Sample & Buy Product Folder Support & Community Tools & Software Technical Documents LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 LM3402/HV 0.5-A Constant Current Buck Regulator for Driving High Power LEDs 1 Features 3 Description * * * * * * * The LM3402/HV are monolithic switching regulators designed to deliver constant currents to high power LEDs. Ideal for automotive, industrial, and general lighting applications, they contain a high-side Nchannel MOSFET switch with a current limit of 735 mA (typical) for step-down (Buck) regulators. Hysteretic control with controlled ON-time coupled with an external resistor allow the converter output voltage to adjust as needed to deliver a constant current to series and series - parallel connected arrays of LEDs of varying number and type, LED dimming by pulse width modulation (PWM), broken/open LED protection, low-power shutdown and thermal shutdown complete the feature set. 1 * * * Integrated 0.5-A N-channel MOSFET VIN Range from 6 V to 42 V (LM3402) VIN Range from 6 V to 75 V (LM3402HV) 500 mA Output Current Over Temperature Cycle-by-Cycle Current Limit No Control Loop Compensation Required Separate PWM Dimming and Low Power Shutdown Supports All Ceramic-Output Capacitors and Capacitor-Less Outputs Thermal Shutdown Protection VSSOP, SO PowerPADTM Packages Device Information(1) 2 Applications * * * * * PART NUMBER LED Drivers Constant Current Source Automotive Lighting General Illumination Industrial Lighting LM3402/HV PACKAGE BODY SIZE (NOM) VSSOP (8) 3.00 mm x 3.00 mm HSOP (8) 4.89 mm x 3.90 mm (1) For all available packages, see the orderable addendum at the end of the data sheet. Typical Application Diagram CB L1 VIN VIN CIN BOOT SW RON D1 IF RON LM3402/02HV CS RSNS DIM GND VCC CF 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. LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Pin Configuration and Functions ......................... Specifications......................................................... 1 1 1 2 3 4 6.1 6.2 6.3 6.4 6.5 6.6 6.7 4 4 4 5 5 6 7 Absolute Maximum Ratings ...................................... ESD Ratings.............................................................. Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Timing Requirements ................................................ Typical Characteristics .............................................. Detailed Description ............................................ 10 7.1 Overview ................................................................. 10 7.2 Functional Block Diagram ....................................... 10 7.3 Feature Description................................................. 10 7.4 Device Functional Modes........................................ 13 8 Application and Implementation ........................ 15 8.1 Application Information............................................ 15 8.2 Typical Application .................................................. 23 9 Power Supply Recommendations...................... 29 10 Layout................................................................... 29 10.1 Layout Guidelines ................................................. 29 10.2 Layout Example .................................................... 30 11 Device and Documentation Support ................. 31 11.1 11.2 11.3 11.4 11.5 11.6 Device Support...................................................... Related Links ........................................................ Community Resources.......................................... Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 31 31 31 31 31 31 12 Mechanical, Packaging, and Orderable Information ........................................................... 31 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision E (April 2013) to Revision F * Page Added ESD Ratings and Timing Requirements tables, 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 Changes from Revision D (May 2013) to Revision E * 2 Page Changed layout of National Data Sheet to TI format ............................................................................................................. 1 Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 5 Pin Configuration and Functions DGK Package 8-Pin VSSOP Top View 1 DDA Package 8-Pin HSOP Top View 8 VIN SW 2 7 BOOT VCC DIM RON 3 1 6 4 2 5 GND 3 CS 4 VIN SW BOOT DIM GND DAP VCC RON CS 8 7 6 5 Pin Functions PIN NO. NAME I/O DESCRIPTION 1 SW O Switch pin. Connect this pin to the output inductor and Schottky diode. 2 BOOT O MOSFET drive bootstrap pin. Connect a 10-nF ceramic capacitor from this pin to SW. 3 DIM I Input for PWM dimming. Connect a logic-level PWM signal to this pin to enable and disable the power MOSFET and reduce the average light output of the LED array. 4 GND -- 5 CS I Current sense feedback pin. Set the current through the LED array by connecting a resistor from this pin to ground. 6 RON I ON-time control pin. A resistor connected from this pin to VIN sets the regulator controlled ON-time. 7 VCC O Output of the internal 7-V linear regulator. Bypass this pin to ground with a minimum 0.1-F ceramic capacitor with X5R or X7R dielectric. 8 VIN I Input voltage pin. Nominal operating input range for this pin is 6 V to 42 V (LM3402) or 6 V to 75 V (LM3402HV). DAP -- Ground pin. Connect this pin to system ground. Thermal Pad. Connect to ground. Place 4-6 vias from DAP to bottom layer ground plane. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 3 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted) (1) (2) VIN to GND BOOT to GND SW to GND MIN MAX LM3402 -0.3 45 LM3402HV -0.3 76 LM3402 -0.3 59 LM3402HV -0.3 90 LM3402 UNIT V V -1.5 V LM3402HV -1.5 LM3402 -0.3 45 LM3402HV -0.3 76 BOOT to SW -0.3 14 V VCC to GND -0.3 14 V DIM to GND -0.3 7 V CS to GND -0.3 7 V RON to GND -0.3 7 V Lead temperature (soldering, 10 s) 260 C Infrared/convection reflow (15 s) 235 C 150 C 125 C BOOT to VCC Soldering information Junction temperature Storage temperature (1) (2) -65 V 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, contact the Texas Instruments Sales Office/ Distributors for availability and specifications. 6.2 ESD Ratings VALUE UNIT LM3402 V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) 2000 Charged-device model (CDM), per JEDEC specification JESD22C101 (2) 1000 Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1) 2000 Charged-device model (CDM), per JEDEC specification JESD22C101 (2) 1000 V LM3402HV V(ESD) (1) (2) Electrostatic discharge V JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. 6.3 Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) VIN MIN MAX LM3402 6 42 LM3402HV 6 75 -40 125 Junction temperature 4 Submit Documentation Feedback UNIT V C Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 6.4 Thermal Information LM3402, LM3402HV THERMAL METRIC (1) DDA (HSOP) DGK (VSSOP) 8 PINS 8 PINS UNIT RJA Junction-to-ambient thermal resistance 45.6 154.4 C/W RJC(top) Junction-to-case (top) thermal resistance 53.1 48.2 C/W RJB Junction-to-board thermal resistance 25.8 74.2 C/W JT Junction-to-top characterization parameter 7.6 4.3 C/W JB Junction-to-board characterization parameter 25.7 72.9 C/W RJC(bot) Junction-to-case (bottom) thermal resistance 3.2 N/A C/W (1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report, SPRA953. 6.5 Electrical Characteristics VIN = 24 V unless otherwise indicated. Typical values apply over -40C TJ 125C; minimum and maximum values apply over the full operating temperature range (1) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 194 200 206 mV REGULATION AND OVERVOLTAGE COMPARATORS VREF-REG CS Regulation Threshold CS Decreasing, SW turns on VREF-0V CS Overvoltage Threshold CS Increasing, SW turns off 300 mV ICS CS Bias Current CS = 0 V 0.1 A VSD-TH Shutdown Threshold RON / SD Increasing VSD-HYS Shutdown Hysteresis RON / SD Decreasing Minimum OFF-time CS = 0 V SHUTDOWN 0.3 0.7 1.05 V 40 mV 300 ns OFF TIMER tOFF-MIN INTERNAL REGULATOR VCC-REG VCC Regulated Output VIN-DO VIN - VCC Dropout ICC = 5 mA, 6 V < VIN < 8 V 6.6 VCC-BP-TH VCC Bypass Threshold VIN Increasing 8.8 V VCC-BP-HYS VCC Bypass Hysteresis VIN Decreasing 225 mV VCC-Z-6 VCC-Z-8 VCC Output Impedance (0 mA < ICC < 5 mA) VCC-Z-24 (2) 7 7.4 300 VIN = 6 V 55 VIN = 8 V 50 VIN = 24 V 0.4 VIN = 24 V, VCC = 0 V 16 V mV VCC-LIM VCC Current Limit VCC-UV-TH VCC Undervoltage Lock-out Threshold mA VCC Increasing 5.25 V VCC-UV-HYS VCC Undervoltage Lock-out Hysteresis VCC Decreasing 150 mV VCC-UV-DLY VCC Undervoltage Lock-out Filter Delay 100-mV Overdrive 3 s IIN-OP IIN Operating Current Non-switching, CS = 0 V IIN-SD IIN Shutdown Current RON / SD = 0 V 600 900 A 90 180 A 735 940 mA CURRENT LIMIT ILIM Current Limit Threshold 530 DIM COMPARATOR VIH Logic High DIM Increasing VIL Logic Low DIM Decreasing IDIM-PU DIM Pullup Current DIM = 1.5 V (1) (2) 2.2 V 0.8 75 V A Typical specifications represent the most likely parametric norm at 25C operation. VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 5 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Electrical Characteristics (continued) VIN = 24 V unless otherwise indicated. Typical values apply over -40C TJ 125C; minimum and maximum values apply over the full operating temperature range (1) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 0.7 1.5 3 4 V N-MOSFET AND DRIVER RDS-ON Buck Switch ON Resistance ISW = 200 mA, BOOT-SW = 6.3 V VDR-UVLO BOOT Undervoltage Lockout Threshold BOOT-SW Increasing VDR-HYS BOOT Undervoltage Lockout Hysteresis BOOT-SW Decreasing 1.7 400 mV THERMAL SHUTDOWN TSD Thermal Shutdown Threshold 165 C TSD-HYS Thermal Shutdown Hysteresis 25 C 6.6 Timing Requirements tON-1 tON-2 6 ON-time 1, VIN = 10 V, RON = 200 k MIN NOM MAX 2.1 2.75 3.4 ON-time 2, VIN = 40 V, RON = 200 k LM3402 490 650 810 ON-time 2, VIN = 70 V, RON = 200 k LM3402HV 290 380 470 Submit Documentation Feedback UNIT s ns Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 6.7 Typical Characteristics Figure 1. VREF vs Temperature (VIN = 24 V) Figure 2. VREF vs VIN, LM3402 (TA = 25C) Figure 3. VREF vs VIN, LM3402HV (TA = 25C) Figure 4. Current Limit vs Temperature (VIN = 24 V) Figure 5. Current Limit vs VIN, LM3402 (TA = 25C) Figure 6. Current Limit vs VIN, LM3402HV (TA = 25C) Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 7 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Typical Characteristics (continued) 8 Figure 7. TON vs VIN, RON = 100 k (TA = 25C) Figure 8. TON vs VIN (TA = 25C) Figure 9. TON vs VIN, (TA = 25C) Figure 10. TON vs RON, LM3402 (TA = 25C) Figure 11. TON vs RON, LM3402HV (TA = 25C) Figure 12. VCC vs VIN (TA = 25C) Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 Typical Characteristics (continued) Figure 13. VO-MAX vs fSW, LM3402 (TA = 25C) Figure 14. VO-MIN vs fSW, LM3402 (TA = 25C) Figure 15. VO-MAX vs fSW, LM3402HV (TA = 25C) Figure 16. VO-MIN vs fSW, LM3402HV (TA = 25C) Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 9 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com 7 Detailed Description 7.1 Overview The LM3402 and LM3402HV are buck regulators with a wide input voltage range, low voltage reference, and a fast output enable/disable function. These features combine to make them ideal for use as a constant current source for LEDs with forward currents as high as 500 mA. The controlled ON-time (COT) architecture is a combination of hysteretic mode control and a one-shot ON-timer that varies inversely with input voltage. Hysteretic operation eliminates the need for small-signal control loop compensation. When the converter runs in continuous conduction mode (CCM) the controlled ON-time maintains a constant switching frequency over the range of input voltage. Fast transient response, PWM dimming, a low power shutdown mode, and simple output overvoltage protection round out the functions of the LM3402/HV. 7.2 Functional Block Diagram 7V BIAS REGULATOR VIN VIN SENSE VCC UVLO BYPASS SWITCH 0.7V VCC THERMAL SHUTDOWN + 300 ns MIN OFF TIMER Complete ON TIMER RON RON Complete 5V BOOT Start Start GATE DRIVE UVLO 75 PA DIM 1.5V 0.2V + + - SD VIN LEVEL SHIFT LOGIC CS SW 0.3V + - GND CURRENT LIMIT OFF TIMER + - 0.735A BUCK SWITCH CURRENT SENSE 7.3 Feature Description 7.3.1 Controlled ON-time Overview Figure 17 shows the feedback system used to control the current through an array of LEDs. A voltage signal, VSNS, is created as the LED current flows through the current setting resistor, RSNS, to ground. VSNS is fed back to the CS pin, where it is compared against a 200-mV reference, VREF. The ON-comparator turns on the power MOSFET when VSNS falls below VREF. The power MOSFET conducts for a controlled ON-time, tON, set by an external resistor, RON, and by the input voltage, VIN. ON-time is governed using Equation 1. RON tON = 1.34 x 10-10 x VIN (1) 10 Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 Feature Description (continued) At the conclusion of tON the power MOSFET turns off for a minimum OFF-time, tOFF-MIN, of 300 ns. Once tOFF-MIN is complete the CS comparator compares VSNS and VREF again, waiting to begin the next cycle. VO LED 1 IF LM3402/02HV LED n CS Comparator One-shot + + - VF VSNS CS VREF VF IF RSNS Figure 17. Comparator and One-Shot The LM3402/HV regulators should be operated in continuous conduction mode (CCM), where inductor current stays positive throughout the switching cycle. During steady-state operation in the CCM, the converter maintains a constant switching frequency, which can be selected using Equation 2. fSW = VO 1.34 x 10-10 x RON VO = n x VF + 200 mV (2) (3) VF = forward voltage of each LED, n = number of LEDs in series 7.3.2 Average LED Current Accuracy The COT architecture regulates the valley of VSNS, the AC portion of VSNS. To determine the average LED current (which is also the average inductor current) the valley inductor current is calculated using Equation 4. 0.2 VO x tSNS IL-MIN = L RSNS (4) In Equation 4 tSNS represents the propagation delay of the CS comparator, and is approximately 220 ns. The average inductor/LED current is equal to IL-MIN plus one-half of the inductor current ripple, iL: IF = IL = IL-MIN + iL / 2 (5) Detailed information for the calculation of iL is given in the Application and Implementation section. 7.3.3 Maximum Output Voltage The 300 ns minimum off-time limits on the maximum duty cycle of the converter, DMAX, and in turn ,the maximum output voltage VO(MAX) is determined by Equation 6: tON DMAX = tON + tOFF-MIN VO(max) = DMAX x VIN (6) Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 11 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Feature Description (continued) The maximum number of LEDs, nMAX, that can be placed in a single series string is governed by VO(MAX) and the maximum forward voltage of the LEDs used, VF(MAX), using the expression: VO(max) - 200 mV nMAX = VF(MAX) (7) At low switching frequency the maximum duty cycle and output voltage are higher, allowing the LM3402/HV to regulate output voltages that are nearly equal to input voltage. The following equation relates switching frequency to maximum output voltage. TSW - 300 ns VO(MAX) = VIN x TSW TSW = 1/fSW (8) 7.3.4 Minimum Output Voltage The minimum recommended ON-time for the LM3402/HV is 300 ns. This lower limit for tON determines the minimum duty cycle and output voltage that can be regulated based on input voltage and switching frequency. The relationship is determined by the following equation: VO(MIN) = VIN x 300 ns TSW (9) 7.3.5 High Voltage Bias Regulator The LM3402/HV contains an internal linear regulator with a 7-V output, connected between the VIN and the VCC pins. The VCC pin should be bypassed to the GND pin with a 0.1-F ceramic capacitor connected as close as possible to the pins of the device. VCC tracks VIN until VIN reaches 8.8 V (typical) and then regulates at 7 V as VIN increases. Operation begins when VCC crosses 5.25 V. 7.3.6 Internal MOSFET and Driver The LM3402/HV features an internal power MOSFET as well as a floating driver connected from the SW pin to the BOOT pin. Both rise time and fall time are 20 ns each (typical) and the approximate gate charge is 3 nC. The high-side rail for the driver circuitry uses a bootstrap circuit consisting of an internal high-voltage diode and an external 10 nF capacitor, CB. VCC charges CB through the internal diode while the power MOSFET is off. When the MOSFET turns on, the internal diode reverse biases. This creates a floating supply equal to the VCC voltage minus the diode drop to drive the MOSFET when its source voltage is equal to VIN. 7.3.7 Fast Shutdown for PWM Dimming The DIM pin of the LM3402/HV is a TTL logic compatible input for low-frequency PWM dimming of the LED. A logic low (less than 0.8V) at DIM will disable the internal MOSFET and shut off the current flow to the LED array. While the DIM pin is in a logic low state the support circuitry (driver, bandgap, VCC) remains active to minimize the time needed to turn the LED array back on when the DIM pin sees a logic high (above 2.2 V). A 75 A (typical) pullup current ensures that the LM3402/HV is on when DIM pin is open circuited, eliminating the need for a pullup resistor. Dimming frequency, fDIM, and duty cycle, DDIM, are limited by the LED current rise time and fall time and the delay from activation of the DIM pin to the response of the internal power MOSFET. In general, fDIM should be at least one order of magnitude lower than the steady state switching frequency to prevent aliasing. 7.3.8 Peak Current Limit The current limit comparator of the LM3402/HV will engage whenever the power MOSFET current (equal to the inductor current while the MOSFET is on) exceeds 735 mA (typical). The power MOSFET is disabled for a cooldown time that is 10x the steady-state ON-time. At the conclusion of this cool-down time the system re-starts. If the current limit condition persists the cycle of cool-down time and restarting will continue, creating a low-power hiccup mode, minimizing thermal stress on the LM3402/HV and the external circuit components. 12 Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 Feature Description (continued) 7.3.9 Overvoltage and Overcurrent Comparator The CS pin includes an output overvoltage/overcurrent comparator that will disable the power MOSFET whenever VSNS exceeds 300 mV. This threshold provides a hard limit for the output current. Output current overshoot is limited to 300 mV / RSNS by this comparator during transients. The OVP/OCP comparator can also be used to prevent the output voltage from rising to VO(MAX) in the event of an output open-circuit. This is the most common failure mode for LEDs, due to breaking of the bond wires. In a current regulator an output open circuit causes VSNS to fall to zero, commanding maximum duty cycle. Figure 18 shows a method using a Zener diode, Z1, and Zener limiting resistor, RZ, to limit output voltage to the reverse breakdown voltage of Z1 plus 200 mV. The Zener diode reverse breakdown voltage, VZ, must be greater than the maximum combined VF of all LEDs in the array. The maximum recommended value for RZ is 1 k. As discussed in the Maximum Output Voltage section, there is a limit to how high VO can rise during an output open-circuit that is always less than VIN. If no output capacitor is used, the output stage of the LM3402/HV is capable of withstanding VO(MAX) indefinitely, however the voltage at the output end of the inductor will oscillate and can go above VIN or less than 0 V. A small (typically 10 nF) capacitor across the LED array dampens this oscillation. For circuits that use an output capacitor, the system can still withstand VO(MAX) indefinitely as long as CO is rated to handle VIN. The high current paths are blocked in output open-circuit and the risk of thermal stress is minimal, hence the user may opt to allow the output voltage to rise in the case of an open-circuit LED failure. CB VIN VIN CIN BOOT L1 SW RON D1 Z1 RON LM3402/02HV RZ CS RSNS DIM GND VCC CF Figure 18. Output Open Circuit Protection 7.4 Device Functional Modes 7.4.1 Low Power Shutdown The LM3402/HV can be switched to a low power state (IIN-SD = 90 A) by grounding the RON pin with a signallevel MOSFET as shown in Figure 19. Low power MOSFETs like the 2N7000, 2N3904, or equivalent are recommended devices for putting the LM3402/HV into low power shutdown. Logic gates can also be used to shut down the LM3402/HV as long as the logic low voltage is below the over temperature minimum threshold of 0.3V. Noise filter circuitry on the RON pin can cause a few pulses with a longer ON-time than normal after RON is grounded or released. In these cases the OVP/OCP comparator will ensure that the peak inductor or LED current does not exceed 300 mV / RSNS. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 13 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Device Functional Modes (continued) CB L1 VIN VIN CIN BOOT SW RON D1 RON IF LM3402/02HV ON/OFF Q1 2N7000 or equivalent CS RSNS DIM GND VCC CF Figure 19. Low Power Shutdown 7.4.2 Thermal Shutdown Internal thermal shutdown circuitry is provided to protect the device in the event that the maximum junction temperature is exceeded. The threshold for thermal shutdown is 165C with a 25C hysteresis (both values typical). During thermal shutdown the MOSFET and driver are disabled. 14 Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 8 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. 8.1 Application Information 8.1.1 Switching Frequency Switching frequency is selected based on the tradeoffs between efficiency (better at low frequency), solution size/cost (smaller at high frequency), and the range of output voltage that can be regulated (wider at lower frequency.) Many applications place limits on switching frequency due to EMI sensitivity. The ON-time of the LM3402/HV can be programmed for switching frequencies ranging from the 10's of kHz to over 1 MHz. The maximum switching frequency is limited only by the minimum ON-time requirement. 8.1.2 LED Ripple Current Selection of the ripple current, iF, through the LED array is analogous to the selection of output ripple voltage in a standard voltage regulator. Where the output ripple in a voltage regulator is commonly 1% to 5% of the DC output voltage, LED manufacturers generally recommend values for iF ranging from 5% to 20% of IF. Higher LED ripple current allows the use of smaller inductors, smaller output capacitors, or no output capacitors at all. The advantages of higher ripple current are reduction in the solution size and cost. Lower ripple current requires more output inductance, higher switching frequency, or additional output capacitance. The advantages of lower ripple current are a reduction in heating in the LED itself and greater range of the average LED current before the current limit of the LED or the driving circuitry is reached. 8.1.3 Buck Converters Without Output Capacitors The buck converter is unique among non-isolated topologies because of the direct connection of the inductor to the load during the entire switching cycle. By definition an inductor will control the rate of change of current that flows through it, and this control overcurrent ripple forms the basis for component selection in both voltage regulators and current regulators. A current regulator such as the LED driver for which the LM3402/HV was designed focuses on the control of the current through the load, not the voltage across it. A constant current regulator is free of load current transients, and has no need of output capacitance to supply the load and maintain output voltage. Referring to the Typical Application Diagram, the inductor and LED can form a single series chain, sharing the same current. When no output capacitor is used, the same equations that govern inductor ripple current, iL, also apply to the LED ripple current, iF. For a controlled ON-time converter such as LM3402/HV the ripple current is described by the following expression: VIN - VO tON 'iL = 'iF = L (10) A minimum ripple voltage of 25 mV is recommended at the CS pin to provide good signal-to-noise ratio (SNR). The CS pin ripple voltage, VSNS, is described by the following: VSNS = iF x RSNS (11) 8.1.4 Buck Converters With Output Capacitors A capacitor placed in parallel with the LED or array of LEDs can be used to reduce the LED current ripple while keeping the same average current through both the inductor and the LED array. This technique is demonstrated in Typical Application. With this topology the output inductance can be lowered, making the magnetics smaller and less expensive. Alternatively, the circuit could be run at lower frequency but keep the same inductor value, improving the efficiency and expanding the range of output voltage that can be regulated. Both the peak current limit and the OVP/OCP comparator still monitor peak inductor current, placing a limit on how large iL can be even if iF is made very small. A parallel output capacitor is also useful in applications where the inductor or input voltage tolerance is poor. Adding a capacitor that reduces iF to well below the target provides headroom for changes in inductance or VIN that might otherwise push the peak LED ripple current too high. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 15 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Application Information (continued) Figure 20 shows the equivalent impedances presented to the inductor current ripple when an output capacitor, CO, and its equivalent series resistance (ESR) are placed in parallel with the LED array. The entire inductor ripple current flows through RSNS to provide the required 25 mV of ripple voltage for proper operation of the CS comparator. 'iL CO rD 'iC 'iF ESR 'iL RSNS Figure 20. LED and CO Ripple Current To calculate the respective ripple currents the LED array is represented as a dynamic resistance, rD. LED dynamic resistance is not always specified on the manufacturer's data sheet, but it can be calculated as the inverse slope of the LED's VF vs. IF curve. Dividing VF by IF will give an incorrect value that is 5x to 10x too high. Total dynamic resistance for a string of n LEDs connected in series can be calculated as the rD of one device multiplied by n. Inductor ripple current is still calculated with the expression from Buck Regulators without Output Capacitors. The following equations can then be used to estimate iF when using a parallel capacitor: 'iL 'iF = rD 1+ ZC 1 ZC = ESR + 2S x fSW x CO (12) The calculation for ZC assumes that the shape of the inductor ripple current is approximately sinusoidal. Small values of CO that do not significantly reduce iF can also be used to control EMI generated by the switching action of the LM3402/HV. EMI reduction becomes more important as the length of the connections between the LED and the rest of the circuit increase. 8.1.5 Input Capacitors Input capacitors at the VIN pin of the LM3402/HV are selected using requirements for minimum capacitance and rms ripple current. The input capacitors supply pulses of current approximately equal to IF while the power MOSFET is on, and are charged up by the input voltage while the power MOSFET is off. Switching converters such as the LM3402/HV have a negative input impedance due to the decrease in input current as input voltage increases. This inverse proportionality of input current to input voltage can cause oscillations (sometimes called `power supply interaction') if the magnitude of the negative input impedance is greater the the input filter impedance. Minimum capacitance can be selected by comparing the input impedance to the converter's negative resistance; however this requires accurate calculation of the input voltage source inductance and resistance, quantities which can be difficult to determine. An alternative method to select the minimum input capacitance, CIN(MIN), is to select the maximum voltage ripple which can be tolerated. This value,vIN(MAX), is equal to the change in voltage across CIN during the converter ON-time, when CIN supplies the load current. CIN(MIN) can be selected with the following: CIN(MIN) = 16 IF x tON 'VIN(MAX) Submit Documentation Feedback (13) Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 Application Information (continued) A good starting point for selection of CIN is to use an input voltage ripple of 5% to 10% of VIN. A minimum input capacitance of 2x the CIN(MIN) value is recommended for all LM3402/HV circuits. To determine the rms current rating, the following formula can be used: IIN(rms) = IF x D(1 - D) (14) Ceramic capacitors are the best choice for the input to the LM3402/HV due to their high ripple current rating, low ESR, low cost, and small size compared to other types. When selecting a ceramic capacitor, special attention must be paid to the operating conditions of the application. Ceramic capacitors can lose one-half or more of their capacitance at their rated DC voltage bias and also lose capacitance with extremes in temperature. A DC voltage rating equal to twice the expected maximum input voltage is recommended. In addition, the minimum quality dielectric which is suitable for switching power supply inputs is X5R, while X7R or better is preferred. 8.1.6 Recirculating Diode The LM3402/HV is a non-synchronous buck regulator that requires a recirculating diode D1 (see the Typical Application circuit) to carrying the inductor current during the MOSFET off-time. The most efficient choice for D1 is a Schottky diode due to low forward drop and near-zero reverse recovery time. D1 must be rated to handle the maximum input voltage plus any switching node ringing when the MOSFET is on. In practice all switching converters have some ringing at the switching node due to the diode parasitic capacitance and the lead inductance. D1 must also be rated to handle the average current, ID, calculated as: ID = (1 - D) x IF (15) This calculation should be done at the maximum expected input voltage. The overall converter efficiency becomes more dependent on the selection of D1 at low duty cycles, where the recirculating diode carries the load current for an increasing percentage of the time. This power dissipation can be calculated by checking the typical diode forward voltage, VD, from the I-V curve on the product data sheet and then multiplying it by ID. Diode data sheets will also provide a typical junction-to-ambient thermal resistance, JA, which can be used to estimate the operating die temperature of the Schottky. Multiplying the power dissipation (PD = ID x VD) by JA gives the temperature rise. The diode case size can then be selected to maintain the Schottky diode temperature below the operational maximum. 8.1.7 LED Current During DIM Mode The LM3402 contains high speed MOSFET gate drive circuitry that switches the main internal power MOSFET between ON and OFF states. This circuitry uses current derived from the VCC regulator to charge the MOSFET during turnon, then dumps current from the MOSFET gate to the source (the SW pin) during turnoff. As shown in the block diagram, the MOSFET drive circuitry contains a gate drive undervoltage lockout (UVLO) circuit that ensures the MOSFET remains off when there is inadequate VCC voltage for proper operation of the driver. This watchdog circuitry is always running including during DIM and shutdown modes, and supplies a small amount of current from VCC to SW. Because the SW pin is connected directly to the LEDs through the buck inductor, this current returns to ground through the LEDs. The amount of current sourced is a function of the SW voltage, as shown in Figure 21. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 17 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Application Information (continued) 25 SW CURRENT (PA) 20 15 10 5 0 0 1 2 3 4 5 6 SW VOLTAGE (V) Figure 21. LED Current From SW Pin Though most power LEDs are designed to run at several hundred milliamps, some can be seen to glow with a faint light at extremely low current levels, as low as a couple microamps in some instances. In lab testing, the forward voltage was found to be approximately 2 V for LEDs that exhibited visible light at these low current levels. For LEDs that did not show light emission at very low current levels, the forward voltage was found to be around 900 mV. It is important to remember that the forward voltage is also temperature dependent, decreasing at higher temperatures. Consequently, with a maximum Vcc voltage of 7.4 V, current will be observed in the LEDs if the total stack voltage is less than about 6 V at a forward current of several microamps. No current is observed if the stack voltage is above 6 V, as shown in Figure 21. The need for absolute darkness during DIM mode is also application dependent. It will not affect regular PWM dimming operation. The fix for this issue is extremely simple. Place a resistor from the SW pin to ground according to Table 1. Table 1. LED Resistor Values 18 Submit Documentation Feedback NUMBER OF LEDs RESISTOR VALUE (k) 1 20 2 50 3 90 4 150 5 200 >5 300 Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 The luminaire designer should ensure that the suggested resistor is effective in eliminating the off-state light output. A combination of calculations based on LED manufacturer data and lab measurements over temperature will ensure the best design. 8.1.8 Transient Protection Considerations Considerations must be made when external sources, loads or connections are made to the switching converter circuit due to the possibility of Electrostatic Discharge (ESD) or Electric Over Stress (EOS) events occurring and damaging the integrated circuit (IC) device. All IC device pins contain Zener based clamping structures that are meant to clamp ESD. ESD events are very low energy events, typically less than 5 J (microjoules). Any event that transfers more energy than this may damage the ESD structure. Damage is typically represented as a short from the pin to ground as the extreme localized heat of the ESD / EOS event causes the aluminum metal on the chip to melt, causing the short. This situation is common to all integrated circuits and not just unique to the LM340X device. 8.1.8.1 CS Pin Protection When hot swapping in a load (for example, test points, load boards, LED stack), any residual charge on the load will be immediately transferred through the output capacitor to the CS pin, which is then damaged as shown in Figure 22 below. The EOS event due to the residual charge from the load is represented as VTRANSIENT. From measurements, we know that the 8V ESD structure on the CS pin can typically withstand 25mA of direct current (DC). Adding a 1-k resistor in series with the CS pin, shown in Figure 23, results in the majority of the transient energy to pass through the discrete sense resistor rather than the device. The series resistor limits the peak current that can flow during a transient event, thus protecting the CS pin. With the 1-k resistor shown, a 33-V, 49-A transient on the LED return connector terminal could be absorbed as calculated by: V = 25 mA x 1 k + 8 V = 33 V I = 33 V / 0.67 = 49 A (16) (17) This is an extremely high energy event, so the protection measures previously described should be adequate to solve this issue. LM3402 SW Module Connector Module Connector VTRANSIENT CS 8V ~ 0.675 GND Figure 22. CS Pin, Transient Path Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 19 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com LM3402 SW Module Connector Module Connector CS VTRANSIENT 1 k5 8V ~ 0.675 GND Figure 23. CS Pin, Transient Path With Protection Adding a resistor in series with the CS pin causes the observed output LED current to shift very slightly. The reason for this is twofold: (1) the CS pin has about 20 pF of inherent capacitance inside it which causes a slight delay (20 ns for a 1-k series resistor), and (2) the comparator that is watching the voltage at the CS pin uses a pnp bipolar transistor at its input. The base current of this pnp transistor is approximately 100 nA, which will cause a 0.1-mV change in the 200-mV threshold. These are both very minor changes and are well understood. The shift in current can either be neglected or taken into consideration by changing the current sense resistance slightly. 8.1.8.2 CS Pin Protection With OVP When designing output overvoltage protection into the switching converter circuit using a Zener diode, transient protection on the CS pin requires additional consideration. As shown in Figure 24, adding a Zener diode from the output to the CS pin (with the series resistor) for output overvoltage protection will now again allow the transient energy to be passed through the CS pin's ESD structure thereby damaging it. Adding an additional series resistor to the CS pin as shown in Figure 25 will result in the majority of the transient energy to pass through the sense resistor, thereby protecting the LM340X device. 20 Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 LM3402 SW Module Connector Module Connector VTRANSIENT CS 1 k5 8V ~ 0.675 GND Figure 24. CS Pin With OVP, Transient Path LM3402 SW Module Connector Module Connector VTRANSIENT CS 1 k5 5005 8V ~ 0.675 GND Figure 25. CS Pin With OVP, Transient Path with Protection 8.1.8.3 VIN Pin Protection The VIN pin also has an ESD structure from the pin to GND with a breakdown voltage of approximately 80 V. Any transient that exceeds this voltage may damage the device. Although transient absorption is usually present at the front end of a switching converter circuit, damage to the VIN pin can still occur. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 21 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com When VIN is hot swapped in, the current that rushes in to charge CIN up to the VIN value also charges (energizes) the circuit board trace inductance as shown in Figure 26. The excited trace inductance then resonates with the input capacitance (similar to an under-damped LC tank circuit) and causes voltages at the VIN pin to rise well in excess of both VIN and the voltage at the module input connector as clamped by the input TVS. If the resonating voltage at the VIN pin exceeds the 80-V breakdown voltage of the ESD structure, the ESD structure will activate and then snap-back to a lower voltage due to its inherent design. If this lower snap-back voltage is less than the applied nominal VIN voltage, then significant current will flow through the ESD structure resulting in the device being damaged. An additional TVS or small Zener diode should be placed as close as possible to the VIN pins of each device on the board, in parallel with the input capacitor as shown in Figure 27. A minor amount of series resistance in the input line would also help, but would lower overall conversion efficiency. For this reason, NTC resistors are often used as inrush limiters instead. LM3402 Board Trace Inductance VIN Module Connector 80V TVS VIN CIN GND Module Connector Figure 26. VIN Pin With Typical Input Protection 22 Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 LM3402 Board Trace Inductance VIN Module Connector 80V VIN TVS CIN TVS or smaller zener diode GND Module Connector Figure 27. VIN Pin With Additional Input Protection 8.1.8.4 General Comments Regarding Other Pins Any pin that goes off-board through a connector should have series resistance of at least 1 k to 10 k in series with it to protect it from ESD or other transients. These series resistors limit the peak current that can flow (or cause a voltage drop) during a transient event, thus protecting the pin and the device. Pins that are not used should not be left floating. They should instead be tied to GND or to an appropriate voltage through resistance. 8.2 Typical Application The first example circuit will guide the user through component selection for an architectural accent lighting application. A regulated DC voltage input of 24 V 10% will power a single 1-W white LED at a forward current of 350 mA 5%. The typical forward voltage of a 1-W InGaN LED is 3.5 V, hence the estimated average output voltage will be 3.7 V. The objective of this application is to place the complete current regulator and LED in the compact space formerly occupied by an MR16 halogen light bulb. (The LED will be on a separate metal-core PCB.) Switching frequency will be as fast as the 300-ns tON limit allows, with the emphasis on space savings over efficiency. Efficiency cannot be ignored, however, because the confined space with little air-flow requires a maximum temperature rise of 40C in each circuit component. A complete bill of materials can be found in Table 2. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 23 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Typical Application (continued) CB L1 VIN = 24V VIN BOOT SW RON CIN D1 RON CO LED1 IF = 350 mA LM3402/02HV CS DIM RSNS VCC GND CF Figure 28. Schematic for Design Example 1 8.2.1 Design Requirements Use the following parameters for this design example: 1. VIN = 24 V 10% 2. ILED = 350 mA 3. VLED = 3.5 V, 1 LED 8.2.2 Detailed Design Procedure Table 2 shows the body of materials for this design example. Table 2. BOM for Design Example 1 ID PART NUMBER TYPE SIZE PARAMETERS QTY VENDOR U1 LM3402 LED Driver VSSOP-8 40 V, 0.5 A 1 NSC L1 SLF7045T-330MR82 Inductor 7 x 7 x 4.5 mm 33 H, 0.82 A, 96 m 1 TDK D1 CMHSH5-4 Schottky Diode SOD-123 40 V, 0.5 A 1 Central Semi Cf VJ0805Y104KXXAT Capacitor 0805 100 nF 10% 1 Vishay Cb VJ0805Y103KXXAT Capacitor 0805 10n F 10% 1 Vishay Cin C3216X7R1H105M Capacitor 1206 1 F 50 V 1 TDK Co C2012X7R1A225M Capacitor 0805 2.2 F 10 V 1 TDK Rsns ERJ6BQFR75V Resistor 0805 0.75 1% 1 Panasonic Ron CRCW08055902F Resistor 0805 59 k 1% 1 Vishay 8.2.2.1 RON and tON To select RON the expression relating tON to input voltage from the Controlled ON-time Overview section can be rewritten as Equation 18 tON x VIN RON = 1.34 x 10-10 (18) Minimum ON-time occurs at the maximum VIN, which is 24 V x 110% = 26.4 V. RON is therefore calculated using Equation 19. RON = (300 x 10-9 x 26.4) / 1.34 x 10-10 = 59105 24 Submit Documentation Feedback (19) Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 The closest 1% tolerance resistor is 59 k. The switching frequency of the circuit can then be found using the equation relating RON to fSW: fSW = 3.7 / (59000 x 1.34 x 10-10) = 468 kHz (20) 8.2.2.2 Using an Output Capacitor The inductor will be the largest component used in this design. Because the application does not require any PWM dimming, an output capacitor can be used to greatly reduce the inductance needed without worry of slowing the potential PWM dimming frequency. The total solution size is reduced by using an output capacitor and small inductor as opposed to one large inductor. 8.2.2.3 Output Inductor Knowing that an output capacitor will be used, the inductor can be selected for a larger current ripple. The desired maximum value for iL is 30%, or 0.6 x 350 mA = 210 mAP-P. Minimum inductance is selected at the maximum input voltage. Re-arranging the equation for current ripple selection yields the following: LMIN = VIN(MAX) - VO 'iL x tON (21) (22) LMIN = [(26.4 - 3.7) x 300 x 10-9] / (0.6 x 0.35) = 32.4 H The closest standard inductor value is 33 H. Off-the-shelf inductors rated at 33 H are available from many magnetics manufacturers. Inductor data sheets should contain three specifications that are used to select the inductor. The first of these is the average current rating, which for a buck regulator is equal to the average load current, or IF. The average current rating is given by a specified temperature rise in the inductor, normally 40C. For this example, the average current rating should be greater than 350 mA to ensure that heat from the inductor does not reduce the lifetime of the LED or cause the LM3402 to enter thermal shutdown. The second specification is the tolerance of the inductance itself, typically 10% to 30% of the rated inductance. In this example, designers use an inductor with a tolerance of 20%. With this tolerance the typical, minimum, and maximum inductor current ripples can be calculated using Equation 23 to Equation 25. iL(TYP) = [(26.4 - 3.7) x 300 x 10-9] / 33 x 10-6 = 206 mAP-P iL(MIN) = [(26.4 - 3.7) x 300 x 10-9] / 39.6 x 10-6 = 172 mAP-P iL(MAX) = [(26.4 - 3.7) x 300 x 10-9] / 26.4 x 10-6 = 258 mAP-P (23) (24) (25) The third specification for an inductor is the peak current rating, normally given as the point at which the inductance drops off by a given percentage due to saturation of the core. The worst-case peak current occurs at maximum input voltage and at minimum inductance, and can be determined with: IL(PEAK) = IF + 'iL(MAX) 2 (26) (27) IL(PEAK) = 0.35 + 0.258 / 2 = 479 mA For this example the peak current rating of the inductor should be greater than 479 mA. In the case of a short circuit across the LED array, the LM3402 will continue to deliver rated current through the short but will reduce the output voltage to equal the CS pin voltage of 200 mV. Worst-case peak current in this condition is equal to: iL(LED-SHORT) = [(26.4 - 0.2) x 300 x 10-9] / 26.4 x 10-6 = 298 mAP-P IL(PEAK) = 0.35 + 0.149 = 499 mA (28) In the case of a short at the switch node, the output, or from the CS pin to ground the short circuit current limit will engage at a typical peak current of 735 mA. To prevent inductor saturation during these short circuits the inductor's peak current rating must be above 735 mA. The device selected is an off-the-shelf inductor rated 33 H 20% with a DCR of 96 m and a peak current rating of 0.82 A. The physical dimensions of this inductor are 7 x 7 x 4.5 mm. 8.2.2.3.1 RSNS The current sensing resistor value can be determined by re-arranging the expression for average LED current from the LED Current Accuracy section: Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 25 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 RSNS = www.ti.com 0.2 x L IF x L + VO x tSNS - VIN - VO x tON 2 (29) (30) RSNS = 0.74, tSNS = 220 ns Sub-1- resistors are available in both 1% and 5% tolerance. A 1%, 0.75- resistor will give the best accuracy of the average LED current. To determine the resistor size the power dissipation can be calculated using Equation 31. PSNS = (IF)2 x RSNS PSNS = 0.352 x 0.75 = 92 mW (31) Standard 0805 size resistors are rated to 125 mW and will be suitable for this application. To select the proper output capacitor the equation from Buck Regulators with Output Capacitors is rearranged to yield the following: ZC = 'iF 'iL - 'iF x rD (32) The target tolerance for LED ripple current is 5% or 10%P-P = 35 mAP-P, and the LED data sheet gives a typical value for rD of 1 at 350 mA. The required capacitor impedance to reduce the worst-case inductor ripple current of 258 mAP-P is therefore: ZC = [0.035 / (0.258 - 0.035] x 1 = 0.157 (33) A ceramic capacitor will be used and the required capacitance is selected based on the impedance at 468 kHz: CO = 1/(2 x x 0.157 x 4.68 x 105) = 2.18 F (34) This calculation assumes that impedance due to the equivalent series resistance (ESR) and equivalent series inductance (ESL) of CO is negligible. The closest 10% tolerance capacitor value is 2.2 F. The capacitor used should be rated to 10 V or more and have an X7R dielectric. Several manufacturers produce ceramic capacitors with these specifications in the 0805 case size. A typical value for ESR of 1 m can be read from the curve of impedance vs frequency in the product data sheet. 8.2.2.4 Input Capacitor Following the calculations from the Input Capacitor section, vIN(MAX) will be 1%P-P = 240 mV. The minimum required capacitance is: CIN(MIN) = (0.35 x 300 x 10-9) / 0.24 = 438 nF (35) In expectation that more capacitance will be needed to prevent power supply interaction a 1-F ceramic capacitor rated to 50 V with X7R dielectric in a 1206 case size will be used. In this case, input rms current is: IIN-RMS = 0.35 x Sqrt(0.154 x 0.846) = 126 mA (36) Ripple current ratings for 1206 size ceramic capacitors are typically higher than 1 A, more than enough for this design. 8.2.2.5 Recirculating Diode The first parameter for D1 which must be determined is the reverse voltage rating. Schottky diodes are available at reverse ratings of 30 V and 40 V, often in the same package, with the same forward current rating. To account for ringing a 40-V Schottky will be used. The next parameters to be determined are the forward current rating and case size. In this example the low duty cycle (D = 3.7 / 24 = 15%) requires the recirculating diode D1 to carry the load current much longer than the internal power MOSFET of the LM3402. The estimated average diode current is: ID = 0.35 x 0.85 = 298 mA 26 Submit Documentation Feedback (37) Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 Schottky diodes are available at forward current ratings of 0.5 A, however the current rating often assumes a 25C ambient temperature and does not take into account the application restrictions on temperature rise. A diode rated for higher current may be needed to keep the temperature rise below 40C. To determine the proper case size, the dissipation and temperature rise in D1 can be calculated as shown in the Design Considerations section. VD for a small case size such as SOD-123 in a 40 V, 0.5-A Schottky diode at 350 mA is approximately 0.4 V and the JA is 206C/W. Power dissipation and temperature rise can be calculated as: PD = 0.298 x 0.4 = 119 mW TRISE = 0.119 x 206 = 24.5C (38) According to these calculations the SOD-123 diode will meet the requirements. Heating and dissipation are among the factors most difficult to predict in converter design. If possible, a footprint should be used that is capable of accepting both SOD-123 and a larger case size, such as SMA. A larger diode with a higher forward current rating will generally have a lower forward voltage, reducing dissipation, as well as having a lower JA, reducing temperature rise. 8.2.2.5.1 CB and CF The bootstrap capacitor CB should always be a 10 nF ceramic capacitor with X7R dielectric. A 25-V rating is appropriate for all application circuits. The linear regulator filter capacitor CF should always be a 100-nF ceramic capacitor, also with X7R dielectric and a 25-V rating. 8.2.2.6 Efficiency To estimate the electrical efficiency of this example the power dissipation in each current carrying element can be calculated and summed. This term should not be confused with the optical efficacy of the circuit, which depends upon the LEDs themselves. Total output power, PO, is calculated as: PO = IF x VO = 0.35 x 3.7 = 1.295 W (39) Conduction loss, PC, in the internal MOSFET: PC = (IF2 x RDSON) x D = (0.352 x 1.5) x 0.154 = 28 mW (40) Gate charging and VCC loss, PG, in the gate drive and linear regulator: PG = (IIN-OP + fSW x QG) x VIN PG = (600 x 10-6 + 468000 x 3 x 10-9) x 24 = 48 mW (41) Switching loss, PS, in the internal MOSFET: PS = 0.5 x VIN x IF x (tR + tF) x fSW PS = 0.5 x 24 x 0.35 x (40 x 10-9) x 468000 = 78 mW (42) AC rms current loss, PCIN, in the input capacitor: PCIN = IIN(rms)2 x ESR = (0.126)2 x 0.006 = 0.1 mW (negligible) (43) DCR loss, PL, in the inductor PL = IF2 x DCR = 0.352 x 0.096 = 11.8 mW (44) Recirculating diode loss, PD = 119 mW Current Sense Resistor Loss, PSNS = 92 mW Electrical efficiency, = PO / (PO + Sum of all loss terms) = 1.295 / (1.295 + 0.377) = 77% 8.2.2.7 Die Temperature TLM3402 = (PC + PG + PS) x JA TLM3402 = (0.028 + 0.05 + 0.078) x 200 = 31C Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV (45) Submit Documentation Feedback 27 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com 8.2.3 Application Curves Top = SW Middle = DIM Bottom = LED Current Figure 29. PWM Dimming, DIM Rising 28 Submit Documentation Feedback Top = SW Middle = DIM Bottom = LED Current Figure 30. PWM Dimming, DIM Falling Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 9 Power Supply Recommendations Use any DC output power supply with a maximum voltage high enough for the application. The power supply should have a minimum current limit of at least 500 mA. 10 Layout 10.1 Layout Guidelines The performance of any switching converter depends as much upon the layout of the PCB as the component selection. The following guidelines will help the user design a circuit with maximum rejection of outside EMI and minimum generation of unwanted EMI. 10.1.1 Compact Layout Parasitic inductance can be reduced by keeping the power path components close together and keeping the area of the loops that high currents travel small. Short, thick traces or copper pours (shapes) are best. In particular, the switch node (where L1, D1, and the SW pin connect) should be just large enough to connect all three components without excessive heating from the current it carries. The LM3402/HV operates in two distinct cycles whose high current paths are shown in Figure 22: + - Figure 31. Buck Converter Current Loops The dark grey, inner loop represents the high current path during the MOSFET ON-time. The light grey, outer loop represents the high current path during the off-time. 10.1.2 Ground Plane and Shape Routing The diagram of Figure 22 is also useful for analyzing the flow of continuous current vs the flow of pulsating currents. The circuit paths with current flow during both the ON-time and off-time are considered to be continuous current, while those that carry current during the ON-time or off-time only are pulsating currents. Preference in routing should be given to the pulsating current paths, as these are the portions of the circuit most likely to emit EMI. The ground plane of a PCB is a conductor and return path, and it is susceptible to noise injection just as any other circuit path. The continuous current paths on the ground net can be routed on the system ground plane with less risk of injecting noise into other circuits. The path between the input source and the input capacitor and the path between the recirculating diode and the LEDs/current sense resistor are examples of continuous current paths. In contrast, the path between the recirculating diode and the input capacitor carries a large pulsating current. This path should be routed with a short, thick shape, preferably on the component side of the PCB. Multiple vias in parallel should be used right at the pad of the input capacitor to connect the component side shapes to the ground plane. A second pulsating current loop that is often ignored is the gate drive loop formed by the SW and BOOT pins and capacitor CB. To minimize this loop at the EMI it generates, keep CB close to the SW and BOOT pins. 10.1.3 Current Sensing The CS pin is a high-impedance input, and the loop created by RSNS, RZ (if used), the CS pin and ground should be made as small as possible to maximize noise rejection. RSNS should therefore be placed as close as possible to the CS and GND pins of the IC. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 29 LM3402, LM3402HV SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 www.ti.com Layout Guidelines (continued) 10.1.4 Remote LED Arrays In some applications the LED or LED array can be far away (several inches or more) from the LM3402/HV, or on a separate PCB connected by a wiring harness. When an output capacitor is used and the LED array is large or separated from the rest of the converter, the output capacitor should be placed close to the LEDs to reduce the effects of parasitic inductance on the AC impedance of the capacitor. The current sense resistor should remain on the same PCB, close to the LM3402/HV. 10.2 Layout Example GND LED+ D1 L1 CIN + SW VIN CB LED- BOOT VCC CF RSNS DIM VIN RON RON GND CS THERMAL/POWER VIA Figure 32. Layout Recommendation 30 Submit Documentation Feedback Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV LM3402, LM3402HV www.ti.com SNVS450F - SEPTEMBER 2006 - REVISED OCTOBER 2015 11 Device and Documentation Support 11.1 Device Support 11.1.1 Third-Party Products Disclaimer TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE. 11.2 Related Links The table below lists quick access links. Categories include technical documents, support and community resources, tools and software, and quick access to sample or buy. Table 3. Related Links PARTS PRODUCT FOLDER SAMPLE & BUY TECHNICAL DOCUMENTS TOOLS & SOFTWARE SUPPORT & COMMUNITY LM3402 Click here Click here Click here Click here Click here LM3402HV Click here Click here Click here Click here Click here 11.3 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. 11.4 Trademarks E2E is a trademark of Texas Instruments. PowerPAD is a trademark of Texas Instruments . All other trademarks are the property of their respective owners. 11.5 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. 11.6 Glossary SLYZ022 -- TI Glossary. This glossary lists and explains terms, acronyms, and definitions. 12 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. Copyright (c) 2006-2015, Texas Instruments Incorporated Product Folder Links: LM3402 LM3402HV Submit Documentation Feedback 31 PACKAGE OPTION ADDENDUM www.ti.com 15-Apr-2017 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (C) Device Marking (4/5) LM3402HVMM/NOPB ACTIVE VSSOP DGK 8 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SNFB LM3402HVMMX/NOPB ACTIVE VSSOP DGK 8 3500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SNFB LM3402HVMR/NOPB ACTIVE SO PowerPAD DDA 8 95 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR L3402 HVMR LM3402HVMRX/NOPB ACTIVE SO PowerPAD DDA 8 2500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR L3402 HVMR LM3402MM/NOPB ACTIVE VSSOP DGK 8 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SNEB LM3402MMX/NOPB ACTIVE VSSOP DGK 8 3500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SNEB LM3402MR/NOPB ACTIVE SO PowerPAD DDA 8 95 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR L3402 MR LM3402MRX/NOPB ACTIVE SO PowerPAD DDA 8 2500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR L3402 MR (1) The marketing status values are defined as follows: 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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com (4) 15-Apr-2017 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/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish 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 23-Oct-2015 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 LM3402HVMM/NOPB VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3402HVMMX/NOPB VSSOP DGK 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3402HVMRX/NOPB SO Power PAD DDA 8 2500 330.0 12.4 6.5 5.4 2.0 8.0 12.0 Q1 LM3402MM/NOPB VSSOP DGK 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3402MMX/NOPB VSSOP DGK 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM3402MRX/NOPB SO Power PAD DDA 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 23-Oct-2015 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM3402HVMM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 LM3402HVMMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0 LM3402HVMRX/NOPB SO PowerPAD DDA 8 2500 367.0 367.0 35.0 LM3402MM/NOPB VSSOP DGK 8 1000 210.0 185.0 35.0 LM3402MMX/NOPB VSSOP DGK 8 3500 367.0 367.0 35.0 LM3402MRX/NOPB SO PowerPAD DDA 8 2500 367.0 367.0 35.0 Pack Materials-Page 2 PACKAGE OUTLINE DDA0008B PowerPAD TM SOIC - 1.7 mm max height SCALE 2.400 PLASTIC SMALL OUTLINE C 6.2 TYP 5.8 A SEATING PLANE PIN 1 ID AREA 0.1 C 6X 1.27 8 1 2X 3.81 5.0 4.8 NOTE 3 4 5 8X B 4.0 3.8 NOTE 4 0.51 0.31 0.25 1.7 MAX C A B 0.25 TYP 0.10 SEE DETAIL A 5 4 EXPOSED THERMAL PAD 3.4 2.8 0.25 GAGE PLANE 9 8 1 0 -8 0.15 0.00 1.27 0.40 DETAIL A 2.71 2.11 TYPICAL 4214849/A 08/2016 PowerPAD is a trademark of Texas Instruments. NOTES: 1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. 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 0.15 mm per side. 4. This dimension does not include interlead flash. Interlead flash shall not exceed 0.25 mm per side. 5. Reference JEDEC registration MS-012. www.ti.com EXAMPLE BOARD LAYOUT DDA0008B PowerPAD TM SOIC - 1.7 mm max height PLASTIC SMALL OUTLINE (2.95) NOTE 9 SOLDER MASK DEFINED PAD (2.71) SOLDER MASK OPENING SEE DETAILS 8X (1.55) 1 8 8X (0.6) 9 SYMM (1.3) TYP (3.4) SOLDER MASK OPENING (4.9) NOTE 9 6X (1.27) 5 4 (R0.05) TYP METAL COVERED BY SOLDER MASK SYMM ( 0.2) TYP VIA (1.3) TYP (5.4) LAND PATTERN EXAMPLE SCALE:10X 0.07 MIN ALL AROUND 0.07 MAX ALL AROUND SOLDER MASK OPENING METAL SOLDER MASK OPENING METAL UNDER SOLDER MASK SOLDER MASK DEFINED NON SOLDER MASK DEFINED SOLDER MASK DETAILS PADS 1-8 4214849/A 08/2016 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. 8. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature numbers SLMA002 (www.ti.com/lit/slma002) and SLMA004 (www.ti.com/lit/slma004). 9. Size of metal pad may vary due to creepage requirement. 10. Vias are optional depending on application, refer to device data sheet. If any vias are implemented, refer to their locations shown on this view. It is recommended that vias under paste be filled, plugged or tented. www.ti.com EXAMPLE STENCIL DESIGN DDA0008B PowerPAD TM SOIC - 1.7 mm max height PLASTIC SMALL OUTLINE (2.71) BASED ON 0.125 THICK STENCIL 8X (1.55) (R0.05) TYP 1 8 8X (0.6) (3.4) BASED ON 0.125 THICK STENCIL 9 SYMM 6X (1.27) 5 4 METAL COVERED BY SOLDER MASK SYMM (5.4) SEE TABLE FOR DIFFERENT OPENINGS FOR OTHER STENCIL THICKNESSES SOLDER PASTE EXAMPLE EXPOSED PAD 100% PRINTED SOLDER COVERAGE BY AREA SCALE:10X STENCIL THICKNESS SOLDER STENCIL OPENING 0.1 0.125 0.150 0.175 3.03 X 3.80 2.71 X 3.40 (SHOWN) 2.47 X 3.10 2.29 X 2.87 4214849/A 08/2016 NOTES: (continued) 11. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. 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