Product Folder Sample & Buy Support & Community Tools & Software Technical Documents LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 LM2671 SIMPLE SWITCHER(R) Power Converter High Efficiency 500-mA Step-Down Voltage Regulator With Features 1 Features 3 Description * * The LM2671 series of regulators are monolithic integrated circuits built with a LMDMOS process. These regulators provide all the active functions for a step-down (buck) switching regulator, capable of driving a 500-mA load current with excellent line and load regulation. These devices are available in fixed output voltages of 3.3 V, 5 V, 12 V, and an adjustable output version. 1 * * * * * * * * * * * * * Efficiency up to 96% Available in 8-Pin SOIC, PDIP, and WSON Packages Simple and Easy to Design With Requires Only 5 External Components Uses Readily Available Standard Inductors 3.3-V, 5-V, 12-V, and Adjustable Output Versions Adjustable Version Output Voltage Range: 1.21 V to 37 V 1.5% Maximum Output Voltage Tolerance Over Line and Load Conditions Ensured 500-mA Output Load Current 0.25- DMOS Output Switch Wide Input Voltage Range: 8 V to 40 V 260-kHz Fixed Frequency Internal Oscillator TTL Shutdown Capability, Low Power Standby Mode Soft-Start and Frequency Synchronization Thermal Shutdown and Current-Limit Protection 2 Applications * * Simple High Efficiency (> 90%) Step-Down (Buck) Regulators Efficient Preregulator for Linear Regulators Requiring a minimum number of external components, these regulators are simple to use and include patented internal frequency compensation, fixed frequency oscillator, external shutdown, soft start, and frequency synchronization. The LM2671 series operates at a switching frequency of 260 kHz, thus allowing smaller sized filter components than what is required with lower frequency switching regulators. Because of its very high efficiency (> 90%), the copper traces on the printed-circuit board are the only heat sinking required. A family of standard inductors for use with the LM2671 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies using these advanced ICs. Also included in the data sheet are selector guides for diodes and capacitors designed to work in switch-mode power supplies. Device Information(1) PART NUMBER LM2674 PACKAGE BODY SIZE (NOM) SOIC (8) 4.90 mm x 3.91 mm PDIP (8) 9.81 mm x 6.35 mm WSON (16) 5.00 mm x 5.00 mm (1) For all available packages, see the orderable addendum at the end of the data sheet. Typical Application For fixed output voltage versions 1 An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA. LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Description (continued)......................................... Pin Configuration and Functions ......................... Specifications......................................................... 1 1 1 2 3 3 4 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 4 4 4 4 5 5 5 6 Absolute Maximum Ratings ...................................... ESD Ratings.............................................................. Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics - 3.3 V .............................. Electrical Characteristics - 5 V ................................. Electrical Characteristics - 12 V ............................... Electrical Characteristics - Adjustable...................... Electrical Characteristics - All Output Voltage Versions ..................................................................... 7.10 Typical Characteristics ............................................ 8 6 7 8.2 Functional Block Diagram ....................................... 10 8.3 Feature Description................................................. 10 8.4 Device Functional Modes........................................ 11 9 Application and Implementation ........................ 13 9.1 Application Information............................................ 13 9.2 Typical Applications ................................................ 14 10 Power Supply Recommendations ..................... 26 11 Layout................................................................... 27 11.1 Layout Guidelines ................................................. 27 11.2 Layout Examples................................................... 27 12 Device and Documentation Support ................. 28 12.1 12.2 12.3 12.4 12.5 12.6 Documentation Support ........................................ Receiving Notification of Documentation Updates Community Resources.......................................... Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 28 28 28 28 28 28 Detailed Description ............................................ 10 13 Mechanical, Packaging, and Orderable Information ........................................................... 28 8.1 Overview ................................................................. 10 13.1 DAP (WSON Package) ......................................... 28 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision K (April 2013) to Revision L Page * Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .................................................................................................. 1 * Removed all references to Computer Design Software LM267X Made Simple (Version 6.0).............................................. 1 Changes from Revision J (April 2013) to Revision K * 2 Page Changed layout of National Data Sheet to TI format ........................................................................................................... 27 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 5 Description (continued) Other features include a ensured 1.5% tolerance on output voltage within specified input voltages and output load conditions, and 10% on the oscillator frequency. External shutdown is included, featuring typically 50-A standby current. The output switch includes current limiting, as well as thermal shutdown for full protection under fault conditions. 6 Pin Configuration and Functions D or P Package 8-Pin SOIC or PDIP Top View CB 1 SS 2 8 7 NHN Package 16-Pin WSON Top View VSW VIN SYNC 3 6 GND FB 4 5 ON/OFF CB NC 1 16 VSW 2 15 VSW NC SS 3 14 13 VIN NC 12 11 GND GND 10 9 NC ON/OFF NC SYNC 4 5 DAP 6 NC 7 FB 8 Not to scale Not to scale Connect DAP to pin 11 and 12 Pin Functions PIN NAME I/O DESCRIPTION SOIC, PDIP WSON CB 1 1 I Bootstrap capacitor connection for high-side driver. Connect a high-quality, 100-nF capacitor from CB to VSW Pin. SS 2 4 I Soft-start Pin. Connect a capacitor from this pin to GND to control the output voltage ramp. If the feature not desired, the pin can be left floating. SYNC 3 6 I This input allows control of the switching clock frequency. If left open-circuited the regulator is switched at the internal oscillator frequency, typically 260 kHz. FB 4 8 I Feedback sense input pin. Connect to the midpoint of feedback divider to set VOUT for ADJ version or connect this pin directly to the output capacitor for a fixed output version. ON/OFF 5 9 I Enable input to the voltage regulator. High = ON and low = OFF. Pull this pin high or float to enable the regulator VSW 8 15, 16 O Source pin of the internal high-side FET. This is a switching node. Attached this pin to an inductor and the cathode of the external diode. GND 6 11, 12 -- Power ground pins. Connect to system ground. Ground pins of CIN and COUT. Path to CIN must be as short as possible. VIN 7 14 I NC -- 2, 3, 5, 7, 10, 13 -- Supply input pin to collector pin of high-side FET. Connect to power supply and input bypass capacitors CIN. Path from VIN pin to high frequency bypass CIN and GND must be as short as possible. No connect pins Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 3 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 7 Specifications 7.1 Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted) (1) (2) MIN MAX UNIT 45 V Supply voltage -0.1 ON/OFF pin voltage, VSH 6 V -1 V VSW + 8 V 14 V Switch voltage to ground Boost pin voltage -0.3 Feedback pin voltage, VFB Power dissipation Internally Limited D package Lead temperature Vapor phase (60 s) 215 Infrared (15 s) 220 P package (soldering, 10 s) WSON package See AN-1187 Maximum junction temperature -65 Storage temperature, Tstg (1) (2) C 260 150 C 150 C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications. 7.2 ESD Ratings V(ESD) (1) (2) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) (2) VALUE UNIT 2000 V JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. The human body model is a 100-pF capacitor discharged through a 1.5-k resistor into each pin. 7.3 Recommended Operating Conditions MIN MAX Supply voltage 6.5 40 UNIT V Junction temperature, TJ -40 125 C 7.4 Thermal Information LM2674 THERMAL METRIC RJA (1) (2) 4 (1) Junction-to-ambient thermal resistance (2) D (SOIC) P (PDIP) NHN (WSON) 8 PINS 8 PINS 16 PINS 105 95 -- UNIT C/W For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report. Junction to ambient thermal resistance with approximately 1 square inch of printed-circuit board copper surrounding the leads. Additional copper area lowers thermal resistance further. The value RJA for the WSON (NHN) package is specifically dependent on PCB trace area, trace material, and the number of layers and thermal vias. For improved thermal resistance and power dissipation for the WSON package, see AN-1187 Leadless Leadframe Package (LLP). Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 7.5 Electrical Characteristics - 3.3 V Specifications are for TJ = 25C (unless otherwise noted). PARAMETER MIN (1) TYP (2) TJ = 25C 3.251 3.3 Over full operating temperature range 3.201 TJ = 25C 3.251 Over full operating temperature range 3.201 TEST CONDITIONS MAX (1) UNIT SYSTEM PARAMETERS (3) VIN = 8 V to 40 V, ILOAD = 20 mA to 500 mA VOUT Output voltage VIN = 6.5 V to 40 V, ILOAD = 20 mA to 250 mA Efficiency (1) (2) (3) VIN = 12 V, ILOAD = 500 mA 3.35 3.399 3.3 V 3.35 3.399 V 86% All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Typical numbers are at 25C and represent the most likely norm. External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator performance. When the LM2671 is used as shown in Figure 15 and Figure 21 test circuits, system performance is as specified by the system parameters section of the Electrical Characteristics. 7.6 Electrical Characteristics - 5 V Specifications are for TJ = 25C (unless otherwise noted). PARAMETER SYSTEM PARAMETERS TEST CONDITIONS VIN = 8 V to 40 V, ILOAD = 20 mA to 500 mA VOUT Output voltage VIN = 6.5 V to 40 V, ILOAD = 20 mA to 250 mA Efficiency (1) (2) (3) MIN (1) TYP (2) 4.925 5 MAX (1) UNIT (3) TJ = 25C Over full operating temperature range TJ = 25C Over full operating temperature range 4.85 4.925 5.15 5 4.85 VIN = 12 V, ILOAD = 500 mA 5.075 V 5.075 5.15 V 90% All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Typical numbers are at 25C and represent the most likely norm. External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator performance. When the LM2671 is used as shown in Figure 15 and Figure 21 test circuits, system performance is as specified by the system parameters section of the Electrical Characteristics. 7.7 Electrical Characteristics - 12 V Specifications are for TJ = 25C (unless otherwise noted). PARAMETER SYSTEM PARAMETERS VOUT Output voltage VIN = 15 V to 40 V, ILOAD = 20 mA to 500 mA Efficiency VIN = 24 V, ILOAD = 500 mA (1) (2) (3) MIN (1) TYP (2) TJ = 25C 11.82 12 Over full operating temperature range 11.64 TEST CONDITIONS MAX (1) UNIT (3) 12.18 12.36 V 94% All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Typical numbers are at 25C and represent the most likely norm. External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator performance. When the LM2671 is used as shown in Figure 15 and Figure 21 test circuits, system performance is as specified by the system parameters section of the Electrical Characteristics. Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 5 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 7.8 Electrical Characteristics - Adjustable Specifications are for TJ = 25C (unless otherwise noted). PARAMETER TEST CONDITIONS MIN (1) TYP (2) 1.21 MAX (1) UNIT SYSTEM PARAMETERS (3) Feedback voltage VFB Efficiency (1) (2) (3) VIN = 8 V to 40 V, ILOAD = 20 mA to 500 mA VOUT programmed for 5 V TJ = 25C 1.192 Over full operating temperature range 1.174 VIN = 6.5 V to 40 V, ILOAD = 20 mA to 250 mA VOUT programmed for 5 V TJ = 25C 1.192 Over full operating temperature range 1.174 VIN = 12 V, ILOAD = 500 mA 1.228 1.246 1.21 V 1.228 1.246 V 90% All room temperature limits are 100% production tested. All limits at temperature extremes are ensured through correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Typical numbers are at 25C and represent the most likely norm. External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator performance. When the LM2671 is used as shown in Figure 15 and Figure 21 test circuits, system performance is as specified by the system parameters section of the Electrical Characteristics. 7.9 Electrical Characteristics - All Output Voltage Versions Specifications are for TJ = 25C, VIN = 12 V for the 3.3-V, 5-V, and Adjustable versions and VIN = 24 V for the 12-V version, and ILOAD = 100 mA (unless otherwise noted). PARAMETERS TEST CONDITIONS MIN TYP MAX VFEEDBACK = 8 V for 3.3-V, 5-V, and adjustable versions 2.5 3.6 VFEEDBACK = 15 V for 12-V versions 2.5 UNIT DEVICE PARAMETERS IQ Quiescent current mA TJ = 25C ISTBY Standby quiescent current ICL Current limit IL Output leakage current ON/OFF pin = 0 V 50 Over full operating temperature range TJ = 25C 150 0.62 Over full operating temperature range TJ = 25C ISWITCH = 500 mA fO Oscillator frequency Measured at switch pin IBIAS 225 275 85 TJ = 25C 1.4 ON/OFF pin current ON/OFF pin = 0 V FSYNC Synchronization frequency VSYNC = 3.5 V, 50% duty cycle VSYNC Synchronization threshold voltage Over full operating temperature range 0.8 TJ = 25C 6 kHz 0% IS/D Soft-start current mA VFEEDBACK = 1.3 V (adjustable version only) ON/OFF pin voltage thresholds ISS 15 0.4 95% VS/D Soft-start voltage 6 0.25 260 Over full operating temperature range Minimum duty cycle VSS A A 0.6 Maximum duty cycle Feedback bias current A 25 Over full operating temperature range TJ = 25C D 1.2 1.25 1 VSWITCH = -1 V, ON/OFF pin = 0 V Switch ON-resistance 0.8 0.575 VIN = 40 V, ON/OFF pin = 0 V VSWITCH = 0 V RDS(ON) 100 nA 2 20 Over full operating temperature range 7 TJ = 25C 37 kHz 1.4 V 0.53 TJ = 25C 0.73 4.5 Over full operating temperature range Submit Documentation Feedback 1.5 A 400 0.63 Over full operating temperature range V 6.9 V A Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 7.10 Typical Characteristics Figure 1. Normalized Output Voltage Figure 2. Line Regulation Figure 3. Efficiency Figure 4. Drain-to-Source Resistance Figure 5. Switch Current Limit Figure 6. Operating Quiescent Current Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 7 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com Typical Characteristics (continued) 8 Figure 7. Standby Quiescent Current Figure 8. ON/OFF Threshold Voltage Figure 9. ON/OFF Pin Current (Sourcing) Figure 10. Switching Frequency Figure 11. Feedback Pin Bias Current Figure 12. Peak Switch Current Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 Typical Characteristics (continued) Figure 13. Dropout Voltage - 3.3-V Option Figure 14. Dropout Voltage - 5-V Option Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 9 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 8 Detailed Description 8.1 Overview The LM2671 provides all of the active functions required for a step-down (buck) switching regulator. The internal power switch is a DMOS power MOSFET to provide power supply designs with high current capability, up to 0.5 A, and highly efficient operation. The LM2671 is part of the SIMPLE SWITCHER(R) family of power converters. A complete design uses a minimum number of external components, which have been predetermined from a variety of manufacturers. Using either this data sheet or TI's WEBENCH(R) design tool, a complete switching power supply can be designed quickly. Also, see LM2670 SIMPLE SWITCHER(R) High Efficiency 3A Step-Down Voltage Regulator with Sync for additional applications information. 8.2 Functional Block Diagram 8.3 Feature Description 8.3.1 Switch Output This is the output of a power MOSFET switch connected directly to the input voltage. The switch provides energy to an inductor, an output capacitor and the load circuitry under control of an internal pulse-width-modulator (PWM). The PWM controller is internally clocked by a fixed 260-kHz oscillator. In a standard step-down application the duty cycle (Time ON/Time OFF) of the power switch is proportional to the ratio of the power supply output voltage to the input voltage. The voltage on the VSW pin cycles between VIN (switch ON) and below ground by the voltage drop of the external Schottky diode (switch OFF). 10 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 Feature Description (continued) 8.3.2 Input The input voltage for the power supply is connected to the VIN pin. In addition to providing energy to the load the input voltage also provides bias for the internal circuitry of the LM2671. For ensured performance the input voltage must be in the range of 6.5 V to 40 V. For best performance of the power supply the VIN pin must always be bypassed with an input capacitor placed close to this pin and GND. 8.3.3 C Boost A capacitor must be connected from the CB pin to the VSW pin. This capacitor boosts the gate drive to the internal MOSFET above VIN to fully turn it ON. This minimizes conduction losses in the power switch to maintain high efficiency. The recommended value for C Boost is 0.01 F. 8.3.4 Ground This is the ground reference connection for all components in the power supply. In fast-switching, high-current applications such as those implemented with the LM2671, TI recommends that a broad ground plane be used to minimize signal coupling throughout the circuit. 8.3.5 Sync This input allows control of the switching clock frequency. If left open-circuited the regulator is switched at the internal oscillator frequency, typically 260 kHz. An external clock can be used to force the switching frequency and thereby control the output ripple frequency of the regulator. This capability provides for consistent filtering of the output ripple from system to system as well as precise frequency spectrum positioning of the ripple frequency which is often desired in communications and radio applications. This external frequency must be greater than the LM2671 internal oscillator frequency, which could be as high as 275 kHz, to prevent an erroneous reset of the internal ramp oscillator and PWM control of the power switch. The ramp oscillator is reset on the positive going edge of the sync input signal. TI recommends that the external TTL or CMOS compatible clock (between 0 V and a level greater than 3 V) be ac coupled to the SYNC pin through a 100-pF capacitor and a 1-k resistor to ground. When the SYNC function is used, current limit frequency foldback is not active. Therefore, the device may not be fully protected against extreme output short-circuit conditions. 8.3.6 Feedback This is the input to a two-stage high gain amplifier, which drives the PWM controller. Connect the FB pin directly to the output for proper regulation. For the fixed output devices (3.3-V, 5-V and 12-V outputs), a direct wire connection to the output is all that is required as internal gain setting resistors are provided inside the LM2671. For the adjustable output version two external resistors are required to set the DC output voltage. For stable operation of the power supply it is important to prevent coupling of any inductor flux to the feedback input. 8.3.7 ON/OFF This input provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any voltage less than 0.8 V is completely turn OFF the regulator. The current drain from the input supply when OFF is only 50 A. The ON/OFF input has an internal pullup current source of approximately 20 A and a protection clamp Zener diode of 7 V to ground. When electrically driving the ON/OFF pin the high voltage level for the ON condition must not exceed the 6 V absolute maximum limit. When ON/OFF control is not required this pin must be left open. 8.4 Device Functional Modes 8.4.1 Shutdown Mode The ON/OFF pin provides electrical ON and OFF control for the LM2671. When the voltage of this pin is lower than 1.4 V, the device enters shutdown mode. The typical standby current in this mode is 50 A. Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 11 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com Device Functional Modes (continued) 8.4.2 Active Mode When the voltage of the ON/OFF pin is higher than 1.4 V, the device starts switching and the output voltage rises until it reaches a normal regulation voltage. 12 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 9 Application and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI's customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 9.1 Application Information The LM2671 is a step-down DC-DC regulator. The device is typically used to convert a higher DC voltage to a lower DC voltage with a maximum output current of 0.5 A. The following design procedure can be used to select components for the LM2671. Alternately, the WEBENCH(R) software may be used to generate complete designs. When generating a design, the WEBENCH software uses iterative design procedure and accesses comprehensive databases of components. See ti.com for more details. When the output voltage is greater than approximately 6 V, and the duty cycle at minimum input voltage is greater than approximately 50%, the designer must exercise caution in selection of the output filter components. When an application designed to these specific operating conditions is subjected to a current limit fault condition, it may be possible to observe a large hysteresis in the current limit. This can affect the output voltage of the device until the load current is reduced sufficiently to allow the current limit protection circuit to reset itself. Under current limiting conditions, the LM267x is designed to respond in the following manner: 1. At the moment when the inductor current reaches the current limit threshold, the ON-pulse is immediately terminated. This happens for any application condition. 2. However, the current limit block is also designed to momentarily reduce the duty cycle to below 50% to avoid subharmonic oscillations, which could cause the inductor to saturate. 3. Therefore, once the inductor current falls below the current limit threshold, there is a small relaxation time during which the duty cycle progressively rises back above 50% to the value required to achieve regulation. If the output capacitance is sufficiently large, it might be possible that as the output tries to recover, the output capacitor charging current is large enough to repeatedly re-trigger the current limit circuit before the output has fully settled. This condition is exacerbated with higher output voltage settings because the energy requirement of the output capacitor varies as the square of the output voltage (1/2 CV2), thus requiring an increased charging current. A simple test to determine if this condition might exist for a suspect application is to apply a short circuit across the output of the converter, and then remove the shorted output condition. In an application with properly selected external components, the output recovers smoothly. Practical values of external components that have been experimentally found to work well under these specific operating conditions are COUT = 47 F, L = 22 H. NOTE Even with these components, for a device's current limit of ICLIM, the maximum load current under which the possibility of the large current limit hysteresis can be minimized is ICLIM/2. For example, if the input is 24 V and the set output voltage is 18 V, then for a desired maximum current of 1.5 A, the current limit of the chosen switcher must be confirmed to be at least 3 A. Under extreme overcurrent or shortcircuit conditions, the LM267X employs frequency foldback in addition to the current limit. If the cycle-by-cycle inductor current increases above the current limit threshold (due to short circuit or inductor saturation for example) the switching frequency is automatically reduced to protect the IC. Frequency below 100 kHz is typical for an extreme short-circuit condition. Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 13 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 9.2 Typical Applications 9.2.1 Fixed Output Voltage Version CIN = 22-F, 50-V Tantalum, Sprague 199D Series COUT = 47-F, 25-V Tantalum, Sprague 595D Series D1 = 3.3-A, 50-V Schottky Rectifier, IR 30WQ05F L1 = 68-H Sumida #RCR110D-680L CB = 0.01-F, 50-V ceramic Figure 15. Typical Application for Fixed Output Voltage Versions 9.2.1.1 Design Requirements Table 1 lists the design parameters for this example. Table 1. Design Parameters PARAMETER VALUE Regulated output voltage (3.3 V, 5 V, or 12 V), VOUT 5V Maximum DC input voltage, VIN(max) 12 V Maximum load current, ILOAD(max) 500 mA 9.2.1.2 Detailed Design Procedure 9.2.1.2.1 Inductor Selection (L1) 1. Select the correct inductor value selection guide from Figure 17 and Figure 18 or Figure 19 (output voltages of 3.3 V, 5 V, or 12 V respectively). For all other voltages, see the design procedure for the adjustable version. Use the inductor selection guide for the 5-V version shown in Figure 18. 2. From the inductor value selection guide, identify the inductance region intersected by the maximum input voltage line and the maximum load current line. Each region is identified by an inductance value and an inductor code (LXX). From the inductor value selection guide shown in Figure 18, the inductance region intersected by the 12-V horizontal line and the 500-mA vertical line is 47 H, and the inductor code is L13. 3. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2. Each manufacturer makes a different style of inductor to allow flexibility in meeting various design requirements. See the following for some of the differentiating characteristics of each manufacturer's inductors: - Schottky: ferrite EP core inductors; these have very low leakage magnetic fields to reduce electromagnetic interference (EMI) and are the lowest power loss inductors - Renco: ferrite stick core inductors; benefits are typically lowest cost inductors and can withstand E*T and transient peak currents above rated value. Be aware that these inductors have an external magnetic field which may generate more EMI than other types of inductors. - Pulse: powered iron toroid core inductors; these can also be low cost and can withstand larger than normal E*T and transient peak currents. Toroid inductors have low EMI. - Coilcraft: ferrite drum core inductors; these are the smallest physical size inductors, available only as SMT components. Be aware that these inductors also generate EMI--but less than stick inductors. Complete specifications for these inductors are available from the respective manufacturers. 14 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 The inductance value required is 47 H. From the table in Table 2, go to the L13 line and choose an inductor part number from any of the four manufacturers shown. In most instances, both through hole and surface mount inductors are available. Table 2. Inductor Manufacturers' Part Numbers IND. REF. DESG. INDUCTANCE (H) CURRENT (A) L2 150 L3 100 L4 SCHOTTKY RENCO THROUGH HOLE SURFACE MOUNT 0.21 67143920 0.26 67143930 68 0.32 L5 47 L6 PULSE ENGINEERING COILCRAFT THROUGH HOLE SURFACE MOUNT THROUGH HOLE SURFACE MOUNT SURFACE MOUNT 67144290 RL-5470-4 RL1500-150 PE-53802 PE-53802-S DO1608-154 67144300 RL-5470-5 RL1500-100 PE-53803 PE-53803-S DO1608-104 67143940 67144310 RL-1284-68-43 RL1500-68 PE-53804 PE-53804-S DO1608-683 0.37 67148310 67148420 RL-1284-47-43 RL1500-47 PE-53805 PE-53805-S DO1608-473 33 0.44 67148320 67148430 RL-1284-33-43 RL1500-33 PE-53806 PE-53806-S DO1608-333 L7 22 0.52 67148330 67148440 RL-1284-22-43 RL1500-22 PE-53807 PE-53807-S DO1608-223 L9 220 0.32 67143960 67144330 RL-5470-3 RL1500-220 PE-53809 PE-53809-S DO3308-224 L10 150 0.39 67143970 67144340 RL-5470-4 RL1500-150 PE-53810 PE-53810-S DO3308-154 L11 100 0.48 67143980 67144350 RL-5470-5 RL1500-100 PE-53811 PE-53811-S DO3308-104 L12 68 0.58 67143990 67144360 RL-5470-6 RL1500-68 PE-53812 PE-53812-S DO3308-683 L13 47 0.7 67144000 67144380 RL-5470-7 RL1500-47 PE-53813 PE-53813-S DO3308-473 L14 33 0.83 67148340 67148450 RL-1284-33-43 RL1500-33 PE-53814 PE-53814-S DO3308-333 L15 22 0.99 67148350 67148460 RL-1284-22-43 RL1500-22 PE-53815 PE-53815-S DO3308-223 L18 220 0.55 67144040 67144420 RL-5471-2 RL1500-220 PE-53818 PE-53818-S DO3316-224 L19 150 0.66 67144050 67144430 RL-5471-3 RL1500-150 PE-53819 PE-53819-S DO3316-154 L20 100 0.82 67144060 67144440 RL-5471-4 RL1500-100 PE-53820 PE-53820-S DO3316-104 L21 68 0.99 67144070 67144450 RL-5471-5 RL1500-68 PE-53821 PE-53821-S DO3316-683 9.2.1.2.2 Output Capacitor Selection (COUT) Select an output capacitor from the output capacitor table in Table 9. Using the output voltage and the inductance value found in the inductor selection guide, step 1, locate the appropriate capacitor value and voltage rating. Use the 5-V section in the output capacitor table in Table 9. Choose a capacitor value and voltage rating from the line that contains the inductance value of 47 H. The capacitance and voltage rating values corresponding to the 47-H inductor are: * Surface mount: - 68-F, 10-V Sprague 594D series - 100-F, 10-V AVX TPS series * Through hole: - 68-F, 10-V Sanyo OS-CON SA series - 150-F, 35-V Sanyo MV-GX series - 150-F, 35-V Nichicon PL series - 150-F, 35-V Panasonic HFQ series The capacitor list contains through-hole electrolytic capacitors from four different capacitor manufacturers and surface mount tantalum capacitors from two different capacitor manufacturers. TI recommends that both the manufacturers and the manufacturer's series that are listed in the table be used. Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 15 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com Table 3. Output Capacitor Table OUTPUT CAPACITOR OUTPUT VOLTAGE (V) 3.3 5 12 INDUCTANCE (H) SURFACE MOUNT THROUGH HOLE SPRAGUE 594D SERIES (F/V) AVX TPS SERIES (F/V) SANYO OS-CON SA SERIES (F/V) SANYO MV-GX SERIES (F/V) NICHICON PL SERIES (F/V) PANASONIC HFQ SERIES (F/V) 22 120/6.3 100/10 100/10 330/35 330/35 330/35 33 120/6.3 100/10 68/10 220/35 220/35 220/35 47 68/10 100/10 68/10 150/35 150/35 150/35 68 120/6.3 100/10 100/10 120/35 120/35 120/35 100 120/6.3 100/10 100/10 120/35 120/35 120/35 150 120/6.3 100/10 100/10 120/35 120/35 120/35 22 100/16 100/10 100/10 330/35 330/35 330/35 33 68/10 10010 68/10 220/35 220/35 220/35 47 68/10 100/10 68/10 150/35 150/35 150/35 68 100/16 100/10 100/10 120/35 120/35 120/35 100 100/16 100/10 100/10 120/35 120/35 120/35 150 100/16 100/10 100/10 120/35 120/35 120/35 22 120/20 (2x) 68/20 68/20 330/35 330/35 330/35 33 68/25 68/20 68/20 220/35 220/35 220/35 47 47/20 68/20 47/20 150/35 150/35 150/35 68 47/20 68/20 47/20 120/35 120/35 120/35 100 47/20 68/20 47/20 120/35 120/35 120/35 150 47/20 68/20 47/20 120/35 120/35 120/35 220 47/20 68/20 47/20 120/35 120/35 120/35 9.2.1.2.3 Catch Diode Selection (D1) 1. In normal operation, the average current of the catch diode is the load current times the catch diode duty cycle, 1-D (D is the switch duty cycle, which is approximately the output voltage divided by the input voltage). The largest value of the catch diode average current occurs at the maximum load current and maximum input voltage (minimum D). For normal operation, the catch diode current rating must be at least 1.3 times greater than its maximum average current. However, if the power supply design must withstand a continuous output short, the diode must have a current rating equal to the maximum current limit of the LM2671. The most stressful condition for this diode is a shorted output condition (refer to Table 4). In this example, a 1-A, 20-V Schottky diode provides the best performance. If the circuit must withstand a continuous shorted output, TI recommends a higher-current Schottky diode. 2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. 3. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency. This Schottky diode must be placed close to the LM2671 using short leads and short printed-circuit traces. 16 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 Table 4. Schottky Diode Selection Table VR 20 V 30 V 40 V 50 V 1-A DIODES 3-A DIODES SURFACE MOUNT THROUGH HOLE SURFACE MOUNT THROUGH HOLE SK12 1N5817 SK32 1N5820 B120 SR102 -- SR302 SK13 1N5818 SK33 1N5821 B130 11DQ03 30WQ03F 31DQ03 MBRS130 SR103 -- -- SK14 1N5819 SK34 1N5822 B140 11DQ04 30BQ040 MBR340 MBRS140 SR104 30WQ04F 31DQ04 10BQ040 -- MBRS340 SR304 10MQ040 -- MBRD340 -- 15MQ040 -- -- -- SK15 MBR150 SK35 MBR350 B150 11DQ05 30WQ05F 31DQ05 10BQ050 SR105 -- SR305 9.2.1.2.4 Input Capacitor (CIN) A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground to prevent large voltage transients from appearing at the input. This capacitor must be placed close to the IC using short leads. In addition, the RMS current rating of the input capacitor must be selected to be at least 1/2 the DC load current. The capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. The curves shown in Figure 16 show typical RMS current ratings for several different aluminum electrolytic capacitor values. A parallel connection of two or more capacitors may be required to increase the total minimum RMS current rating to suit the application requirements. For an aluminum electrolytic capacitor, the voltage rating must be at least 1.25 times the maximum input voltage. Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating must be twice the maximum input voltage. Table 5 and Table 6 show the recommended application voltage for AVX TPS and Sprague 594D tantalum capacitors. TI also recommends that they be surge current tested by the manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small inductor in series with the input supply line. Table 5. AVX TPS RECOMMENDED APPLICATION VOLTAGE VOLTAGE RATING 85C RATING 3.3 6.3 5 10 10 20 12 25 15 35 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 17 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com Table 6. Sprague 594D RECOMMENDED APPLICATION VOLTAGE VOLTAGE RATING 85C RATING 2.5 4 3.3 6.3 5 10 8 16 12 20 18 25 24 35 29 50 Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN pin. The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a maximum input voltage of 12 V, an aluminum electrolytic capacitor with a voltage rating greater than 15 V (1.25 x VIN) is required. The next higher capacitor voltage rating is 16 V. The RMS current rating requirement for the input capacitor in a buck regulator is approximately 1/2 the DC load current. In this example, with a 500-mA load, a capacitor with a RMS current rating of at least 250 mA is required. The curves shown in Figure 16 can be used to select an appropriate input capacitor. From the curves, locate the 16-V line and note which capacitor values have RMS current ratings greater than 250 mA. Figure 16. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical) For a through-hole design, a 100-F, 16-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design, electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components NACZ series could be considered. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating and voltage rating. In this example, checking the Sprague 594D series datasheet, a Sprague 594D 15-F, 25-V capacitor is adequate. 9.2.1.2.5 Boost Capacitor (CB) This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a 0.01-F, 50-V ceramic capacitor. For this application, and all applications, use a 0.01-F, 50-V ceramic capacitor. 18 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 9.2.1.2.6 Soft-Start Capacitor (CSS) - Optional This capacitor controls the rate at which the device starts up. The formula for the soft-start capacitor CSS is Equation 1. where * * * * * * ISS= soft-start current (4.5 A typical) tSS= soft-start time (selected) VSSTH= soft-start threshold voltage (0.63 V typical) VOUT= output voltage (selected) VSCHOTTKY= schottky diode voltage drop (0.4 V typical) VIN= input voltage (selected) (1) For this application, selecting a start-up time of 10 ms and using Equation 2 for CSS. (2) If this feature is not desired, leave this pin open. With certain soft-start capacitor values and operating conditions, the LM2671 can exhibit an overshoot on the output voltage during turnon. Especially when starting up into no load or low load, the soft-start function may not be effective in preventing a larger voltage overshoot on the output. With larger loads or lower input voltages during start-up this effect is minimized. In particular, avoid using soft-start capacitors between 0.033 F and 1 F. 9.2.1.2.7 Frequency Synchronization (optional) The LM2671 (oscillator) can be synchronized to run with an external oscillator, using the sync pin (pin 3). By doing so, the LM2671 can be operated at higher frequencies than the standard frequency of 260 kHz. This allows for a reduction in the size of the inductor and output capacitor. As shown in the drawing below, a signal applied to a RC filter at the sync pin causes the device to synchronize to the frequency of that signal. For a signal with a peak-to-peak amplitude of 3 V or greater, a 1-k resistor and a 100-pF capacitor are suitable values. For all applications, use a 1-k resistor and a 100-pF capacitor for the RC filter. Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 19 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 9.2.1.3 Application Curves for continuous mode operation Figure 17. LM2671-3.3 Figure 18. LM2671-5 Figure 19. LM2671-12 Figure 20. LM2671-ADJ 9.2.2 Adjustable Output Voltage Version CIN = 22-F, 50-V Tantalum, Sprague 199D Series COUT = 47-F, 25-V Tantalum, Sprague 595D Series D1 = 3.3-A, 50-V Schottky Rectifier, IR 30WQ05F L1 = 68-H Sumida #RCR110D-680L R1 =1.5 k, 1% CB = 0.01-F, 50-V ceramic Figure 21. Typical Application for Adjustable Output Voltage Versions 20 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 9.2.2.1 Design Requirements Table 7 lists the design parameters for this example. Table 7. Design Parameters PARAMETER VALUE Regulated output voltage, VOUT 20 V Maximum input voltage, VIN(max) 28 V Maximum load current, ILOAD(max) 500 mA Switching frequency, F Fixed at a nominal 260 kHz 9.2.2.2 Detailed Design Procedure 9.2.2.2.1 Programming Output Voltage Select R1 and R2, as shown in Figure 21. Use the following formula to select the appropriate resistor values. where * VREF = 1.21 V (3) Select R1 to be 1 k, 1%. Solve for R2. (4) Select a value for R1 between 240 and 1.5 k. The lower resistor values minimize noise pickup in the sensitive feedback pin. For the lowest temperature coefficient and the best stability with time, use 1% metal film resistors. (5) R2 = 1 k (16.53 - 1) = 15.53 k, closest 1% value is 15.4 k. R2 = 15.4 k. 9.2.2.2.2 Inductor Selection (L1) 1. Calculate the inductor Volt * microsecond constant E * T (V * s) from Equation 6. where * * VSAT = internal switch saturation voltage = 0.25 V VD = diode forward voltage drop = 0.5 V (6) Calculate the inductor Volt * microsecond constant (E * T) with Equation 7. (7) 2. Use the E * T value from the previous formula and match it with the E * T number on the vertical axis of the inductor value selection guide shown in Figure 20. E * T = 21.6 (V * s) (8) 3. On the horizontal axis, select the maximum load current in Equation 9. ILOAD(max) = 500 mA (9) 4. Identify the inductance region intersected by the E * T value and the maximum load current value. Each region is identified by an inductance value and an inductor code (LXX). From the inductor value selection guide shown in Figure 20, the inductance region intersected by the 21.6 (V * s) horizontal line and the 500mA vertical line is 100 H, and the inductor code is L20. 5. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2. For information Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 21 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com on the different types of inductors, see the inductor selection in the fixed output voltage design procedure. From the table in Table 2, locate line L20, and select an inductor part number from the list of manufacturers' part numbers. 9.2.2.2.3 Output Capacitor Selection (COUT) 1. Select an output capacitor from the capacitor code selection guide in Table 8. Using the inductance value found in the inductor selection guide, step 1, locate the appropriate capacitor code corresponding to the desired output voltage. Use the appropriate row of the capacitor code selection guide, in Table 8. For this example, use the 15-V to 20-V row. The capacitor code corresponding to an inductance of 100 H is C20. 2. Select an appropriate capacitor value and voltage rating, using the capacitor code, from the output capacitor selection table in Table 9. There are two solid tantalum (surface mount) capacitor manufacturers and four electrolytic (through hole) capacitor manufacturers to choose from. TI recommends using the manufacturers and the manufacturer's series that are listed in the table. From the output capacitor selection table in Table 9, choose a capacitor value (and voltage rating) that intersects the capacitor code(s) selected in section A, C20. The capacitance and voltage rating values corresponding to the capacitor code C20 are: - Surface mount: - 33-F, 25-V Sprague 594D series - 33-F, 25-V AVX TPS series - Through hole: - 33-F, 25-V Sanyo OS-CON SC series - 120-F, 35-V Sanyo MV-GX series - 120-F, 35-V Nichicon PL series - 120-F, 35-V Panasonic HFQ series Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications (especially the 100-kHz ESR) closely match the characteristics of the capacitors listed in the output capacitor table. See the capacitor manufacturers' data sheet for this information. Table 8. Capacitor Code Selection Guide INDUCTANCE (H) CASE STYLE (1) OUTPUT VOLTAGE (V) 22 33 47 68 100 150 220 SM and TH 1.21-2.5 -- -- -- -- C1 C2 C3 SM and TH 2.5-3.75 -- -- -- C1 C2 C3 C3 SM and TH 3.75-5 -- -- C4 C5 C6 C6 C6 SM and TH 5-6.25 -- C4 C7 C6 C6 C6 C6 SM and TH 6.25-7.5 C8 C4 C7 C6 C6 C6 C6 SM and TH 7.5-10 C9 C10 C11 C12 C13 C13 C13 SM and TH 10-12.5 C14 C11 C12 C12 C13 C13 C13 SM and TH 12.5-15 C15 C16 C17 C17 C17 C17 C17 SM and TH 15-20 C18 C19 C20 C20 C20 C20 C20 SM and TH 20-30 C21 C22 C22 C22 C22 C22 C22 TH 30-37 C23 C24 C24 C25 C25 C25 C25 (1) SM - Surface Mount, TH - Through Hole 22 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 Table 9. Output Capacitor Selection Table OUTPUT CAPACITOR CAP. REF. DESG. # SPRAGUE 594D SERIES (F/V) AVX TPS SERIES (F/V) SANYO OS-CON SA SERIES (F/V) SANYO MV-GX SERIES (F/V) NICHICON PL SERIES (F/V) PANASONIC HFQ SERIES (F/V) C1 120/6.3 100/10 100/10 220/35 220/35 220/35 C2 120/6.3 100/10 100/10 150/35 150/35 150/35 C3 120/6.3 100/10 100/35 120/35 120/35 120/35 C4 68/10 100/10 68/10 220/35 220/35 220/35 C5 100/16 100/10 100/10 150/35 150/35 150/35 C6 100/16 100/10 100/10 120/35 120/35 120/35 C7 68/10 100/10 68/10 150/35 150/35 150/35 C8 100/16 100/10 100/10 330/35 330/35 330/35 THROUGH HOLE C9 100/16 100/16 100/16 330/35 330/35 330/35 C10 100/16 100/16 68/16 220/35 220/35 220/35 C11 100/16 100/16 68/16 150/35 150/35 150/35 C12 100/16 100/16 68/16 120/35 120/35 120/35 C13 100/16 100/16 100/16 120/35 120/35 120/35 C14 100/16 100/16 100/16 220/35 220/35 220/35 C15 47/20 68/20 47/20 220/35 220/35 220/35 C16 47/20 68/20 47/20 150/35 150/35 150/35 C17 47/20 68/20 47/20 120/35 120/35 120/35 C18 68/25 (2x) 33/25 47/25 (1) 220/35 220/35 220/35 150/35 150/35 150/35 120/35 120/35 120/35 C19 33/25 33/25 33/25 (1) C20 33/25 33/25 33/25 (1) C21 33/35 (2x) 22/25 (2) 150/35 150/35 150/35 22/35 (2) C22 (1) (2) SURFACE MOUNT 120/35 120/35 120/35 C23 33/35 (2) (2) (2) 220/50 100/50 120/50 C24 (2) (2) (2) 150/50 100/50 120/50 C25 (2) (2) (2) 150/50 82/50 82/50 The SC series of Os-Con capacitors (others are SA series) The voltage ratings of the surface mount tantalum chip and Os-Con capacitors are too low to work at these voltages. 9.2.2.2.4 Catch Diode Selection (D1) 1. In normal operation, the average current of the catch diode is the load current times the catch diode duty cycle, 1-D (D is the switch duty cycle, which is approximately VOUT/VIN). The largest value of the catch diode average current occurs at the maximum input voltage (minimum D). For normal operation, the catch diode current rating must be at least 1.3 times greater than its maximum average current. However, if the power supply design must withstand a continuous output short, the diode must have a current rating greater than the maximum current limit of the LM2671. The most stressful condition for this diode is a shorted output condition. Refer to the table shown in Table 4. Schottky diodes provide the best performance, and in this example a 1A, 40-V Schottky diode would be a good choice. If the circuit must withstand a continuous shorted output, a higher current (at least 1.2 A) Schottky diode is recommended. 2. The reverse voltage rating of the diode must be at least 1.25 times the maximum input voltage. 3. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency. The Schottky diode must be placed close to the LM2671 using short leads and short printed-circuit traces. Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 23 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 9.2.2.2.5 Input Capacitor (CIN) A low ESR aluminum or tantalum bypass capacitor is required between the input pin and ground to prevent large voltage transients from appearing at the input. This capacitor must be placed close to the IC using short leads. In addition, the RMS current rating of the input capacitor must be selected to be at least 1/2 the DC load current. The capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. The curves shown in Figure 16 show typical RMS current ratings for several different aluminum electrolytic capacitor values. A parallel connection of two or more capacitors may be required to increase the total minimum RMS current rating to suit the application requirements. For an aluminum electrolytic capacitor, the voltage rating must be at least 1.25 times the maximum input voltage. Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating must be twice the maximum input voltage. The Table 10 and Table 11 show the recommended application voltage for AVX TPS and Sprague 594D tantalum capacitors. TI also recommends that they be surge current tested by the manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small inductor in series with the input supply line. Table 10. AVX TPS RECOMMENDED APPLICATION VOLTAGE VOLTAGE RATING 85C RATING 3.3 6.3 5 10 10 20 12 25 15 35 Table 11. Sprague 594D RECOMMENDED APPLICATION VOLTAGE VOLTAGE RATING 85C RATING 2.5 4 3.3 6.3 5 10 8 16 12 20 18 25 24 35 29 50 Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN pin. The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a maximum input voltage of 28 V, an aluminum electrolytic capacitor with a voltage rating of at least 35 V (1.25 x VIN) is required. The RMS current rating requirement for the input capacitor in a buck regulator is approximately 1/2 the DC load current. In this example, with a 500-mA load, a capacitor with a RMS current rating of at least 250 mA is required. The curves shown in Figure 22 can be used to select an appropriate input capacitor. From the curves, locate the 35-V line and note which capacitor values have RMS current ratings greater than 250 mA. 24 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 Figure 22. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical) For a through-hole design, a 68-F, 35-V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MVGX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design, electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components NACZ series could be considered. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating and voltage rating. In this example, checking the Sprague 594D series data sheet, a Sprague 594D 15-F, 50-V capacitor is adequate. 9.2.2.2.6 Boost Capacitor (CB) This capacitor develops the necessary voltage to turn the switch gate on fully. All applications must use a 0.01-F, 50-V ceramic capacitor. For this application, and all applications, use a 0.01-F, 50-V ceramic capacitor. If the soft-start and frequency synchronization features are desired, look at steps 6 and 7 in Detailed Design Procedure. Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 25 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 9.2.2.3 Application Curves Continuous Mode Switching Waveforms, VIN = 20 V, VOUT = 5 V, ILOAD = 500 mA, L = 100 H, COUT = 100 F, COUTESR = 0.1 A: VSW pin voltage, 10 V/div. B: Inductor current, 0.2 A/div C: Output ripple voltage, 50 mV/div ac-coupled Discontinuous Mode Switching Waveforms, VIN = 20 V, VOUT = 5 V, ILOAD = 300 mA, L = 15 H, COUT = 68 F (2x), COUTESR = 25 m A: VSW pin voltage, 10 V/div. B: Inductor current, 0.5 A/div C: Output ripple voltage, 20 mV/div ac-coupled Figure 24. Horizontal Time Base: 1 s/div Figure 23. Horizontal Time Base: 1 s/div Load Transient Response for Continuous Mode, VIN = 20 V, VOUT = 5 V, L = 100 H, COUT = 100 F, COUTESR = 0.1 A: Output voltage, 100 mV/div, ac-coupled B: Load current: 100-mA to 500-mA load pulse Load Transient Response for Discontinuous Mode, VIN = 20 V, VOUT = 5 V, L = 47 H, COUT = 68 F, COUTESR = 50 m A: Output voltage, 100 mV/div, ac-coupled B: Load current: 100-mA to 400-mA load pulse Figure 25. Horizontal Time Base: 50 s/div Figure 26. Horizontal Time Base: 200 s/div 10 Power Supply Recommendations The LM2671 is designed to operate from an input voltage supply up to 40 V. This input supply must be well regulated and able to withstand maximum input current and maintain a stable voltage. 26 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 LM2671 www.ti.com SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 11 Layout 11.1 Layout Guidelines Layout is very important in switching regulator designs. Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by heavy lines (in Figure 15 and Figure 21) must be wide printed-circuit traces and must be kept as short as possible. For best results, external components must be placed as close to the switcher IC as possible using ground plane construction or single point grounding. If open core inductors are used, take special care as to the location and positioning of this type of inductor. Allowing the inductor flux to intersect sensitive feedback, IC ground path, and COUT wiring can cause problems. When using the adjustable version, take special care as to the location of the feedback resistors and the associated wiring. Physically place both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor. 11.2 Layout Examples CIN = 15-F, 25-V Solid Tantalum Sprague, 594D series COUT = 68-F, 10-V Solid Tantalum Sprague, 594D series D1 = 1-A, 40-V Schottky Rectifier, surface mount L1 = 47-H, L13 Coilcraft DO3308 CB = 0.01-F, 50-V ceramic Figure 27. Typical Surface Mount PCB Layout, Fixed Output (4x Size) CIN = 15 F, 50 V Solid Tantalum Sprague, 594D series COUT = 33 F, 25 V Solid Tantalum Sprague, 594D series D1 = 1-A, 40-V Schottky Rectifier, surface mount L1 = 100-H, L20 Coilcraft DO3316 CB = 0.01-F, 50-V ceramic R1 = 1 k, 1% R2 = Use formula in Detailed Design Procedure Figure 28. Typical Surface Mount PCB Layout, Adjustable Output (4x Size) Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 27 LM2671 SNVS008L - SEPTEMBER 1998 - REVISED JUNE 2016 www.ti.com 12 Device and Documentation Support 12.1 Documentation Support 12.1.1 Related Documentation For related documentation see the following: * AN-1187 Leadless Leadfram Package (LLP) * LM2670 SIMPLE SWITCHER(R) High Efficiency 3A Step-Down Voltage Regulator with Sync 12.2 Receiving Notification of Documentation Updates To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper right corner, click on Alert me to register and receive a weekly digest of any product information that has changed. For change details, review the revision history included in any revised document. 12.3 Community Resources The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of Use. TI E2ETM Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help solve problems with fellow engineers. Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and contact information for technical support. 12.4 Trademarks E2E is a trademark of Texas Instruments. SIMPLE SWITCHER, WEBENCH are registered trademarks of Texas Instruments. All other trademarks are the property of their respective owners. 12.5 Electrostatic Discharge Caution 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. 12.6 Glossary SLYZ022 -- TI Glossary. This glossary lists and explains terms, acronyms, and definitions. 13 Mechanical, Packaging, and Orderable Information The following pages include mechanical, packaging, and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation. 13.1 DAP (WSON Package) The die attach pad (DAP) can and must be connected to the PCB Ground plane. For CAD and assembly guidelines refer to AN-1187 Leadless Leadfram Package (LLP). 28 Submit Documentation Feedback Copyright (c) 1998-2016, Texas Instruments Incorporated Product Folder Links: LM2671 PACKAGE OPTION ADDENDUM www.ti.com 11-Jan-2021 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (C) Device Marking (3) (4/5) (6) (1) LM2671LD-ADJ NRND WSON NHN 16 1000 Non-RoHS & Green Call TI Call TI -40 to 125 S0008B LM2671LD-ADJ/NOPB ACTIVE WSON NHN 16 1000 RoHS & Green SN Level-3-260C-168 HR -40 to 125 S0008B LM2671M-12/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 M-12 LM2671M-3.3/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 M3.3 LM2671M-5.0 NRND SOIC D 8 95 Non-RoHS & Green Call TI Call TI -40 to 125 2671 M5.0 LM2671M-5.0/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 M5.0 LM2671M-ADJ NRND SOIC D 8 95 Non-RoHS & Green Call TI Call TI -40 to 125 2671 MADJ LM2671M-ADJ/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 MADJ LM2671MX-12/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 M-12 LM2671MX-3.3/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 M3.3 LM2671MX-5.0/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 M5.0 LM2671MX-ADJ/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 2671 MADJ LM2671N-12/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2671 N-12 LM2671N-3.3/NOPB ACTIVE PDIP P 8 40 RoHS & Green Call TI | SN Level-1-NA-UNLIM -40 to 125 LM2671 N-3.3 LM2671N-5.0/NOPB ACTIVE PDIP P 8 40 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM2671 N-5.0 LM2671N-ADJ/NOPB ACTIVE PDIP P 8 40 RoHS & Green SN Level-1-NA-UNLIM -40 to 125 LM2671 N-ADJ The marketing status values are defined as follows: Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 11-Jan-2021 ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based flame retardants must also meet the <=1000ppm threshold requirement. (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two lines if the finish value exceeds the maximum column width. 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. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 29-Sep-2019 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 LM2671LD-ADJ WSON NHN 16 1000 178.0 12.4 5.3 5.3 1.3 8.0 12.0 Q1 LM2671LD-ADJ/NOPB WSON NHN 16 1000 178.0 12.4 5.3 5.3 1.3 8.0 12.0 Q1 LM2671MX-12/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LM2671MX-3.3/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LM2671MX-5.0/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LM2671MX-ADJ/NOPB SOIC D 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 29-Sep-2019 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM2671LD-ADJ WSON NHN 16 1000 210.0 185.0 35.0 LM2671LD-ADJ/NOPB WSON NHN 16 1000 210.0 185.0 35.0 LM2671MX-12/NOPB SOIC D 8 2500 367.0 367.0 35.0 LM2671MX-3.3/NOPB SOIC D 8 2500 367.0 367.0 35.0 LM2671MX-5.0/NOPB SOIC D 8 2500 367.0 367.0 35.0 LM2671MX-ADJ/NOPB SOIC D 8 2500 367.0 367.0 35.0 Pack Materials-Page 2 MECHANICAL DATA NHN0016A LDA16A (REV A) www.ti.com PACKAGE OUTLINE D0008A SOIC - 1.75 mm max height SCALE 2.800 SMALL OUTLINE INTEGRATED CIRCUIT C SEATING PLANE .228-.244 TYP [5.80-6.19] A .004 [0.1] C PIN 1 ID AREA 6X .050 [1.27] 8 1 2X .150 [3.81] .189-.197 [4.81-5.00] NOTE 3 4X (0 -15 ) 4 5 B 8X .012-.020 [0.31-0.51] .010 [0.25] C A B .150-.157 [3.81-3.98] NOTE 4 .069 MAX [1.75] .005-.010 TYP [0.13-0.25] 4X (0 -15 ) SEE DETAIL A .010 [0.25] .004-.010 [0.11-0.25] 0 -8 .016-.050 [0.41-1.27] DETAIL A (.041) [1.04] TYPICAL 4214825/C 02/2019 NOTES: 1. Linear dimensions are in inches [millimeters]. Dimensions in parenthesis are for reference only. Controlling dimensions are in inches. Dimensioning and tolerancing per ASME Y14.5M. 2. This drawing is subject to change without notice. 3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not exceed .006 [0.15] per side. 4. This dimension does not include interlead flash. 5. Reference JEDEC registration MS-012, variation AA. www.ti.com EXAMPLE BOARD LAYOUT D0008A SOIC - 1.75 mm max height SMALL OUTLINE INTEGRATED CIRCUIT 8X (.061 ) [1.55] SYMM SEE DETAILS 1 8 8X (.024) [0.6] 6X (.050 ) [1.27] SYMM 5 4 (R.002 ) TYP [0.05] (.213) [5.4] LAND PATTERN EXAMPLE EXPOSED METAL SHOWN SCALE:8X METAL SOLDER MASK OPENING EXPOSED METAL .0028 MAX [0.07] ALL AROUND SOLDER MASK OPENING METAL UNDER SOLDER MASK EXPOSED METAL .0028 MIN [0.07] ALL AROUND SOLDER MASK DEFINED NON SOLDER MASK DEFINED SOLDER MASK DETAILS 4214825/C 02/2019 NOTES: (continued) 6. Publication IPC-7351 may have alternate designs. 7. Solder mask tolerances between and around signal pads can vary based on board fabrication site. www.ti.com EXAMPLE STENCIL DESIGN D0008A SOIC - 1.75 mm max height SMALL OUTLINE INTEGRATED CIRCUIT 8X (.061 ) [1.55] SYMM 1 8 8X (.024) [0.6] 6X (.050 ) [1.27] SYMM 5 4 (R.002 ) TYP [0.05] (.213) [5.4] SOLDER PASTE EXAMPLE BASED ON .005 INCH [0.125 MM] THICK STENCIL SCALE:8X 4214825/C 02/2019 NOTES: (continued) 8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate design recommendations. 9. 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