Sample & Buy Product Folder Support & Community Tools & Software Technical Documents LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 LM2738 550-kHz/1.6-MHz 1.5-A Step-Down DC-DC Switching Regulator 1 Features 3 Description * The LM2738 regulator is a monolithic, highfrequency, PWM step-down DC-DC converter in an 8pin WSON or 8-pin MSOP-PowerPAD package. It provides all the active functions for local DC-DC conversion with fast transient response and accurate regulation in the smallest possible PCB area. 1 * * * * * * * * * * Space-Saving WSON and MSOP-PowerPADTM Packages 3-V to 20-V Input Voltage Range 0.8-V to 18-V Output Voltage Range 1.5-A Output Current 550-kHz (LM2738Y) and 1.6-MHz (LM2738X) Switching Frequencies 250-m NMOS Switch 400-nA Shutdown Current 0.8-V, 2% Internal Voltage Reference Internal Soft-Start Current-Mode, PWM Operation Thermal Shutdown 2 Applications * * * * * * Local Point of Load Regulation Core Power in HDDs Set-Top Boxes Battery Powered Devices USB Powered Devices DSL Modems With a minimum of external components, the LM2738 is easy to use. The ability to drive 1.5-A loads with an internal 250-m NMOS switch using state-of-the-art 0.5-m BiCMOS technology results in the best power density available. Switching frequency is internally set to 550 kHz (LM2738Y) or 1.6 MHz (LM2738X), allowing the use of extremely small surface-mount inductors and chip capacitors. Even though the operating frequencies are very high, efficiencies up to 90% are easy to achieve. External enable is included, featuring an ultralow standby current of 400 nA. The LM2738 utilizes current-mode control and internal compensation to provide high-performance regulation over a wide range of operating conditions. Additional features include internal soft-start circuitry to reduce in-rush current, cycle-by-cycle current limit, thermal shutdown, and output over-voltage protection. Device Information(1) PART NUMBER LM2738 PACKAGE BODY SIZE (NOM) WSON (8) 3.00 mm x 3.00 mm MSOP-PowerPAD (8) 3.00 mm x 3.00 mm (1) For all available packages, see the orderable addendum at the end of the data sheet. Typical Application Circuit Efficiency vs Load Current VIN = 12 V, VOUT = 3.3 V D2 VIN BOOST VIN C3 C1 L1 SW LM2738 ON OFF VOUT D1 EN C2 R1 FB GND R2 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. LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 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 4 4 4 5 5 6 Absolute Maximum Ratings ...................................... ESD Ratings.............................................................. Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Typical Characteristics .............................................. Detailed Description ............................................ 10 7.1 7.2 7.3 7.4 Overview ................................................................. Functional Block Diagram ....................................... Feature Description................................................. Device Functional Modes........................................ 10 11 11 14 8 Application and Implementation ........................ 15 8.1 Application Information............................................ 15 8.2 Typical Applications ................................................ 15 9 Power Supply Recommendations...................... 30 10 Layout................................................................... 30 10.1 Layout Guidelines ................................................. 30 10.2 Layout Example .................................................... 31 10.3 Thermal Considerations ........................................ 31 11 Device and Documentation Support ................. 33 11.1 11.2 11.3 11.4 11.5 11.6 Device Support...................................................... Documentation Support ........................................ Community Resources.......................................... Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 33 33 33 33 33 33 12 Mechanical, Packaging, and Orderable Information ........................................................... 33 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision B (April 2013) to Revision C * Added Device Information table, ESD Ratings table, Thermal Information 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 Changes from Revision A (April 2013) to Revision B * 2 Page Page Changed layout of National Data Sheet to TI format ........................................................................................................... 29 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 5 Pin Configuration and Functions NGQ Package 8-Pin WSON With Exposed Thermal Pad Top View DGN Package 8-Pin MSOP-PowerPAD Top View Pin Functions PIN TYPE (1) DESCRIPTION NO. NAME 1 BOOST I 2 VIN PWR 3 VCC I Input supply voltage of the device. Connect a bypass capacitor to this pin. Must tie pins 2 and 3 together at the package. 4 EN I Enable control input. Logic high enables operation. Do not allow this pin to float or be greater than VIN + 0.3 V. GND PWR Signal and power ground pins. Place the bottom resistor of the feedback network as close as possible to these pins. 5, 7 Boost voltage that drives the internal NMOS control switch. A bootstrap capacitor is connected between the BOOST and SW pins. Supply voltage for output power stage. Connect a bypass capacitor to this pin. Must tie pins 2 and 3 together at package. 6 FB I Feedback pin. Connect FB to the external resistor divider to set output voltage. 8 SW O Output switch. Connects to the inductor, catch diode, and bootstrap capacitor. GND -- Signal and power ground. Must be connected to GND on the PCB. DAP (1) I = Input, O = Output, and PWR = Power Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 3 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted) (1) (2) MIN MAX UNIT VIN, VCC -0.5 24 V SW voltage -0.5 24 V Boost voltage -0.5 30 V Boost to SW voltage -0.5 6 V FB voltage -0.5 3 V EN voltage -0.5 VIN + 0.3 V 150 C Infrared and convection reflow (15 s) 220 C Wave soldering lead temperature (10 s) 260 C 150 C Junction temperature Soldering information Storage temperature, Tstg (1) (2) -65 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 or Aerospace specified devices are required, contact the Texas Instruments Sales Office or Distributors for availability and specifications. 6.2 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. Human body model, 1.5 k in series with 100 pF. 6.3 Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) MIN MAX 3 20 V SW voltage -0.5 20 V Boost voltage V VIN, VCC UNIT -0.5 25.5 Boost to SW voltage 2.5 5.5 V Junction temperature -40 125 C 165 C Thermal shutdown 4 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 6.4 Thermal Information LM2738 THERMAL METRIC (1) NGQ (WSON) DGN (MSOP PowerPAD) 8 PINS 8 PINS (2) UNIT RJA Junction-to-ambient thermal resistance 45.9 50.3 C/W RJC(top) Junction-to-case (top) thermal resistance 44.6 54.2 C/W RJB Junction-to-board thermal resistance 13.2 31.4 C/W JT Junction-to-top characterization parameter 0.5 4.8 C/W JB Junction-to-board characterization parameter 13.2 31.2 C/W RJC(bot) Junction-to-case (bottom) thermal resistance 5.8 4 C/W (1) (2) For more information about traditional and new thermal metrics, see the Semiconductor and device Package Thermal Metrics application report, SPRA953. Typical thermal shutdown occurs if the junction temperature exceeds 165C. The maximum power dissipation is a function of TJ(MAX) , RJA and TA . The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) - TA) / RJA. All numbers apply for packages soldered directly onto a 3 inches x 3 inches PC board with 2 oz. copper on 4 layers in still air in accordance to JEDEC standards. Thermal resistance varies greatly with layout, copper thickness, number of layers in PCB, power distribution, number of thermal vias, board size, ambient temperature, and air flow. 6.5 Electrical Characteristics All typical limits apply over TJ = 25C, and all maximum and minimum limits apply over the full operating temperature range (TJ = -40C to +125C). VIN = 12 V, VBOOST - VSW = 5 V unless otherwise specified. Data sheet minimum and maximum specification limits are ensured by design, test, or statistical analysis. PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) 0.784 0.800 0.816 VFB Feedback voltage VFB/VIN Feedback voltage line regulation VIN = 3 V to 20 V IFB Feedback input bias current Sink or source 0.1 100 Undervoltage lockout VIN Rising 2.7 2.9 Undervoltage lockout VIN Falling UVLO 0.02 2 UVLO hysteresis FSW Switching frequency DMAX Maximum duty cycle 1.28 1.6 1.92 LM2738Y 0.364 0.55 0.676 LM2738X , Load = 150 mA 95% LM2738X 7.5% LM2738Y 2% VBOOST - VSW = 3 V, Load = 400 mA 250 ICL Switch current limit VBOOST - VSW = 3 V, VIN = 3 V Boost pin current 500 2.9 m A 1.9 Non-Switching 1.9 mA VEN = 0 V 400 nA LM2738X (27% Duty Cycle) 4.5 LM2738Y (27% Duty Cycle) 2.5 VEN Falling Enable threshold voltage VEN Rising IEN Enable pin current Sink / Source ISW Switch leakage VIN = 20 V (1) (2) 2 Switching Shutdown threshold voltage VEN_TH MHz 92% LM2738Y, Load = 150 mA Switch ON resistance IBOOST V LM2738X RDS(ON) Quiescent current (shutdown) nA 0.4 Minimum duty cycle Quiescent current V %/V 2.3 DMIN IQ UNIT 3 mA mA 0.4 1.4 V 10 nA 100 nA Ensured to average outgoing quality level (AOQL). Typicals represent the most likely parametric norm. Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 5 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 6.6 Typical Characteristics All curves taken at VIN = 12 V, VBOOST - VSW = 5 V, and TA = 25C, unless specified otherwise. VOUT = 5 V VOUT = 5 V Figure 1. Efficiency vs Load Current - X Version VOUT = 3.3 V VOUT = 3.3 V Figure 3. Efficiency vs Load Current - X Version VOUT = 1.5 V Figure 4. Efficiency vs Load Current - Y Version VOUT = 1.5 V Figure 5. Efficiency vs Load Current - X Version 6 Figure 2. Efficiency vs Load Current - Y Version Figure 6. Efficiency vs Load Current - Y Version Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 Typical Characteristics (continued) All curves taken at VIN = 12 V, VBOOST - VSW = 5 V, and TA = 25C, unless specified otherwise. Figure 7. Oscillator Frequency vs Temperature - X Version Figure 8. Oscillator Frequency vs Temperature - Y Version VIN = 5 V Figure 9. Current Limit vs Temperature Figure 10. IQ Non-Switching vs Temperature Figure 11. VFB vs Temperature Figure 12. RDSON vs Temperature Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 7 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com Typical Characteristics (continued) All curves taken at VIN = 12 V, VBOOST - VSW = 5 V, and TA = 25C, unless specified otherwise. VOUT = 1.5 V IOUT = 750 mA VOUT = 1.5 V Figure 13. Line Regulation - X Version VOUT = 3.3 V Figure 14. Line Regulation - Y Version VOUT = 3.3 V IOUT = 750 mA VOUT = 1.5 V Figure 17. Load Regulation - X Version 8 IOUT = 750 mA Figure 16. Line Regulation - Y Version Figure 15. Line Regulation - X Version VOUT = 1.5 V IOUT = 750 mA Submit Documentation Feedback Figure 18. Load Regulation - Y Version Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 Typical Characteristics (continued) All curves taken at VIN = 12 V, VBOOST - VSW = 5 V, and TA = 25C, unless specified otherwise. VOUT = 3.3 V VOUT = 3.3 V Figure 19. Load Regulation - X Version Figure 20. Load Regulation - Y Version VOUT = 3.3 V Figure 22. Load Transient - X Version Figure 21. IQ Switching vs Temperature VOUT = 3.3 V VIN = 12 V IOUT = 1.5 A Figure 23. Startup - X Version (Resistive Load) VIN = 12 V VOUT = 3.3 V VIN = 12 V IOUT = 1.5 A Figure 24. In-Rush Current - X Version (Resistive Load) Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 9 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 7 Detailed Description 7.1 Overview The LM2738 is a constant frequency PWM buck regulator device that delivers a 1.5-A load current. The regulator has a preset switching frequency of either 550 kHz (LM2738Y) or 1.6 MHz (LM2738X). These high frequencies allow the LM2738 to operate with small surface-mount capacitors and inductors, resulting in DC-DC converters that require a minimum amount of board space. The LM2738 is internally compensated, so it is simple to use and requires few external components. The LM2738 uses current-mode control to regulate the output voltage. The LM2738 supplies a regulated output voltage by switching the internal NMOS control switch at constant frequency and variable duty cycle. A switching cycle begins at the falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output control logic turns on the internal NMOS control switch. During this on time, the SW pin voltage (VSW) swings up to approximately VIN, and the inductor current (IL) increases with a linear slope. IL is measured by the current-sense amplifier, which generates an output proportional to the switch current. The sense signal is summed with the regulator's corrective ramp and compared to the error amplifier's output, which is proportional to the difference between the feedback voltage and VREF. When the PWM comparator output goes high, the output switch turns off until the next switching cycle begins. During the switch off-time, inductor current discharges through Schottky diode D1, which forces the SW pin to swing below ground by the forward voltage (VD) of the catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage. See Functional Block Diagram and Figure 25. VSW D = TON/TSW VIN SW Voltage TOFF TON 0 VD IL t TSW IPK Inductor Current t 0 Figure 25. LM2738 Waveforms of SW Pin Voltage and Inductor Current 10 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 7.2 Functional Block Diagram VIN VIN Current-Sense Amplifier EN OFF RSENSE + - CIN D2 Thermal Shutdown BOOST VBOOST Under Voltage Lockout Current Limit Oscillator Output Control Logic Reset Pulse + ISENSE + + Corrective Ramp 0.25: Switch Driver SW OVP Comparator - ON Internal Regulator and Enable Circuit Error Signal D1 + PWM Comparator CBOOST VSW L IL VOUT COUT 0.93V + - R1 FB Internal Compensation + Error Amplifier + - VREF 0.8V R2 GND 7.3 Feature Description 7.3.1 Boost Function Capacitor CBOOST and diode D2 in Figure 26 are used to generate a voltage VBOOST. VBOOST - VSW is the gatedrive voltage to the internal NMOS control switch. To properly drive the internal NMOS switch during its on time, VBOOST must be at least 2.5 V greater than VSW. TI recommends that VBOOST be greater than 2.5 V above VSW for best efficiency. VBOOST - VSW must not exceed the maximum operating limit of 5.5 V. For best performance, see Equation 1. 5.5 V > VBOOST - VSW > 2.5 V (1) When the LM2738 starts up, internal circuitry from the BOOST pin supplies a maximum of 20 mA to CBOOST. This current charges CBOOST to a voltage sufficient to turn the switch on. The BOOST pin continues to source current to CBOOST until the voltage at the feedback pin is greater than 0.76 V. There are various methods to derive VBOOST: 1. From the input voltage (3 V < VIN < 5.5 V) 2. From the output voltage (2.5 V < VOUT < 5.5 V) 3. From an external distributed voltage rail (2.5 V < VEXT < 5.5 V) 4. From a shunt or series Zener diode As seen on the Functional Block Diagram, capacitor CBOOST and diode D2 supply the gate-drive voltage for the NMOS switch. Capacitor CBOOST is charged via diode D2 by VIN. During a normal switching cycle, when the internal NMOS control switch is off (TOFF) (refer to Figure 25), VBOOST equals VIN minus the forward voltage of D2 (VFD2), during which the current in the inductor (L) forward biases the Schottky diode D1 (VFD1). Therefore the voltage stored across CBOOST is Equation 2: VBOOST - VSW = VIN - VFD2 + VFD1 (2) When the NMOS switch turns on (TON), the switch pin rises to Equation 3: VSW = VIN - (RDSON x IL), (3) forcing VBOOST to rise, thus reverse biasing D2. The voltage at VBOOST is then Equation 4: VBOOST = 2 VIN - (RDSON x IL) - VFD2 + VFD1 (4) which is approximately 2 VIN - 0.4 V for many applications. Thus the gate-drive voltage of the NMOS switch is approximately VIN - 0.2 V. Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 11 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com Feature Description (continued) An alternate method for charging CBOOST is to connect D2 to the output as shown in Figure 26. The output voltage must be between 2.5 V and 5.5 V so that proper gate voltage is applied to the internal switch. In this circuit, CBOOST provides a gate-drive voltage that is slightly less than VOUT. VBOOST D2 BOOST VIN VIN LM2738 CIN CBOOST L SW VOUT GND COUT D1 Figure 26. VOUT Charges CBOOST In applications where both VIN and VOUT are greater than 5.5 V, or less than 3 V, CBOOST cannot be charged directly from these voltages. If VIN and VOUT are greater than 5.5 V, CBOOST can be charged from VIN or VOUT minus a Zener voltage by placing a Zener diode D3 in series with D2, as shown in Figure 27. When using a series Zener diode from the input, ensure that the regulation of the input supply does not create a voltage that falls outside the recommended VBOOST voltage. (VINMAX - VD3) < 5.5 V (VINMIN - VD3) > 2.5 V D2 D3 VIN VIN CIN BOOST VBOOST CBOOST LM2738 L SW VOUT GND D1 COUT Figure 27. Zener Reduces Boost Voltage from VIN An alternative method is to place the Zener diode D3 in a shunt configuration as shown in Figure 28. A small 350-mW to 500-mW 5.1-V Zener in a SOT-23 or SOD package can be used for this purpose. A small ceramic capacitor such as a 6.3-V, 0.1-F capacitor (C4) must be placed in parallel with the Zener diode. When the internal NMOS switch turns on, a pulse of current is drawn to charge the internal NMOS gate capacitance. The 0.1-F parallel shunt capacitor ensures that the VBOOST voltage is maintained during this time. 12 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 Feature Description (continued) VZ C4 D2 D3 R3 VIN BOOST VIN CIN VBOOST CBOOST LM2738 L SW VOUT GND D1 COUT Figure 28. Boost Voltage Supplied from the Shunt Zener on VIN Resistor R3 must be selected to provide enough RMS current to the Zener diode (D3) and to the BOOST pin. A recommended choice for the Zener current (IZENER) is 1 mA. The current IBOOST into the BOOST pin supplies the gate current of the NMOS control switch and varies typically according to the formula in Equation 5 for the X version: IBOOST = 0.56 x (D + 0.54) x (VZENER - VD2) mA (5) IBOOST can be calculated for the Y version using Equation 6: IBOOST = 0.22 x (D + 0.54) x (VZENER - VD2) A where * * * * * D is the duty cycle VZENER and VD2 are in volts IBOOST is in milliamps VZENER is the voltage applied to the anode of the boost diode (D2) VD2 is the average forward voltage across D2 (6) The formula for IBOOST in Equation 6 gives typical current. For the worst case IBOOST, increase the current by 40%. In that case, the worst case boost current is Equation 7: IBOOST-MAX = 1.4 x IBOOST (7) R3 is then given by Equation 8: R3 = (VIN - VZENER) / (1.4 x IBOOST + IZENER) (8) For example, using the X-version let VIN = 10 V, VZENER = 5 V, VD2 = 0.7 V, IZENER = 1 mA, and duty cycle D = 50%. Then Equation 9 and Equation 10: IBOOST = 0.56 x (0.5 + 0.54) x (5 - 0.7) mA = 2.5 mA R3 = (10 V - 5 V) / (1.4 x 2.5 mA + 1 mA) = 1.11 k (9) (10) 7.3.2 Soft-Start This function forces VOUT to increase at a controlled rate during start-up. During soft-start, the error amplifier's reference voltage ramps from 0 V to its nominal value of 0.8 V in approximately 600 s. This forces the regulator output to ramp up in a more linear and controlled fashion, which helps reduce in-rush current. 7.3.3 Output Overvoltage Protection The overvoltage comparator compares the FB pin voltage to a voltage that is 16% higher than the internal reference VREF. Once the FB pin voltage goes 16% above the internal reference, the internal NMOS control switch is turned off, which allows the output voltage to decrease toward regulation. Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 13 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com Feature Description (continued) 7.3.4 Undervoltage Lockout Undervoltage lockout (UVLO) prevents the LM2738 from operating until the input voltage exceeds 2.7 V (typical). The UVLO threshold has approximately 400 mV of hysteresis, so the part operates until VIN drops below 2.3 V (typical). Hysteresis prevents the part from turning off during power up if the VIN ramp-up is non-monotonic. 7.3.5 Current Limit The LM2738 uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a current limit comparator detects if the output switch current exceeds 2.9 A (typical), and turns off the switch until the next switching cycle begins. 7.3.6 Thermal Shutdown Thermal shutdown limits total power dissipation by turning off the output switch when the device junction temperature exceeds 165C. After thermal shutdown occurs, the output switch doesn't turn on until the junction temperature drops to approximately 150C. 7.4 Device Functional Modes 7.4.1 Enable Pin and Shutdown Mode The LM2738 has a shutdown mode that is controlled by the enable pin (EN). When a logic low voltage is applied to EN, the part is in shutdown mode, and its quiescent current drops to typically 400 nA. The voltage at this pin must never exceed VIN + 0.3 V. 14 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 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 must validate and test their design implementation to confirm system functionality. 8.1 Application Information The LM2738 operates over a wide range of conditions, which is limited by the ON time of the device. Figure 29 shows the recommended operating area for the X version at the full load (1.5 A) and at 25C ambient temperature. The Y version of the LM2738 operates at a lower frequency, and therefore operates over the entire range of operating voltages. Figure 29. LM2738X - 1.6 MHz (25C, Load = 1.5 A) 8.2 Typical Applications 8.2.1 LM2738X Circuit Example 1 D2 VIN BOOST VIN C3 C1 R3 LM2738 ON OFF L1 SW VOUT D1 EN C2 R1 FB GND R2 Figure 30. LM2738X (1.6 MHz) VBOOST Derived from VIN 5 V to 1.5 V/1.5 A 8.2.1.1 Design Requirements The device must be able to operate at any voltage within the Recommended Operating Conditions. The load current must be defined to properly size the inductor, input, and output capacitors. The inductor must be able to support the full expected load current as well as the peak current generated from load transients and start-up. Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 15 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com Typical Applications (continued) 8.2.1.2 Detailed Design Procedure Table 1. Bill of Materials for Figure 30 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738X Texas Instruments C1, Input Cap 10 F, 6.3 V, X5R C3216X5ROJ106M TDK C2, Output Cap 22 F, 6.3 V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.1 uF, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. L1 2.2 H, 1.9 A, MSS5131-222ML Coilcraft R1 8.87 k, 1% CRCW06038871F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay 8.2.1.2.1 Inductor Selection The duty cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN), using Equation 11: VO D= VIN (11) The catch diode (D1) forward voltage drop and the voltage drop across the internal NMOS switch must be included to calculate a more accurate duty cycle. Calculate D by using Equation 12: VO + VD D= VIN + VD - VSW (12) VSW can be approximated by Equation 13: VSW = IOUT x RDSON (13) The diode forward drop (VD) can range from 0.3 V to 0.7 V depending on the quality of the diode. The lower the VD, the higher the operating efficiency of the converter. The inductor value determines the output ripple current. Lower inductor values decrease the size of the inductor, but increase the output ripple current. An increase in the inductor value decreases the output ripple current. One must ensure that the minimum current limit (2 A) is not exceeded, so the peak current in the inductor must be calculated. The peak current (ILPK) in the inductor is calculated by Equation 14 and Equation 15: ILPK = IOUT + iL (14) Figure 31. Inductor Current VIN - VOUT 2DiL = L DTS (15) In general in Equation 16, 16 iL = 0.1 x (IOUT) 0.2 x (IOUT) (16) Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 Typical Applications (continued) If iL = 33.3% of 1.5 A, the peak current in the inductor is 2 A. The minimum specified current limit over all operating conditions is 2 A. One can either reduce iL, or make the engineering judgment that zero margin is safe enough. The typical current limit is 2.9 A. The LM2738 operates at frequencies allowing the use of ceramic output capacitors without compromising transient response. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple. See the Output Capacitor section for more details on calculating output voltage ripple. Now that the ripple current is determined, the inductance is calculated by Equation 17: 2 ae 1 ae Di o o PCOND = (IOUT 2 D) c 1 + c L / / RDSON c 3 e IOUT o / e o where TS = * 1 fS (17) When selecting an inductor, make sure that it is capable of supporting the peak output current without saturating. Inductor saturation results in a sudden reduction in inductance and prevents the regulator from operating correctly. Because of the speed of the internal current limit, the peak current of the inductor need only be specified for the required maximum output current. For example, if the designed maximum output current is 1 A and the peak current is 1.25 A, the inductor must be specified with a saturation current limit of > 1.25 A. There is no must specify the saturation or peak current of the inductor at the 2.9-A typical switch current limit. Because of the operating frequency of the LM2738, ferrite based inductors are preferred to minimize core losses. This presents little restriction because of the variety of ferrite-based inductors available. Lastly, inductors with lower series resistance (RDCR) provide better operating efficiency. For recommended inductors see LM2738X Circuit Example 1. 8.2.1.2.2 Input Capacitor An input capacitor is necessary to ensure that VIN does not drop excessively during switching transients. The primary specifications of the input capacitor are capacitance, voltage, RMS current rating, and equivalent series inductance (ESL). The recommended input capacitance is 10 F. The input voltage rating is specifically stated by the capacitor manufacturer. Make sure to check any recommended deratings and also verify if there is any significant change in capacitance at the operating input voltage and the operating temperature. The input capacitor maximum RMS input current rating (IRMS-IN) must be greater than Equation 18: 2DiL u e IRMS _ IN D eIOUT 2 (1- D) + 3 uu e (18) Neglecting inductor ripple simplifies Equation 18 to Equation 19: IRMS _ IN = IOUT D(1- D) (19) Equation 19 shows that maximum RMS capacitor current occurs when D = 0.5. Always calculate the RMS at the point where the duty cycle D is closest to 0.5. The ESL of an input capacitor is usually determined by the effective cross-sectional area of the current path. A large leaded capacitor has high ESL and a 0805 ceramicchip capacitor has very low ESL. At the operating frequencies of the LM2738, leaded capacitors may have an ESL so large that the resulting impedance (2fL) is higher than that required to provide stable operation. As a result, surface-mount capacitors are strongly recommended. Sanyo POSCAP, Tantalum or Niobium, Panasonic SP, and multilayer ceramic capacitors (MLCC) are all good choices for both input and output capacitors and have very low ESL. For MLCCs, TI recommends using X7R or X5R type capacitors due to their tolerance and temperature characteristics. Consult the capacitor manufacturer's data sheets to see how rated capacitance varies over operating conditions. 8.2.1.2.3 Output Capacitor The output capacitor is selected based upon the desired output ripple and transient response. The initial current of a load transient is provided mainly by the output capacitor. The output ripple of the converter is Equation 20: Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 17 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com Typical Applications (continued) ae o 1 DVOUT = DIL c RESR + / 8 FSW COUT o e (20) When using MLCCs, the equivalent series resistance (ESR) is typically so low that the capacitive ripple may dominate. When this occurs, the output ripple is approximately sinusoidal and 90 phase shifted from the switching action. Given the availability and quality of MLCCs and the expected output voltage of designs using the LM2738, there is really no must review any other capacitor technologies. Another benefit of ceramic capacitors is the ability to bypass high-frequency noise. A certain amount of switching edge noise couples through parasitic capacitances in the inductor to the output. A ceramic capacitor bypasses this noise while a tantalum capacitor does not. Since the output capacitor is one of the two external components that control the stability of the regulator control loop, most applications require a minimum of 22 F of output capacitance. Capacitance, in general, is often increased when operating at lower duty cycles. Refer to the Circuit Examples for suggested output capacitances of common applications. Like the input capacitor, recommended multilayer ceramic capacitors are X7R or X5R types. 8.2.1.2.4 Catch Diode The catch diode (D1) conducts during the switch off time. A Schottky diode is recommended for its fast switching times and low forward voltage drop. The catch diode must be chosen so that its current rating is greater than Equation 21: ID1 = IOUT x (1-D) (21) The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin. To improve efficiency, choose a Schottky diode with a low forward-voltage drop. 8.2.1.2.5 Output Voltage The output voltage is set using Equation 22 and Equation 23 where R2 is connected between the FB pin and GND, and R1 is connected between VO and the FB pin. A good value for R2 is 10 k. When designing a unity gain converter (VO = 0.8 V), R1 must be between 0 and 100 , and R2 must not be loaded. ae V o R1 = c O - 1/ R2 V e REF o (22) (23) VREF = 0.80 V 8.2.1.2.6 Calculating Efficiency and Junction Temperature The complete LM2738 DC-DC converter efficiency can be calculated by Equation 24 or Equation 25: P h = OUT PIN (24) or, h= POUT POUT + PLOSS (25) Calculations for determining the most significant power losses are shown in Equation 26. Other losses totaling less than 2% are not discussed. Power loss (PLOSS) is the sum of two basic types of losses in the converter: switching and conduction. Conduction losses usually dominate at higher output loads, whereas switching losses remain relatively fixed and dominate at lower output loads. The first step in determining the losses is to calculate the duty cycle (D): VOUT + VD D= VIN + VD - VSW (26) VSW is the voltage drop across the internal NFET when it is on, and is equal to Equation 27: VSW = IOUT x RDSON 18 (27) Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 Typical Applications (continued) VD is the forward voltage drop across the Schottky catch diode. It can be obtained from the diode manufacturer's data sheet Electrical Characteristics section. If the voltage drop across the inductor (VDCR) is accounted for, the equation becomes Equation 28: VOUT + VD + VDCR D= VIN + VD + VDCR - VSW (28) The conduction losses in the free-wheeling Schottky diode are calculated by Equation 29: PDIODE = VD x IOUT x (1-D) (29) Often this is the single most significant power loss in the circuit. Care must be taken to choose a Schottky diode that has a low forward-voltage drop. Another significant external power loss is the conduction loss in the output inductor. The equation can be simplified to Equation 30: PIND = IOUT2 x RDCR (30) The LM2738 conduction loss is mainly associated with the internal NFET switch in Equation 31: 2 ae 1 ae DiL o /o 2 c PCOND = (IOUT D) 1 + c / RDSON c 3 e IOUT o / e o (31) If the inductor ripple current is fairly small, the conduction losses can be simplified to Equation 32: PCOND = IOUT2 x RDSON x D (32) Switching losses are also associated with the internal NFET switch. They occur during the switch on and off transition periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss is to empirically measure the rise and fall times (10% to 90%) of the switch at the switch node. Switching Power Loss is calculated as follows in Equation 33, Equation 34, and Equation 35: PSWR = 1/2(VIN x IOUT x FSW x TRISE) PSWF = 1/2(VIN x IOUT x FSW x TFALL) PSW = PSWR + PSWF (33) (34) (35) Another loss is the power required for operation of the internal circuitry in Equation 36: PQ = IQ x VIN (36) IQ is the quiescent operating current, and is typically around 1.9 mA for the 0.55-MHz frequency option. Table 2 lists the power losses for a typical application, and in Equation 37, Equation 38, and Equation 39. Table 2. Typical Configuration and Power Loss Calculation PARAMETER VALUE POWER PARAMETER VIN 12 V -- CALCULATED POWER -- VOUT 3.3 V POUT 4.125 W IOUT 1.25 A -- -- VD 0.34 V PDIODE 317 mW FSW 550 kHz -- -- IQ 1.9 mA PQ 22.8 mW TRISE 8 nS PSWR 33 mW TFALL 8 nS PSWF 33 mW RDS(ON) 275 m PCOND 118 mW INDDCR 70 m PIND 110 mW D 0.275 PLOSS 634 mW 86.7% PINTERNAL 207 mW Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 19 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com PCOND + PSW + PDIODE + PIND + PQ = PLOSS PCOND + PSWF + PSWR + PQ = PINTERNAL PINTERNAL = 207 mW (37) (38) (39) 8.2.1.3 Application Curve VOUT = 5 V Figure 32. Efficiency vs Load Current - X Version 20 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 8.2.2 LM2738X Circuit Example 2 Figure 33. LM2738X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V / 1.5 A 8.2.2.1 Detailed Design Procedure Table 3. Bill of Materials for Figure 33 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738X Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 33 F, 6.3 V, X5R C3216X5ROJ336M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. L1 5 H, 2.9 A MSS7341- 502NL Coilcraft R1 31.6 k, 1% CRCW06033162F Vishay R2 10 k, 1% CRCW06031002F Vishay R3 100 k, 1% CRCW06031003F Vishay 8.2.2.2 Application Curve VOUT = 3.3 V Figure 34. Efficiency vs Load Current - X Version Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 21 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 8.2.3 LM2738X Circuit Example 3 C4 D3 R4 D2 BOOST VIN VIN C3 C1 R3 L1 SW VOUT LM2738 ON D1 EN OFF C2 R1 FB GND R2 Figure 35. LM2738X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 1.5 A 8.2.3.1 Detailed Design Procedure Table 4. Bill of Materials for Figure 35 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738X Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 47 F, 6.3 V, X5R C3216X5ROJ476M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK C4, Shunt Cap 0.1 F, 6.3 V, X5R C1005X5R0J104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. D3, Zener Diode 5.1-V 250-Mw SOT-23 BZX84C5V1 Vishay L1 2.7 H, 1.76 A VLCF5020T-2R7N1R7 TDK R1 8.87 k, 1% CRCW06038871F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay R4 4.12 k, 1% CRCW06034121F Vishay 22 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 8.2.3.2 Application Curve VOUT = 1.5 V Figure 36. Efficiency vs Load Current - X Version 8.2.4 LM2738X Circuit Example 4 D3 D2 BOOST VIN VIN C1 C3 R3 LM2738 ON VOUT D1 EN OFF L1 SW C2 R1 FB GND R2 Figure 37. LM2738X (1.6 MHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 1.5 A 8.2.4.1 Detailed Design Procedure Table 5. Bill of Materials for Figure 37 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738X Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 47 F, 6.3 V, X5R C3216X5ROJ476M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. D3, Zener Diode 11-V 350-Mw SOT-23 BZX84C11T Diodes, Inc. L1 3.3 H, 3.5 A MSS7341-332NL Coilcraft R1 8.87 k, 1% CRCW06038871F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 23 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 8.2.5 LM2738X Circuit Example 5 D3 D2 VIN BOOST VIN C3 C1 R3 LM2738 ON VOUT D1 EN OFF L1 SW C2 R1 FB GND R2 Figure 38. LM2738X (1.6 MHz) VBOOST Derived from Series Zener Diode (VOUT) 15 V to 9 V / 1.5 A 8.2.5.1 Detailed Design Procedure Table 6. Bill of Materials for Figure 38 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738X Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 22 F, 16 V, X5R C3216X5R1C226M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. D3, Zener Diode 4.3-V 350-mw SOT-23 BZX84C4V3 Diodes, Inc. L1 6.2 H, 2.5 A MSS7341-622NL Coilcraft R1 102 k, 1% CRCW06031023F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay 24 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 8.2.6 LM2738Y Circuit Example 6 D2 VIN BOOST VIN C3 C1 R3 L1 SW LM2738 ON VOUT D1 EN OFF C2 R1 FB GND R2 Figure 39. LM2738Y (550 kHz) VBOOST Derived from VIN 5 V to 1.5 V / 1.5 A 8.2.6.1 Detailed Design Procedure Table 7. Bill of Materials for Figure 39 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738Y Texas Instruments C1, Input Cap 10 F, 6.3 V, X5R C3216X5ROJ106M TDK C2, Output Cap 47 F, 6.3 V, X5R C3216X5ROJ476M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. L1 6.2 H, 2.5 A, MSS7341-622NL Coilcraft R1 8.87 k, 1% CRCW06038871F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay 8.2.6.2 Application Curve VOUT = 1.5 V Figure 40. Efficiency vs Load Current - Y Version Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 25 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 8.2.7 LM2738Y Circuit Example 7 Figure 41. LM2738Y (550 kHz) VBOOST Derived from VOUT 12 V to 3.3 V / 1.5 A 8.2.7.1 Detailed Design Procedure Table 8. Bill of Materials for Figure 41 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738Y Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 47 F, 6.3 V, X5R C3216X5ROJ476M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Vishay L1 12 H, 1.7 A, MSS7341-123NL Coilcraft R1 31.6 k, 1% CRCW06033162F Vishay R2 10 k, 1% CRCW06031002F Vishay R3 100 k, 1% CRCW06031003F Vishay 8.2.7.2 Application Curve VOUT = 3.3 V Figure 42. Efficiency vs Load Current - Y Version 26 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 8.2.8 LM2738Y Circuit Example 8 C4 D3 R4 D2 BOOST VIN VIN C3 C1 R3 L1 SW VOUT LM2738 ON D1 EN OFF C2 R1 FB GND R2 Figure 43. LM2738Y (550 kHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 1.5 A 8.2.8.1 Detailed Design Procedure Table 9. Bill of Materials for Figure 43 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738Y Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap (47 F, 6.3 V, X5R) x 2 = 94 F C3216X5ROJ476M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK C4, Shunt Cap 0.1 F, 6.3 V, X5R C1005X5R0J104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. D3, Zener Diode 5.1-V 250-Mw SOT-23 BZX84C5V1 Vishay L1 8.7 H, 2.2 A MSS7341-872NL Coilcraft R1 8.87 k, 1% CRCW06038871F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay R4 4.12 k, 1% CRCW06034121F Vishay Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 27 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 8.2.8.2 Application Curve VOUT = 1.5 V Figure 44. Efficiency vs Load Current - Y Version 8.2.9 LM2738Y Circuit Example 9 D3 D2 BOOST VIN VIN C1 C3 R3 LM2738 ON VOUT D1 EN OFF L1 SW C2 R1 FB GND R2 Figure 45. LM2738Y (550 kHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 1.5 A 8.2.9.1 Detailed Design Procedure Table 10. Bill of Materials for Figure 45 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738Y Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap (47 F, 6.3 V, X5R) x 2 = 94 F C3216X5ROJ476M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. D3, Zener Diode 11-V 350-Mw SOT-23 BZX84C11T Diodes, Inc. L1 8.7 H, 2.2 A MSS7341-872NL Coilcraft R1 8.87 k, 1% CRCW06038871F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay 28 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 8.2.9.2 Application Curve VOUT = 1.5 V Figure 46. Efficiency vs Load Current - Y Version 8.2.10 LM2738Y Circuit Example 10 D3 D2 VIN BOOST VIN C3 C1 R3 LM2738 ON VOUT D1 EN OFF L1 SW C2 R1 FB GND R2 Figure 47. LM2738Y (550 kHz) VBOOST Derived from Series Zener Diode (VOUT) 15 V to 9 V / 1.5 A 8.2.10.1 Detailed Design Procedure Table 11. Bill of Materials for Figure 47 PART ID PART VALUE PART NUMBER MANUFACTURER U1 1.5-A Buck Regulator LM2738Y Texas Instruments C1, Input Cap 10 F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 22 F, 16 V, X5R C3216X5R1C226M TDK C3, Boost Cap 0.1 F, 16 V, X7R C1005X7R1C104K TDK D1, Catch Diode 0.34 VF Schottky 1.5 A, 30 V CRS08 Toshiba D2, Boost Diode 1 VF at 100-mA Diode BAT54WS Diodes, Inc. D3, Zener Diode 4.3-V 350-mw SOT-23 BZX84C4V3 Diodes, Inc. L1 15 H, 2.1 A SLF7055T150M2R1-3PF TDK R1 102 k, 1% CRCW06031023F Vishay R2 10.2 k, 1% CRCW06031022F Vishay R3 100 k, 1% CRCW06031003F Vishay Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 29 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com 9 Power Supply Recommendations The input voltage is rated as 3 V to 20 V. Care must be taken in certain circuit configurations, such as when VBOOST is derived from VIN, where the requirement that VBOOST - VSW is less than 5.5 V must be observed. Also for best efficiency, VBOOST must be at least 2.5 V above VSW. The voltage on the enable (EN) pin must not exceed VIN by more than 0.3 V. 10 Layout 10.1 Layout Guidelines When planning layout there are a few things to consider when trying to achieve a clean, regulated output. The most important consideration is the close coupling of the GND connections of the input capacitor and the catch diode D1. These ground ends must be close to one another and be connected to the GND plane with at least two through-holes. Place these components as close as possible to the device. Next in importance is the location of the GND connection of the output capacitor, which must be near the GND connections of CIN and D1. There must be a continuous ground plane on the bottom layer of a two-layer board except under the switching node island. The FB pin is a high-impedance node, and take care to make the FB trace short to avoid noise pickup and inaccurate regulation. The feedback resistors must be placed as close to the device as possible, with the GND of R1 placed as close to the GND of the device as possible. The VOUT trace to R2 must be routed away from the inductor and any other traces that are switching. High AC currents flow through the VIN, SW, and VOUT traces, so they must be as short and wide as possible. However, making the traces wide increases radiated noise, so the designer must make this trade-off. Radiated noise can be decreased by choosing a shielded inductor. The remaining components must also be placed as close to the device as possible. See AN-1229 SIMPLE SWITCHER(R) PCB Layout Guidelines (SNVA054) for further considerations, and the LM2738 demo board as an example of a four-layer layout. 10.1.1 WSON Package Figure 48. Internal WSON Connection For certain high power applications, the PCB land may be modified to a dog-bone shape (see Figure 49). By increasing the size of ground plane, and adding thermal vias, the RJA for the application can be reduced. 30 Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 10.2 Layout Example Figure 49. 8-Lead WSON PCB Dog Bone Layout 10.3 Thermal Considerations Heat in the LM2738 due to internal power dissipation is removed through conduction and/or convection. Conduction: Heat transfer occurs through cross sectional areas of material. Depending on the material, the transfer of heat can be considered to have poor to good thermal conductivity properties (insulator vs. conductor). Heat Transfer goes as: Silicon package lead frame PCB Convection: Heat transfer is by means of airflow. This could be from a fan or natural convection. Natural convection occurs when air currents rise from the hot device to cooler air. Thermal impedance is defined as Equation 40: DT Rq = Power (40) Thermal impedance from the silicon junction to the ambient air is defined as Equation 41: T -T RqJA = J A Power (41) The PCB size, weight of copper used to route traces and ground plane, and number of layers within the PCB can greatly effect RJA. The type and number of thermal vias can also make a large difference in the thermal impedance. Thermal vias are necessary in most applications. They conduct heat from the surface of the PCB to the ground plane. Four to six thermal vias must be placed under the exposed pad to the ground plane if the WSON package is used. Thermal impedance also depends on the thermal properties due to the application's operating conditions (VIN, VO, IO and so forth), and the surrounding circuitry. 10.3.1 Silicon Junction Temperature Determination Methods To accurately measure the silicon temperature for a given application, two methods can be used. 10.3.1.1 Method 1 The first method requires the user to know the thermal impedance of the silicon junction to top case temperature. Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 31 LM2738 SNVS556C - APRIL 2008 - REVISED JANUARY 2016 www.ti.com Thermal Considerations (continued) To clarify: RJC is the thermal impedance from all six sides of a device package to silicon junction. In this data sheet RJC is used, allowing the user to measure top case temperature with a small thermocouple attached to the top case. RJC is approximately 30C/W for the 8-pin WSON package with the exposed pad. With the internal dissipation from the efficiency calculation given previously, and the case temperature, RJC can be empirically measured on the bench as Equation 42. T -T RF JC = J C Power (42) Therefore in Equation 43: Tj = (RJC x PLOSS) + TC (43) From the previous example, shows Equation 44 and Equation 45: Tj = (RJC x PINTERNAL) + TC Tj = 30C/W x 0.207 W + TC (44) (45) 10.3.1.2 Method 2 The second method can give a very accurate silicon junction temperature. The first step is to determine RJA of the application. The LM2738 has overtemperature protection circuitry. When the silicon temperature reaches 165C, the device stops switching. The protection circuitry has a hysteresis of about 15C. Once the silicon temperature has decreased to approximately 150C, the device starts to switch again. Knowing this, the RJA for any application can be characterized during the early stages of the design one may calculate the RJA by placing the PCB circuit into a thermal chamber. Raise the ambient temperature in the given working application until the circuit enters thermal shutdown. If the SW pin is monitored, it is obvious when the internal NFET stops switching, indicating a junction temperature of 165C. Knowing the internal power dissipation from the above equations, the junction temperature and the ambient temperature RJA can be determined with Equation 46. 165 - TA RqJA = PINTERNAL (46) Once RJA is determined, the maximum ambient temperature allowed for a desired junction temperature can be calculated. An example of calculating RJA for an application using the Texas Instruments LM2738 WSON demonstration board is shown in Equation 48. The four-layer PCB is constructed using FR4 with 1/2 oz copper traces. The copper ground plane is on the bottom layer. The ground plane is accessed by two vias. The board measures 3 cm x 3 cm. It was placed in an oven with no forced airflow. The ambient temperature was raised to 144C, and at that temperature, the device went into thermal shutdown. From the previous example, Equation 47 and Equation 48 shows: PINTERNAL = 207 mW (47) 165C - 144C RqJA = = 102C/W 207 mW (48) If the junction temperature is kept below 125C, then the ambient temperature cannot go above 109C, seen in Equation 49 and Equation 50. Tj - (RJA x PLOSS) = TA 125C - (102C/W x 207 mW) = 104C 32 (49) (50) Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 LM2738 www.ti.com SNVS556C - APRIL 2008 - REVISED JANUARY 2016 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 Documentation Support 11.2.1 Related Documentation For related documentation see the following: AN-1229 SIMPLE SWITCHER(R) PCB Layout Guidelines (SNVA054) 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 PowerPAD, E2E are trademarks 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. Submit Documentation Feedback Copyright (c) 2008-2016, Texas Instruments Incorporated Product Folder Links: LM2738 33 PACKAGE OPTION ADDENDUM www.ti.com 8-Oct-2015 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) LM2738XMY/NOPB ACTIVE MSOPPowerPAD DGN 8 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 STDB LM2738XSD/NOPB ACTIVE WSON NGQ 8 1000 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 L237B LM2738YMY/NOPB ACTIVE MSOPPowerPAD DGN 8 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 SJBB LM2738YSD/NOPB ACTIVE WSON NGQ 8 1000 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 125 L174B (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. (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/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. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 8-Oct-2015 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 28-Oct-2016 TAPE AND REEL INFORMATION *All dimensions are nominal Device LM2738XMY/NOPB 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 MSOPPower PAD DGN 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM2738XSD/NOPB WSON NGQ 8 1000 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 LM2738YMY/NOPB MSOPPower PAD DGN 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1 LM2738YSD/NOPB WSON NGQ 8 1000 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 28-Oct-2016 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM2738XMY/NOPB LM2738XSD/NOPB MSOP-PowerPAD DGN 8 1000 210.0 185.0 35.0 WSON NGQ 8 1000 210.0 185.0 35.0 LM2738YMY/NOPB LM2738YSD/NOPB MSOP-PowerPAD DGN 8 1000 210.0 185.0 35.0 WSON NGQ 8 1000 210.0 185.0 35.0 Pack Materials-Page 2 MECHANICAL DATA DGN0008A MUY08A (Rev A) BOTTOM VIEW www.ti.com PACKAGE OUTLINE NGQ0008A WSON - 0.8 mm max height SCALE 4.000 PLASTIC SMALL OUTLINE - NO LEAD 3.1 2.9 B A PIN 1 INDEX AREA 3.1 2.9 C 0.8 0.7 SEATING PLANE 0.08 C 1.6 0.1 (0.1) TYP SYMM EXPOSED THERMAL PAD 0.05 0.00 4 5 SYMM 9 2X 1.5 2 0.1 8 1 6X 0.5 8X PIN 1 ID 8X 0.5 0.3 0.3 0.2 0.1 0.05 C A B C 4214922/A 03/2018 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. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance. www.ti.com EXAMPLE BOARD LAYOUT NGQ0008A WSON - 0.8 mm max height PLASTIC SMALL OUTLINE - NO LEAD (1.6) SYMM 8X (0.6) 1 8 (0.75) 8X (0.25) 9 SYMM (2) 6X (0.5) 5 4 (R0.05) TYP ( 0.2) VIA TYP (2.8) LAND PATTERN EXAMPLE EXPOSED METAL SHOWN SCALE:20X 0.07 MIN ALL AROUND 0.07 MAX ALL AROUND EXPOSED METAL EXPOSED METAL SOLDER MASK OPENING METAL METAL UNDER SOLDER MASK NON SOLDER MASK DEFINED (PREFERRED) SOLDER MASK OPENING SOLDER MASK DEFINED SOLDER MASK DETAILS 4214922/A 03/2018 NOTES: (continued) 4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature number SLUA271 (www.ti.com/lit/slua271). 5. 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 NGQ0008A WSON - 0.8 mm max height PLASTIC SMALL OUTLINE - NO LEAD 8X (0.6) SYMM 9 METAL TYP 8 1 8X (0.25) SYMM (1.79) 6X (0.5) 5 4 (R0.05) TYP (1.47) (2.8) SOLDER PASTE EXAMPLE BASED ON 0.1 mm THICK STENCIL EXPOSED PAD 9: 82% PRINTED SOLDER COVERAGE BY AREA UNDER PACKAGE SCALE:20X 4214922/A 03/2018 NOTES: (continued) 6. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. 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