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NATIONAL SEMICONDUCTOR LM5000 Manual

1. 16X 0 25 0 05 0 1 c ASO BO 2x DIMENSIONS ARE IN MILLIMETERS LLP 16 Pin Package SDA For Ordering Refer to Ordering Information Table NS Package Number SDA16A SDA16A Rev A www national com 16 Notes www national com 000SIN1T LM5000 High Voltage Switch Mode Regulator Notes THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION NATIONAL PRODUCTS NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE NO LICENSE WHETHER EXPRESS IMPLIED ARISING BY ESTOPPEL OR OTHERWISE TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL S PRODUCT WARRANTY EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS BUYERS SHOULD PROVIDE ADEQUATE DESIGN TESTING AND OPERATING SAFEGUARDS EXCEPT AS PROVIDED IN NA
2. National Semiconductor LM5000 High Voltage Switch Mode Regulator Features General Description The LM5000 is a monolithic integrated circuit specifically de signed and optimized for flyback boost or forward power converter applications The internal power switch is rated for maximum of 80V with a current limit set to 2A Protecting the power switch are current limit and thermal shutdown cir cuits The current mode control scheme provides excellent rejection of line transients and cycle by cycle current limiting An external compensation pin and the built in slope compen sation allow the user to optimize the frequency compensation Other distinctive features include softstart to reduce stresses during start up and an external shutdown pin for remote ON OFF control There are two operating frequency ranges avail able The LM5000 3 is pin selectable for either 300kHz FS Grounded or 700kHz FS Open The LM5000 6 is pin se lectable for either 600kHz FS Grounded or 1 3MHz FS Open The device is available in a low profile 16 lead TSSOP package or a thermally enhanced 16 lead LLP package Typical Application Circuit 100 16V 36V 4 7 0 47 uF LM5000 Flyback Converter Applications LM5000 3 COMP February 2007 80V internal switch Operating input voltage range of 3 1V to 40V Pin selectable operating frequency 2 700 3 600 2 1 3 6 Adjustable output voltage Extern
3. PWM L j Vin Cout Rioap V Cycle 1 a OUT V LOAD OUT Cycle 2 b 20031902 FIGURE 3 Simplified Boost Converter Diagram a First Cycle of Operation b Second Cycle Of Operation CONTINUOUS CONDUCTION MODE The LM5000 is a current mode PWM regulator When used as a boost regulator the input voltage is stepped up to a higher output voltage In continuous conduction mode when the in ductor current never reaches zero at steady state the boost regulator operates in two cycles In the first cycle of operation shown in Figure 3 a the tran sistor is closed and the diode is reverse biased Energy is collected in the inductor and the load current is supplied by Cour The second cycle is shown in Figure 3 b During this cycle the transistor is open and the diode is forward biased The energy stored in the inductor is transferred to the load and output capacitor The ratio of these two cycles determines the output voltage The output voltage is defined approximately as V V Vout mp D 1 V OUT where D is the duty cycle of the switch D and D will be re quired for design calculations SETTING THE OUTPUT VOLTAGE The output voltage is set using the feedback pin and a resistor divider connected to the output as shown in Figure 1 The feedback pin is always at 1 259V so the ratio of the feedback resistors sets the output voltage Vour 1 259 1 259 R FB1 rg
4. device may occur Operating Ratings are conditions for which the device is intended to be functional but device parameter specifications may not be guaranteed For guaranteed specifications and test conditions see the Electrical Characteristics Note 2 The maximum allowable power dissipation is a function of the maximum junction temperature T MAX the junction to ambient thermal resistance Ja and the ambient temperature T See the Electrical Characteristics table for the thermal resistance of various layouts The maximum allowable power dissipation at any ambient temperature is calculated using Pp MAX Timax ja Exceeding the maximum allowable power dissipation will cause excessive die temperature and the regulator will go into thermal shutdown Note 3 The human body model is a 100 pF capacitor discharged through a 1 5k resistor into each pin The machine model is a 200pF capacitor discharged directly into each pin Note 4 All limits guaranteed at room temperature standard typeface and at temperature extremes bold typeface All room temperature limits are 100 production tested All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control SQC methods All limits are used to calculate Average Outgoing Quality Level AOQL Note 5 Typical numbers are at 25 C and represent the most likely norm Note 6 Bias current flows into FB pin Note 7 Supply voltage bias current pr
5. 12066191F Resistor 6 19 5 Resistor 11111106 6 RCW 12062000F Res 7 CRCW12061002F Resistor Wk Q CXT5551 NSA Central NPN 180V LM5000 3 Regulator National 4 O UO UO UO UO m u c VALUE 10 C1206C221K1GAC Capacitor CER KEMET 220p 100V C1206C102K5RAC Capacitor CER KEMET 1000p 500V www national com 14 Physical Dimensions inches millimeters unless otherwise noted SYMM 5 94 SYMM z 1 ALL LEAD TIPS 14 0 65 aex 0 427 E 0 65 GAGE PLANE RECOMMENDED LAND PATTERN 0 25 T ff 2 ae 1 Nu PLANE DETAIL A TYPICAL 0 2 ALL LEAD TIPS _ _ 0 19 0 30 0 130 05 TYP 0 13 4 BO DIMENSIONS ARE IN MILLIMETERS DIMENSIONS IN FOR REFERENCE ONLY TSSOP 16 Pin Package MTC For Ordering Refer to Ordering Information Table NS Package Number MTC16 MTC16 Rev D 15 www national com 000SIN 1 LM5000 3 6 4 2 1010000000 oud i aex 0 25 gt k 4 0 5 c RECOMMENDED LAND PATTERN TS PIN 1 INDEX AREA e i Z PIN 1 ID A 27 221 22 22 22 16X 0 4 0 1 L
6. 2X INTRODUCTION TO COMPENSATION 1 A D Ts Ts 20031905 FIGURE 4 a Inductor current b Diode current The LM5000 is a current mode PWM regulator The signal flow of this control scheme has two feedback loops one that senses switch current and one that senses output voltage To keep a current programmed control converter stable above duty cycles of 50 the inductor must meet certain cri teria The inductor along with input and output voltage will determine the slope of the current through the inductor see www national com 10 Figure 4 a If the slope of the inductor current is too great the circuit will be unstable above duty cycles of 50 The LM5000 provides a compensation pin COMP to cus tomize the voltage loop feedback It is recommended that a series combination of and Cc be used for the compensa tion network as shown in Figure 1 The series combination of Rc and Cg introduces pole zero pair according to the follow ing equations 1 FIR RC 2 where Ro is the output impedance of the error amplifier 850k For most applications performance can be optimized by choosing values within the range 5k Rc 20k and 680pF Cc 4 7nF COMPENSATION This section will present a general design procedure to help insure a stable and operational circuit The designs in this datasheet are optimized for particular requirements If differ ent conversions are required some of the
7. 3 315 310 305 300 295 290 285 0 5 10 15 20 25 30 35 40 Vy V 20031928 fsw vs Temperature FS Low 3 330 320 310 300 290 280 270 40 20 0 20 40 60 80 100 120 TEMPERATURE C 20031930 CURRENT LIMIT A 770 750 730 710 690 FREQUENCY KHZ 670 650 630 Current Limit vs Vy 15 20 25 30 35 40 Vin V 20031927 fsw VS Vy FS OPEN 3 au 15 20 25 30 35 40 Vin 20031929 fsw vs Temperature FS OPEN 3 770 750 630 40 20 0 tu 20 40 60 80 100 120 TEMPERATURE C 20031931 www national com few kHz fsw vs Temperature FS Low 6 40 20 0 20 40 60 80 100 120 TEMPERATURE C 20031974 Error Amp Transconductance vs Temp Gm umho 600 550 500 450 400 350 300 250 40 20 0 20 40 60 80 100 120 TEMPERATURE C 20031932 fsw vs Temperature FS OPEN 6 few KHz BYP PIN VOLTAGE V 40 20 0 20 40 60 80 100 120 TEMPERATURE C 20031975 BYP Pin Voltage vs Vy 0 5 10 15 20 25 30 35 40 Vw V 20031933 www national com 000SIN1T LM5000 18V 36V Battery or Power Source 18V 3
8. 6V Battery or Power Source 33 uH SW ViN 8p LM5000 SHDN 48V FB SS COMP GND TEST 22 uH SW 8p LM5000 SHDN Cour 2x 4 7 pF Ceramic 20031953 FIGURE 1 300 kHz operation 48V output 48V FB SS COMP GND TEST Cour 2 x 4 7 pF Ceramic 20031954 FIGURE 2 700 kHz operation 48V output www national com Block Diagram COMP LI FBL ERROR 1 259V AMP I OVP 0 6V COMP Bandgap Voltage Reference ss Boost Regulator Operation The LM5000 utilizes a PWM control scheme to regulate the output voltage over all load conditions The operation can best be understood referring to the block diagram and Figure 3 At the start of each cycle the oscillator sets the driver logic and turns on the NMOS power device conducting current through the inductor cycle 1 of Figure 3 a During this cycle the voltage at the COMP pin controls the peak inductor current The COMP voltage will increase with larger loads and de crease with smaller This voltage is compared with the sum mation of the SW volatge and the ramp compensation The ramp compensation is used in PWM architectures to eliminate the sub harmonic oscillations that occur during duty cycles greater than 50 Once the summation of the ramp compen sation and switch voltage equals the COMP voltage the PWM comparator resets the driver logic turning off the NMOS power device The inductor current then flows through the ou
9. TIONAL S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS NATIONAL ASSUMES NO LIABILITY WHATSOEVER AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE AND OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE MERCHANTABILITY OR INFRINGEMENT OF ANY PATENT COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT LIFE SUPPORT POLICY NATIONAL S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION As used herein Life support devices or systems are devices which a are intended for surgical implant into the body or b support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation All other brand or product names may be trademarks or registered trademarks of their respective holders Copyright 2007 National Semiconduct
10. al compensation Input undervoltage lockout Softstart Current limit Over temperature protection External shutdown Small 16 Lead TSSOP or 16 Lead LLP package Flyback Regulator Forward Regulator Boost Regulator DSL Modems Distributed Power Converters 5V 8 18 11 10k 47 uF 3 36k 20031901 2007 National Semiconductor Corporation 200319 www national com yms eBeyoA y IH 0009 71 LM5000 Connection Diagram Top View Ordering Information Order Number Supplied As LM5000 3MTC MTC16 94 Units Rail LM5000 3MTCX 2500 Units Tape and Reel 45000803 5 6 1000 Unis Rai LM5000SDX 3 4500 Units Tape and Reel iMs000sD 6 urme 50 6 1o00 Unis Rai LM5000SDX 6 4500 Units Tape and Reel Pin Descriptions Pin Function 1 COMP Compensation network connection Connected to the output of the voltage error amplifier The RC compenstion network should be connected from this pin to AGND An additional 100pF high frequency capacitor to AGND is recommended 2 Output voltage feedback input 3 SHDN Shutdown control input Open enable Ground disable 4 Analog ground connect directly to PGND 5 Power ground 6 Power ground 74 Power ground 8 Power ground 9 Power switch input Switch connected between SW pins and PGND pins 10 Power switch input Switch connected between SW pins and PGND pins 11 Power switch input Switch connected be
11. components may need to be changed to ensure stability Below is a set of gen eral guidelines in designing a stable circuit for continuous conduction operation loads greater than 100mA in most all cases this will provide for stability during discontinuous oper ation as well The power components and their effects will be determined first then the compensation components will be chosen to produce stability INDUCTOR SELECTION To ensure stability at duty cycles above 50 the inductor must have some minimum value determined by the minimum input voltage and the maximum output voltage This equation is oe 2 IN DSON T in H 0 144 fs 2 where fs is the switching frequency D is the duty cycle and Roson is the ON resistance of the internal switch This equa tion is only good for duty cycles greater than 50 D gt 0 5 w _ V D Al 7 2Lfs in Amps The inductor ripple current is important for a few reasons One reason is because the peak switch current will be the average inductor current input current plus ij Care must be taken to make sure that the switch will not reach its current limit during normal operation The inductor must also be sized ac cordingly It should have a saturation current rating higher than the peak inductor current expected The output voltage ripple is also affected by the total ripple current DC GAIN AND OPEN LOOP GAIN Since the control stage of the converter forms a complete fe
12. cycle of a flyback regulator is determined by the fol lowing equation Vout VF lt Vout N ViN VsAT Vout Vr N ViN Vout Theoretically the maximum output voltage can be as large as desired just keep increasing the turns ratio of the trans former However there exists some physical limitations that prevent the turns ratio and thus the output voltage from in creasing to infinity The physical limitations are capacitances and inductances in the LM5000 switch the output diode s and the transformer such as reverse recovery time of the output diode mentioned above INPUT LINE CONDITIONING A small low pass RC filter should be used at the input pin of the LM5000 if the input voltage has an unusually large amount of transient noise Additionally the RC filter can reduce the dissipation within the device when the input voltage is high 20 55V D4 Flyback Regulator Operation The LM5000 is ideally suited for use in the flyback regulator topology The flyback regulator can produce a single output voltage or multiple output voltages The operation of a flyback regulator is as follows When the switch is on current flows through the primary winding of the transformer T1 storing energy in the magnetic field of the transformer Note that the primary and secondary windings are out of phase so no current flows through the secondary when current flows through the primary When the switch turns off
13. e Rc is generally much less than Ro it does not have much effect on the above equation and can be neglected until a value is chosen to set the zero fzc is created to cancel out the pole created by the output capacitor fp4 The output capacitor pole will shift with different load currents as shown by the equation so setting the zero is not exact De termine the range of fp over the expected loads and then set the zero fz to a point approximately in the middle The fre quency of this zero is determined by L 2 nC Ry in Hz Now Rc can be chosen with the selected value for Cc Check to make sure that the pole fpg is still in the 10Hz to 100Hz range change each value slightly if needed to ensure both component values are in the recommended range After checking the design at the end of this section these values can be changed a little more to optimize performance if de sired This is best done in the lab on a bench checking the load step response with different values until the ringing and overshoot on the output voltage at the edge of the load steps is minimal This should produce a stable high performance circuit For improved transient response higher values of Rc within the range of values should be chosen This will improve the overall bandwidth which makes the regulator re spond more quickly to transients If more detail is required or the most optimal performance is desired refer to a more in depth discus
14. edback loop with the power components it forms a closed loop system that must be stabilized to avoid positive feedback and instability A value for open loop DC gain will be required from which you can calculate or place poles and zeros to determine the crossover frequency and the phase margin A high phase margin greater than 45 is desired for the best stability and transient response For the purpose of stabilizing the LM5000 choosing a crossover point well below where the right half plane zero is located will ensure sufficient phase margin A discussion of the right half plane zero and checking the crossover using the DC gain will follow OUTPUT CAPACITOR SELECTION The choice of output capacitors is somewhat more arbitrary It is recommended that low ESR Equivalent Series Resis tance denoted capacitors be used such as ceramic polymer electrolytic or low ESR tantalum Higher ESR ca pacitors may be used but will require more compensation which will be explained later on in the section The ESR is also important because it determines the output voltage ripple ac cording to the approximate equation Vour i Resp in Volts After choosing the output capacitor you can determine a pole zero pair introduced into the control loop by the following equations 1 fa in Hz 2n Rgss R Cour 1 2mReseCour in Hz Where is the minimum load resistance corresponding to the maximum
15. load current The zero created by the ESR of the output capacitor is generally very high frequency if the ESR is small If low ESR capacitors are used it can be ne glected If higher ESR capacitors are used see the High Output Capacitor ESR Compensation section RIGHT HALF PLANE ZERO A current mode control boost regulator has an inherent right half plane zero RHP zero This zero has the effect of a zero in the gain plot causing an imposed 20dB decade on the rolloff but has the effect of a pole in the phase subtracting another 90 in the phase plot This can cause undesirable effects if the control loop is influenced by this zero To ensure the RHP zero does not cause instability issues the control loop should be designed to have a bandwidth of the fre quency of the RHP zero or less This zero occurs at a fre quency of Vo D in Hz RHPzero 2 where l gap is the maximum load current SELECTING THE COMPENSATION COMPONENTS The first step in selecting the compensation components Rc and Cc is to set a dominant low frequency pole in the control loop Simply choose values for Rc and Cc within the ranges given in the Introduction to Compensation section to set this pole in the area of 10Hz to 100Hz The frequency of the pole created is determined by the equation 11 www national com 000SIN 1 LM5000 1 tho 248 ROC in Hz where Ro is the output impedance of the error amplifier 850k Sinc
16. nless otherwise specified Symbol Parameter Conditions hee 4 hae 4 Units lo Quiescent Current FB 2V Not Switching FS 0V 2 0 mA FB 2V Not Switching 2 1 A FS Open m Mass m m n le Switch Current Limit N gt Feedback Voltage Line Regulation lg FB Pin Bias Current Note 6 BV Output Switch Breakdown Ty 25 lay 0 1pA Voltage T 40 C to 125 C ley 0 5yA dD lt E lt 2 lt lt gt BR e lt T 3 o ViN Input Voltage Range Error Amp Transconductance 5yA Q 3 Ay Error Amp Voltage Gain Dmax Maximum Duty Cycle FS 0V a 2 eo Maximum Duty Cycle FS 0V a 2 Minimum On Time 4 2 ns Switching Frequency FS 0V kHz FS Open a A o Switching Frequency FS 20V 600 75 FS Open 18 1 amp 5 MH Shutdown Pin Current 2 Switch Leakage Current Vow 80V 0 008 5 ThsupN SHDN Threshold Output High os Output Low os os V UVLO On Threshold 29 31 Off Threshold 27 29 r 5 gt 2 9 O e o 2 O pa 5 2 II e lt wo www national com 000SIN 1 LM5000 m Thermal Resistance TSSOP Package only 1 C W Note 1 Absolute maximum ratings are limits beyond which damage to the
17. oduct will result in aditional device power dissipation This power may be significant The thermal dissipation design should take this into account www national com 4 Typical Performance Characteristics Iq non switching vs Vy fs 300kHz Iq mA Iq mA FEEDBACK VOLTAGE V 3 000 2 800 2 600 2 400 2 200 2 000 1 800 1 600 1 400 1 200 1 000 0 5 10 15 20 25 30 35 40 Vin 20031920 Iq switching vs Vy fgy 300kHz 1 2300 5 10 15 20 25 30 35 40 Vin V 20031922 Vg VS Temperature 40 20 0 20 40 60 80 100 120 TEMPERATURE C 20031924 Iq mA Iq mA Iq non switching vs Vi fsw 700kHz 3 000 2 800 2 600 2 400 2 200 2 000 1 800 1 600 1 400 1 200 1 000 0 5 10 15 20 25 30 35 40 Vin 20031921 Iq switching vs Vi fs 700kHz n 5 10 15 20 25 30 35 40 20031923 VS Vin lgy 1 0 5 10 15 20 25 30 35 40 VIN V 20031925 www national com 000SIN 1 LM5000 CURRENT LIMIT fsw kHz few KHz Current Limit vs Temperature 2 1 95 1 9 1 85 1 8 1 75 1 7 1 65 1 6 1 55 1 5 40 20 0 20 40 60 80 100 120 TEMPERATURE C 20031926 fsw VS Vin FS Low
18. olithic IC pin causes erratic and unpredictable operation of that IC This holds true for the LM5000 IC as well When used in a flyback regulator the voltage at the Switch pin can go negative when the switch turns on The ringing voltage at the switch pin is caused by the output diode capacitance and the transformer leakage inductance forming a resonant circuit at the sec ondary ies The resonant circuit generates the ringing volt age which gets reflected back through the transformer to the Switch pin There are two common methods to avoid this problem One is to add an RC snubber around the output rec tifier s The values of the resistor and the capacitor must be chosen so that the voltage at the Switch pin does not drop below 0 4V The resistor may range in value between 10 and 1 k and the capacitor will vary from F to F Adding a snubber will slightly reduce the efficiency of the overall circuit The other method to reduce or eliminate the ringing is to insert a Schottky diode clamp between the SW pin and the PGND pin The reverse voltage rating of the diode must be greater than the switch off voltage www national com 12 OUTPUT VOLTAGE LIMITATIONS The maximum output voltage of a boost regulator is the max imum switch voltage minus a diode drop In a flyback regula tor the maximum output voltage is determined by the turns ratio N and the duty cycle D by the equation Vout N x Vin x D 1 D The duty
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20. sion of compensating current mode DC DC switching regulators HIGH OUTPUT CAPACITOR ESR COMPENSATION When using an output capacitor with a high ESR value or just to improve the overall phase margin of the control loop an other pole may be introduced to cancel the zero created by the ESR This is accomplished by adding another capacitor directly from the compensation pin to ground in par allel with the series combination of Rc and Cc The pole should be placed at the same frequency f7 the ESR zero The equation for this pole follows 1 in Hz fica 21C Rc To ensure this equation is valid and that Cc can be used without negatively impacting the effects of Rc and Cc foc must be greater than 10fpc CHECKING THE DESIGN The final step is to check the design This is to ensure a band width of 7 or less of the frequency of the RHP zero This is done by calculating the open loop DC gain Apc After this value is known you can calculate the crossover visually by placing a 20dB decade slope at each pole and a 20dB decade slope for each zero The point at which the gain plot crosses unity gain or OdB is the crossover frequency If the crossover frequency is at less than the RHP zero the phase margin should be high enough for stability The phase margin can also be improved some by adding Cc as discussed ear lier in the section The equation for Apc is given below
21. the magnetic field collapses reversing the voltage polarity of the primary and secondary windings Now rectifier D5 is forward biased and current flows through it releasing the energy stored in the transformer This produces voltage at the output The output voltage is controlled by modulating the peak switch current This is done by feeding back a portion of the output voltage to the error amp which amplifies the difference between the feedback voltage and a 1 259V reference The error amp output voltage is compared to a ramp voltage pro portional to the switch current i e inductor current during the switch on time The comparator terminates the switch on time when the two voltages are equal thereby controlling the peak Switch current to maintain a constant output voltage N 18T 3 3V 2A R3 10k c9 C8 68u 68u AV AV R4 6 19k 2 20031972 FIGURE 5 LM5000 Flyback Converter 13 www national com 000SIN 1 LM5000 ITEM PART NUMBER DESCRIPTION 8 C4532X7S0G686M Capacitor CER TDK 68y 4V 9 C4532X780G686M Capacitor CER TDK 68 4V 1 1 1 0 BZX84C10 NSA Central 10V Zener SOT 23 CMZ5930B NSA Central 16V Zener SMA CMPD914 NSA Central Switching SOT 23 CMPD914 NSA Central Switching SOT 23 CMSH3 40L NSA Central Schottky SMC 0009 Coilcraft Transformer 1 CRCW12064992F 2 CRCWI2061001F Resistor s CRCW12061002F Rest Wk CRCW
22. tput diode to the load and output capacitor cycle 2 of Figure 3 b The NMOS power device is then set by the oscillator at the Oscillator Thermal Shutdown ovP LOGIC SS Reset 89 Duty Vus Load Current Mit Measurement LJ SW Set Reset Drive UVP Thermal SD PGND 2 9V Internal Shutdown UVP Comparator CUMP SHDN AGND 20031903 end of the period and current flows through the inductor once again The LM5000 has dedicated protection circuitry running during the normal operation to protect the IC The Thermal Shutdown circuitry turns off the NMOS power device when the die tem perature reaches excessive levels The UVP comparator pro tects the NMOS power device during supply power startup and shutdown to prevent operation at voltages less than the minimum input voltage The OVP comparator is used to pre vent the output voltage from rising at no loads allowing full PWM operation over all load conditions The LM5000 also features a shutdown mode An external capacitor sets the softstart time by limiting the error amp output range as the capacitor charges up via an internal 10pA current source The LM5000 is available in two operating frequency ranges The LM5000 3 is pin selectable for either 300kHz FS Grounded or 700kHz FS Open The LM5000 6 is pin se lectable for either 600kHz FS Grounded or 1 8MHz FS Open www national com 000SIN 1 LM5000 Operation L Vin
23. tween SW pins and PGND pins 12 Bypass Decouple Capacitor Connection 0 1uF ceramic capacitor recommended 13 Vin Analog power input A small RC filter is recommended to suppress line glitches Typical values of 10 and O 1pF are recommended 14 Softstart Input External capacitor and internal current source sets the softstart time 15 Switching frequency select input Open Fhign Ground 16 TEST Factory test pin connect to ground Exposed Pad Connect to system ground plane for reduced thermal resistance underside of LLP package www national com 2 Absolute Maximum Ratings 1 far ed 15 566 2357 ESD Susceptibility Note 3 If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office puman Body Model 2kV Distributors for availability and specifications Machine Model 200V Vig 0 3V to 40V Storage Temperature 65 C to 150 C SW Voltage 0 3V to 80V PH FB Voltage 0 3V to 5V Operating Conditions COMP Voltage 0 3V to Operating Junction All Other Pins 0 3V to 7V ao Range p Maximum Junction Temperature 150 C Supply Voltage Note 7 3 1V to 40V Power Dissipation Note 2 Internally Limited Lead Temperature 216 C Electrical Characteristics Specifications in standard type face are for T 25 C and those with boldface type apply over the full Operating Temperature Range T 40 C to 125 C Unless otherwise specified V 12V and OA u
24. with additional equations required for the calculation R 9 840 Apcom 2009 HE O R JIR in dB Ree Rea Roson 85 3 10 Leff _ 2 1 MT no unit mc 0 072fs in A s m1 VinRoson in V s where is the minimum load resistance Vi is the maximum input voltage and Rpsoy is the value chosen from the graph Rpson VS in the Typical Performance Characteristics section SWITCH VOLTAGE LIMITS In a flyback regulator the maximum steady state voltage ap pearing at the switch when it is off is set by the transformer turns ratio N the output voltage and the maximum in put voltage Max Vsw orr Vin Max where V is the forward biased voltage of the output diode and is typically 0 5V for Schottky diodes and 0 8V for ultra fast recovery diodes In certain circuits there exists a voltage Spike V superimposed on top of the steady state voltage Usually this voltage spike is caused by the transformer leak age inductance and or the output rectifier recovery time To clamp the voltage at the switch from exceeding its maximum value a transient suppressor in series with a diode is inserted across the transformer primary If poor circuit layout techniques are used negative voltage transients may appear on the Switch pin Applying a negative voltage with respect to the IC s ground to any mon

NATIONAL SEMICONDUCTOR LM5000 Manual

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