustable line under-voltage lockout. Typical Application © 2011 National Semiconductor Corporation LM25117 Features ■ Emulated peak current mode control ■ ...

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... Connection Diagrams Ordering Information Order Number Package Type LM25117PMH TSSOP-20EP LM25117PMHE TSSOP-20EP LM25117PMHX TSSOP-20EP LM25117PSQ LLP-24 LM25117PSQE LLP-24 LM25117PSQX LLP-24 www.national.com Top View 20-Lead TSSOP EP 30155002 Top View LLP-24 (4mmx4mm) NSC Package Supplied As Drawing MXA20A 73 Units Per Rail MXA20A 250 Units on Tape and Reel ...

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Pin Descriptions TSSOP LLP Name Description Pin Pin 1 24 UVLO Under-voltage lockout programming pin. If the UVLO pin voltage is below 0.4V, the regulator is in the shutdown mode with all functions disabled. If the UVLO pin voltage is ...

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TSSOP LLP Name Description Pin Pin High-side NMOS gate drive output. Connect to the gate of the high-side NMOS transistor through a short, low inductance path High-side driver supply for the bootstrap gate drive. ...

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Absolute Maximum Ratings VIN to AGND SW to AGND VCC to AGND (Note AGND FB, DEMB, RES, VCCDIS, UVLO to AGND CM, COMP to AGND(Note 3) Electrical Characteristics junction temperature range ...

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Symbol Parameter t Minimum HO On-time ON(MIN) COMP to PWM comparator offset Oscillator f Frequency 1 SW1 f Frequency 2 SW2 RT Output Voltage RT Sync Positive Threshold Sync Pulse Width Current Limit V Cycle-by-cycle Sense Voltage CS(TH) Threshold CS ...

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Symbol Parameter θ Junction to Case JC θ Junction to Ambient JA θ Junction to Case JC Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of ...

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Typical Performance Characteristics HO Peak Driver Current vs Output Voltage Driver Dead Time vs V Forced HO Off-time vs Temperature www.national.com LO Peak Driver Current vs Output Voltage 30155003 Driver Dead Time vs Temperature VCC 30155005 30155007 8 30155004 30155006 ...

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VCC VCC 30155009 V vs Temperature CS(TH) 30155070 V vs Temperature VCC 30155073 VCC VIN V vs Temperature REF Error Amp Gain and Phase vs Frequency 9 30155069 30155071 301550162 www.national.com ...

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OUT www.national.com V 30155072 CSG-CS 30155078 ...

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Block Diagram and Typical Application Circuit FIGURE 1. Block Diagram and Typical Application Circuit 11 30155010 www.national.com ...

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Functional Description The LM25117 high voltage switching controller features all of the functions necessary to implement an efficient high voltage buck regulator that operates over a very wide input voltage range. This easy to use controller integrates high-side and low-side ...

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For 14.5V <V , the external supply voltage can be regulat- OUT ed by using a series Zener diode from the output to VCC. FIGURE 5. External VCC Supply for 14.5V <V In high input voltage applications, extra care should ...

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Ramp Generator and Emulated Current Sense The ramp signal used in the pulse width modulator for tradi- tional current mode control is typically derived directly from the high-side switch current. This switch current corresponds to the positive slope portion of ...

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and C configure the error amplifier gain and COMP COMP HF phase characteristics to achieve a stable voltage loop gain. This network creates a pole for phase boost, and a high ...

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FIGURE 10. Inductor Current During an output short condition, the worst case peak inductor current is limited to: Where t is the minimum HO on-time. ON(MIN) If the saturation current of the inductor is less than I peak inductor current ...

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HO and LO Drivers The LM25117 contains high current NMOS drivers and an associated high-side level shifter to drive the external high- side NMOS device. This high-side gate driver works in con- junction with an external diode D , and ...

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Application Information FEEDBACK COMPENSATION Open loop response of the regulator is defined as the product of modulator transfer function and feedback transfer function. When plotted scale, the open loop gain is shown as the sum of modulator ...

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SUB-HARMONIC OSCILLATION Peak current mode regulators can exhibit unstable behavior when operating above 50% duty cycle. This behavior is known as sub-harmonic oscillation and is characterized by alternating wide and narrow pulses at the SW pin. Sub-har- monic oscillation can ...

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The LM25117 has an exposed thermal pad to aid power dis- sipation. Adding several vias under the exposed pad helps conduct heat away from the IC. The junction to ambient ther- mal resistance varies with application. The most significant variables ...

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TABLE 1. LM25117 Frequency Analysis Formulas SIMPLE FORMULA MODULATOR TRANSFER FUNCTION Modulator DC Gain ESR Zero ESR Pole Not considered Dominant Load Pole Sampled Gain Not considered Inductor Pole Quality Factor Not considered Sub-harmonic Not considered Double Pole K Factor ...

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SIMPLE FORMULA Cross Over Frequency (Open Loop Bandwidth) Maximum Cross Over Frequency * Comprehensive Equation includes an inductor pole and a gain peaking at f that a ceramic capacitor C (No ESR) is connected in parallel with C OUT2 www.national.com ...

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Design Example OPERATING CONDITIONS • Output Voltage • Full Load Current • Minimum Input Voltage • Maximum Input Voltage • Switching Frequency • Diode Emulation • External VCC Supply TIMING RESISTOR R T Generally, higher frequency applications are smaller but ...

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The standard value of 105 kΩ was selected for R UVLO DIVIDER AND C UV2 UV1 The desired startup voltage and the hysteresis are set by the voltage divider R and R . Capacitor C UV1 UV2 ...

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OUTPUT CAPACITOR C O The output capacitors smooth the output voltage ripple caused by inductor ripple current and provide a source of charge during transient loading conditions. For this design example, a 680μF electrolytic capacitor with maximum 10mΩ ESR was ...

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STEP2: Determine required R COMP Knowing calculated as follows: CROSS COMP The standard value of 27.4kΩ was selected for R STEP3: Determine C to cancel load pole COMP Knowing calculated as follows: ...

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Application Circuit FIGURE 19. 3.3V, 9A Typical Application Schematic 30155021 27 www.national.com ...

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Example of Constant Current Regulator The LM25117 can be configured as a constant current regu- lator by using the current monitor feature (CM) as the feed- back input. A voltage divider at the VCCDIS pin from VOUT to AGND can ...

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The LM25117 also can be configured as a constant voltage and constant current regulator, known as CV+CC regulator. In this configuration, there is much less variation in the current limiting as compared to peak cycle-by-cycle current limiting of the inductor ...

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Physical Dimensions www.national.com inches (millimeters) unless otherwise noted 20 Pin TSSOP with Exposed Pad NS Package Number MXA20A 24 Pin LLP NS Package Number SQA24A 30 ...

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Notes 31 www.national.com ...

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... National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. ...

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