LM2734 LM2734 Thin SOT23 1A Load Step-Down DC-DC Regulator Literature Number: SNVS288H LM2734 Thin SOT23 1A Load Step-Down DC-DC Regulator General Description Features The LM2734 regulator is a monolithic, high frequency, PWM step-down DC/DC converter in a 6-pin Thin SOT23 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. With a minimum of external components and online design support through WEBENCH(R)TM, the LM2734 is easy to use. The ability to drive 1A loads with an internal 300m NMOS switch using state-of-the-art 0.5m BiCMOS technology results in the best power density available. The world class control circuitry allows for on-times as low as 13ns, thus supporting exceptionally high frequency conversion over the entire 3V to 20V input operating range down to the minimum output voltage of 0.8V. Switching frequency is internally set to 550kHz (LM2734Y) or 1.6MHz (LM2734X), 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 30nA. The LM2734 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 inrush current, pulse-by-pulse current limit, thermal shutdown, and output over-voltage protection. Thin SOT23-6 package 3.0V to 20V input voltage range 0.8V to 18V output voltage range 1A output current 550kHz (LM2734Y) and 1.6MHz (LM2734X) switching frequencies 300m NMOS switch 30nA shutdown current 0.8V, 2% internal voltage reference Internal soft-start Current-Mode, PWM operation WEBENCH(R) online design tool Thermal shutdown LM2734XQ/LM2734YQ are AEC-Q100 Grade 1 qualified and are manufactured on an Automotive Grade Flow Applications Local Point of Load Regulation Core Power in HDDs Set-Top Boxes Battery Powered Devices USB Powered Devices DSL Modems Notebook Computers Automotive Typical Application Circuit Efficiency vs Load Current VIN = 5V, VOUT = 3.3V 20102301 20102345 WEBENCHTM is a trademark of Transim. (c) 2010 National Semiconductor Corporation 201023 www.national.com LM2734 Thin SOT23 1A Load Step-Down DC-DC Regulator June 21, 2010 LM2734 Connection Diagrams 20102360 20102305 Pin 1 Indentification 6-Lead TSOT NS Package Number MK06A Ordering Information Order Number Package Type NSC Package Drawing Package Marking Supplied As LM2734XMK SFDB 1000 Units on Tape and Reel LM2734XMKX SFDB 3000 Units on Tape and Reel LM2734XQMKE SUKB 250 Units on Tape and Reel LM2734XQMK SUKB LM2734XQMKX LM2734YMK TSOT-6 MK06A Features SUKB AEC-Q100 Grade 1 Qualified. Automotive 1000 Units on Tape and Reel Grade Production Flow* 3000 Units on Tape and Reel SFEB 1000 Units on Tape and Reel 3000 Units on Tape and Reel LM2734YMKX SFEB LM2734YQMKE SVCB LM2734YQMK SVCB LM2734YQMKX SVCB 250 Units on Tape and Reel AEC-Q10-0 Grade 1 Qualified. Automotive 3000 Units on Tape and Reel Grade Production Flow* 1000 Units on Tape and Reel *Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including defect detection methodologies. Reliability qualification is compliant with the requirements and temperature grades defined in the AEC-Q100 standard. Automotive grade products are identified with the letter Q. For more information go to http://www.national.com/automotive. Pin Descriptions Pin Name Function 1 BOOST Boost voltage that drives the internal NMOS control switch. A bootstrap capacitor is connected between the BOOST and SW pins. 2 GND 3 FB Feedback pin. Connect FB to the external resistor divider to set output voltage. 4 EN Enable control input. Logic high enables operation. Do not allow this pin to float or be greater than VIN + 0.3V. 5 VIN Input supply voltage. Connect a bypass capacitor to this pin. 6 SW Output switch. Connects to the inductor, catch diode, and bootstrap capacitor. www.national.com Signal and Power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin for accurate regulation. 2 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN SW Voltage Boost Voltage Boost to SW Voltage FB Voltage EN Voltage Junction Temperature ESD Susceptibility (Note 2) Operating Ratings -0.5V to 24V -0.5V to 24V -0.5V to 30V -0.5V to 6.0V -0.5V to 3.0V -0.5V to (VIN + 0.3V) 150C 2kV -65C to 150C 260C (Note 1) VIN SW Voltage Boost Voltage Boost to SW Voltage Junction Temperature Range 3V to 20V -0.5V to 20V -0.5V to 25V 1.6V to 5.5V -40C to +125C Thermal Resistance JA (Note 3) 118C/W Electrical Characteristics Specifications with standard typeface are for TJ = 25C, and those in boldface type apply over the full Operating Temperature Range (TJ = -40C to 125C). VIN = 5V, VBOOST - VSW = 5V unless otherwise specified. Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Symbol VFB Parameter Conditions Feedback Voltage Min (Note 4) Typ (Note 5) Max (Note 4) Units 0.784 0.800 0.816 V VFB/VIN Feedback Voltage Line Regulation VIN = 3V to 20V IFB UVLO Feedback Input Bias Current Sink/Source Undervoltage Lockout VIN Rising Undervoltage Lockout VIN Falling 0.01 Switching Frequency DMAX Maximum Duty Cycle DMIN Minimum Duty Cycle RDS(ON) 10 250 2.74 2.90 V 2.0 2.3 0.44 0.62 LM2734X 1.2 1.6 1.9 LM2734Y 0.40 0.55 0.66 LM2734X 85 92 LM2734Y 90 96 LM2734X 2 LM2734Y 1 % VBOOST - VSW = 3V ICL Switch Current Limit VBOOST - VSW = 3V IQ Quiescent Current Switching Quiescent Current (shutdown) VEN = 0V 30 LM2734X (50% Duty Cycle) 2.5 3.5 LM2734Y (50% Duty Cycle) 1.0 1.8 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 MHz % Switch ON Resistance IBOOST nA 0.30 UVLO Hysteresis FSW %/V 300 600 1.7 2.5 A 1.5 2.5 mA nA 0.4 1.8 m mA V 10 nA 40 nA Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see Electrical Characteristics. Note 2: Human body model, 1.5k in series with 100pF. Note 3: 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. Note 4: Guaranteed to National's Average Outgoing Quality Level (AOQL). Note 5: Typicals represent the most likely parametric norm. 3 www.national.com LM2734 Storage Temp. Range Soldering Information Reflow Peak Pkg. Temp.(15sec) Absolute Maximum Ratings (Note 1) LM2734 Typical Performance 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. Efficiency vs Load Current - "X" VOUT = 5V Efficiency vs Load Current - "Y" VOUT = 5V 20102336 20102334 Efficiency vs Load Current - "X" VOUT = 3.3V Efficiency vs Load Current - "Y" VOUT = 3.3V 20102351 20102352 Efficiency vs Load Current - "X" VOUT = 1.5V Efficiency vs Load Current - "Y" VOUT = 1.5V 20102337 20102335 www.national.com 4 Oscillator Frequency vs Temperature - "Y" 20102327 20102328 Current Limit vs Temperature VIN = 5V Current Limit vs Temperature VIN = 20V 20102329 20102347 VFB vs Temperature RDSON vs Temperature 20102333 20102330 5 www.national.com LM2734 Oscillator Frequency vs Temperature - "X" LM2734 IQ Switching vs Temperature Line Regulation - "X" VOUT = 1.5V, IOUT = 500mA 20102346 20102356 Line Regulation - "Y" VOUT = 1.5V, IOUT = 500mA Line Regulation - "X" VOUT = 3.3V, IOUT = 500mA 20102354 20102355 Line Regulation - "Y" VOUT = 3.3V, IOUT = 500mA 20102353 www.national.com 6 LM2734 Block Diagram 20102306 FIGURE 1. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage. Application Information THEORY OF OPERATION The LM2734 is a constant frequency PWM buck regulator IC that delivers a 1A load current. The regulator has a preset switching frequency of either 550kHz (LM2734Y) or 1.6MHz (LM2734X). These high frequencies allow the LM2734 to operate with small surface mount capacitors and inductors, resulting in DC/DC converters that require a minimum amount of board space. The LM2734 is internally compensated, so it is simple to use, and requires few external components. The LM2734 uses current-mode control to regulate the output voltage. The following operating description of the LM2734 will refer to the Simplified Block Diagram (Figure 1) and to the waveforms in Figure 2. The LM2734 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. 20102307 FIGURE 2. LM2734 Waveforms of SW Pin Voltage and Inductor Current BOOST FUNCTION Capacitor CBOOST and diode D2 in Figure 3 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 1.6V greater than VSW. Although the LM2734 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 2.5V above VSW 7 www.national.com LM2734 for best efficiency. VBOOST - VSW should not exceed the maximum operating limit of 5.5V. 5.5V > VBOOST - VSW > 2.5V for best performance. (VINMAX - VD3) < 5.5V (VINMIN - VD3) > 1.6V 20102309 20102308 FIGURE 4. Zener Reduces Boost Voltage from VIN FIGURE 3. VOUT Charges CBOOST An alternative method is to place the zener diode D3 in a shunt configuration as shown in Figure 5. A small 350mW to 500mW 5.1V zener in a SOT-23 or SOD package can be used for this purpose. A small ceramic capacitor such as a 6.3V, 0.1F 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 I BOOST 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: When the LM2734 starts up, internal circuitry from the BOOST pin supplies a maximum of 20mA 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 0.76V. 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 Simplifed Block Diagram of Figure 1, 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 2), 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 IBOOST = 0.56 x (D + 0.54) x (VZENER - VD2) mA IBOOST can be calculated for the Y version using the following: IBOOST = 0.22 x (D + 0.54) x (VZENER - VD2) A 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 VBOOST - VSW = VIN - VFD2 + VFD1 When the NMOS switch turns on (TON), the switch pin rises to VSW = VIN - (RDSON x IL), IBOOST-MAX = 1.4 x IBOOST forcing VBOOST to rise thus reverse biasing D2. The voltage at VBOOST is then R3 will then be given by R3 = (VIN - VZENER) / (1.4 x IBOOST + IZENER) VBOOST = 2VIN - (RDSON x IL) - VFD2 + VFD1 For example, using the X-version let VIN = 10V, VZENER = 5V, VD2 = 0.7V, IZENER = 1mA, and duty cycle D = 50%. Then which is approximately 2VIN - 0.4V IBOOST = 0.56 x (0.5 + 0.54) x (5 - 0.7) mA = 2.5mA for many applications. Thus the gate-drive voltage of the NMOS switch is approximately R3 = (10V - 5V) / (1.4 x 2.5mA + 1mA) = 1.11k VIN - 0.2V An alternate method for charging CBOOST is to connect D2 to the output as shown in Figure 3. The output voltage should be between 2.5V and 5.5V, 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 5.5V, or less than 3V, CBOOST cannot be charged directly from these voltages. If VIN and VOUT are greater than 5.5V, 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 4. 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. www.national.com 8 Design Guide INDUCTOR SELECTION The Duty Cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN): 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. Calculate D by using the following formula: 20102348 FIGURE 5. Boost Voltage Supplied from the Shunt Zener on VIN ENABLE PIN / SHUTDOWN MODE The LM2734 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 30nA. Switch leakage adds another 40nA from the input supply. The voltage at this pin should never exceed VIN + 0.3V. VSW can be approximated by: VSW = IO x RDS(ON) The diode forward drop (VD) can range from 0.3V to 0.7V 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 1A. The ratio r is defined as: 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 0V to its nominal value of 0.8V in approximately 200s. This forces the regulator output to ramp up in a more linear and controlled fashion, which helps reduce inrush current. Under some circumstances at start-up, an output voltage overshoot may still be observed. This may be due to a large output load applied during start up. Large amounts of output external capacitance can also increase output voltage overshoot. A simple solution is to add a feed forward capacitor with a value between 470pf and 1000pf across the top feedback resistor (R1). See Figure 7 for further detail. One must also ensure that the minimum current limit (1.2A) is not exceeded, so the peak current in the inductor must be calculated. The peak current (ILPK) in the inductor is calculated by: 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. ILPK = IO + IL/2 If r = 0.5 at an output of 1A, the peak current in the inductor will be 1.25A. The minimum guaranteed current limit over all operating conditions is 1.2A. One can either reduce r to 0.4 resulting in a 1.2A peak current, or make the engineering judgement that 50mA over will be safe enough with a 1.7A 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 0.1A, 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. An equation empirically developed for the maximum ripple ratio at any current below 2A is: UNDERVOLTAGE LOCKOUT Undervoltage lockout (UVLO) prevents the LM2734 from operating until the input voltage exceeds 2.74V(typ). The UVLO threshold has approximately 440mV of hysteresis, so the part will operate until VIN drops below 2.3V(typ). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic. CURRENT LIMIT The LM2734 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 1.7A (typ), and turns off the switch until the next switching cycle begins. r = 0.387 x IOUT-0.3667 Note that this is just a guideline. The LM2734 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 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 9 www.national.com LM2734 doesn't turn on until the junction temperature drops to approximately 150C. LM2734 capacitor section for more details on calculating output voltage ripple. Now that the ripple current or ripple ratio is determined, the inductance is calculated by: 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: 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 0.5A and the peak current is 0.7A, then the inductor should be specified with a saturation current limit of >0.7A. There is no need to specify the saturation or peak current of the inductor at the 1.7A typical switch current limit. The difference in inductor size is a factor of 5. Because of the operating frequency of the LM2734, 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. 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 LM2734, 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: 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 10F, although 4.7F works well for input voltages below 6V. 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: 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) 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. 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 LM2734, 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. www.national.com BOOST DIODE A standard diode such as the 1N4148 type is recommended. For VBOOST circuits derived from voltages less than 3.3V, a small-signal Schottky diode is recommended for greater efficiency. A good choice is the BAT54 small signal diode. BOOST CAPACITOR A ceramic 0.01F capacitor with a voltage rating of at least 6.3V is sufficient. The X7R and X5R MLCCs provide the best performance. 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 10k. 10 PCB Layout Considerations When planning layout there are a few things to consider when trying to achieve a clean, regulated output. The most important consideration 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. 11 www.national.com LM2734 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 for further considerations and the LM2734 demo board as an example of a four-layer layout. LM2734 LM2734X Circuit Examples 20102342 FIGURE 6. LM2734X (1.6MHz) VBOOST Derived from VIN 5V to 1.5V/1A Bill of Materials for Figure 6 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734X National Semiconductor C1, Input Cap 10F, 6.3V, X5R C3216X5ROJ106M TDK C2, Output Cap 10F, 6.3V, X5R C3216X5ROJ106M TDK C3, Boost Cap 0.01uF, 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 4.7H, 1.7A, VLCF4020T- 4R7N1R2 TDK R1 8.87k, 1% CRCW06038871F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay www.national.com 12 LM2734 20102343 FIGURE 7. LM2734X (1.6MHz) VBOOST Derived from VOUT 12V to 3.3V/1A Bill of Materials for Figure 7 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator NSC LM2734X 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 CFF 1000pF 25V C0603X5R1E102K TDK D1, Catch Diode 0.34VF Schottky 1A, 30VR SS1P3L Vishay D2, Boost Diode 1VF @ 50mA Diode 1N4148W Diodes, Inc. L1 4.7H, 1.7A VLCF4020T- 4R7N1R2 TDK R1 31.6k, 1% CRCW06033162F Vishay R2 10k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay 13 www.national.com LM2734 20102344 FIGURE 8. LM2734X (1.6MHz) VBOOST Derived from VSHUNT 18V to 1.5V/1A Bill of Materials for Figure 8 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734X National Semiconductor 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-23 BZX84C5V1 Vishay L1 6.8H, 1.6A, SLF7032T-6R8M1R6 TDK R1 8.87k, 1% CRCW06038871F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay R4 4.12k, 1% CRCW06034121F Vishay www.national.com 14 LM2734 20102349 FIGURE 9. LM2734X (1.6MHz) VBOOST Derived from Series Zener Diode (VIN) 15V to 1.5V/1A Bill of Materials for Figure 9 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734X National Semiconductor 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-23 BZX84C11T Diodes, Inc. L1 6.8H, 1.6A, SLF7032T-6R8M1R6 TDK R1 8.87k, 1% CRCW06038871F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay 15 www.national.com LM2734 20102350 FIGURE 10. LM2734X (1.6MHz) VBOOST Derived from Series Zener Diode (VOUT) 15V to 9V/1A Bill of Materials for Figure 10 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734X National Semiconductor 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-23 BZX84C4V3 Diodes, Inc. L1 6.8H, 1.6A, SLF7032T-6R8M1R6 TDK R1 102k, 1% CRCW06031023F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay www.national.com 16 LM2734 LM2734Y Circuit Examples 20102342 FIGURE 11. LM2734Y (550kHz) VBOOST Derived from VIN 5V to 1.5V/1A Bill of Materials for Figure 11 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734Y National Semiconductor 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 8.87k, 1% CRCW06038871F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay 17 www.national.com LM2734 20102343 FIGURE 12. LM2734Y (550kHz) VBOOST Derived from VOUT 12V to 3.3V/1A Bill of Materials for Figure 12 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734Y National Semiconductor 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 0.6VF @ 30mA Diode BAT17 Vishay L1 10H, 1.6A, SLF7032T-100M1R4 TDK R1 31.6k, 1% CRCW06033162F Vishay R2 10.0 k, 1% CRCW06031002F Vishay R3 100k, 1% CRCW06031003F Vishay www.national.com 18 LM2734 20102344 FIGURE 13. LM2734Y (550kHz) VBOOST Derived from VSHUNT 18V to 1.5V/1A Bill of Materials for Figure 13 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734Y National Semiconductor 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-23 BZX84C5V1 Vishay L1 15H, 1.5A SLF7045T-150M1R5 TDK R1 8.87k, 1% CRCW06038871F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay R4 4.12k, 1% CRCW06034121F Vishay 19 www.national.com LM2734 20102349 FIGURE 14. LM2734Y (550kHz) VBOOST Derived from Series Zener Diode (VIN) 15V to 1.5V/1A Bill of Materials for Figure 14 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734Y National Semiconductor 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-23 BZX84C11T Diodes, Inc. L1 15H, 1.5A, SLF7045T-150M1R5 TDK R1 8.87k, 1% CRCW06038871F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay www.national.com 20 LM2734 20102350 FIGURE 15. LM2734Y (550kHz) VBOOST Derived from Series Zener Diode (VOUT) 15V to 9V/1A Bill of Materials for Figure 15 Part ID Part Value Part Number Manufacturer U1 1A Buck Regulator LM2734Y National Semiconductor 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-23 BZX84C4V3 Diodes, Inc. L1 22H, 1.4A, SLF7045T-220M1R3-1PF TDK R1 102k, 1% CRCW06031023F Vishay R2 10.2k, 1% CRCW06031022F Vishay R3 100k, 1% CRCW06031003F Vishay 21 www.national.com LM2734 Physical Dimensions inches (millimeters) unless otherwise noted 6-Lead TSOT Package NS Package Number MK06A www.national.com 22 LM2734 Notes 23 www.national.com LM2734 Thin SOT23 1A Load Step-Down DC-DC Regulator Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH(R) Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise(R) Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagicTM www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise(R) Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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