Datasheet

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LM3481

SEN

COMP

AGND

UVLO

PGND

FA/SYNC/SD

= 3.0V to 48V

OUT

= 5V, 1A

OUT

SEN

BYP

SEN

LM3481

www.ti.com

SNVS346E –NOVEMBER 2007–REVISED APRIL 2012

LM3481/LM3481Q High Efficiency Low-Side N-Channel Controller for Switching

Regulators

Check for Samples: LM3481

FEATURES

KEY SPECIFICATIONS

• LM3481QMM in the VSSOP-10 Package are

• Wide Supply Voltage Range of 2.97V to 48V

Automotive Grade Products that are AEC-Q100

• 100 kHz to 1 MHz Adjustable and

Grade 1 Qualified (-40°C to +125°C Operating

Synchronizable Clock Frequency

Junction Temperature)

• ±1.5% (Over Temperature) Internal Reference

• 10-Lead VSSOP Package

• 10 µA Shutdown Current (Over Temperature)

• Internal Push-Pull Driver with 1A Peak Current

Capability

DESCRIPTION

• Current Limit and Thermal Shutdown

The LM3481 is a versatile Low-Side N-FET high

performance controller for switching regulators. It is

• Frequency Compensation Optimized with a

suitable for use in topologies requiring a low-side

Capacitor and a Resistor

FET, such as boost, flyback, SEPIC, etc. The

• Internal Softstart

LM3481 can be operated at extremely high switching

• Current Mode Operation

frequencies in order to reduce the overall solution

size. The switching frequency of the LM3481 can be

• Adjustable Undervoltage Lockout with

adjusted to any value between 100 kHz and 1 MHz

Hysteresis

by using a single external resistor or by synchronizing

• Pulse Skipping at Light Loads

it to an external clock. Current mode control provides

superior bandwidth and transient response in addition

APPLICATIONS

to cycle-by-cycle current limiting. Current limit can be

programmed with a single external resistor.

• Distributed Power Systems

The LM3481 has built in protection features such as

• Notebook, PDA, Digital Camera, and other

thermal shutdown, short-circuit protection and over

Portable Applications

voltage protection. Power saving shutdown mode

• Offline Power Supplies

reduces the total supply current to 5µA and allows

• Set-Top Boxes

power supply sequencing. Internal soft-start limits the

inrush current at start-up.

TYPICAL APPLICATION CIRCUIT

Figure 1. Typical SEPIC Converter

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

Summary of content (30 pages)

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LM3481 www.ti.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. CONNECTION DIAGRAM ISEN UVLO COMP FB AGND 1 10 2 9 3 8 LM3481 4 7 5 6 VIN VCC DR PGND FA/SYNC/SD Figure 2. 10-Lead VSSOP Package (DGS-10 Package) PIN DESCRIPTIONS 2 Pin Name Pin Number ISEN 1 Current sense input pin.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 ABSOLUTE MAXIMUM RATINGS (1) VIN pin Voltage -0.4V to 50V FB Pin Voltage -0.4V to 6V FA/SYNC/SD Pin Voltage -0.4V to 6V COMP Pin Voltage -0.4V to 6V UVLO Pin Voltage -0.4V to 6V VCC Pin Voltage -0.4V to 6V DR Pin Voltage -0.4V to 6V ISEN Pin Voltage –0.4V to 600 mV Peak Driver Output Current 1.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com ELECTRICAL CHARACTERISTICS (continued) VIN=12V, RFA=40 kΩ unless otherwise indicated under the Conditions column. Typicals and limits appearing in plain type apply for TJ = 25°C. Limits appearing in boldfacetype apply over the full Operating Temperature Range (-40°C to 125°C). Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 TYPICAL PERFORMANCE CHARACTERISTICS Unless otherwise specified, VIN = 12V, TJ = 25°C. Comp Pin Voltage vs. Load Current Switching Frequency vs. RFA Figure 3. Figure 4. Efficiency vs. Load Current (3.3VIN and 12VOUT) Efficiency vs. Load Current (5VIN and 12VOUT) Figure 5. Figure 6. Efficiency vs. Load Current (9VIN and 12VOUT) Frequency vs. Temperature Figure 7. Figure 8.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. 6 COMP Pin Source Current vs. Temperature ISupply vs. Input Voltage (Non-Switching) Figure 9. Figure 10. ISupply vs. Input Voltage (Switching) Shutdown Threshold Hysteresis vs. Temperature Figure 11. Figure 12. Drive Voltage vs. Input Voltage Short Circuit Protection vs. VIN Figure 13. Figure 14.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 TYPICAL PERFORMANCE CHARACTERISTICS (continued) Unless otherwise specified, VIN = 12V, TJ = 25°C. Current Sense Threshold vs. Input Voltage Compensation Ramp Amplitude vs. Input Voltage Figure 15. Figure 16. Minimum On-Time vs. Temperature Figure 17.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com FUNCTIONAL BLOCK DIAGRAM Shutdown Detect VIN SYNC/Fixed Frequency detect FA/SYNC/SD Oscillator Set/Blankout Slope Compensation 6V Soft-start UVLO Bias Voltages UVLO Thermal Shutdown 40 éA 1.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 Blank-Out prevents false reset PWM Comparator resets the RS latch VSL _ + PWM Comparator Oscillator Sets the RS Latch Tmin (on) Blank-Out time Figure 18. Basic Operation of the PWM Comparator OVER VOLTAGE PROTECTION The LM3481 has over voltage protection (OVP) for the output voltage. OVP is sensed at the feedback pin (FB). If at anytime the voltage at the feedback pin rises to VFB + VOVP, OVP is triggered.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com From the above equation, when D > 0.5, ΔVsamp1 will be greater than ΔVsamp0. In other words, the disturbance is divergent. So a very small perturbation in the load will cause the disturbance to increase. To ensure that the perturbed signal converges we must maintain: - M2 < M1 1 Control Signal MC = 0 Perturbed Signal -M2 _ M1 'Vsamp0 'Vsamp1 Steady State Signal Vsamp + PWM Comparator (1-D)TS DTS Figure 19.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 Control Signal Compensation Ramp with RSL Control Signal Compensation Ramp without RSL 'VSL -MC VSL Figure 21. Additional Slope Compensation Added Using External Resistor RSL Where, ΔVSL = K x RSL K = 40 µA typically and changes slightly as the switching frequency changes. Figure 23 shows the effect the current K has on ΔVSLand different values of RSL as the switching frequency changes.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com Figure 23. ΔVSL vs RSL FREQUENCY ADJUST/SYNCHRONIZATION/SHUTDOWN The switching frequency of the LM3481 can be adjusted between 100 kHz and 1 MHz using a single external resistor. This resistor must be connected between the FA/SYNC/SD pin and ground, as shown in Figure 24. Please refer to the typical performance characteristics to determine the value of the resistor required for a desired switching frequency.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 RFA FA/SYNC/SD LM3481 Freq. clock 100 kHz to 1 MHz Figure 25. Frequency Synchronization RFA 10 k: >1.3V FA/SYNC/SD LM3481 MOSFET State On-Normal Operation OFF- Shutdown Figure 26. Shutdown Operation in Frequency Adjust Mode 30 Ps 40 k: FA/SYNC/SD LM3481 DR Figure 27. Shutdown Operation in Synchronization Mode UNDER VOLTAGE LOCKOUT (UVLO) Pin The UVLO pin provides user programmable enable and shutdown thresholds.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com VIN IUVLO R7 2 + UVLO R8 VUVLOSEN + - Figure 28. UVLO Pin Resistor Divider If the UVLO pin function is not desired, select R8 and R7 of equal magnitude greater than 100 kΩ. This will allow VIN to be in control of the UVLO thresholds. The UVLO pin may also be used to implement the enable/disable function. If a signal pulls the UVLO pin below the 1.43V (typical) threshold, the converter will be disabled.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 L VIN D1 + VOUT + Q PWM L COUT L D1 + VOUT + + VOUT RLOAD VIN + - - COUT + + VIN - COUT RLOAD - Figure 29. Simplified Boost Converter Diagram (a) First cycle of operation. (b) Second cycle of operation POWER INDUCTOR SELECTION The inductor is one of the two energy storage elements in a boost converter. Figure 30 shows how the inductor current varies during a switching cycle.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com The important quantities in determining a proper inductance value are IL (the average inductor current) and ΔiL (the inductor current ripple difference between the peak inductor current and the average inductor current). If ΔiL is larger than IL, the inductor current will drop to zero for a portion of the cycle and the converter will operate in discontinuous conduction mode.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 Combining the two equations yields an expression for RSEN VSENSE - (D x VSL) RSEN = (D x VIN) IOUT(max) + (1-D) (2 x fS x L) Evaluate RSEN at the maximum and minimum VIN values and choose the smallest RSEN calculated. VIN L D1 DR VOUT Q + LM3481 COUT ISEN FB RF1 RSEN RF2 Figure 31.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com Power MOSFET Selection The drive pin, DR, of the LM3481 must be connected to the gate of an external MOSFET. In a boost topology, the drain of the external N-Channel MOSFET is connected to the inductor and the source is connected to the ground. The drive pin voltage, VDR, depends on the input voltage (see typical performance characteristics). In most applications, a logic level MOSFET can be used.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 RIN VIN VIN LM3481 CBYPASS CIN Figure 32. Reducing IC Input Noise Output Capacitor Selection The output capacitor in a boost converter provides all the output current when the inductor is charging. As a result it sees very large ripple currents. The output capacitor should be capable of handling the maximum rms current.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com Figure 33. Current Flow In A Boost Application The PGND and AGND pins have to be connected to the same ground very close to the IC. To avoid ground loop currents attach all the grounds of the system only at one point. A ceramic input capacitor should be connected as close as possible to the Vin pin and grounded close to the GND pin. For a layout example please see Application Note 1204 (SNVA042).
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 Power MOSFET Selection As in a boost converter, the parameters governing the selection of the MOSFET are the minimum threshold voltage, VTH(MIN), the on-resistance, RDS(ON), the total gate charge, Qg, the reverse transfer capacitance, CRSS, and the maximum drain to source voltage, VDS(MAX).
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com Peak to peak ripple current, to calculate core loss if necessary: Maintaining the condition IL > ΔIL/2 to ensure continuous conduction mode yields the following minimum values for L1 and L2: (VIN - VQ)(1-D) L1 > 2IOUTfS L2 > (VIN - VQ)D 2IOUTfS Peak current in the inductor, to ensure the inductor does not saturate: IL1PK must be lower than the maximum current rating set by the current sense resistor.
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LM3481 www.ti.com SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 The SEPIC capacitor must be rated for a large ACrms current relative to the output power. This property makes the SEPIC much better suited to lower power applications where the rms current through the capacitor is small (relative to capacitor technology). The voltage rating of the SEPIC capacitor must be greater than the maximum input voltage. Tantalum capacitors are the best choice for SMT, having high rms current ratings relative to size.
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LM3481 SNVS346E – NOVEMBER 2007 – REVISED APRIL 2012 www.ti.com OTHER APPLICATION CIRCUITS R7 121 k: VIN = 5V R8 121 k: C8 390 pF ISEN VIN UVLO L1 6.8 PH 1 PF VCC C9 COMP RC 22.6 k: CC 82 nF FB RF2 20 k: RF1 169 k: LM3481 Q1 DR D1 + CIN1, CIN2 150 PF VOUT = 12V IOUT = 1.8A + COUT1, COUT2 150 PF PGND AGND FA/SYNC/SD RFA 90.9 k: CSEN 1 nF RSEN 20 m: Figure 35.
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PACKAGE OPTION ADDENDUM www.ti.
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PACKAGE OPTION ADDENDUM www.ti.com 18-Mar-2014 Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties.
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PACKAGE MATERIALS INFORMATION www.ti.com 18-Mar-2014 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LM3481MM/NOPB VSSOP DGS 10 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3481MMX/NOPB VSSOP DGS 10 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3481QMM/NOPB VSSOP DGS 10 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.
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PACKAGE MATERIALS INFORMATION www.ti.com 18-Mar-2014 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM3481MM/NOPB VSSOP DGS 10 1000 210.0 185.0 35.0 LM3481MMX/NOPB VSSOP DGS 10 3500 367.0 367.0 35.0 LM3481QMM/NOPB VSSOP DGS 10 1000 210.0 185.0 35.0 LM3481QMMX/NOPB VSSOP DGS 10 3500 367.0 367.0 35.
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