LM2831ZMFX

LM2831 NSC | Alldatasheet

Document overview

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Technical content

Features

n Space Saving SOT23-5 Package n Input voltage range of 3.0V to 5.5V n Output voltage range of 0.6V to 4.5V n 1.5A output current n High Switching Frequencies 1.6MHz (LM2831X) 0.55MHz (LM2831Y) 3.0MHz (LM2831Z) n 130mΩ PMOS switch n 0.6V, 2% Internal Voltage Reference n Internal soft-start n Current mode, PWM operation n Thermal Shutdown n Over voltage protection

Applications

n Local 5V to Vcore Step-Down Converters n Core Power in HDDs n Set-Top Boxes n USB Powered Devices n DSL Modems Typical Application Circuit 20174864 20174881 August 2006 LM2831 High Frequency 1.5A Load - Step-Down DC-DC Regulator © 2006 National Semiconductor Corporation DS201748 www.national.com

Ordering Information

Option Package Type NSC Package Drawing Top Mark Supplied As LM2831XMF 1.6MHz SOT23-5 MF05A SKYB 1000 units Tape and Reel LM2831XMFX 3000 units Tape and Reel LM2831XSD LLP-6 SDE06A L193B 1000 units Tape and Reel LM2831XSDX 4500 units Tape and Reel LM2831YMF 0.55MHz SOT23-5 MF05A SKZB 1000 units Tape and Reel LM2831YMFX 3000 units Tape and Reel LM2831YSD LLP-6 SDE06A L194B 1000 units Tape and Reel LM2831YSDX 4500 units Tape and Reel LM2831ZMF 3MHz SOT23-5 MF05A SLAB 1000 units Tape and Reel LM2831ZMFX 3000 units Tape and Reel LM2831ZSD LLP-6 SDE06A L195B 1000 units Tape and Reel LM2831ZSDX 4500 units Tape and Reel NOPB versions available as well LM2831 www.national.com 2

Pin Descriptions 5-Pin SOT23 Pin Name Function 1 SW Output switch. Connect to the inductor and catch diode. 2 GND Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin. 3 FB Feedback pin. Connect to external resistor divider to set output voltage. 4 EN Enable control input. Logic high enables operation. Do not allow this pin to float or be greater than VIN + 0.3V. 5 VIN Input supply voltage. Pin Descriptions 6-Pin LLP Pin Name Function 1 FB Feedback pin. Connect to external resistor divider to set output voltage. 2 GND Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin. 3 SW Output switch. Connect to the inductor and catch diode. 4 VIND Power Input supply. 5 VINA Control circuitry supply voltage. Connect VINA to VIND on PC board. 6 EN Enable control input. Logic high enables operation. Do not allow this pin to float or be greater than VINA + 0.3V. DAP Die Attach Pad Connect to system ground for low thermal impedance, but it cannot be used as a primary GND connection. LM2831 www.national.com3

Absolute Maximum Ratings(Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN -0.5V to 7V FB Voltage -0.5V to 3V EN Voltage -0.5V to 7V SW Voltage -0.5V to 7V ESD Susceptibility 2kV Junction Temperature (Note 2) 150˚C Storage Temperature −65˚C to +150˚C Soldering Information Infrared or Convection Reflow (15 sec) 220˚C Operating Ratings VIN 3V to 5.5V Junction Temperature −40˚C to +125˚C Electrical Characteristics VIN = 5V unless otherwise indicated under theConditions column. Limits in standard type are for TJ = 25˚C only; limits inboldface typeapply over the junction temperature (TJ) range of -40˚C to +125˚C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at T J = 25˚C, and are provided for reference purposes only. Symbol Parameter Conditions Min Typ Max Units VFB Feedback Voltage LLP-6 and SOT23-5 Package 0.588 0.600 0.612 V ∆VFB/VIN Feedback Voltage Line Regulation V IN = 3V to 5V 0.02 %/V IB Feedback Input Bias Current 0.1 100 nA UVLO Undervoltage Lockout VIN Rising 2.73 2.90 V VIN Falling 1.85 2.3 UVLO Hysteresis 0.43 V FSW Switching Frequency LM2831-X 1.2 1.6 1.95 MHzLM2831-Y 0.4 0.55 0.7 LM2831-Z 2.25 3.0 3.75 DMAX Maximum Duty Cycle LM2831-X 86 94 %LM2831-Y 90 96 LM2831-Z 82 90 DMIN Minimum Duty Cycle LM2831-X 5 %LM2831-Y 2 LM2831-Z 7 RDS(ON) Switch On Resistance LLP-6 Package 150 mΩSOT23-5 Package 130 195 ICL Switch Current Limit V IN = 3.3V 1.8 2.5 A VEN_TH Shutdown Threshold Voltage 0.4 VEnable Threshold Voltage 1.8 ISW Switch Leakage 100 nA IEN Enable Pin Current Sink/Source 100 nA IQ Quiescent Current (switching) LM2831X VFB = 0.55 3.3 5 mA LM2831Y VFB = 0.55 2.8 4.5 LM2831Z VFB = 0.55 4.3 6.5 Quiescent Current (shutdown) All Options V EN =0 V 3 0 n A LM2831 www.national.com 4

Electrical CharacteristicsVIN = 5V unless otherwise indicated under theConditions column. Limits in standard type are for TJ = 25˚C only; limits inboldface typeapply over the junction temperature (TJ) range of -40˚C to +125˚C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at T J = 25˚C, and are provided for reference purposes only. (Continued) Symbol Parameter Conditions Min Typ Max Units θJA Junction to Ambient

0 LFPM Air Flow (Note 3)

θJC Junction to Case (Note 3) LLP-6 Package 18 ˚C/WSOT23-5 Package 80 TSD Thermal Shutdown Temperature 165 ˚C Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating Range indicates conditions for which the device is intended to be functional, but does not guarantee specfic performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device. Note 3: Applies for packages soldered directly onto a 3” x 3” PC board with 2oz. copper on 4 layers in still air. LM2831 www.national.com5

Typical Performance CharacteristicsAll curves taken at VIN = 5.0V with configuration in typical ap- plication circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. η vs Load "X" Vin = 5V, Vo = 1.8V & 3.3V η vs Load - "Y" Vin = 5V, Vo = 3.3V & 1.8V 20174839 20174886 η vs Load "Z" Vin = 5V, Vo = 3.3V & 1.8V η vs Load "X, Y and Z" Vin = 5V, Vo = 3.3V & 1.8V 20174842 20174885 Load Regulation Vin = 3.3V, Vo = 1.8V (All Options) Load Regulation Vin = 5V, Vo = 1.8V (All Options) 20174844 20174845 LM2831 www.national.com 6

Typical Performance CharacteristicsAll curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. (Continued) Load Regulation Vin = 5V, Vo = 3.3V (All Options) Oscillator Frequency vs Temperature - "X" 20174846 20174824 Oscillator Frequency vs Temperature - "Y" Oscillator Frequency vs Temperature - "Z" 20174825 20174836 Current Limit vs Temperature Vin = 3.3V RDSON vs Temperature (LLP-6 Package) 20174823 20174883 LM2831 www.national.com7

Typical Performance CharacteristicsAll curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. (Continued) RDSON vs Temperature (SOT23-5 Package) LM2831X I Q (Quiescent Current) 20174884 20174828 LM2831Y IQ (Quiescent Current) LM2831Z I Q (Quiescent Current) 20174829 20174837 LM2831 www.national.com 8

Typical Performance CharacteristicsAll curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. (Continued) Line Regulation Vo = 1.8V, Io = 500mA V FB vs Temperature 20174853 20174827 Gain vs Frequency (Vin = 5V, Vo = 1.2V@ 1A) Phase Plot vs Frequency (Vin = 5V, Vo = 1.2V@ 1A) 20174856 20174857 LM2831 www.national.com9

FIGURE 1. LM2831 www.national.com 10

uses current-mode control to regulate the output voltage. decrease the output ripple current. FIGURE 2. Typical Waveforms

enough. The typical current limit is 2.5A. current of the inductor at the 2.5A typical switch current limit. inductors see Example Circuits. mount capacitors are strongly recommended. for both input and output capacitors and have very low ESL. how rated capacitance varies over operating conditions. FIGURE 3. Inductor Current

Design Guide (Continued) significantly with little detriment to the regulator stability. Like the input capacitor, recommended multilayer ceramic ca- pacitors are X7R or X5R types. CATCH DIODE The catch diode (D1) conducts during the switch off-time. A Schottky diode is recommended for its fast switching times and low forward voltage drop. The catch diode should be chosen so that its current rating is greater than: I D1 =I OUT x (1-D) The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin. To im- prove efficiency, choose a Schottky diode with a low forward voltage drop. OUTPUT VOLTAGE The output voltage is set using the following equation where R2 is connected between the FB pin and GND, and R1 is connected between V O and the FB pin. A good value for R2 is 10k. When designing a unity gain converter (Vo = 0.6V), R1 should be between 0Ω and 100Ω, and R2 should be equal or greater than 10kΩ. VREF = 0.60V PCB LAYOUT CONSIDERATIONS When planning layout there are a few things to consider when trying to achieve a clean, regulated output. The most important consideration is the close coupling of the GND connections of the input capacitor and the catch diode D1. These ground ends should be close to one another and be connected to the GND plane with at least two through-holes. Place these components as close to the IC as possible. Next in importance is the location of the GND connection of the output capacitor, which should be near the GND connections of CIN and D1. There should be a continuous ground plane on the bottom layer of a two-layer board except under the switching node island. The FB pin is a high impedance node and care should be taken to make the FB trace short to avoid noise pickup and inaccurate regulation. The feedback resis- tors should be placed as close as possible to the IC, with the GND of R1 placed as close as possible to the GND of the IC. The V OUT trace to R2 should be routed away from the inductor and any other traces that are switching. High AC currents flow through the V IN, SW and VOUT traces, so they should be as short and wide as possible. However, making the traces wide increases radiated noise, so the designer must make this trade-off. Radiated noise can be decreased by choosing a shielded inductor. The remaining components should also be placed as close as possible to the IC. Please see Application Note AN-1229 for further considerations and the LM2831 demo board as an example of a four-layer layout. LM2831 www.national.com13

Calculating Efficiency, and Junction Temperature The complete LM2831 DC/DC converter efficiency can be calculated in the following manner. Or Calculations for determining the most significant power losses are shown below. Other losses totaling less than 2% are not discussed. Power loss (P LOSS) is the sum of two basic types of losses in the converter: switching and conduction. Conduction losses usually dominate at higher output loads, whereas switching losses remain relatively fixed and dominate at lower output loads. The first step in determining the losses is to calculate the duty cycle (D): VSW is the voltage drop across the internal PFET when it is on, and is equal to: VSW =I OUT xR DSON VD is the forward voltage drop across the Schottky catch diode. It can be obtained from the diode manufactures Elec- trical Characteristics section. If the voltage drop across the inductor (V DCR) is accounted for, the equation becomes: The conduction losses in the free-wheeling Schottky diode are calculated as follows: P DIODE =V D xI OUT x (1-D) Often this is the single most significant power loss in the circuit. Care should be taken to choose a Schottky diode that has a low forward voltage drop. Another significant external power loss is the conduction loss in the output inductor. The equation can be simplified to: P IND =I OUT 2 xR DCR The LM2831 conduction loss is mainly associated with the internal PFET: If the inductor ripple current is fairly small, the conduction losses can be simplified to: P COND =I OUT 2 xR DSON xD Switching losses are also associated with the internal PFET. They occur during the switch on and off transition periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss is to empirically measuring the rise and fall times (10% to 90%) of the switch at the switch node. Switching Power Loss is calculated as follows: P SWR = 1/2(VIN xI OUT xF SW xT RISE) PSWF = 1/2(VIN xI OUT xF SW xT FALL) PSW =P SWR +P SWF Another loss is the power required for operation of the inter- nal circuitry: PQ =I Q xV IN IQ is the quiescent operating current, and is typically around 2.5mA for the 0.55MHz frequency option. Typical Application power losses are: Power Loss Tabulation VIN 5.0V VOUT 3.3V P OUT 4.125W IOUT 1.25A VD 0.45V P DIODE 188mW FSW 550kHz IQ 2.5mA P Q 12.5mW TRISE 4nS P SWR 7mW TFALL 4nS P SWF 7mW RDS(ON) 150mΩ PCOND 156mW INDDCR 70mΩ PIND 110mW D 0.667 P LOSS 481mW η 88% P INTERNAL 183mW ΣPCOND +P SW +P DIODE +P IND +P Q =P LOSS ΣPCOND +P SWF +P SWR +P Q =P INTERNAL PINTERNAL = 183mW Thermal Definitions TJ = Chip junction temperature TA = Ambient temperature RθJC = Thermal resistance from chip junction to device case RθJA = Thermal resistance from chip junction to ambient air Heat in the LM2831 due to internal power dissipation is removed through conduction and/or convection. Conduction: Heat transfer occurs through cross sectional areas of material. Depending on the material, the transfer of heat can be considered to have poor to good thermal con- ductivity properties (insulator vs. conductor). Heat Transfer goes as: Silicon → package → lead frame → PCB Convection: Heat transfer is by means of airflow. This could be from a fan or natural convection. Natural convection occurs when air currents rise from the hot device to cooler air. Thermal impedance is defined as: LM2831 www.national.com 14

also make a large difference in the thermal impedance. duct heat from the surface of the PCB to the ground plane. pad to the ground plane if the LLP package is used. silicon junction to top case temperature. package to silicon junction. ing. The protection circuitry has a hysteresis of about 15˚C. allowed for a desired junction temperature can be found. for the application can be reduced. FIGURE 4. Internal LLP Connection

FIGURE 5. 6-Lead LLP PCB Dog Bone Layout

FIGURE 6. LM2831X (1.6MHz): Vin = 5V, Vo = 1.2V@ 1.5A

FIGURE 7. LM2831X (1.6MHz): Vin = 5V, Vo = 0.6V@ 1.5A

FIGURE 8. LM2831X (1.6MHz): Vin = 5V, Vo = 3.3V@ 1.5A

FIGURE 9. LM2831Y (550kHz): Vin = 5V, Vout = 3.3V@ 1.5A

FIGURE 10. LM2831Y (550kHz): Vin = 5V, Vout = 1.2V@ 1.5A

FIGURE 11. LM2831Z (3MHz): Vin = 5V, Vo = 3.3V@ 1.5A

FIGURE 12. LM2831Z (3MHz): Vin = 5V, Vo = 1.2V@ 1.5A

Physical Dimensions inches (millimeters) unless otherwise noted 5-Lead SOT-23 Package 6-Lead LLP Package LM2831 www.national.com 26

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at: www.national.com/quality/green. Lead free products are RoHS compliant. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: ap.support@nsc.com National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560 www.national.com LM2831 High Frequency 1.5A Load - Step-Down DC-DC Regulator