Sample & Buy Product Folder Support & Community Tools & Software Technical Documents LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 LM2736 Thin SOT 750 mA Load Step-Down DC-DC Regulator 1 Features 3 Description * * * * * The LM2736 regulator is a monolithic, high frequency, PWM step-down DC/DC converter in a 6-pin Thin SOT package. It provides all the active functions to provide local DC/DC conversion with fast transient response and accurate regulation in the smallest possible PCB area. 1 * * * * * * * Thin SOT-6 Package 3.0 V to 18 V Input Voltage Range 1.25 V to 16 V Output Voltage Range 750 mA Output Current 550 kHz (LM2736Y) and 1.6 MHz (LM2736X) Switching Frequencies 350 m NMOS Switch 30 nA Shutdown Current 1.25 V, 2% Internal Voltage Reference Internal Soft-Start Current-Mode, PWM Operation WEBENCH(R) Online Design Tool Thermal Shutdown With a minimum of external components and online design support through WEBENCH(R), the LM2736 is easy to use. The ability to drive 750 mA loads with an internal 350 m NMOS switch using state-of-the-art 0.5 m BiCMOS technology results in the best power density available. The world class control circuitry allows for on-times as low as 13 ns, thus supporting exceptionally high frequency conversion over the entire 3 V to 18 V input operating range down to the minimum output voltage of 1.25 V. Switching frequency is internally set to 550 kHz (LM2736Y) or 1.6 MHz (LM2736X), 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 shutdown is included, featuring an ultra-low stand-by current of 30 nA. The LM2736 utilizes current-mode control and internal compensation to provide highperformance regulation over a wide range of operating conditions. Additional features include internal soft-start circuitry to reduce inrush current, pulse-by-pulse current limit, thermal shutdown, and output over-voltage protection. 2 Applications * * * * * * * Local Point of Load Regulation Core Power in HDDs Set-Top Boxes Battery Powered Devices USB Powered Devices DSL Modems Notebook Computers Device Information(1) PART NUMBER LM2736 PACKAGE SOT (6) BODY SIZE (NOM) 2.90 mm x 1.60 mm (1) For all available packages, see the orderable addendum at the end of the datasheet. Typical Application Circuit Efficiency vs. Load Current "X" VIN = 5 V, VOUT = 3.3 V D2 VIN BOOST VIN C3 C1 L1 SW ON VOUT D1 EN C2 R1 OFF 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. LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 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 4 5 6 Absolute Maximum Ratings ...................................... ESD Ratings ............................................................ Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Typical Characteristics .............................................. Detailed Description .............................................. 8 7.1 Overview ................................................................... 8 7.2 Functional Block Diagram ......................................... 9 7.3 Feature Description................................................... 9 7.4 Device Functional Modes........................................ 10 8 Application and Implementation ........................ 11 8.1 Application Information .......................................... 11 8.2 Typical Applications ............................................... 13 9 Power Supply Recommendations...................... 27 10 Layout................................................................... 27 10.1 Layout Guidelines ................................................. 27 10.2 Layout Example .................................................... 28 11 Device and Documentation Support ................. 29 11.1 11.2 11.3 11.4 11.5 Device Support...................................................... Documentation Support ........................................ Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 29 29 29 29 29 12 Mechanical, Packaging, and Orderable Information ........................................................... 29 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision G (October 2014) to Revision H * Updated Design Requirements and moved Bill of Materials to Detailed Design Procedures.............................................. 13 Changes from Revision F (April 2013) to Revision G * 2 Page Page Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section. ................................................................................................. 4 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 5 Pin Configuration and Functions Package DDC (R-PDSO-G6) 6-Lead SOT Top View BOOST 1 6 SW GND 2 5 VIN FB 3 4 EN Pin Functions PIN I/O DESCRIPTION NAME NO. BOOST 1 I GND 2 GND FB 3 I Feedback pin. Connect FB to the external resistor divider to set output voltage. EN 4 I Enable control input. Logic high enables operation. Do not allow this pin to float or be greater than VIN + 0.3 V. VIN 5 I Input supply voltage. Connect a bypass capacitor to this pin. SW 6 O Output switch. Connects to the inductor, catch diode, and bootstrap capacitor. Boost voltage that drives the internal NMOS control switch. A bootstrap capacitor is connected between the BOOST and SW pins. Signal and Power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin for accurate regulation. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 3 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted) (1) MIN MAX UNIT VIN -0.5 22 V SW Voltage -0.5 22 V Boost Voltage -0.5 28 V Boost to SW Voltage -0.5 8 V FB Voltage -0.5 3 V EN Voltage -0.5 VIN + 0.3 V 150 C Junction Temperature Soldering Information Infrared/Convection Reflow (15sec) 220 C Wave Soldering Lead temperature (10sec) 260 C Tstg Storage temperature 150 C (1) -65 If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. 6.2 ESD Ratings V(ESD) (1) Electrostatic discharge VALUE UNIT 2000 V Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins (1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. 6.3 Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) MIN VIN NOM MAX UNIT 3 18 V SW Voltage -0.5 18 V Boost Voltage -0.5 23 V 1.6 5.5 V -40 125 C Boost to SW Voltage Junction Temperature Range 6.4 Thermal Information LM2736 THERMAL METRIC (1) DDC UNIT 6 PINS RJA (2) Junction-to-ambient thermal resistance 158.1 RJC(top) Junction-to-case (top) thermal resistance 46.5 RJB Junction-to-board thermal resistance 29.5 JT Junction-to-top characterization parameter 0.8 JB Junction-to-board characterization parameter 29.2 RJC(bot) Junction-to-case (bottom) thermal resistance n/a (1) (2) 4 C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Thermal shutdown will occur if the junction temperature exceeds 165C. The maximum power dissipation is a function of TJ(MAX) , JA and TA . The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX) - TA)/JA . All numbers apply for packages soldered directly onto a 3" x 3" PC board with 2oz. copper on 4 layers in still air. For a 2 layer board using 1 oz. copper in still air, JA = 204C/W. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 6.5 Electrical Characteristics Specifications with standard typeface are for TJ = 25C unless otherwise specified. Datasheet min/max specification limits are ensured by design, test, or statistical analysis. PARAMETER TEST CONDITIONS TJ = 25C MIN (1) TYP (2) TJ = -40C to 125C MAX (1) VFB Feedback Voltage VFB/ VIN Feedback Voltage Line Regulation VIN = 3V to 18V IFB Feedback Input Bias Current Sink/Source Undervoltage Lockout VIN Rising 2.74 Undervoltage Lockout VIN Falling 2.3 2.0 UVLO 1.250 MIN 1.225 TYP MAX 1.275 0.01 250 V 0.44 0.30 1.6 1.2 1.9 LM2736Y 0.55 0.40 0.66 LM2736X 92% 85% LM2736Y 96% 90% LM2736X 2% LM2736Y 1% RDS(ON) Switch ON Resistance VBOOST - VSW = 3V 350 ICL Switch Current Limit VBOOST - VSW = 3V 1.5 IQ Quiescent Current Switching 1.5 Quiescent Current (shutdown) VEN = 0V 30 LM2736X (50% Duty Cycle) 2.2 3.3 LM2736Y (50% Duty Cycle) 0.9 1.6 Switching Frequency DMAX Maximum Duty Cycle DMIN IBOOST Minimum Duty Cycle Boost Pin Current Shutdown Threshold Voltage VEN Falling Enable Threshold Voltage VEN Rising IEN Enable Pin Current Sink/Source ISW Switch Leakage VEN_TH (1) (2) nA 2.90 LM2736X FSW V %/V 10 UVLO Hysteresis UNIT 0.62 650 1.0 MHz m 2.3 A 2.5 mA nA mA 0.4 1.8 V 10 nA 40 nA Specified to Texas Instruments' Average Outgoing Quality Level (AOQL). Typicals represent the most likely parametric norm. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 5 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 6.6 Typical Characteristics All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 H ("X"), L1 = 10 H ("Y"), and TA = 25C, unless specified otherwise. 6 Figure 1. Oscillator Frequency vs Temperature - "X" Figure 2. Oscillator Frequency vs Temperature - "Y" Figure 3. Current Limit vs Temperature Figure 4. VFB vs Temperature Figure 5. RDSON vs Temperature Figure 6. IQ Switching vs Temperature Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 Typical Characteristics (continued) All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 H ("X"), L1 = 10 H ("Y"), and TA = 25C, unless specified otherwise. Figure 7. Line Regulation - "X" Figure 8. Line Regulation - "Y" VOUT = 3.3 V, IOUT = 500 mA VOUT = 3.3 V, IOUT = 500 mA Figure 9. Line Regulation - "X" Figure 10. Line Regulation - "Y" Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 7 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 7 Detailed Description 7.1 Overview The LM2736 device is a constant frequency PWM buck regulator IC that delivers a 750 mA load current. The regulator has a preset switching frequency of either 550 kHz (LM2736Y) or 1.6 MHz (LM2736X). These high frequencies allow the LM2736 device to operate with small surface mount capacitors and inductors, resulting in DC/DC converters that require a minimum amount of board space. The LM2736 device is internally compensated, so it is simple to use, and requires few external components. The LM2736 device uses currentmode control to regulate the output voltage. The following operating description of the LM2736 device will refer to the Simplified Block Diagram (Functional Block Diagram) and to the waveforms in Figure 11. The LM2736 device 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. VSW D = TON/TSW VIN SW Voltage TOFF TON 0 t VD IL TSW IPK Inductor Current t 0 Figure 11. LM2736 Waveforms of SW Pin Voltage and Inductor Current 8 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 7.2 Functional Block Diagram VIN VIN Current-Sense Amplifier EN OFF Internal Regulator and Enable Circuit + - BOOST VBOOST Under Voltage Lockout Oscillator CIN D2 Thermal Shutdown Current Limit Output Control Logic Reset Pulse + ISENSE + + Corrective Ramp 0.3: Switch Driver SW OVP Comparator - ON RSENSE Error Signal D 1 + PWM Comparator CBOOST VSW L IL VOUT COUT 1.375V + - R1 FB Internal Compensation + Error Amplifier + - VREF 1.25V R2 GND 7.3 Feature Description 7.3.1 Output Overvoltage Protection The overvoltage comparator compares the FB pin voltage to a voltage that is 10% higher than the internal reference Vref. Once the FB pin voltage goes 10% above the internal reference, the internal NMOS control switch is turned off, which allows the output voltage to decrease toward regulation. 7.3.2 Undervoltage Lockout Undervoltage lockout (UVLO) prevents the LM2736 device from operating until the input voltage exceeds 2.74 V (typ). The UVLO threshold has approximately 440mV of hysteresis, so the part will operate until VIN drops below 2.3 V (typ). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic. 7.3.3 Current Limit The LM2736 device 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 1.5 A (typ), and turns off the switch until the next switching cycle begins. 7.3.4 Thermal Shutdown Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature exceeds 165C. After thermal shutdown occurs, the output switch doesn't turn on until the junction temperature drops to approximately 150C. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 9 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 7.4 Device Functional Modes 7.4.1 Enable Pin / Shutdown Mode The LM2736 device 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 30 nA. Switch leakage adds another 40 nA from the input supply. The voltage at this pin should never exceed VIN + 0.3 V. 7.4.2 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 1.25 V in approximately 200 s. This forces the regulator output to ramp up in a more linear and controlled fashion, which helps reduce inrush current. 10 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 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 Boost Function Capacitor CBOOST and diode D2 in Figure 12 are used to generate a voltage VBOOST. VBOOST - VSW is the gate drive voltage to the internal NMOS control switch. To properly drive the internal NMOS switch during its on-time, VBOOST needs to be at least 1.6 V greater than VSW. Although the LM2736 device will operate with this minimum voltage, it may not have sufficient gate drive to supply large values of output current. Therefore, it is recommended that VBOOST be greater than 2.5 V above VSW for best efficiency. VBOOST - VSW should not exceed the maximum operating limit of 5.5 V. 5.5 V > VBOOST - VSW > 2.5 V for best performance. VBOOST D2 BOOST VIN VIN CIN CBOOST L SW VOUT GND D1 COUT Figure 12. VOUT Charges CBOOST When the LM2736 device 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 will continue to source current to CBOOST until the voltage at the feedback pin is greater than 1.18 V. There are various methods to derive VBOOST: 1. From the input voltage (VIN) 2. From the output voltage (VOUT) 3. From an external distributed voltage rail (VEXT) 4. From a shunt or series zener diode In the Functional Block Diagram, capacitor CBOOST and diode D2 supply the gate-drive current 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 11), 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 VBOOST - VSW = VIN - VFD2 + VFD1 (1) When the NMOS switch turns on (TON), the switch pin rises to VSW = VIN - (RDSON x IL), (2) forcing VBOOST to rise thus reverse biasing D2. The voltage at VBOOST is then VBOOST = 2VIN - (RDSON x IL) - VFD2 + VFD1 (3) which is approximately 2 VIN - 0.4 V (4) for many applications. Thus the gate-drive voltage of the NMOS switch is approximately Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 11 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com Application Information (continued) VIN - 0.2 V (5) An alternate method for charging CBOOST is to connect D2 to the output as shown in Figure 12. The output voltage should be between 2.5 V and 5.5 V, so that proper gate voltage will be applied to the internal switch. In this circuit, CBOOST provides a gate drive voltage that is slightly less than VOUT. 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 13. When using a series zener diode from the input, ensure that the regulation of the input supply doesn't create a voltage that falls outside the recommended VBOOST voltage. (VINMAX - VD3) < 5.5 V (VINMIN - VD3) > 1.6 V (6) (7) D2 D3 VIN VIN BOOST VBOOST CBOOST CIN L GND VOUT SW D1 COUT Figure 13. Zener Reduces Boost Voltage from VIN An alternative method is to place the zener diode D3 in a shunt configuration as shown in Figure 14. A small 350 mW to 500 mW 5.1 V zener in a SOT or SOD package can be used for this purpose. A small ceramic capacitor such as a 6.3 V, 0.1 F capacitor (C4) should 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. Resistor R3 should be chosen 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 following formula for the X version: IBOOST = 0.49 x (D + 0.54) x (VZENER - VD2) mA (8) IBOOST can be calculated for the Y version using the following: IBOOST = 0.20 x (D + 0.54) x (VZENER - VD2) A (9) where D is the duty cycle, VZENER and VD2 are in volts, and IBOOST is in milliamps. VZENER is the voltage applied to the anode of the boost diode (D2), and VD2 is the average forward voltage across D2. Note that this formula for IBOOST gives typical current. For the worst case IBOOST, increase the current by 40%. In that case, the worst case boost current will be IBOOST-MAX = 1.4 x IBOOST (10) R3 will then be given by R3 = (VIN - VZENER) / (1.4 x IBOOST + IZENER) (11) 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 IBOOST = 0.49 x (0.5 + 0.54) x (5 - 0.7) mA = 2.19mA R3 = (10 V - 5 V) / (1.4 x 2.19 mA + 1 mA) = 1.23 k 12 Submit Documentation Feedback (12) (13) Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 Application Information (continued) VZ C4 D2 D3 R3 VIN BOOST VIN VBOOST CBOOST CIN L VOUT SW GND COUT D1 Figure 14. Boost Voltage Supplied from the Shunt Zener on VIN 8.2 Typical Applications 8.2.1 LM2736X (1.6 MHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA D2 VIN BOOST VIN C3 C1 L1 R3 VOUT SW ON D1 EN C2 R1 OFF FB GND R2 Figure 15. LM2736X (1.6 MHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA 8.2.1.1 Design Requirements Derive charge for VBOOST from the input supply (VIN). VBOOST - VSW should not exceed the maximum operating limit of 5.5 V. 8.2.1.2 Detailed Design Procedures Table 1. Bill of Materials for Figure 15 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750 mA Buck Regulator LM2736X TI C1, Input Cap 10-F, 6.3V, X5R C3216X5ROJ106M TDK C2, Output Cap 10-F, 6.3V, X5R C3216X5ROJ106M TDK C3, Boost Cap 0.01-uF, 16V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.3 VF Schottky 1 A, 10 VR MBRM110L ON Semi D2, Boost Diode 1 VF @ 50 mA Diode 1N4148W Diodes, Inc. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 13 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com Typical Applications (continued) Table 1. Bill of Materials for Figure 15 (continued) PART ID PART VALUE PART NUMBER MANUFACTURER L1 4.7-H, 1.7 A, VLCF4020T- 4R7N1R2 TDK R1 2 k, 1% CRCW06032001F Vishay R2 10 k, 1% CRCW06031002F 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) as shown in Equation 14: VO D= VIN (14) The catch diode (D1) forward voltage drop and the voltage drop across the internal NMOS must be included to calculate a more accurate duty cycle. Use Equation 15 to Calculate D. VO + VD D= VIN + VD - VSW (15) VSW can be approximated by: VSW = IO x RDS(ON) (16) The diode forward drop (VD) can range from 0.3 V to 0.7 V depending on the quality of the diode. The lower VD is, 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 will decrease the output ripple current. The ratio of ripple current (iL) to output current (IO) is optimized when it is set between 0.3 and 0.4 at 750 mA. The ratio r is defined in . r= 'iL lO (17) One must also ensure that the minimum current limit (1.0 A) is not exceeded, so the peak current in the inductor must be calculated. Use Equation 18 to calculate the peak current (ILPK) in the inductor. ILPK = IO + IL/2 (18) If r = 0.7 at an output of 750 mA, the peak current in the inductor will be 1.0125 A. The minimum ensured current limit over all operating conditions is 1.0 A. One can either reduce r to 0.6 resulting in a 975 mA peak current, or make the engineering judgement that 12.5 mA over will be safe enough with a 1.5 A typical current limit and 6 sigma limits. When the designed maximum output current is reduced, the ratio r can be increased. At a current of 0.1 A, r can be made as high as 0.9. The ripple ratio can be increased at lighter loads because the net ripple is actually quite low, and if r remains constant the inductor value can be made quite large. Equation 19 is empirically developed for the maximum ripple ratio at any current below 2 A. r = 0.387 x IOUT-0.3667 (19) Note that this is just a guideline. The LM2736 device 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 or ripple ratio is determined, the inductance is calculated using Equation 20 L= 14 VO + VD IO x r x fS x (1-D) (20) Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 where fs is the switching frequency and IO is the output current. When selecting an inductor, make sure that it is capable of supporting the peak output current without saturating. Inductor saturation will result in a sudden reduction in inductance and prevent 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 0.5 A and the peak current is 0.7 A, then the inductor should be specified with a saturation current limit of >0.7 A. There is no need to specify the saturation or peak current of the inductor at the 1.5 A typical switch current limit. The difference in inductor size is a factor of 5. Because of the operating frequency of the LM2736, ferrite based inductors are preferred to minimize core losses. This presents little restriction since the variety of ferrite based inductors is huge. Lastly, inductors with lower series resistance (DCR) will provide better operating efficiency. For recommended inductors see Example Circuits. 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 ESL (Equivalent Series Inductance). The recommended input capacitance is 10-F, although 4.7-F works well for input voltages below 6 V. 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: IRMS-IN = IO x r2 D x 1-D + 12 (21) It can be shown from the above equation 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 will have high ESL and a 0805 ceramic chip capacitor will have very low ESL. At the operating frequencies of the LM2736, certain capacitors may have an ESL so large that the resulting impedance (2fL) will be higher than that required to provide stable operation. As a result, surface mount capacitors are strongly recommended. Sanyo POSCAP, Tantalum or Niobium, Panasonic SP or Cornell Dubilier ESR, and multilayer ceramic capacitors (MLCC) are all good choices for both input and output capacitors and have very low ESL. For MLCCs it is recommended to use X7R or X5R dielectrics. Consult capacitor manufacturer datasheet 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: 'VO = 'iL x (RESR + 1 ) 8 x fS x CO (22) When using MLCCs, the ESR is typically so low that the capacitive ripple may dominate. When this occurs, the output ripple will be 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 LM2736, there is really no need to review any other capacitor technologies. Another benefit of ceramic capacitors is their ability to bypass high frequency noise. A certain amount of switching edge noise will couple through parasitic capacitances in the inductor to the output. A ceramic capacitor will bypass this noise while a tantalum will not. Since the output capacitor is one of the two external components that control the stability of the regulator control loop, most applications will require a minimum at 10-F of output capacitance. Capacitance can be increased significantly with little detriment to the regulator stability. Like the input capacitor, recommended multilayer ceramic capacitors are X7R or X5R. Again, verify actual capacitance at the desired operating voltage and temperature. Check the RMS current rating of the capacitor. The RMS current rating of the capacitor chosen must also meet the following condition: IRMS-OUT = IO x r 12 (23) Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 15 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 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 should be chosen so that its current rating is greater than: ID1 = IO x (1-D) (24) 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 Boost Diode A standard diode such as the 1N4148 type is recommended. For VBOOST circuits derived from voltages less than 3.3 V, a small-signal Schottky diode is recommended for greater efficiency. A good choice is the BAT54 small signal diode. 8.2.1.2.6 Boost Capacitor A ceramic 0.01-F capacitor with a voltage rating of at least 16 V is sufficient. The X7R and X5R MLCCs provide the best performance. 8.2.1.2.7 Output Voltage The output voltage is set using the following equation where R2 is connected between the FB pin and GND, and R1 is connected between VO and the FB pin. A good value for R2 is 10 k. R1 = VO VREF - 1 x R2 (25) 8.2.1.3 Application Curves VOUT = 5 V VOUT = 5 V Figure 16. Efficiency vs Load Current - "X" 16 Submit Documentation Feedback Figure 17. Efficiency vs Load Current - "Y" Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 VOUT = 3.3 V VOUT = 3.3 V Figure 18. Efficiency vs Load Current - "X" VOUT = 1.5 V Figure 19. Efficiency vs Load Current - "Y" VOUT = 1.5 V Figure 20. Efficiency vs Load Current - "X" Figure 21. Efficiency vs Load Current - "Y" Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 17 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 8.2.2 LM2736X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA D2 VIN BOOST VIN C3 C1 R3 L1 SW ON VOUT D1 C2 EN OFF R1 FB GND R2 Figure 22. LM2736X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA 8.2.2.1 Design Requirements Derive charge for VBOOST from the output voltage, (VOUT). The output voltage should be between 2.5V and 5.5V. 8.2.2.2 Detailed Design Procedures Table 2. Bill of Materials for Figure 22 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750mA Buck Regulator LM2736X TI C1, Input Cap 10F, 25V, X7R C3225X7R1E106M TDK C2, Output Cap 22F, 6.3V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.01F, 16V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.34VF Schottky 1A, 30VR SS1P3L Vishay D2, Boost Diode 30V, 200 mA Schottky BAT54 Diodes Inc. L1 4.7H, 1.7A, VLCF4020T- 4R7N1R2 TDK R1 16.5k, 1% CRCW06031652F Vishay R2 10.0 k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay Please refer to Detailed Design Procedures. 8.2.2.3 Application Curves Please refer to Application Curves 18 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 8.2.3 LM2736X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA C4 D3 R4 D2 BOOST VIN VIN C3 C1 R3 L1 VOUT SW ON D1 C2 EN OFF R1 FB GND R2 Figure 23. LM2736X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA 8.2.3.1 Design Requirements An alternative method when VIN is greater than 5.5V is to place the zener diode D3 in a shunt configuration. A small 350 mW to 500 mW 5.1 V zener in a SOT or SOD package can be used for this purpose. A small ceramic capacitor such as a 6.3 V, 0.1 F capacitor (C4) should 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 8.2.3.2 Detailed Design Procedure Table 3. Bill of Materials for Figure 23 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750mA Buck Regulator LM2736X TI C1, Input Cap 10F, 25V, X7R C3225X7R1E106M TDK C2, Output Cap 22F, 6.3V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.01F, 16V, X7R C1005X7R1C103K TDK C4, Shunt Cap 0.1F, 6.3V, X5R C1005X5R0J104K TDK D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc. D3, Zener Diode 5.1V 250Mw SOT BZX84C5V1 Vishay L1 6.8H, 1.6A, SLF7032T-6R8M1R6 TDK R1 2k, 1% CRCW06032001F Vishay R2 10k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay R4 4.12k, 1% CRCW06034121F Vishay Please refer to Detailed Design Procedures. 8.2.3.3 Application Curves Please refer to Application Curves. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 19 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 8.2.4 LM2736X (1.6 MHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA D3 D2 BOOST VIN VIN C1 C3 L1 R3 VOUT SW ON D1 EN C2 R1 OFF FB GND R2 Figure 24. LM2736X (1.6 MHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA 8.2.4.1 Design Requirements 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 is greater than 5.5 V, CBOOST can be charged from VIN minus a zener voltage by placing a zener diode D3 in series with D2. When using a series zener diode from the input, ensure that the regulation of the input supply doesn't create a voltage that falls outside the recommended VBOOST voltage. (VINMAX - VD3) < 5.5 V (VINMIN - VD3) > 1.6 V (26) (27) 8.2.4.2 Detailed Design Procedure Table 4. Bill of Materials for Figure 24 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750 mA Buck Regulator LM2736X TI C1, Input Cap 10-F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 22-F, 6.3 V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.01-F, 16 V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.4 VF Schottky 1 A, 30VR SS1P3L Vishay D2, Boost Diode 1VF @ 50 mA Diode 1N4148W Diodes, Inc. D3, Zener Diode 11 V 350 Mw SOT BZX84C11T Diodes, Inc. L1 6.8H, 1.6 A, SLF7032T-6R8M1R6 TDK R1 2 k, 1% CRCW06032001F Vishay R2 10 k, 1% CRCW06031002F Vishay R3 100 k, 1% CRCW06031003F Vishay Please refer to Detailed Design Procedures. 8.2.4.3 Application Curves Please refer to Application Curves 20 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 8.2.5 LM2736X (1.6 MHz) VBOOST Derived from Series Zener Diode (VOUT) 15 V to 9 V / 750 mA D3 D2 VIN BOOST VIN C3 C1 R3 L1 VOUT SW ON D1 EN C2 R1 OFF FB GND R2 Figure 25. 8.2.5.1 Design Requirements 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 VOUT minus a zener voltage by placing a zener diode D3 in series with D2. 8.2.5.2 Detailed Design Procedure Table 5. Bill of Materials for Figure 25 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750mA Buck Regulator LM2736X TI C1, Input Cap 10F, 25V, X7R C3225X7R1E106M TDK C2, Output Cap 22F, 16V, X5R C3216X5R1C226M TDK C3, Boost Cap 0.01F, 16V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc. D3, Zener Diode 4.3V 350mw SOT BZX84C4V3 Diodes, Inc. L1 6.8H, 1.6A, SLF7032T-6R8M1R6 TDK R1 61.9k, 1% CRCW06036192F Vishay R2 10k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay Please refer to Detailed Design Procedures. 8.2.5.3 Application Curves Please refer to Application Curves Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 21 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 8.2.6 LM2736Y (550 kHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA D2 VIN BOOST VIN C3 C1 L1 R3 VOUT SW ON D1 EN C2 R1 OFF FB GND R2 Figure 26. LM2736Y (550 kHz) VBOOST Derived from VIN 5 V to 1.5 V / 750 mA 8.2.6.1 Design Requirements Derive charge for VBOOST from the input voltage, (VIN). VBOOST should be greater than 2.5 V above VSW for best efficiency. VBOOST - VSW should not exceed the maximum operating limit of 5.5 V. 8.2.6.2 Detailed Design Procedure Table 6. Bill of Materials for Figure 26 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750mA Buck Regulator LM2736Y TI C1, Input Cap 10F, 6.3V, X5R C3216X5ROJ106M TDK C2, Output Cap 22F, 6.3V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.01F, 16V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.3VF Schottky 1A, 10VR MBRM110L ON Semi D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc. L1 10H, 1.6A, SLF7032T-100M1R4 TDK R1 2k, 1% CRCW06032001F Vishay R2 10k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay Please refer toDetailed Design Procedures. 8.2.6.3 Application Curves Please refer to Application Curves. 22 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 8.2.7 LM2736Y (550 kHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA D2 VIN BOOST VIN C3 C1 R3 L1 SW ON VOUT D1 C2 EN OFF R1 FB GND R2 Figure 27. LM2736Y (550 kHz) VBOOST Derived from VOUT 12 V to 3.3 V / 750 mA 8.2.7.1 Design Requirements Derive charge for VBOOST from the output voltage, (VOUT). The output voltage should be between 2.5V and 5.5V. 8.2.7.2 Detailed Design Procedure Table 7. Bill of Materials for Figure 27 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750mA Buck Regulator LM2736Y TI C1, Input Cap 10F, 25V, X7R C3225X7R1E106M TDK C2, Output Cap 22F, 6.3V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.01F, 16V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.34VF Schottky 1A, 30VR SS1P3L Vishay D2, Boost Diode 30V, 200 mA Schottky BAT54 Diodes Inc. L1 10H, 1.6A, SLF7032T-100M1R4 TDK R1 16.5k, 1% CRCW06031652F Vishay R2 10.0 k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay Please refer to Detailed Design Procedures. 8.2.7.3 Application Curves Please refer to Application Curves. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 23 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 8.2.8 LM2736Y (550 kHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA C4 D3 R4 D2 BOOST VIN VIN C3 C1 R3 L1 VOUT SW ON D1 C2 EN OFF R1 FB GND R2 Figure 28. LM2736Y (550 kHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 750 mA 8.2.8.1 Design Requirements An alternative method when VIN is greater than 5.5V is to place the zener diode D3 in a shunt configuration. A small 350 mW to 500 mW 5.1 V zener in a SOT or SOD package can be used for this purpose. A small ceramic capacitor such as a 6.3 V, 0.1 F capacitor (C4) should 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. 8.2.8.2 Detailed Design Procedure Table 8. Bill of Materials for Figure 28 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750mA Buck Regulator LM2736Y TI C1, Input Cap 10F, 25V, X7R C3225X7R1E106M TDK C2, Output Cap 22F, 6.3V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.01F, 16V, X7R C1005X7R1C103K TDK C4, Shunt Cap 0.1F, 6.3V, X5R C1005X5R0J104K TDK D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc. D3, Zener Diode 5.1V 250Mw SOT BZX84C5V1 Vishay L1 15H, 1.5A SLF7045T-150M1R5 TDK R1 2k, 1% CRCW06032001F Vishay R2 10k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay R4 4.12k, 1% CRCW06034121F Vishay Please refer to Detailed Design Procedures. 8.2.8.3 Application Curves Please refer to Application Curves. 24 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 8.2.9 LM2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA D3 D2 BOOST VIN VIN C1 C3 L1 R3 VOUT SW ON D1 EN C2 R1 OFF FB GND R2 Figure 29. M2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 750 mA 8.2.9.1 Design Requirements 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 is greater than 5.5 V, CBOOST can be charged from VIN minus a zener voltage by placing a zener diode D3 in series with D2. When using a series zener diode from the input, ensure that the regulation of the input supply doesn't create a voltage that falls outside the recommended VBOOST voltage. (VINMAX - VD3) < 5.5 V (VINMIN - VD3) > 1.6 V (28) (29) 8.2.9.2 Detailed Design Procedure Table 9. Bill of Materials for Figure 29 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750mA Buck Regulator LM2736Y TI C1, Input Cap 10F, 25V, X7R C3225X7R1E106M TDK C2, Output Cap 22F, 6.3V, X5R C3216X5ROJ226M TDK C3, Boost Cap 0.01F, 16V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.4VF Schottky 1A, 30VR SS1P3L Vishay D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc. D3, Zener Diode 11V 350Mw SOT BZX84C11T Diodes, Inc. L1 15H, 1.5A, SLF7045T-150M1R5 TDK R1 2k, 1% CRCW06032001F Vishay R2 10k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay Please refer to Detailed Design Procedures. 8.2.9.3 Application Curves Please refer to Application Curves. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 25 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 8.2.10 LM2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VOUT) 15 V to 9 V / 750 mA D3 D2 VIN BOOST VIN C3 C1 R3 L1 VOUT SW ON D1 EN C2 R1 OFF FB GND R2 Figure 30. LM2736Y (550 kHz) VBOOST Derived from Series Zener Diode (VOUT) 15 V to 9 V / 750 mA 8.2.10.1 Design Requirements 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 VOUT minus a zener voltage by placing a zener diode D3 in series with D2. 8.2.10.2 Detailed Design Procedure Table 10. Bill of Materials for Figure 30 PART ID PART VALUE PART NUMBER MANUFACTURER U1 750 mA Buck Regulator LM2736Y TI C1, Input Cap 10-F, 25 V, X7R C3225X7R1E106M TDK C2, Output Cap 22-F, 16 V, X5R C3216X5R1C226M TDK C3, Boost Cap 0.01-F, 16 V, X7R C1005X7R1C103K TDK D1, Catch Diode 0.4 VF Schottky 1 A, 30 VR SS1P3L Vishay D2, Boost Diode 1 VF @ 50 mA Diode 1N4148W Diodes, Inc. D3, Zener Diode 4.3 V 350 mw SOT BZX84C4V3 Diodes, Inc. L1 22 H, 1.4 A, SLF7045T-220M1R3-1PF TDK R1 61.9 k, 1% CRCW06036192F Vishay R2 10 k, 1% CRCW06031002F Vishay R3 100 k, 1% CRCW06031003F Vishay Please refer to Detailed Design Procedures. 8.2.10.3 Application Curves Please refer to Application Curves. 26 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 9 Power Supply Recommendations Input voltage is rated as 3 V to 18 V however care should be taken in certain circuit configurations eg. VBOOST derived from VIN where the requirement that VBOOST - VSW < 5.5 V should be observed. Also for best efficiency VBOOST should be at least 2.5 V above VSW. The voltage on the Enable pin should 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 when completing the layout is the close coupling of the GND connections of the CIN capacitor and the catch diode D1. These ground ends should be close to one another and be connected to the GND plane with at least two through-holes. Place these components as close to the IC as possible. Next in importance is the location of the GND connection of the COUT capacitor, which should be near the GND connections of CIN and D1. There should be a continuous ground plane on the bottom layer of a two-layer board except under the switching node island. The FB pin is a high impedance node and care should be taken to make the FB trace short to avoid noise pickup and inaccurate regulation. The feedback resistors should be placed as close as possible to the IC, with the GND of R2 placed as close as possible to the GND of the IC. The VOUT trace to R1 should 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 should be as short and wide as possible. However, making the traces wide increases radiated noise, so the designer must make this trade-off. Radiated noise can be decreased by choosing a shielded inductor. The remaining components should also be placed as close as possible to the IC. Please see Application Note AN-1229 SNVA054 for further considerations and the LM2736 device demo board as an example of a four-layer layout. Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 27 LM2736 SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 www.ti.com 10.2 Layout Example Figure 31. Top Layer D2 VIN VIN BOOST C3 C1 R5 L1 VOUT SW D1 VEN C2 R1 EN FB GND R2 Figure 32. Layout Schematic 28 Submit Documentation Feedback Copyright (c) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 LM2736 www.ti.com SNVS316H - SEPTEMBER 2004 - REVISED DECEMBER 2014 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 Trademarks WEBENCH, SIMPLE SWITCHER are registered trademarks of Texas Instruments. All other trademarks are the property of their respective owners. 11.4 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. 11.5 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) 2004-2014, Texas Instruments Incorporated Product Folder Links: LM2736 29 PACKAGE OPTION ADDENDUM www.ti.com 6-Feb-2020 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) LM2736XMK NRND SOT-23-THIN DDC 6 1000 TBD Call TI Call TI -40 to 125 SHAB LM2736XMK/NOPB ACTIVE SOT-23-THIN DDC 6 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHAB LM2736XMKX/NOPB ACTIVE SOT-23-THIN DDC 6 3000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHAB LM2736YMK NRND SOT-23-THIN DDC 6 1000 TBD Call TI Call TI -40 to 125 SHBB LM2736YMK/NOPB ACTIVE SOT-23-THIN DDC 6 1000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHBB LM2736YMKX/NOPB ACTIVE SOT-23-THIN DDC 6 3000 Green (RoHS & no Sb/Br) SN Level-1-260C-UNLIM -40 to 125 SHBB (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) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based flame retardants must also meet the <=1000ppm threshold requirement. (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/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 6-Feb-2020 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. 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Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 29-Sep-2019 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) LM2736XMK SOT23-THIN DDC 6 1000 178.0 8.4 LM2736XMK/NOPB SOT23-THIN DDC 6 1000 178.0 LM2736XMKX/NOPB SOT23-THIN DDC 6 3000 LM2736YMK SOT23-THIN DDC 6 LM2736YMK/NOPB SOT23-THIN DDC LM2736YMKX/NOPB SOT23-THIN DDC 3.2 3.2 1.4 4.0 8.0 Q3 8.4 3.2 3.2 1.4 4.0 8.0 Q3 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3 6 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3 Pack Materials-Page 1 W Pin1 (mm) Quadrant PACKAGE MATERIALS INFORMATION www.ti.com 29-Sep-2019 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM2736XMK SOT-23-THIN DDC 6 1000 210.0 185.0 35.0 LM2736XMK/NOPB SOT-23-THIN DDC 6 1000 210.0 185.0 35.0 LM2736XMKX/NOPB SOT-23-THIN DDC 6 3000 210.0 185.0 35.0 LM2736YMK SOT-23-THIN DDC 6 1000 210.0 185.0 35.0 LM2736YMK/NOPB SOT-23-THIN DDC 6 1000 210.0 185.0 35.0 LM2736YMKX/NOPB SOT-23-THIN DDC 6 3000 210.0 185.0 35.0 Pack Materials-Page 2 PACKAGE OUTLINE DDC0006A SOT - 1.1 max height SCALE 4.000 SOT 3.05 2.55 1.75 1.45 PIN 1 INDEX AREA 1.1 MAX B 1 0.1 C A 6 4X 0.95 3.05 2.75 1.9 4 3 0.5 0.3 0.2 0.1 TYP 0.0 6X 0 -8 TYP 0.20 TYP 0.12 C A B C SEATING PLANE 0.6 TYP 0.3 0.25 GAGE PLANE 4214841/A 08/2016 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. Reference JEDEC MO-193. www.ti.com EXAMPLE BOARD LAYOUT DDC0006A SOT - 1.1 max height SOT SYMM 6X (1.1) 1 6 6X (0.6) SYMM 4X (0.95) 4 3 (R0.05) TYP (2.7) LAND PATTERN EXAMPLE EXPLOSED METAL SHOWN SCALE:15X SOLDER MASK OPENING METAL UNDER SOLDER MASK METAL SOLDER MASK OPENING EXPOSED METAL EXPOSED METAL 0.07 MIN ARROUND 0.07 MAX ARROUND NON SOLDER MASK DEFINED SOLDER MASK DEFINED SOLDERMASK DETAILS 4214841/A 08/2016 NOTES: (continued) 4. Publication IPC-7351 may have alternate designs. 5. Solder mask tolerances between and around signal pads can vary based on board fabrication site. www.ti.com EXAMPLE STENCIL DESIGN DDC0006A SOT - 1.1 max height SOT SYMM 6X (1.1) 1 6 6X (0.6) SYMM 4X(0.95) 4 3 (R0.05) TYP (2.7) SOLDER PASTE EXAMPLE BASED ON 0.125 THICK STENCIL SCALE:15X 4214841/A 08/2016 NOTES: (continued) 6. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate design recommendations. 7. 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