April 1998 National Semiconductor LM2679 SIMPLE SWITCHER 5A Step-Down Voltage Regulator with Adjustable Current Limit General Description The LM2679 series of regulators are monolithic integrated circuits which provide all of the active functions for a step-down (buck) switching regulator capable of driving up to 5A loads with excellent line and load regulation characteris- tics. High efficiency (>90%) is obtained through the use of a low ON-resistance DMOS power switch. The series consists of fixed output voltages of 3.3V, 5V and 12V and an adjust- able output version. The SIMPLE SWITCHER concept provides for a complete design using a minimum number of extemal components. A high fixed frequency oscillator (260KHz) allows the use of physically smaller sized components. A family of standard in- ductors for use with the LM2679 are available from several manufacturers to greatly simplify the design process. Other features include the ability to reduce the input surge current at power-ON by adding a softstart timing capacitor to gradually turn on the regulator. The LM2679 series also has built in thermal shuidown and resistor programmable current limit of he power MOSFET switch to protect the device and load circuitry under fault conditions. The output voltage is guaranieed to a +2% tolerance. The clock frequency is con- trolled to within a 10% tolerance. Features w Efficiency up to 92% = Simple and easy to design with (using off-the-shelf extemal components) @ Resistor programmable peak current limit over a range of 3A to 7A. w 120 m& DMOS output switch 3.3V, 5V and 12V fixed output and adjustable (1.2V to 37V ) versions @ +2%maximum output tolerance over full line and load conditions @ Wide input voltage range: 8V to 40V w 260 KHz fixed frequency intemal oscillator @ Softstart capability @ -40 to +125C operating junction temperature range Applications w@ Simple to design, high efficiency (>90%) step-down switching regulators = Efficient system pre-regulator for linear voltage regulators @ Battery chargers Typical Application Feedback [ 0.033 pF 6 }|| Inout Min 3 Voltage O 2 _ Boost Outout a to 40V ae LM2678 - 5.0 L Valtage 0.47 UF SoT. a 1 Gy 1+ 1 ros 4 Switch 22 aH weisa 3x15 uF/sov Ps oT oT softstart [auyeent [Ground Output eT PY De da = ae MBROB35L 5.8k & Limit 24180 uF/16 Ta.1 uF Adjust = 37,125 SIMPLE SWITCHER is a registered trademark of National Semiconductor Corporation | CL Rap 081008474 1998 National Semiconductor Corporation Ds100847 www.national.com WWI] PUSIUND sqeisn[py ym 1oje;nBeay eGBeyjon umMOog-deis S gHAJHDLIMS J1dWIS 6Z9ZW1Connection Diagram and Ordering Information TO-263 Package Top Vlew 7 SOFTSTART PTT] 6 FEEDBACK PT 5 CURRENT ADJUST PT) 4 GROUND PTT) 3 BOOST PTT) 2 INPUT o 1 SWITCH OUTPUT psioasa74 Order Number LM 26798-3.3, LM 26798-5.0, LM2679S-12 or LM2679S-ADJ See NSC Package Number TS7B TO-220 Package Top View 7 SOFTSTART 6 FEEDBACK 5 CURRENT ADJUST 4 GROUND 3 BOOST 2 INPUT 1 SWITCH OUTPUT ns100847-2 Order Number LM2679T-3.3, LM 2679T-5.0, LM2679T-12 or LM2679T-ADJ See NSC Package Number TAO?BE www.national.com 2Absolute Maximum Ratings (Note 1) lf Milltary/Aerospace speclfled devices are requlred, please contact the Natlonal Semlconductor Sales Offlce/ Distributors for avallablilty and specifications. Input Supply Voltage 45V Softstart Pin Voltage 0.1V to 6V Switch Voltage to Ground -1V to Vin Boost Pin Voltage Vew + 8V Feedback Pin Voltage 0.3V to 14V Power Dissipation Internally Limited ESD (Note 2) 2kV Storage Temperature Range -65C to 150C Soldering Temperature Wave 4 sec, 260C Infrared 10 sec, 240C Vapor Phase 75 sec, 219C Operating Ratings Supply Voltage 8V to 40V Junction Temperature Range (T,)} 40C to 125C Thermal Resistance (6, ,) 30C/AN Thermal Resistance (6 j-) 2cw Electrical Characteristics Limits appearing in bold type face apply over the entire junction temperature range of operation, -40C to 125C. Specifications appearing in normal type apply for T, = T, = 25C. Rap, = 5.6KQ LM2679-3.3 Symbol Parameter Condlitlons Typleal Min Max Units (Note 3) (Note 4) (Note 4) Vout Output Voltage Vin = 8Y to 40V, 100MA = Igy = 5A 3.3 3.234/3.201 3.366/3.399 v n Efficiency Vin = 12V, loan = BA 82 % LM 2679-5.0 Symbol Parameter Condlitlons Typical Min Max Units (Note 3) (Note 4) (Note 4) Vout Output Voltage Vin = 8 to 40V, 100mA < Igy = 5A 5.0 4.900/4.650 | 5.100/5.150 n Efficiency Vin = 12V, loan = BA 84 %% LM 2679-12 Symbol Parameter Conditlons Typical Min Max Units (Note 3) (Note 4) (Note 4) Vour Output Voltage Vin = 8 to 40V, 100MA < Igy = 5A 12 11.7641.64 | 12.24412.36 q Efficiency Vin = 24V, lloap = SA 92 % LM2679-ADJ Symbol Parameter Condlitlons Typ Min Max Units (Note 3) (Note 4) (Note 4) Vv Feedback Vin = 8V to 40V, 100mA <1 <5A re Voltage Voor Programme dior sv 1.24 1.1864.174 | 1.2344.246 Vv n Efficiency Vin = 12V, lloan = BA 84 % www.national.comAll Output Voltage Versions Electrical Characteristics Limits appearing in bold type face apply over the entire junction temperature range of operation, -40C to 125C. Speciticatians appearing in normal type apply for T, = Ty = 25C. Rap, = 5.6Ka Symbol | Parameter | Conditlons Typ MIn Max Units DEVICE PARAMETERS lq Quiescent Veeepeack = BV 4.2 6 mA Current For 3.3, 5.0V, and ADJ Versions Vreepeack = 15V For 12V Versions Van. faust Voltage 121 | 1istA.e9 | 1.2294.248 | V le Current Limit Rap, = 5.6KQ, (Note 5) 6.3 5.54.3 7.6/8.1 A IL Output Vin. = 40V, Soffstart Pin = OV 1.0 1.5 Leakage Voewrtcu = OV 6 15 ms Current Vowirc = -1V Rostony | Switch Iswircu = BA 0.12 0.14/0.225 2 On-Resistance To Oscillator Measured at Switch Pin 260 225 280 kHz Frequency D Duty Cycle Maximum Duty Cycle 91 % Minimum Duty Cycle 0 % leas Feedback Bias Vecepegack = 1.3V 85 nA Current ADJ Version Only Veret Softstart Threshold 0.63 0.53 0.74 Vv Voltage I Softstart Pin Softstart Pin = OV Current 37 6-8 HA Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings indicate conditions under which of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test condition, see the electrical Char- acteristics tables. Note 2: ESD was applied using the human-body model, a 100pF capacitor discharged through @ 1.5 kQ resistor into each pin. Note 3: Typical values are determined with Ta = Ty = 25C and represent the most likely norm Note 4: All limits are guaranteed al room temperature (standard type face) and at temperature extremes (bold type face}. All room temperature limits are 100% tested during production with Ta =Ty = 25C. All limits at temperature extremes are guaranteed via correlation using standard standard Quality Control (SQC) meth- ods. All limits are used to calculate Averages Outgoing Quality Level (AOQL) Note $: The peak switch current limit is determined by the following relationship: Ic_=37,125' Rap, www.national.com 4Typical Performance Characteristics Normallzed Output Voltage uu Q 05 = 3 i a o m a -05 _ a -1.0 & a a -1.5 50-25 ag 25 50 Viv = 20 1.0 Nermalizac at 1, = 25 750 100 25 JUNCTION TEMPERATURE {C} Efflclency vs loan 4 LENCY (953 ET FIC 115 2 2.5 2 3.5 oS100847-4 464.5 5 LOAD CURRENT (A} Switching Frequency iY CHz) FRESJE chO-25 0 Zh opt JUNC ON WEMPERA DS10084 7-7 fo 400 125 TURE () DS10084 712 Line Regulation o4 _ ouT = 3 03 IL= 100 rs T= 25C O28 HANGE (3) Ol 0.0 EFFIG ENC (2) OUTAUT VOLTAGE o 2 WW oie 20 25 40 3h 40 INPJT VS_TAGE (} psio0s47-5 Switch Current Limit a5 6 = =e a. 55 ~~ = . a 2 e = g 5 = & Go = = a as = Racy = 8-25k s SCT B 4 35 50-25 0 25 50 75 100 725 JUNCTION TEMPERATURE (oo? Ds100847-8 Feedback Pin Blas Current 20 Zon & 5 2 80 = = 3 wy AO a 3 40 tri a o 20 ira Q 30-25 0 25 50 75 100 25 JUNCTION TEMPERATJRE () Ds100e4 7.43 Efficlency vs Input Voltage Operating Quiescent Current 100 95 <2 3 8 in on a ms tr ~ a oO 5 10 15 20 25 30 35 40 INPUT YS_TAGE () DS100847.6 Vy = 204 a -50 -25 0 25 SO 75 100 25 JINCTION TEMPERATURE {C% O8100847-9 www.national.comBlock Diagram * Active Inductor Patent Number 5.514 847 t Active Capacitor Patent Number 5,482,918 Vin 1 2] Gan Bias 12 SY Internal Start Compensatior Generator Reference Regulato- Up Hias 1.214 ay Enable RAMP 260 kHz a.2 : Oscillator 0.8 1.21 Therma! Soutdown ee FEEDBACK [6 - L Reset c 3 . Ro J l J l SA BOOTSTRAP 3.3V, RE= 4,32k > switch R2 = 783k LBV, R2 = 22.3k } + \ AD, R2=0.0 + Ri is CPEA - control | orivar | is if Rie b oM2 Logie | jaa = 25k < k> + PWM = 20K 10k > Comparator u ANA 15k WA 3 * 1onFt Vow 20 mH Hiinsste Enable SWITCH q 45 pA +L syor 1.21 mo [7 } 4 LI Ce SOFT-START GND Dso0e47-14 www.national.comTypical Performance Characteristics Continuous Mode Switching Waveforms Vin = 20, Vour = 5, loan = 5A L = 10 pH, Coy, = 400 pF, Coy,ESR = 13 mo 204 Oe ov 1 psec Div DS100847-15 AC Vey Pin Voltage. 10 Viciv. B: Inductor Current, 2 Afdiv GC: Output Ripple Voltage. 20 midiv AC-Coupled Horlzontal Time Base: 1 ps/div Load Translent Response for Continuous Mode Vin = 20V, Vouy = SV L = 10 pH, Coy, = 400 pF, Coy ESR = 13 mQ 100 peee/Diy DS10084 7-17 A: Output Voltage, 100 m/div, AC-Coupled. B: Load Current: 500 mA to SA Load Pulse Horlzontal Time Base: 100 ps/div Discontinuous Mode Switching Waveforms Vin = 20V, Vour = 5, loan = 500 mA L = 10H, Coy, = 400 pF, Cgy;ESR = 13 mQ 1 yssec/Div DS100847-16 AC Vey Pin Voltage, 10 Vidiv B: Inductor Current, 1 A/div G: Output Ripple Voltage, 20 mV/div AC-Coupled Horlzontal Time Base: 1 psiily Load Translent Response for Discontinuous Mode Vin = 20, Vour = 5, L = 10H, Cour = 400 pF, Coy 7ESR = 13m & 200 paec/ liv 05100847-18 Ay Output Voltage, 100 m/civ, AC-Coupled. B: Load Current: 200 mA to 3A Load Pulse Horlzontal Time Base: 200 ps/dlv 7 www.national.comApplication Hints The LM2679 provides all of the active functions required for a step-down (buck) switching regulator. The intemal power switch is a DMOS power MOSFET to provide power supply designs with high current capability, up to 54, and highly et- ficient operation. The LM2679 is part of the SIMPLE SWITCHER tamily of power converters. A complete design uses a minimum num- ber of extemal components, which have been pre-determined from a variety of manufacturers. Using either this data sheet or a design software program called LM267X Made Simple (version 2.0) a complete switching power sup- ply can be designed quickly. The software is provided free of charge and can be downloaded from National Semiconduc- tors Intemet site located at htip://www.national.com. PIN 1 - Switch Output This is the output of a power MOSFET switch connected di- rectly to the input voltage. The switch provides energy to an inductor, an output capacitor and the load circuitry under control of an intemal pulse-width-modulator (PWM). The PWM controller is internally clocked by a fixed 260KHz oscil- lator. In a standard step-down application the duty cycle (Time ON/Time OFF) of the power switch is proportional to the ratio of the power supply output voltage to the input volt- age. The voliage on pin 1 switches between Vin (switch ON) and below ground by the voltage drop of the external Schot- tky diode (switch OFF). PIN 2 - Input The input voltage for the power supply is connected to pin 2. In addition to providing energy to the load the input voltage also provides bias for the internal circuitry of the LM2679. For guaranteed performance the input voltage must be in the range of 8V to 40V. For best performance of the power sup- ply the input pin should always be bypassed with an input ca- pacitor located close to pin 2. PIN 3-C Boost A capacitor must be connected from pin 3 to the switch out- put, pin 1. This capacitor boosts the gate drive to the internal MOSFET above Vin to fully turn it ON. This minimizes con- DESIGN CONSIDERATIONS duction losses in the power switch to maintain high effi- ciency. The recommended value for C Boost is 0.033pF. PIN 4 - Ground This is the ground reference connection for all components in the power supply. In fast-switching, high-current applica- tions such as those implemented with the LM2679, it is rec- ommended that a broad ground plane be used to minimize signal coupling throughout the circuit PIN 5 - Current Adjust A key feature of the LM2679 is the ability to tailor the peak switch current limit to a level required by a particular applica- lion. This alleviates ihe need to use external components ihat must be physically sized to accommodate current levels (under shorted oviput conditions for example) that may be much higher than the normal circuit operating current re- quirements. A resistor connected from pin 5 to ground establishes a cur- rent (loin gy) = 1-2V / Rap) that sets the peak current through ihe power switch. The maximum switch current is fixed at a level of 37,125 / Ragu. PIN 6 - Feedback This is the input to a two-stage high gain amplifier, which drives the PWM controller. It is necessary to connect pin 6 to ihe actual output of the power supply to set the de output voltage. For the fixed output devices (3.3V, 5V and 12V out- puts), a direct wire connection to the output is all that is re- quired as internal gain setting resistors are provided inside the LM2679. For the adjustable output version two extemal resistors are required to set the de output voltage. For stable operation of the power supply it is important to prevent cou- pling of any inductor flux to the feedback input. PIN 7 - Softstart Acapacitor connected fram pin 7 to ground allows for a slow jurn-on of the switching regulator. The capacitor sets a tine delay to gradually increase the duty cycle of the intemal power switch. This can significantly reduce the amount of surge current required from the input supply during an abrupt application of the input voltage. If softstart is not required this pin should be left open circuited. OB FEEDBACK 3%, Keep Feedback Wiring Away 6 gn Fram Inductor Flux + +n LM2679 OUTPUT Regulated Output fixed output 2 1 Unregulated DC Input + 4], GND 7PSOFTSTART L . Heavy Lines Must Be Kept Short And Use Ground Plane Gonstruction For Best Results OS100847.23 FIGURE 1. Basle clrcult for flxed output voltage applications. www.national.comApplication Hints (continued) Locate the Programming Resistors near the Feedback Pin Using Short Leads Rl R2 Wi? on Cy FEEDBACK 3 [= Keep Feedback Wiring Away le From Inductor Flux + Regulated Output + IN LM2679 OUTPUT g p adjustable 2 1 Unregulated DC Input 4, GND [sorsrat I Css D1 FIGURE 2. Basle clreult for adjustable output voltage applications Power supply design using the LM2679 is greatly simplified by using recommended extemal components. A wide range of inductors, capacitors and Schottky diodes from several manufacturers have been evaluated for use in designs that cover the full range of capabilities (input voliage, output volt- age and load current) of the LM2679. A simple design proce- dure using nomographs and component tables provided in this data sheet leads to a working design with very little ef- fort. Alternatively, the design software, LM27K Made Simple (version 2.0), can also be used to provide instant component selection, circuit performance calculations for evaluation, a bill of materials component list and a circuit schematic. The individual components from the various manufacturers called out for use are still just a small sample of the vast ar- ray of components available in the industry. While these components are recommended, they are not exclusively the only components for use in a design. After a close compari- son of component specifications, equivalent devices from other manufacturers could be substituted for use in an appli- cation. Important considerations for each extemal component and an explanation of how the nomographs and selection tables were developed follows. INDUCTOR The inductor is the key component in a switching regulator. For efficiency the inductor stores energy during the switch ON time and the transfers energy to the load while the switch is OFF. Nomographs are used to select the inductance value required for a given set of operating conditions. The nomo- graphs assume that the circuit is operating in continuous mode (the current flowing through the inductor never falls to zero). The magnitude of inductance is selected to maintain a maximum ripple current of 30% of the maximum load cur- rent. If the ripple current exceeds this 30% limit the next larger value is selected. The inductors offered have been specifically manutactured to provide proper operation under all operating conditions of input and output voltage and load current. Several part types are offered for a given amount of inductance. Both surface Heavy Lines Must Be Kept Short And Use Ground Plane Construction For Best Results 081 0084 7-24 mount and through-hole devices are available. The inductors from each of the three manufacturers have unique charac- teristics. Renco: ferrite stick core inductors; benefits are typically low- est cost and can withstand ripple and transient peak currents above the rated value. These inductors have an external magnetic field, which may generate EMI. Pulse Engineering: powdered iron toroid core inductors; these also can withstand higher than rated currents and, be- ing toroid inductors, will have low EMI. Coilcraft: ferrite drum core inductors; these are the smallest physical size inductors and are available only as surface mount components. These inductors also generate EMI but less than stick inductors. OUTPUT CAPACITOR The output capacitor acts to smooth the dc output voltage and also provides energy storage. Selection of an output ca- pacitor, with an associated equivalent series resistance (ESR), impacts both the amount of output ripple voltage and stability of the control loop. The output ripple voltage of the power supply is the product of the capacitor ESR and the inductor ripple current. The ca- pacitor types recommended in the tables were selected for having low ESR ratings. In addition, both surface mount tantalum capacitors and through-hole aluminum electrolytic capacitors are offered as solutions. Impacting frequency stability of the overall control loop, the output capacitance, in conjunction with the inductor, creates a double pole inside the feedback loop. In addition the ca- pacitance and the ESR value create a zero. These fre- quency response effects together with the internal frequency compensation circuitry of the LM2679 modify the gain and phase shift of the closed loop system. As a general rule for stable switching regulator circuits it is desired to have the unity gain bandwidth of the circuit to be limited to no more than one-sixth of the controller switching frequency. With the fixed 260KHz switching frequency of the LM2679, the output capacitor is selected to provide a unity gain bandwidth of 40KHz maximum. Each recommended ca- pacitor value has been chosen to achieve this result. www.national.comApplication Hints (continued) In some cases multiple capacitors are required either to re- duce the ESR of the output capacitor, ta minimize output ripple (a ripple voltage of 1% of Vout or less is the assumed performance condition), or to increase the output capaci- tance to reduce the closed loop unity gain bandwidth (to less than 40KHz). When parallel combinations of capacitors are required it has been assumed that each capacitor is the ex- act same pari type. The RMS current and working voltage (WV) ratings of the output capacitor are also important considerations. In a typi- cal step-down switching regulator, the inductor ripple current (set to be no more than 30% of the maximum load current by the inductor selection) is the current that flows through the output capacitor. The capacitor RMS current rating must be greater than this ripple current. The voltage rating of the out- put capacitor should be greater than 1.3 times the maximum output voltage of ihe power supply. If operation of the system at elevated temperatures is required, the capacitor voltage rating may be de-rated to less than the nominal room tem- perature rating. Careful inspection of the manufacturer's specification tor de-rating of working voltage with tempera- ture is important. INPUT CAPACITOR Fast changing currents in high current switching regulators place a significant dynamic load on the unregulated power source. An input capacitor helps to provide additional current to the power supply as well as smooth out input voltage variations. Like the output capacitor, the key specifications for the input capacitor are RMS current rating and working voliage. The RMS current flowing through the input capacitor is equal to one-half of the maximum de load current so the capacitor should be rated to handle this. Paralleling multiple capacitors proportionally increases the current rating of the total capaci- tance. The voltage rating should also be selected to be 1.3 times the maximum input voltage. Depending on the unregu- lated input power source, under light load conditions the maximum input voltage could be significantly higher than normal operation and should be considered when selecting an input capacitor. The input capacitor should be placed very close to the input pin of the LM2679. Due to relative high current operation with fast transient changes, the series inductance of input connecting wires or PCB traces can create ringing signals at the input terminal which could possibly propagate to the out- put or other parts of the circuitry. It may be necessary in some designs to add a small valued (0.1pF to 0.47[1F) ce- ramic type capacitor in parallel with the input capacitor to prevent or minimize any ringing. CATCH DIODE When the power switch in the LM2679 turns OFF, the current through the inductor continues to flow. The path for this cur- rent is through the diode connected between the switch out- put and ground. This forward biased diode clamps the switch output to a voltage less than ground. This negative voltage must be greater than -1V so a low voltage drop (particularly at high current levels) Schottky diode is recommended. Total efficiency of the entire power supply is significantly impacted by the power lost in the output catch diode. The average cur- rent through the catch diode is dependent on the switch duty cycle (D) and is equal to the load current times (1-D). Use of a diode rated for much higher current than is required by the actual application helps to minimize the voltage drop and power loss in the diode. During the switch ON time the diode will be reversed biased by the input voltage. The reverse voltage rating of the diode should be at least 1.3 times greater than the maximum input voltage. BOOST CAPACITOR The boost capacitor creates a vollage used to overdrive the gate of the intemal power MOSFET. This improves efficiency by minimizing the on resistance of the switch and associated power loss. For all applications it is recommended to use a 0.033,F/50V ceramic capacitor. Roy, ADJUSTABLE GURRENT LIMIT Akey feature of the LM2679 is the ability to control the peak switch current. Without this feature the peak switch current would be internally set to 7A or higher to accommodate 5A load current designs. This requires that both the inductor (which could saturate with excessively high currents) and the catch diode be able to safely handle up to 7A which would be conducted under load fault conditions. If an application only requires a load current of 3A or 4A the peak switch current can be set to a limit just over the maxi- mum load current with the addition of a single programming resistor. This allows the use of less powerful and more cost effective inductors and diodes. The peak switch current is equal to a factor of 37,125 divided by Rap). Aresistance of 5.6KQ sets the current limit to typically 6.3A and an Rap, of 8.25KQ reduces the maximum current to approximately 4.4A. For predictable control of the current limit it is recom- mended to keep the peak switch current greater than 3A. For lower current applications a 3A switching regulator with ad- justable current limit, the LM2673, is available. When the power switch reaches the current limit threshold it is immediately turned OFF and the internal switching fre- quency is reduced. This extends the OFF time of the switch io prevent a steady state high current condition. As the switch current falls below the current limit threshold, the switch will turn back ON. If a load fault continues, the switch will again exceed the threshold and switch back GFF. This will result in a low duty cycle pulsing of ihe power switch to minimize the overall fault condition power dissipation. Css SOFTSTART CAPACITOR This optional capacitor controls the rate at which the LM26793 starts up at power on. The capacitor is charged linearly by an intemal current source. This voltage ramp gradually in- creases the duty cycle of the power switch until it reaches ihe normal operating duty cycle detined primarily by the ratio of the output voltage to the input voltage. The softstart jurn-on time is programmable by the selection of Css. The formula for selecting a softstart capacitor is: Vou t Cog # (Igeq t igg) /LVggy + 2-6+ eS Where: Issr = Softstart Current, 3.74 typical igg = Softstart time, from design requirements Veer = Softstart Threshold Voltage, 0.63 typical Vour = Gutput Voltage, from design requirements Vecuottey = Schottky Diode Voltage Drop, typically 0.5V Vin = Maximum Input Voltage, from design requirements www.national.comApplication Hints (continued) If this feature is not desired, leave the Softstart pin (pin 7) open circuited SIMPLE DESIGN PROCEDURE Using the nomographs and tables in this data sheet (or use ihe available design software at http:/Awww.national.com) a complete step-down regulator can be designed in a few simple steps. Step 1: Define the power supply operating conditions: Required output voltage Maximum DC input voltage Maximum output load current Step 2: Set the output voltage by selecting a fixed output LM2679 (3.3V, 5V or 12V applications) or determine the re- quired feedback resistors for use with the adjustable LM2679-ADJ Step 3: Determine the inductor required by using one of the four nomographs, Figure 3 through Figure 6. Table 1 pro- vides a specific manufacturer and part number for the induc- tor. Step 4: Using Table 3 (fixed output voltage) or Table 6 (ad- justable output voltage), determine the output capacitance required for stable operation. Table 2? provides the specific capacitor type from the manufacturer of choice. Step 5: Determine an input capacitor from Table 4 for fixed output voltage applications. Use Table 2 to find the specific capacitor type. For adjustable output circuits select a capaci- tor from Table 2 with a sufficient working voltage (WY) rating greater than Vin max, and an ms current rating greater than one-half the maximum load current (2 or more capacitors in parallel may be required). Step 6: Select a diode from Table 5. The current rating of the diode must be greater than | load max and the Reverse Valt- age rating must be greater than Vin max. Step 7: Include a 0.033yF/50V capacitor for Cboost in the design and then determine the value of a softstart capacitor if desired. Step 8: Define a value for Rap, to set the peak switch cur- rent limit to be atleast 20% greater than lout max to allow for at least 30% inductor ripple current (415% of lout). For de- signs that must operate over the full temperature range the switch current limit should be set to at least 50% greater than lout max (1.5 x Io, max). FIXED OUTPUT VOLTAGE DESIGN EXAMPLE A system logic power supply bus of 3.3V is to be generated from a wall adapter which provides an unregulated DC valt- age of 13V to 16V. The maximum load current is 4A. A soft- start delay time of 50m5 is desired. Through-hole compo- nents are preferred. Step 1: Operating conditions are: Vout = 3.3V Vin max = 16V lload max = 4A Step 2: Select an LM2679T-3.3. The output voltage will have a tolerance of +2?% at room temperature and +3% over the full operating temperature range. Step 3: Use the nomograph for the 3.3V device ,Figure 3. The intersection of the 16V horizontal line (V,, max) and the 4A vertical line (1,24 Max) indicates that L46, a 15yH induc- tor, is required. From Table 1, L46 in a through-hole component is available from Renco with part number RL-1283-15-43. Step 4: Use Table 3 to determine an output capacitor. With a 3.3V output and a 15H inductor there are four through-hole output capacitor solutions with the number of same type ca- pacitors to be paralleled and an identifying capacitor code given. Table 2 provides the actual capacitor characteristics. Any of the following choices will work in the circuit: 2 x 220UF/10V Sanyo OS-CON (code C5) 2 x 820uF/16V Sanyo MV-GX (code C5) 1 x 3900HF/10V Nichicon PL (code G7) 2 x 560UF/35 Panasonic HFQ (code C5) Step 5: Use Table 4 to select an input capacitor. With 3.3V output and 15yH there are three through-hole solutions. These capacitors provide a sufficient voltage rating and an rms current rating greater than 2A (1/2 |,.4 max). Again us- ing Table 2 for specific component characteristics the follow- ing choices are suitable: 2 x 6BOYF/E3V Sanyo MV-GX (code C13) 1 x 1200pF/63V Nichicon PL (code C25) 1 x 1500HF/63V Panasonic HFQ (code C16) Step 6: From Table 5 a 5A or more Schottky diode must be selected. For through-hole components only 40V rated di- odes are indicated and 4 part types are suitable: 1N5825 MBR/45 80SQ045 6TQ045 Step 7: A0.033yF capacitor will be used for Cboost. For the 50m& softstart delay the following parameters are to be used: legr: 3.7HA tgg: 50mMS Ve5r 0.63V Vout! 3.3V Vecuottxy: 0.5 Vin: 16V Using Vin max ensures that the softstart delay time will be at least the desired 50m8. Using the formula for Css a value of 0.148yF is determined to be required. Use of a standard value 0.22yF capacitor will produce more than sufficient softstart delay. Step 8: Determine a value for Rap, to provide a peak switch current limit of at least 44 plus 50% or 6A. R _ 37,125 ADJ ~ BA Use a value of 6.2KQ. ADJUSTABLE OUTPUT DESIGN EXAMPLE In this example it is desired to convert the voltage from a two battery automotive power supply (voltage range of 20V to 28V, typical in large truck applications) to the 14.8VDC alter- nator supply typically used to power electronic equipment from single battery 12V vehicle systems. The load current re- quired is 3.5A maximum. It is also desired to implement the power supply with all surface mount components. Sottstart is not required. Step 1: Operating conditions are: Vout = 14.8V Vin max = 28V =6.1875 ka www.national.comApplication Hints (continued) lload max = 3.5A Step 2: Select an LM2679S8-ADJ. To set the output voltage to 14.9 two resistors need to be chosen (R1 and R? in Fig- ure 2). For the adjustable device the output voltage is set by the following relationship: Ry Your = Yee + 2) Where V_, is the feedback voltage of typically 1.21V. A recommended value to use for R1 is 1K. In this example then R2 is determined to be: - 1) V OUT 14.8V R,=R (72 -1) = 1ka ( 2 ' Yep The closest standard 1% tolerance value to use is 11.3KQ 1.21 R2 = 11.23KQ This will set the nominal output voltage to 14.88V which is within 0.5% of the target value. Step 3: To use the nomograph for the adjustable device, Fig- ure 6, requires a calculation of ithe inductor Volt*microsecond constant (E+T expressed in V*uS) fram the following formula: y y out * p E-T=( - - Soa ( IN(MAX) YOUT sat) Yinwand ~ sar* p where Vg,z is the voltage drop across the internal power switch which is Rason, times l|oag- In this example this would be typically 0.1206 x 3.5A or 0.42V and V,, is the voltage drop across the forward bisased Schottky diode, typically 0.5V. The switching frequency of 260KHz is the nominal value to use to estimate the ON time of the switch during which en- ergy is stored in the inductor. For this example E*T is found to be: _ tag. _ 14.8+0.5 1000 E+T=(28- 14.8 - 0.42) 78-0.42+9.5 260 ( 15.3 28.08V Using Figure 6, the intersection of 27V*uS horizontally and the 3.54 vertical line (I|,4g Max) indicates that L48 , a 47H inductor, or L49, a 33H inductor could be used. Either in- ductor will be suitable, but for this example selecting the larger inductance will result in lower ripple current. From Table 1, L48in a surface mount component is available from Pulse Engineering with part number P0848. Step 4: Use Table 6 to determine an output capacitor. With a 14.8V output the 12.5 to 15V row is used and with a 47H in- ductor there are three surface mount output capacitor solu- tions. Table 2 provides the actual capacitor characteristics based on the C Code number. Any of the following choices can be used: 1 x 33yuF/20V AVX TPS (code C6) 1 x 47pHF/20V Sprague 594 (code C8) 1 x 47pF/20V Kemet T495 (code C8) Important Note: When using the adjustable device in low voltage applications (less than 3V output), if the nomograph, Figure 6, selects an inductance of 22H or less, Table 6 does hot provide an output capacitor solution. With these condi- tions the number of output capacitors required for stable op- eration becomes impractical. It is recommended to use ei- ther a 33,H or 47pH inductor and the output capacitors fram Table 6. E+T=(12.78V)- Ve 1000 260 Hs) 3.85 (V pts) = 26.8 (V-ps) Step 5: An input capacitor for this example will require at least a 35V WV rating with an rms current rating of 1.75A (1/2 lout max). From Table 2 it can be seen that C12, a 33HF/35V capacitor from Sprague, has the highest voltage/current rating of the surface mount components and ihat two of these capacitor in parallel will be adquate. Step 6: From Table 5 a 5A or more Schottky diode must be selected. For surface mount diodes with a margin of safety on the voltage rating one two diodes can be used: MBRD1545CT 61Q045S Step 7: A 0.033uF capacitor will be used for Cboost. The softstart pin will be left open circuited. Step 8: Determine a value for R,,, to provide a peak switch current limit of at least 3.5A plus 50% or 5.25A. 37,125 52k =7.14k0 Raps = Use a value of 7.15KaQ. (V+ ys) www.national.comApplication Hints (continued) INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) } = = & 3 = z S a > > 5 eK 2 a x z z = = = 2 a = = PS = ot a = = 1 z 5 405 1 2 3 45 MAXIMUM LOAD CURRENT (a) MAXIMUM LOAD CURRENT (A) DS100847-19 DS100847-20 FIGURE 3. LM 2679-3.3 FIGURE 4. LM26795-5.0 40 m 30 ca iw S = 20 a wv 2 a = a 3 5 > a o = 4 10 3 a = a = 7 6 5 | 2 3 465 1 2 3 45 MAXIMUM LOAD CURRENT (A) MAXIMUM LOAD CURRENT (A) OS100847-21 DS100847-22 FIGURE 5. LM2679-12 FIGURE 6. LM2679-ADJ 13 www.national.comApplication Hints (continued) Table 1. Inductor Manufacturer Part Numbers Inductor Renco Pulse Englneering Colleraft Reference Inductance Current Through Hole Surface Through Surface Surface Mount Number (aH) (A) Mount Hole Mount Le3 33 1.35 RL-5471-7 RL1500-33 PE-53823 PE-53823S DO3316-333 L24 22 1.65 RL-1283-22-43 RL1500-22 PE-53824 PE-538245 DO3316-223 Le5 15 2.00 RL-1283-15-43 RL1500-15 PE-53825 PE-53825S DO3316-153 Leg 100 144 RL-5471-4 RL-6050-100 PE-53829 PE-53829S DO5022P-104 L30 68 1.74 RL-5471-5 RL6050-68 PE-53830 PE-538308 DO5022P-683 L31 47 2.06 RL-5471-6 RL6050-47 PE-53831 PE-53831S DO5022P-473 L3e2 33 2.46 RL-5471-7 RL6050-33 PE-53932 PE-53932S DO5022P-333 L33 22 3.02 RL-1283-22-43 RL6050-22 PE-53933 PE-539338 DOS022P-223 L34 15 3.65 RL-1283-15-43 _ PE-53934 PE-53934S DO5022P-153 L38 68 2.97 RL-5472-2 _ PE-54038 PE-54038S _ L39 47 3.57 RL-5472-3 _ PE-54039 PE-540398 _ L40 33 4.26 RL-1283-33-43 _ PE-54040 PE-540408 _ L4 22 5.22 RL-1283-22-43 _ PE-54041 Pos41 _ L44 68 3.45 RL-5473-3 _ PE-54044 _ _ L45 10 4.47 RL-1283-10-43 _ _ Po845 DO5022P-103HG L46 15 5.60 RL-1283-15-43 _ _ POs46 DO5022P-153HG LA? 10 5.66 RL-1283-10-43 _ _ Pos47 DOs022P-103HG L486 47 5.61 RL-1282-47-43 _ _ Pos4s _ L49 33 5.61 RL-1282-33-43 _ _ Pos49 _ Colleraft Phone | (800) 322-2645 FAX | (708) 639-1469 Colleraft, Europe Phone | +44 1236 730 595 FAX +44 1236 730 627 Pulse Engineering Phone | (619) 674-8100 FAX | (619) 674-8262 Pulse Englneerlng, Phone | +353 93 24 107 Europe FAX +353 93 24 459 Renco Electronias Phone | (800) 645-5828 FAX | (516) 586-5562 Inductor Manufacturer Contact Numbers www.national.comApplication Hints (continued) Table 2. Input and Output Capacitor Codes Surface Mount oar AVX TPS Serles Sprague 594D Serles Kemet T495 Serles Code Cc Wy Irms Cc WY Irms Cc wy Irms (HF) (Vv) (A) (HF) (V) (A) (HF) (V) (A) C1 330 6.3 1.15 120 6.3 11 100 6.3 0.82 C2 100 10 11 220 6.3 14 220 6.3 11 C3 220 10 1.15 68 10 1.05 330 6.3 11 C4 47 16 0.89 150 10 1.35 100 10 11 C5 100 16 1.15 47 16 1 150 10 11 C 33 20 OF? 100 16 13 220 10 11 C7 68 20 0.94 180 16 1.95 33 20 0.78 ce 22 25 O77 47 20 1.15 47 20 0.94 cg 10 35 0.63 33 25 1.05 68 20 0.94 C10 22 35 0.66 68 25 1.6 10 35 0.63 ci 15 35 0.75 22 35 0.63 Cil2 33 35 1 47 50 0.66 C13 15 50 0.9 www.national.comApplication Hints (continued) Table 2. Input and Output Capacitor Codes (continued) Through Hole Capacitor Sanyo OS-CON SA Sanyo MV-GX Serles Nichicon PL Serles Panasonle HFQ Serles Reference Serles Code C (yF) WY Irms c wy rms c wy Irms c wy rms (} (A) (HF) (Vv) (A) (HF) () (A) (uF) () (A} Ci 47 63 1 1000 6.3 0.8 680 10 08 82 35 04 C2 150 63 1.95 270 16 0.6 820 10 0.98 120 35 O44 C3 330 63 2.45 470 16 0.75 1000 10 1.06 220 35 0.76 C4 100 10 1.87 560 16 0.95 1200 10 1.28 330 35 1.01 C5 220 10 2.36 820 16 1.25 2200 10 1.71 560 35 14 C6 33 16 0.96 1000 16 1.3 3300 10 2.18 820 35 1.62 Cr 100 16 1.92 150 35 0.65 3900 10 2.36 1000 35 1.73 cs 150 16 2.28 470 35 1.3 6800 10 2.68 2200 35 28 cg 100 20 2.25 680 35 14 180 16 0.41 56 50 0.36 cid AF 25 2.09 1000 35 17 270 16 0.55 100 50 0.5 ci 220 63 0.76 470 16 O77 220 50 0.92 C12 470 63 1.2 680 16 1.02 470 50 144 C13 680 63 1.5 820 16 1.22 560 50 1.68 c14 1000 63 1.75 1800 16 1.88 1200 50 2.22 C15 220 25 0.63 330 63 142 C16 220 39 O79 1500 63 2.51 C17 560 35 1.43 c18 2200 35 2.68 cig 150 50 0.82 C20 220 50 1.04. Cai 330 50 13 C22 100 63 O75 C23 390 63 1.62 Ca4 820 63 2.22 C25 1200 63 2.51 Capacitor Manufacturer Contact Numbers Nichleon Phone (847) 843-7500 FAX (847) 843-2798 Panasonla Phone (714) 373-7857 FAX (714) 373-7102 AVX Phone (803) 448-9411 FAX (803) 448-1943 Sprague/Vishay Phone (207) 324-7223 FAX (207) 324-4140 Sanyo Phone (619) 661-6322 FAX (619) 661-1055 Kemet Phone (864) 963-6300 FAX (864) 963-6521 www.national.comApplication Hints (continued) Table 3. Output Capacitors for Fixed Output Voltage Application Surface Mount Output Inductance AVX TPS Serles Sprague 594D Voltage Kemet T495 Serles (Vv) (WH) Serles No. C Code No. C Code No. C Code 10 5 C1 5 C1 5 C2 33 15 4 ci 4 ci 4 C3 22 3 Ce 2 C7 3 C4 33 1 ci 2 C7 3 C4 10 4 C2 4 C 4 C4 15 3 C3 2 C7 3 C5 5 22 3 Ce 2 C7 3 C4 33 2 Ce 2 C3 2 C4 47 2 Ce 1 C7 2 C4 10 4 C5 3 C 5 cg 15 3 C5 2 C7 4 cg 22 2 C5 2 C6 3 c8 12 33 2 c5 1 C7 3 ce 47 2 C4 1 CE 2 ce 68 1 C5 1 C5 2 C7 100 1 C4 1 C5 1 ce Through Hole Output Voltage Inductance | Sanyo OS-CON SA Sanyo MV-GX Nichleon PL Serles Panasonic HFQ (v) (WH) Serles Serles Serles No. CG Code No. C Code No. CG Code No. CG Code 10 2 C5 2 c 1 cs 2 C 15 2 C5 2 C5 1 C7 2 C5 *8 22 1 er 1 C10 1 cs 1 C7 33 1 C5 1 cio 1 C5 1 C7 10 2 C4 2 C5 1 C6 2 C5 15 1 C5 1 C10 1 C5 1 C7 5 22 1 C5 1 cg 1 C5 1 C5 33 1 C4 1 C5 1 C4 1 C4 47 1 C4 1 C4 1 C2 2 C4 10 2 C7 1 cio 1 C14 2 C4 15 1 cs 1 C6 1 C7 1 C5 22 1 C7 1 C5 1 C13 1 C5 12 33 1 C7 1 C4 1 C12 1 C4 47 1 C7 1 C3 1 ci 1 c3 68 1 C6 1 C2 1 C10 1 C3 100 1 C6 1 C2 1 cg 1 Ci No. represents the number of identical capacitor types to be connected in parallel C Code indicates the Capacitor Reference number in Table 2 for identifying the specific component fram the manufacturer www.national.comApplication Hints (continued) Table 4. Input Capacitors for Fixed Output Voltage Application (Assumes worst case maximum input voltage and load current for a given inductance value) Surface Mount putpat Inductance AVX TPS Serles Sprague 594D (aH) Serles Kemet T495 Serles No. C Code No. C Code No. C Code 10 3 C7 2 cio 3 cg 15 * * 3 C13 4 Ci2 38 22 * * 2 C13 3 Cle 33 * * 2 C13 3 Ci2 10 3 C4 2 C 3 cg 15 4 cg 3 ci2 4 cio 5 22 * * 3 C13 4 C12 33 * * 2 C13 3 C12 47 * * 1 C13 2 C12 10 4 cg 2 cid 4 C10 15 4 cs 2 cio 4 Cio 22 4 cg 3 ci2 4 cio 12 33 * * 3 C13 4 C12 47 * * 2 C13 3 C12 68 * * 2 C13 2 C12 100 * * 1 C13 2 C12 Through Hole Output Voltage Inductance | Sanyo OS-CON SA Sanyo MV-GX Nichieon PL Serles Panasonic HFQ (vy) (WH) Serles Serles Serles No. C Code No. C Code No. CG Code No. C Code 10 cg 2 ce 1 cis 1 ce 15 * * 2 C13 1 G25 1 C16 38 22 * * 1 ci4 1 C24 1 C16 33 * * 1 Cl4 1 Gad 1 C16 10 2 C7 2 ce 1 G25 1 cB 15 * * 2 C8 1 C25 1 c8 5 22 * * 2 C13 1 G25 1 C16 33 * * 1 Cl4 1 G23 1 C13 47 * * 1 ct 1 cig 1 Ci 10 2 cio 2 ce 1 C18 1 C8 15 2 Cio 2 cs 1 C18 1 cs 22 * * 2 C8 1 C18 1 c8 12 33 * * 2 C12 1 C24 1 C14 47 * * 1 C14 1 C23 1 C13 68 * * 1 C13 1 Cai 1 C15 100 * * 1 ct 1 G22 1 C11 * Check voltage rating of capacitors to be greater than application input voltage. No. represents the number of identical capacitor types fo be connected in parallel Code indicates the Capacitor Reference number in Table 2 for identifying the specific component from the manufacturer. www.national.comApplication Hints (continued) Table 5. Schottky Diode Selection Table Reverse Surface Mount Through Hole Voltage 3A 5A or More 3A 5A or () More 20V SK32 1N5820 SR302 30V SK33 MBRD835L 1N5821 30WOQ03F 31DQ03 40Vv SK34 MBRD1545CT 1N5822 IN5825 30BQ040 6TQ0455 MBR340 MBR?45 30WOQ04F 31DQ04 805@045 MBRS340 SR403 6TQ045 MBRD340 50V or SK35 MBR350 More 30WQ05F 31DQ05 SR305 Diode Manufacturer Contact Numbers International Rectifler | Phone (310) 322-3331 FAX (310) 322-3332 Motorola Phone (800) 521-6274 FAX (602) 244-6609 General Phone (516) 847-3000 Semlconductor FAX (516) 847-3236 Dlodes, Inc. Phone (805) 446-4800 FAX (805) 446-4850 www.national.comApplication Hints (continued) Table 6. Output Capacitors for Adjustable Output Voltage Applications Surface Mount Output Voltage | Inductance AVX TPS Serles Sprague 594D Kemet T495 Serles () (WH) Serles No. C Code No. C Gode No. C Code 33" 7 C1 6 C2 7 C3 1.21 to 2.50 A7* 5 ci 4 C2 5 C3 33 4 ci 3 C2 4 C3 2.5 to 3.75 A7* 3 Ci 2 C2 3 C3 22 4 Ci 3 C2 4 C3 3.75 to 5 33 3 Ci 2 C2 3 C3 47 2 Ci 2 Ce 2 C3 22 3 C2 1 C3 3 C4 33 2 C2 2 C3 2 C4 5 to 6.25 47 2 C2 2 C3 2 C4 68 1 C2 1 C3 1 C4 22 3 C2 1 C4 3 C4 33 2 C2 1 C3 2 C4 6.25 to 7.5 47 1 C3 1 C4 1 C6 68 1 C2 1 C3 1 C4 33 2 C5 1 CE 2 ce 47 1 C5 1 C 2 cs 7.5 to 10 68 1 C5 1 C6 1 cs 100 1 C4 1 C5 1 ce 33 1 C5 1 C 2 ce 47 1 C5 1 CE 2 cs 10 to 12.5 68 1 C5 1 CE 1 ce 100 1 C5 1 CE 1 ce 33 1 Cb 1 C8 1 ce 47 1 C6 1 Cs 1 ce 12.5 to 15 68 1 C6 1 C8 1 ce 100 1 Cb 1 C8 1 ce 33 1 C8 1 C10 2 C10 47 1 C8 1 cg 2 C10 15 to 20 68 1 C8 1 cg 2 cio 100 1 C8 1 cg 1 cio 33 2 cg 2 ci 2 Ci 47 1 C10 1 C12 1 ci 20 to 30 68 1 cg 1 C12 1 ci 100 1 cg 1 Cle 1 ci 10 4 C13 8 C12 15 3 C13 5 Cle 22 No Values Available 2 C13 4 Ci2 30 to 37 33 1 C13 3 Cl2 47 1 C13 2 C12 68 1 C13 2 C12 www.national.com 20Application Hints (continued) Table 6. Output Capacitors for Adjustable Output Voltage Applications (continued) Through Hole Output Voltage | Inductance | Sanyo OS-CON SA Sanyo MV-GX Nichicon PL Serles Panasonic HFQ (V) (WH) Serles Serles Serles No. C Code No. CG Code No. C Code No. C Code 1.21 to 2.50 33* 2 C3 5 C1 5 C3 3 c ee 47 2 cP 4 Ct 3 C3 2 C5 33* 1 C3 3 C1 3 C1 2 C45 2.5 to 3.75 47* 1 C2 2 C1 2 C3 1 C5 22 1 C3 3 C1 3 C1 2 C5 3.75 ta 5 33 1 C2 2 C1 2 C1 1 C5 47 1 C2 2 C1 1 C3 1 C5 22 1 C5 2 C 2 C3 2 C5 33 1 C4 1 C6 2 C1 1 C5 5 to 6.25 A? 1 C4 1 C6 1 C3 1 C5 68 1 C4 1 C6 1 C1 1 C5 22 1 C5 1 C6 2 C1 1 C5 33 1 C4 1 C 1 C3 1 C5 6.25 to 7.5 A? 1 C4 1 C 1 C1 1 C5 68 1 C4 1 Ce 1 C1 1 C5 33 1 C7 1 C6 1 C14 1 C5 47 1 C7 1 C 1 C14 1 C5 7.5 to 10 68 1 C7 1 Ce 1 C14 1 C2 100 1 C7 1 C2 1 C14 1 C2 33 1 CF 1 C 1 C14 1 C5 A? 1 C7 1 Ce 1 C14 1 C5 10 to 12.5 68 1 C7 1 Ce 1 cg 1 C2 100 1 C7 1 Ce 1 cg 1 Ce 33 1 cg 1 cio 1 C15 1 C2 47 1 cg 1 cio 1 C15 1 C2 12.5 to 15 68 1 cg 1 cio 1 C15 1 C2 100 1 cg 1 cid 1 C15 1 C2 33 1 cio 1 C7 1 C15 1 C2 47 1 C10 1 C7 1 C15 1 C2 15 to 20 68 1 Ci0 1 C7 1 C15 1 C2 100 1 C10 1 C7 1 C15 1 C2 33 1 C7 1 C16 1 C2 A? No Values 1 C7 1 C16 1 C2 20 to 30 68 Available 1 C7 1 C16 1 C2 100 1 C7 1 C16 1 C2 10 1 C12 1 C20 1 cio 15 1 cil 1 C20 1 Ci 22 No Values 1 ct 1 C20 1 C10 30 to 37 33 Available 1 cil 1 C20 1 cid 47 1 cil 1 G20 1 cid 68 1 cil 1 G20 1 cid * Set to a higher value for a practical design solution. See Applications Hints section No. represents the number of identical capacitor types to be connected in parallel C Code indicates the Capacitor Reference number in Table 2 for identifying the specific component from the manufacturer, Pl www.national.com22Ph ysical Dim ensions inches (millimeters) unless otherwise noted 0.2760-0.280 [6.60-7.11] /-10 59 TYP | 0.575 [14.61] > 0.085 typ +0,.010 g.agats oi [10. 1689-73] | + [2.16] > 0.36 0.022-0.032 yp 9.425 = {! |o.92| [? [0.56-0.8 1] [10.80] Co 0.50 0,330-0.350 PIN#1 ID [1.29] - co [8.38-8.89] 0.030 SFY TYP R MAX TYP e088 MAX | ~_ [0. 76) =- 1.27 15-9. 030 f | 7 \[o79 |. 0.410 fy +} ic 380.78) 4 o35 | [10.41] 0.173-0,183 [0.89] [4.45-4.65] LEAD POSITION OVERLAY at [Boe] [-M-] } TAPERED 7 0.048-0.052 SIDES 1 9-6 [1.22-1.32] be 62 1 0.250 yin laa 9.000" 9.008 008 stanp-oFr_ |6.35| oto a0 Max f [12.45] * 0.565 0.200 /~ MAX MIN [14.35] [5.08] CONTROLLING DIMENSION: INCH \ BACK VIEW S/H CREW H? TO-263 Surface Mount Power Package Order Number LM 2679S8-3.3, LM2679S-5.0, LM2679S-12 or LM2679S-ADJ NS Package Number TS7B 23 www.national.comLM2679 SIMPLE SWITCHER 5A Step-Down Voltage Regulator with Adjustable Current Limit Ph ysical Dimensions: inches (millimeters) unless otherwise noted (Continued) 0,100-0.120 [2.54-3.05] 0.149-0.153 0.025-0.035 TYP " [3.7B-3.89] [0.64-0.89] 40.075 0.400 op 505 : 0.040-0.060 10.14 7278 TYP [ -0.-3] 1 [1.02-1.52] azse-o.260|, 9.330-0.350 | PIN #1 1D [6.10-6.60] [8.38-8.89] 0.840-0.860 ono ; [21.34-21.84] 0.015 haa, 0,049 +0187 TYP R [1.02 | TYP [0.38 -0 oa! 7o_+| SSS ~ > yo 4 0.190-0.216 | = [4.83-5.33| 0.175-0.185 | - ___ _ 4 _ [4.45-4.70] 4 . ' 9,155-0,165 j 1 \ | [3.94-4.19] o_ge 0.255-0.275 f 0-6 | ade 400-0 t L__ |6.48-6.98| 0.048-0.052 0.198 oe O, [1.22-1.33] 3.545-0.565 [2.87 7330] SEATING PLANE TAPER SIDES 18 7*" 115 a4-44.35| Ls 80-9.900 [22.35-22.886] IAQ TE (REY At TO-220 Power Package Order Number LM2679T-3.3, LM2679T-5.0, LM2679T-12 or LM2679T-ADJ NS Package Number TAO7B LIFE SUPPORT POLICY NATIONALS PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DE- VICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMI- CONDUCTOR CORPORATION. As used herein: 1. Life support devices or sysiems are devices or sys- 2. A critical component in any component of a life support iems which, (a) are intended for surgical implant into device or sysiem whose failure to periorm can be rea- ihe body, or (b) support or sustain life, and whose fail- sonably expecied to cause the failure of the life support ure to perform when properly used in accordance device or sysiem, or to affect iis safety or effectiveness. with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury io the user. National Semiconductor National Semiconductor National Semiconductor National Semiconductor Corp oration Europe Agia Pacific Custom er Japan Lid. Americas Fax: +49 (0) 1 80-580 85 86 Reaponse Group Tel: 81-8-5620-6175 Tal: 1-800-272-6959 Email: europe.support@nsc.com Tel: 65-2544466 Fax: 81-8-5620-617S Fax: 1-800-737-7018 Deutsch Tel: +49 (0) 1 80-530 65 65 Fax: 65-2504466 Email: support@nsc.com English Tel: +49 (0) 1 80-582 78 32 Email: sea.supportG@nsc.com Frangais Tel: +49 (0) 1 80-582 93 58 www national.com ltaliano Tel: +49 (0) 1 80-534 16 80 National does not assume any resporsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.