LM2588_05

LM2588 SIMPLE SWITCHER 5A Flyback Regulator with Shutdown July 2005 LM2588 SIMPLE SWITCHER ® 5A Flyback Regulator with Shutdown General Description The LM2588 series of regulators are monolithic integrated circuits specifically designed for flyback, step-up (boost), and forward converter applications. The device is available in 4 different output voltage versions: 3.3V, 5.0V, 12V, and adjustable. Requiring a minimum number of external components, these regulators are cost effective, and simple to use. Included in the datasheet are typical circuits of boost and flyback regulators. Also listed are selector guides for diodes and capacitors and a family of standard inductors and flyback transformers designed to work with these switching regulators. The power switch is a 5.0A NPN device that can stand-off 65V. Protecting the power switch are current and thermal limiting circuits, and an undervoltage lockout circuit. This IC contains an adjustable frequency oscillator that can be programmed up to 200 kHz. The oscillator can also be synchronized with other devices, so that multiple devices can operate at the same switching frequency. Other features include soft start mode to reduce in-rush current during start up, and current mode control for improved rejection of input voltage and output load transients and cycle-by-cycle current limiting. The device also has a shutdown pin, so that it can be turned off externally. An output voltage tolerance of ± 4%, within specified input voltages and output load conditions, is guaranteed for the power supply system. Features Requires few external components Family of standard inductors and transformers NPN output switches 5.0A, can stand off 65V Wide input voltage range: 4V to 40V Adjustable switching frequency: 100 kHz to 200 kHz External shutdown capability Draws less than 60 µA when shut down Frequency synchronization Current-mode operation for improved transient response, line regulation, and current limit n Internal soft-start function reduces in-rush current during start-up n Output transistor protected by current limit, under voltage lockout, and thermal shutdown n System output voltage tolerance of ± 4% max over line and load conditions n n n n n n n n n Typical Applications n n n n Flyback regulator Forward converter Multiple-output regulator Simple boost regulator Connection Diagrams Bent, Staggered Leads 7-Lead TO-220 (T) Top View Bent, Staggered Leads 7-Lead TO-220 (T) Side View 01242018 01242017 Order Number LM2588T-3.3, LM2588T-5.0, LM2588T-12 or LM2588T-ADJ See NS Package Number TA07B SIMPLE SWITCHER ® and Switchers Made Simple ® are registered trademarks of National Semiconductor Corporation. © 2005 National Semiconductor Corporation DS012420 www.national.com LM2588 Connection Diagrams (Continued) 7-Lead TO-263 (S) Side View 7-Lead TO-263 (S) Top View 01242020 01242019 Order Number LM2588S-3.3, LM2588S-5.0, LM2588S-12 or LM2588S-ADJ Tape and Reel Order Number LM2588SX-3.3, LM2588SX-5.0, LM2588SX-12 or LM2588SX-ADJ See NS Package Number TS7B Ordering Information Package Type 7-Lead TO-220 Bent, Staggered Leads 7-Lead TO-263 7-Lead TO-263 Tape and Reel NSC Package Drawing TA07B TS7B TS7B LM2588T-3.3, LM2588T-5.0, LM2588T-12, LM2588T-ADJ LM2588S-3.3, LM2588S-5.0, LM2588S-12, LM2588S-ADJ LM2588SX-3.3, LM2588SX-5.0, LM2588SX-12, LM2588SX-ADJ Order Number www.national.com 2 LM2588 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Voltage Switch Voltage Switch Current (Note 2) Compensation Pin Voltage Feedback Pin Voltage ON /OFF Pin Voltage Sync Pin Voltage Power Dissipation (Note 3) Storage Temperature Range −0.4V ≤ VIN ≤ 45V −0.4V ≤ VSW ≤ 65V Internally Limited −0.4V ≤ VCOMP ≤ 2.4V −0.4V ≤ VFB ≤ 2 VOUT −0.4V ≤ VSH ≤ 6V −0.4V ≤ VSYNC ≤ 2V Internally Limited −65˚C to +150˚C Lead Temperature (Soldering, 10 sec.) Maximum Junction Temperature (Note 3) Minimum ESD Rating (C = 100 pF, R = 1.5 kΩ) 2 kV 150˚C 260˚C Operating Ratings Supply Voltage Output Switch Voltage Output Switch Current Junction Temperature Range 4V ≤ VIN ≤ 40V 0V ≤ VSW ≤ 60V ISW ≤ 5.0A −40˚C ≤ TJ ≤ +125˚C LM2588-3.3 Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Symbol VOUT ∆VOUT/ ∆VIN ∆VOUT/ ∆ILOAD η VREF ∆VREF GM AVOL Efficiency Output Reference Voltage Reference Voltage Line Regulation Error Amp Transconductance Error Amp Voltage Gain ICOMP = −30 µA to +30 µA VCOMP = 1.0V VCOMP = 0.5V to 1.6V RCOMP = 1.0 MΩ (Note 6) 260 151/75 V/V 1.193 0.678 2.259 mmho Load Regulation Parameters Output Voltage Line Regulation Conditions VIN = 4V to 12V ILOAD = 400 mA to 1.75A VIN = 4V to 12V ILOAD = 400 mA VIN = 12V ILOAD = 400 mA to 1.75A VIN = 12V, ILOAD = 1A Measured at Feedback Pin VCOMP = 1.0V VIN = 4V to 40V 2.0 mV 75 3.3 3.242/3.234 3.358/3.366 % V 20 50/100 mV 20 50/100 mV Typical 3.3 Min 3.17/3.14 Max 3.43/3.46 Units V SYSTEM PARAMETERS Test Circuit of Figure 1 (Note 4) UNIQUE DEVICE PARAMETERS (Note 5) LM2588-5.0 Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Symbol VOUT ∆VOUT/ ∆VIN ∆VOUT/ ∆ILOAD η Efficiency Load Regulation Parameters Output Voltage Line Regulation Conditions VIN = 4V to 12V ILOAD = 500 mA to 1.45A VIN = 4V to 12V ILOAD = 500 mA VIN = 12V ILOAD = 500 mA to 1.45A VIN = 12V, ILOAD = 750 mA 80 % 20 50/100 mV 20 50/100 mV Typical 5.0 Min 4.80/4.75 Max 5.20/5.25 Units V SYSTEM PARAMETERS Test Circuit of Figure 1 (Note 4) UNIQUE DEVICE PARAMETERS (Note 5) 3 www.national.com LM2588 LM2588-5.0 Electrical Characteristics Symbol VREF ∆VREF GM AVOL Parameters Output Reference Voltage Reference Voltage Line Regulation Error Amp Transconductance Error Amp Voltage Gain ICOMP = −30 µA to +30 µA VCOMP = 1.0V VCOMP = 0.5V to 1.6V RCOMP = 1.0 MΩ (Note 6) Conditions Measured at Feedback Pin VCOMP = 1.0V VIN = 4V to 40V (Continued) Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Typical 5.0 3.3 0.750 165 0.447 99/49 1.491 Min 4.913/4.900 Max 5.088/5.100 Units V mV mmho V/V LM2588-12 Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Symbol VOUT ∆VOUT/ ∆VIN ∆VOUT/ ∆ILOAD η VREF ∆VREF GM AVOL Efficiency Output Reference Voltage Reference Voltage Line Regulation Error Amp Transconductance Error Amp Voltage Gain ICOMP = −30 µA to +30 µA VCOMP = 1.0V VCOMP = 0.5V to 1.6V RCOMP = 1.0 MΩ (Note 6) 70 41/21 V/V 0.328 0.186 0.621 mmho Load Regulation Parameters Output Voltage Line Regulation Conditions VIN = 4V to 10V ILOAD = 300 mA to 1.2A VIN = 4V to 10V ILOAD = 300 mA VIN = 10V ILOAD = 300 mA to 1.2A VIN = 10V, ILOAD = 1A Measured at Feedback Pin VCOMP = 1.0V VIN = 4V to 40V 7.8 mV 90 12.0 11.79/11.76 12.21/12.24 % V 20 100/200 mV 20 100/200 mV Typical 12.0 Min 11.52/11.40 Max 12.48/12.60 Units V SYSTEM PARAMETERS Test Circuit of Figure 2 (Note 4) UNIQUE DEVICE PARAMETERS (Note 5) LM2588-ADJ Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Symbol VOUT ∆VOUT/ ∆VIN ∆VOUT/ ∆ILOAD η Efficiency Load Regulation Parameters Output Voltage Line Regulation Conditions VIN = 4V to 10V ILOAD = 300 mA to 1.2A VIN = 4V to 10V ILOAD = 300 mA VIN = 10V ILOAD = 300 mA to 1.2A VIN = 10V, ILOAD = 1A 90 % 20 100/200 mV 20 100/200 mV Typical 12.0 Min 11.52/11.40 Max 12.48/12.60 Units V SYSTEM PARAMETERS Test Circuit of Figure 2 (Note 4) www.national.com 4 LM2588 LM2588-ADJ Electrical Characteristics Symbol VREF ∆VREF GM AVOL IB Parameters Output Reference Voltage Reference Voltage Line Regulation Error Amp Transconductance Error Amp Voltage Gain Error Amp Input Bias Current ICOMP = −30 µA to +30 µA VCOMP = 1.0V VCOMP = 0.5V to 1.6V RCOMP = 1.0 MΩ (Note 6) VCOMP = 1.0V Conditions Measured at Feedback Pin VCOMP = 1.0V VIN = 4V to 40V (Continued) Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Typical 1.230 1.5 3.200 670 125 1.800 400/200 425/600 6.000 Min 1.208/1.205 Max 1.252/1.255 Units V mV mmho V/V nA UNIQUE DEVICE PARAMETERS (Note 5) (Note 5) Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Symbol IS Parameters Input Supply Current Switch Off (Note 8) ISWITCH = 3.0A IS/D VUV fO Shutdown Input Supply Current Input Supply Undervoltage Lockout Oscillator Frequency Measured at Switch Pin RLOAD = 100Ω, VCOMP = 1.0V Freq. Adj. Pin Open (Pin 1) RSET = 22 kΩ fSC Short-Circuit Frequency VEAO Error Amplifier Output Swing Measured at Switch Pin RLOAD = 100Ω VFEEDBACK = 1.15V Upper Limit (Note 7) Lower Limit (Note 8) IEAO Error Amp Output Current (Source or Sink) ISS DMAX IL VSUS VSAT Soft Start Current Maximum Duty Cycle Switch Leakage Current Switch Sustaining Voltage Switch Saturation Voltage VFEEDBACK = 0.92V VCOMP = 1.0V RLOAD = 100Ω (Note 7) Switch Off VSWITCH = 60V dV/dT = 1.5V/ns ISWITCH = 5.0A 0.7 65 1.1/1.4 V V 15 300/600 µA 98 93/90 % 11.0 8.0/7.0 17.0/19.0 µA (Note 9) 165 110/70 260/320 µA 0.25 0.40/0.55 V 2.8 2.6/2.4 V 25 kHz 200 kHz 100 85/75 115/125 kHz RLOAD = 100Ω 3.30 3.05 3.75 V VSH = 3V 85 16 140/165 100/300 mA µA Conditions Typical 11 Min Max 15.5/16.5 Units mA All Output Voltage Versions Electrical Characteristics 5 www.national.com LM2588 All Output Voltage Versions Electrical Characteristics Symbol ICL VSTH ISYNC VSHTH ISH θJA θJA θJC θJA θJA θJA θJC Parameters NPN Switch Current Limit Synchronization Threshold Voltage Synchronization Pin Current ON /OFF Pin (Pin 1) Threshold Voltage ON /OFF Pin (Pin 1) Current Thermal Resistance FSYNC = 200 kHz VCOMP = 1V, VIN = 5V VIN = 5V VCOMP = 1V, VSYNC = VSTH VCOMP = 1V (Note 10) VCOMP = 1V VSH = VSHTH T Package, Junction to Ambient (Note 11) T Package, Junction to Ambient (Note 12) T Package, Junction to Case S Package, Junction to Ambient (Note 13) S Package, Junction to Ambient (Note 14) S Package, Junction to Ambient (Note 15) S Package, Junction to Case 2 26 35 2 56 45 65 40 1.6 100 Conditions Typical 6.5 0.75 (Note 5) (Continued) Specifications with standard type face are for TJ = 25˚C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 5V. Min 5.0 0.625/0.40 Max 9.5 0.875/1.00 200 1.0/0.8 15/10 2.2/2.4 65/75 Units A V µA V µA ˚C/W Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. These ratings apply when the current is limited to less than 1.2 mA for pins 1, 2, 3, and 6. Operating ratings indicate conditions for which the device is intended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: Note that switch current and output current are not identical in a step-up regulator. Output current cannot be internally limited when the LM2588 is used as a step-up regulator. To prevent damage to the switch, the output current must be externally limited to 5A. However, output current is internally limited when the LM2588 is used as a flyback regulator (see the Application Hints section for more information). Note 3: The junction temperature of the device (TJ) is a function of the ambient temperature (TA), the junction-to-ambient thermal resistance (θJA), and the power dissipation of the device (PD). A thermal shutdown will occur if the temperature exceeds the maximum junction temperature of the device: PD x θJA + TA(MAX) ≥ TJ(MAX). For a safe thermal design, check that the maximum power dissipated by the device is less than: PD ≤ [TJ(MAX) − TA(MAX)]/θJA. When calculating the maximum allowable power dissipation, derate the maximum junction temperature — this ensures a margin of safety in the thermal design. Note 4: External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the LM2588 is used as shown in Figure 1 and Figure 2, system performance will be as specified by the system parameters. Note 5: All room temperature limits are 100% production tested, and all limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. Note 6: A 1.0 MΩ resistor is connected to the compensation pin (which is the error amplifier output) to ensure accuracy in measuring AVOL. Note 7: To measure this parameter, the feedback voltage is set to a low value, depending on the output version of the device, to force the error amplifier output high and the switch on. Note 8: To measure this parameter, the feedback voltage is set to a high value, depending on the output version of the device, to force the error amplifier output low and the switch off. Note 9: To measure the worst-case error amplifier output current, the LM2588 is tested with the feedback voltage set to its low value (specified in (Note 7)) and at its high value (specified in (Note 8)). Note 10: When testing the minimum value, do not sink current from this pin — isolate it with a diode. If current is drawn from this pin, the frequency adjust circuit will begin operation (see Figure 41). Note 11: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with 1⁄2 inch leads in a socket, or on a PC board with minimum copper area. Note 12: Junction to ambient thermal resistance (no external heat sink) for the 7 lead TO-220 package mounted vertically, with 1⁄2 inch leads soldered to a PC board containing approximately 4 square inches of (1 oz.) copper area surrounding the leads. Note 13: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.136 square inches (the same size as the TO-263 package) of 1 oz. (0.0014 in. thick) copper. Note 14: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board area of 0.4896 square inches (3.6 times the area of the TO-263 package) of 1 oz. (0.0014 in. thick) copper. Note 15: Junction to ambient thermal resistance for the 7 lead TO-263 mounted horizontally against a PC board copper area of 1.0064 square inches (7.4 times the area of the TO-263 package) of 1 oz. (0.0014 in. thick) copper. Additional copper area will reduce thermal resistance further. See the thermal model in Switchers Made Simple ® software. www.national.com 6 LM2588 Typical Performance Characteristics Supply Current vs Temperature Reference Voltage vs Temperature 01242002 01242003 ∆Reference Voltage vs Supply Voltage Supply Current vs Switch Current 01242004 01242005 Current Limit vs Temperature Feedback Pin Bias Current vs Temperature 01242006 01242007 7 www.national.com LM2588 Typical Performance Characteristics Switch Saturation Voltage vs Temperature (Continued) Switch Transconductance vs Temperature 01242008 01242009 Oscillator Frequency vs Temperature Error Amp Transconductance vs Temperature 01242010 01242011 Error Amp Voltage Gain vs Temperature Short Circuit Frequency vs Temperature 01242012 01242013 www.national.com 8 LM2588 Typical Performance Characteristics Shutdown Supply Current vs Temperature (Continued) ON /OFF Pin Current vs Voltage 01242014 01242015 Oscillator Frequency vs Resistance 01242016 Flyback Regulator 01242001 9 www.national.com LM2588 Test Circuits 01242021 CIN1 — 100 µF, 25V Aluminum ElectrolyticCIN2 — 0.1 µF CeramicT — 22 µH, 1:1 Schott #67141450D — 1N5820COUT — 680 µF, 16V Aluminum ElectrolyticCC — 0.47 µF CeramicRC — 2k FIGURE 1. LM2588-3.3 and LM2588-5.0 01242022 CIN1 — 100 µF, 25V Aluminum ElectrolyticCIN2 — 0.1 µF CeramicL — 15 µH, Renco #RL-5472-5D — 1N5820COUT — 680 µF, 16V Aluminum ElectrolyticCC — 0.47 µF CeramicRC — 2kFor 12V Devices: R1 = Short (0Ω) andR2 = OpenFor ADJ Devices: R1 = 48.75k, ± 0.1% andR2 = 5.62k, ± 0.1% FIGURE 2. LM2588-12 and LM2588-ADJ www.national.com 10 LM2588 Block Diagram 01242023 For Fixed Versions 3.3V, R1 = 3.4k, R2 = 2k5.0V, R1 = 6.15k, R2 = 2k12V, R1 = 8.73k, R2 = 1kFor Adj. VersionR1 = Short (0Ω), R2 = Open FIGURE 3. Block Diagram Flyback Regulator Operation The LM2588 is ideally suited for use in the flyback regulator topology. The flyback regulator can produce a single output voltage, such as the one shown in Figure 4, or multiple output voltages. In Figure 4, the flyback regulator generates an output voltage that is inside the range of the input voltage. This feature is unique to flyback regulators and cannot be duplicated with buck or boost regulators. The operation of a flyback regulator is as follows (refer to Figure 4): 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, the magnetic field col- lapses, reversing the voltage polarity of the primary and secondary windings. Now rectifier D1 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 1.230V reference. The error amp output voltage is compared to a ramp voltage proportional 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. 11 www.national.com LM2588 Flyback Regulator Operation (Continued) 01242024 As shown in Figure 4, the LM2588 can be used as a flyback regulator by using a minimum number of external components. The switching waveforms of this regulator are shown in Figure 5. Typical Performance Characteristics observed during the operation of this circuit are shown in Figure 6. FIGURE 4. 12V Flyback Regulator Design Example Typical Performance Characteristics 01242060 A: Switch Voltage, 10V/div B: Switch Current, 5A/div C: Output Rectifier Current, 5A/div D: Output Ripple Voltage, 100 mV/div AC-Coupled FIGURE 5. Switching Waveforms www.national.com 12 LM2588 Typical Performance Characteristics (Continued) 01242061 FIGURE 6. VOUT Response to Load Current Step Typical Flyback Regulator Applications Figure 7 through 12 show six typical flyback applications, varying from single output to triple output. Each drawing contains the part number(s) and manufacturer(s) for every component except the transformer. For the transformer part numbers and manufacturers’ names, see the table in Figure 13. For applications with different output voltages — requiring the LM2588-ADJ — or different output configurations that do not match the standard configurations, refer to the Switchers Made Simple™ software. 01242025 FIGURE 7. Single-Output Flyback Regulator 13 www.national.com LM2588 Typical Flyback Regulator Applications (Continued) 01242026 FIGURE 8. Single-Output Flyback Regulator 01242027 FIGURE 9. Single-Output Flyback Regulator www.national.com 14 LM2588 Typical Flyback Regulator Applications (Continued) 01242028 FIGURE 10. Dual-Output Flyback Regulator 01242029 FIGURE 11. Dual-Output Flyback Regulator 15 www.national.com LM2588 Typical Flyback Regulator Applications (Continued) 01242030 FIGURE 12. Triple-Output Flyback Regulator TRANSFORMER SELECTION (T) Figure 13 lists the standard transformers available for flyback regulator applications. Included in the table are the turns ratio(s) for each transformer, as well as the output voltages, input voltage ranges, and the maximum load currents for each circuit. Applications Transformers VIN VOUT1 IOUT1 (Max) N1 VOUT2 IOUT2 (Max) N2 VOUT3 IOUT3 (Max) N3 Figure 7 T1 4V–6V 3.3V 1.8A 1 Figure 8 T1 4V–6V 5V 1.4A 1 Figure 9 T1 8V–16V 12V 1.2A 1 Figure 10 T2 4V–6V 12V 0.3A 2.5 −12V 0.3A 2.5 Figure 11 T3 18V–36V 12V 1A 0.8 −12V 1A 0.8 Figure 12 T4 18V–36V 5V 2.5A 0.35 12V 0.5A 0.8 −12V 0.5A 0.8 FIGURE 13. Transformer Selection Table www.national.com 16 LM2588 Typical Flyback Regulator Applications Transformer Type T1 T2 T3 T4 Note 16: Coilcraft Inc.,: (Continued) Manufacturers’ Part Numbers Coilcraft (Note 16) Q4434-B Q4337-B Q4343-B Q4344-B Phone: (800) 322-2645 Fax: (708) 639-1469 Phone: +44 1236 730 595 Fax: +44 1236 730 627 Fax: (619) 674-8262 Coilcraft (Note 16) Surface Mount Q4435-B Q4436-B — — Pulse (Note 17) Surface Mount PE-68411 PE-68412 PE-68421 PE-68422 Renco (Note 18) RL-5530 RL-5531 RL-5534 RL-5535 Schott (Note 19) 67141450 67140860 67140920 67140930 1102 Silver Lake Road, Cary, IL 60013: European Headquarters, 21 Napier Place: Note 17: Pulse Engineering Inc.,: Wardpark North, Cumbernauld, Scotland G68 0LL: 12220 World Trade Drive, San Diego, CA 92128: European Headquarters, Dunmore Road: Tuam, Co. Galway, Ireland: Note 18: Renco Electronics Inc.,: Note 19: Schott Corp.,: Fax: +353 93 24 459 Phone: (619) 674-8100 Phone: +353 93 24 107 Phone: (800) 645-5828 Fax: (516) 586-5562 Fax: (612) 475-1786 60 Jeffryn Blvd. East, Deer Park, NY 11729: Phone: (612) 475-1173 1000 Parkers Lane Road, Wayzata, MN 55391: FIGURE 14. Transformer Manufacturer Guide TRANSFORMER FOOTPRINTS Figure 15 through 32 show the footprints of each transformer, listed in Figure 14. T1 T3 01242033 Top View 01242031 Top View FIGURE 17. Coilcraft Q4343-B FIGURE 15. Coilcraft Q4434-B T4 T2 01242032 Top View 01242034 Top View FIGURE 16. Coilcraft Q4337-B FIGURE 18. Coilcraft Q4344-B 17 www.national.com LM2588 Typical Flyback Regulator Applications (Continued) T1 T2 01242038 01242035 Top View FIGURE 22. Pulse PE-68412 (Surface Mount) Top View FIGURE 19. Coilcraft Q4435-B (Surface Mount) T3 T2 01242039 Top View 01242036 Top View FIGURE 20. Coilcraft Q4436-B (Surface Mount) FIGURE 23. Pulse PE-68421 (Surface Mount) T4 T1 01242040 01242037 Top View FIGURE 24. Pulse PE-68422 (Surface Mount) Top View FIGURE 21. Pulse PE-68411 (Surface Mount) www.national.com 18 LM2588 Typical Flyback Regulator Applications (Continued) T1 T1 01242045 Top View FIGURE 29. Schott 67141450 01242041 Top View T2 FIGURE 25. Renco RL-5530 T2 01242046 Top View FIGURE 30. Schott 67140860 01242042 Top View T3 FIGURE 26. Renco RL-5531 T3 01242047 Top View FIGURE 31. Schott 67140920 01242043 Top View FIGURE 27. Renco RL-5534 T4 01242044 Top View FIGURE 28. Renco RL-5535 19 www.national.com LM2588 Typical Flyback Regulator Applications T4 (Continued) 01242048 Top View FIGURE 32. Schott 67140930 Step-Up (Boost) Regulator Operation Figure 33 shows the LM2588 used as a step-up (boost) regulator. This is a switching regulator that produces an output voltage greater than the input supply voltage. A brief explanation of how the LM2588 Boost Regulator works is as follows (refer to Figure 33). When the NPN switch turns on, the inductor current ramps up at the rate of VIN/L, storing energy in the inductor. When the switch turns off, the lower end of the inductor flies above VIN, discharging its current through diode (D) into the output capacitor (COUT) at a rate of (VOUT − VIN)/L. Thus, energy stored in the inductor during the switch on time is transferred to the output during the switch off time. The output voltage is controlled by adjusting the peak switch current, as described in the flyback regulator section. 01242049 FIGURE 33. 12V Boost Regulator By adding a small number of external components (as shown in Figure 33), the LM2588 can be used to produce a regulated output voltage that is greater than the applied input voltage. The switching waveforms observed during the operation of this circuit are shown in Figure 34. Typical performance of this regulator is shown in Figure 35. www.national.com 20 LM2588 Typical Performance Characteristics 01242062 A: Switch Voltage,10V/div B: Switch Current, 5A/div C: Inductor Current, 5A/div D: Output Ripple Voltage, 100 mV/div, AC-Coupled FIGURE 34. Switching Waveforms 01242063 FIGURE 35. VOUT Response to Load Current Step Typical Boost Regulator Applications Figure 36 and 38 through 40 show four typical boost applications — one fixed and three using the adjustable version of the LM2588. Each drawing contains the part num- ber(s) and manufacturer(s) for every component. For the fixed 12V output application, the part numbers and manufacturers’ names for the inductor are listed in a table in Figure 37. For applications with different output voltages, refer to the Switchers Made Simplesoftware. 21 www.national.com LM2588 Typical Boost Regulator Applications (Continued) 01242050 FIGURE 36. +5V to +12V Boost Regulator Figure 37 contains a table of standard inductors, by part number and corresponding manufacturer, for the fixed output regulator of Figure 36. Coilcraft (Note 20) R4793-A Note 20: Coilcraft Inc.,: Phone: (800) 322-2645 1102 Silver Lake Road, Cary, IL 60013: Pulse (Note 21) PE-53900 Renco (Note 22) RL-5472-5 Schott (Note 23) 67146520 Fax: (708) 639-1469 Phone: +44 1236 730 595 Fax: +44 1236 730 627 Fax: (619) 674-8262 European Headquarters, 21 Napier Place: Note 21: Pulse Engineering Inc.,: Wardpark North, Cumbernauld, Scotland G68 0LL: 12220 World Trade Drive, San Diego, CA 92128: European Headquarters, Dunmore Road: Tuam, Co. Galway, Ireland: Note 22: Renco Electronics Inc.,: Note 23: Schott Corp.,: Fax: +353 93 24 459 Phone: (619) 674-8100 Phone: +353 93 24 107 Phone: (800) 645-5828 Fax: (516) 586-5562 Fax: (612) 475-1786 60 Jeffryn Blvd. East, Deer Park, NY 11729: Phone: (612) 475-1173 1000 Parkers Lane Road, Wayzata, MN 55391: FIGURE 37. Inductor Selection Table www.national.com 22 LM2588 Typical Boost Regulator Applications (Continued) 01242051 FIGURE 38. +12V to +24V Boost Regulator 01242052 FIGURE 39. +24V to +36V Boost Regulator 23 www.national.com LM2588 Typical Boost Regulator Applications (Continued) 01242053 *The LM2588 will require a heat sink in these applications. The size of the heat sink will depend on the maximum ambient temperature. To calculate the thermal resistance of the IC and the size of the heat sink needed, see the “Heat Sink/Thermal Considerations” section in the Application Hints. FIGURE 40. +24V to +48V Boost Regulator Application Hints LM2588 SPECIAL FEATURES FREQUENCY ADJUSTMENT The switching frequency of the LM2588 can be adjusted with the use of an external resistor. This feature allows the user to optimize the size of the magnetics and the output capacitor(s) by tailoring the operating frequency. A resistor connected from pin 1 (the Freq. Adj. pin) to ground will set the switching frequency from 100 kHz to 200 kHz (maximum). As shown in Figure 41, the pin can be used to adjust the frequency while still providing the shut down function. A curve in the Performance Characteristics Section graphs the resistor value to the corresponding switching frequency. The table in Figure 42 shows resistor values corresponding to commonly used frequencies. However, changing the LM2588’s operating frequency from its nominal value of 100 kHz will change the magnetics selection and compensation component values. 01242054 RSET(kΩ) Open 200 47 33 22 Frequency (kHz) 100 125 150 175 200 FIGURE 41. Shutdown Operation SHUTDOWN CONTROL A feature of the LM2588 is its ability to be shut down using the ON /OFF pin (pin 1). This feature conserves input power by turning off the device when it is not in use. For proper operation, an isolation diode is required (as shown in Figure 41). The device will shut down when 3V or greater is applied on the ON /OFF pin, sourcing current into pin 1. In shut down mode, the device will draw typically 56 µA of supply current (16 µA to VIN and 40 µA to the ON /OFF pin). To turn the device back on, leave pin 1 floating, using an (isolation) diode, as shown in Figure 41 (for normal operation, do not source or sink current to or from this pin — see the next section). FIGURE 42. Frequency Setting Resistor Guide 01242055 FIGURE 43. Frequency Synchronization www.national.com 24 LM2588 Application Hints (Continued) FREQUENCY SYNCHRONIZATION Another feature of the LM2588 is the ability to synchronize the switching frequency to an external source, using the sync pin (pin 6). This feature allows the user to parallel multiple devices to deliver more output power. A negative falling pulse applied to the sync pin will synchronize the LM2588 to an external oscillator (see Figure 43 and 44). Use of this feature enables the LM2588 to be synchronized to an external oscillator, such as a system clock. This operation allows multiple power supplies to operate at the same frequency, thus eliminating frequency-related noise problems. PROGRAMMING OUTPUT VOLTAGE (SELECTING R1 AND R2) Referring to the adjustable regulator in Figure 45, the output voltage is programmed by the resistors R1 and R2 by the following formula: where VREF = 1.23V VOUT = VREF (1 + R1/R2) Resistors R1 and R2 divide the output voltage down so that it can be compared with the 1.23V internal reference. With R2 between 1k and 5k, R1 is: where VREF = 1.23V R1 = R2 (VOUT/VREF − 1) For best temperature coefficient and stability with time, use 1% metal film resistors. SHORT CIRCUIT CONDITION Due to the inherent nature of boost regulators, when the output is shorted (see Figure 45 ), current flows directly from the input, through the inductor and the diode, to the output, bypassing the switch. The current limit of the switch does not limit the output current for the entire circuit. To protect the load and prevent damage to the switch, the current must be externally limited, either by the input supply or at the output with an external current limit circuit. The external limit should be set to the maximum switch current of the device, which is 5A. In a flyback regulator application (Figure 46 ), using the standard transformers, the LM2588 will survive a short circuit to the main output. When the output voltage drops to 80% of its nominal value, the frequency will drop to 25 kHz. With a lower frequency, off times are larger. With the longer off times, the transformer can release all of its stored energy before the switch turns back on. Hence, the switch turns on initially with zero current at its collector. In this condition, the switch current limit will limit the peak current, saving the device. 01242064 FIGURE 44. Waveforms of a Synchronized 12V Boost Regulator The scope photo in Figure 44 shows a LM2588 12V Boost Regulator synchronized to a 200 kHz signal. There is a 700 ns delay between the falling edge of the sync signal and the turning on of the switch. 01242056 FIGURE 45. Boost Regulator 25 www.national.com LM2588 Application Hints (Continued) 01242057 FIGURE 46. Flyback Regulator FLYBACK REGULATOR INPUT CAPACITORS A flyback regulator draws discontinuous pulses of current from the input supply. Therefore, there are two input capacitors needed in a flyback regulator — one for energy storage and one for filtering (see Figure 46). Both are required due to the inherent operation of a flyback regulator. To keep a stable or constant voltage supply to the LM2588, a storage capacitor (≥100 µF) is required. If the input source is a recitified DC supply and/or the application has a wide temperature range, the required rms current rating of the capacitor might be very large. This means a larger value of capacitance or a higher voltage rating will be needed for the input capacitor. The storage capacitor will also attenuate noise which may interfere with other circuits connected to the same input supply voltage. In addition, a small bypass capacitor is required due to the noise generated by the input current pulses. To eliminate the noise, insert a 1.0 µF ceramic capacitor between VIN and ground as close as possible to the device. SWITCH VOLTAGE LIMITS In a flyback regulator, the maximum steady-state voltage appearing at the switch, when it is off, is set by the transformer turns ratio, N, the output voltage, VOUT, and the maximum input voltage, VIN (Max): VSW(OFF) = VIN (Max) + (VOUT +VF)/N where VF is the forward biased voltage of the output diode, and is typically 0.5V for Schottky diodes and 0.8V for ultrafast recovery diodes. In certain circuits, there exists a voltage spike, VLL, superimposed on top of the steady-state voltage (see Figure 5, waveform A). Usually, this voltage spike is caused by the transformer leakage 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 (as shown in the circuit in Figure 4 www.national.com 26 and other flyback regulator circuits throughout the datasheet). The schematic in Figure 46 shows another method of clamping the switch voltage. A single voltage transient suppressor (the SA51A) is inserted at the switch pin. This method clamps the total voltage across the switch, not just the voltage across the primary. If poor circuit layout techniques are used (see the “Circuit Layout Guideline” section), negative voltage transients may appear on the Switch pin (pin 5). Applying a negative voltage (with respect to the IC’s ground) to any monolithic IC pin causes erratic and unpredictable operation of that IC. This holds true for the LM2588 IC as well. When used in a flyback regulator, the voltage at the Switch pin (pin 5) 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 secondary(ies). The resonant circuit generates the “ringing” voltage, 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 rectifier(s), as in Figure 46. 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 10Ω and 1 kΩ, and the capacitor will vary from 0.001 µF to 0.1 µF. 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 pins 5 and 4 (ground), also shown in Figure 46. This prevents the voltage at pin 5 from dropping below −0.4V. The reverse voltage rating of the diode must be greater than the switch off voltage. LM2588 Application Hints (Continued) former. However, there exists some physical limitations that prevent the turns ratio, and thus the output voltage, from increasing to infinity. The physical limitations are capacitances and inductances in the LM2588 switch, the output diode(s), and the transformer — such as reverse recovery time of the output diode (mentioned above). NOISY INPUT LINE CONDITION A small, low-pass RC filter should be used at the input pin of the LM2588 if the input voltage has an unusually large amount of transient noise, such as with an input switch that bounces. The circuit in Figure 47 demonstrates the layout of the filter, with the capacitor placed from the input pin to ground and the resistor placed between the input supply and the input pin. Note that the values of RIN and CIN shown in the schematic are good enough for most applications, but some readjusting might be required for a particular application. If efficiency is a major concern, replace the resistor with a small inductor (say 10 µH and rated at 200 mA). STABILITY All current-mode controlled regulators can suffer from an instability, known as subharmonic oscillation, if they operate with a duty cycle above 50%. To eliminate subharmonic oscillations, a minimum value of inductance is required to ensure stability for all boost and flyback regulators. The minimum inductance is given by: 01242058 FIGURE 47. Input Line Filter OUTPUT VOLTAGE LIMITATIONS The maximum output voltage of a boost regulator is the maximum switch voltage minus a diode drop. In a flyback regulator, 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 cycle of a flyback regulator is determined by the following equation: where VSAT is the switch saturation voltage and can be found in the Characteristic Curves. Theoretically, the maximum output voltage can be as large as desired — just keep increasing the turns ratio of the trans- 01242059 FIGURE 48. Circuit Board Layout CIRCUIT LAYOUT GUIDELINES As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance generate voltage transients which can cause problems. For minimal inductance and ground loops, keep the length of the leads and traces as short as possible. Use single point grounding or ground plane construction for best results. 27 Separate the signal grounds from the power grounds (as indicated in Figure 48). When using the Adjustable version, physically locate the programming resistors as near the regulator IC as possible, to keep the sensitive feedback wiring short. www.national.com LM2588 Application Hints (Continued) HEAT SINK/THERMAL CONSIDERATIONS In many cases, a heat sink is not required to keep the LM2588 junction temperature within the allowed operating temperature range. For each application, to determine whether or not a heat sink will be required, the following must be identified: 1) Maximum ambient temperature (in the application). 2) Maximum regulator power dissipation (in the application). 3) Maximum allowed junction temperature (125˚C for the LM2588). For a safe, conservative design, a temperature approximately 15˚C cooler than the maximum junction temperature should be selected (110˚C). 4) LM2588 package thermal resistances θJA and θJC (given in the Electrical Characteristics). Total power dissipated (PD) by the LM2588 can be estimated as follows: Boost: Adding the junction temperature rise to the maximum ambient temperature gives the actual operating junction temperature: TJ = ∆TJ + TA. If the operating junction temperature exceeds the maximum junction temperatue in item 3 above, then a heat sink is required. When using a heat sink, the junction temperature rise can be determined by the following: ∆TJ = PD • (θJC + θInterface + θHeat Sink) Again, the operating junction temperature will be: TJ = ∆TJ + TA As before, if the maximum junction temperature is exceeded, a larger heat sink is required (one that has a lower thermal resistance). Included in the Switchers Made Simple design software is a more precise (non-linear) thermal model that can be used to determine junction temperature with different input-output parameters or different component values. It can also calculate the heat sink thermal resistance required to maintain the regulator junction temperature below the maximum operating temperature. To further simplify the flyback regulator design procedure, National Semiconductor is making available computer design software Switchers Made Simple. Software is available on a (31⁄2") diskette for IBM compatible computers from a National Semiconductor sales office in your area or the National Semiconductor Customer Response Center (1-800-272-9959). VIN is the minimum input voltage, VOUT is the output voltage, N is the transformer turns ratio, D is the duty cycle, and ILOAD is the maximum load current (and ∑ILOAD is the sum of the maximum load currents for multiple-output flyback regulators). The duty cycle is given by: Boost: where VF is the forward biased voltage of the diode and is typically 0.5V for Schottky diodes and 0.8V for fast recovery diodes. VSAT is the switch saturation voltage and can be found in the Characteristic Curves. When no heat sink is used, the junction temperature rise is: ∆TJ = PD • θJA. www.national.com 28 LM2588 Physical Dimensions inches (millimeters) unless otherwise noted Order Number LM2588T-3.3, LM2588T-5.0, LM2588T-12 or LM2588T-ADJ NS Package Number TA07B Order Number LM2588S-3.3, LM2588S-5.0, LM2588S-12 or LM2588S-ADJ Tape and Reel Order Number LM2588SX-3.3, LM2588SX-5.0, LM2588SX-12 or LM2588SX-ADJ NS Package Number TS7B 29 www.national.com LM2588 SIMPLE SWITCHER 5A Flyback Regulator with Shutdown Notes National does not assume any responsibility 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. For the most current product information visit us at www.national.com. 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