LM1577/LM2577 SIMPLE SWITCHER ® Step-Up Voltage Regulator General Description Features The LM1577/LM2577 are monolithic integrated circuits that provide all of the power and control functions for step-up (boost), flyback, and forward converter switching regulators. The device is available in three different output voltage versions: 12V, 15V, and adjustable. Requiring a minimum number of external components, these regulators are cost effective, and simple to use. Listed in this data sheet are a family of standard inductors and flyback transformers designed to work with these switching regulators. Requires few external components NPN output switches 3.0A, can stand off 65V Wide input voltage range: 3.5V to 40V Current-mode operation for improved transient response, line regulation, and current limit n 52 kHz internal oscillator n Soft-start function reduces in-rush current during start-up n Output switch protected by current limit, under-voltage lockout, and thermal shutdown Included on the chip is a 3.0A NPN switch and its associated protection circuitry, consisting of current and thermal limiting, and undervoltage lockout. Other features include a 52 kHz fixed-frequency oscillator that requires no external components, a 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. Typical Applications n n n n n Simple boost regulator n Flyback and forward regulators n Multiple-output regulator Connection Diagrams Straight Leads 5-Lead TO-220 (T) Bent, Staggered Leads 5-Lead TO-220 (T) 01146804 Top View Order Number LM2577T-12, LM2577T-15, or LM2577T-ADJ See NS Package Number T05A 01146805 Top View Order Number LM2577T-12 Flow LB03, LM2577T-15 Flow LB03, or LM2577T-ADJ Flow LB03 See NS Package Number T05D SIMPLE SWITCHER ® is a registered trademark of National Semiconductor Corporation. © 2005 National Semiconductor Corporation DS011468 www.national.com LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator April 2005 LM1577/LM2577 Connection Diagrams (Continued) 16-Lead DIP (N) 24-Lead Surface Mount (M) 01146806 *No internal Connection Top View Order Number LM2577N-12, LM2577N-15, or LM2577N-ADJ See NS Package Number N16A 01146807 *No internal Connection Top View Order Number LM2577M-12, LM2577M-15, or LM2577M-ADJ See NS Package Number M24B TO-263 (S) 5-Lead Surface-Mount Package 01146833 Side View Order Number LM2577S-12, LM2577S-15, or LM2577S-ADJ See NS Package Number TS5B 01146832 Top View 4-Lead TO-3 (K) 01146808 Bottom View Order Number LM1577K-12/883, LM1577K-15/883, or LM1577K-ADJ/883 See NS Package Number K04A www.national.com 2 Temperature Range Package Type Output Voltage 12V 15V NSC ADJ Package Package Drawing −40˚C ≤ TA ≤ +125˚C 24-Pin Surface Mount LM2577M-12 LM2577M-15 LM2577M-ADJ M24B SO 16-Pin Molded DIP LM2577N-12 LM2577N-15 LM2577N-ADJ N16A N 5-Lead Surface Mount LM2577S-12 LM2577S-15 LM2577S-ADJ TS5B TO-263 5-Straight Leads LM2577T-12 LM2577T-15 LM2577T-ADJ T05A TO-220 5-Bent Staggered LM2577T-12 LM2577T-15 LM2577T-ADJ T05D TO-220 Flow LB03 Flow LB03 Flow LB03 K04A TO-3 Leads −55˚C ≤ TA ≤ +150˚C 4-Pin TO-3 LM1577K-12/883LM1577K-15/883 LM1577KADJ/883 Typical Application 01146801 Note: Pin numbers shown are for TO-220 (T) package. 3 www.national.com LM1577/LM2577 Ordering Information LM1577/LM2577 Absolute Maximum Ratings (Note 1) Minimum ESD Rating (C = 100 pF, R = 1.5 kΩ) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. 2 kV Operating Ratings Supply Voltage 45V Output Switch Voltage 65V Supply Voltage 6.0A Output Switch Voltage 0V ≤ VSWITCH ≤ 60V Internally Limited Output Switch Current ISWITCH ≤ 3.0A −65˚C to +150˚C Junction Temperature Range Output Switch Current (Note 2) Power Dissipation Storage Temperature Range Lead Temperature (Soldering, 10 sec.) 260˚C Maximum Junction Temperature 3.5V ≤ VIN ≤ 40V LM1577 −55˚C ≤ TJ ≤ +150˚C LM2577 −40˚C ≤ TJ ≤ +125˚C 150˚C Electrical Characteristics—LM1577-12, LM2577-12 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, and ISWITCH = 0. Symbol Parameter Conditions Typical LM1577-12 LM2577-12 Units Limit Limit (Limits) (Notes 3, 4) (Note 5) 11.60/11.40 11.60/11.40 V(min) 12.40/12.60 12.40/12.60 V(max) SYSTEM PARAMETERS Circuit of Figure 1 (Note 6) VOUT Output Voltage VIN = 5V to 10V 12.0 ILOAD = 100 mA to 800 mA (Note 3) Line Regulation VIN = 3.5V to 10V 20 ILOAD = 300 mA Load Regulation Efficiency mV 50/100 VIN = 5V 50/100 20 ILOAD = 100 mA to 800 mA η V mV(max) mV 50/100 50/100 mV(max) VIN = 5V, ILOAD = 800 mA 80 % VFEEDBACK = 14V (Switch Off) 7.5 mA ISWITCH = 2.0A 25 DEVICE PARAMETERS IS Input Supply Current VCOMP = 2.0V (Max Duty Cycle) VUV Input Supply ISWITCH = 100 mA Oscillator Frequency Measured at Switch Pin Output Reference Measured at Feedback Pin Voltage VIN = 3.5V to 40V 50/85 50/85 mA(max) 2.70/2.65 2.70/2.65 V(min) 3.10/3.15 3.10/3.15 V(max) mA 12 VIN = 3.5V to 40V V kHz 48/42 48/42 kHz(min) 56/62 56/62 kHz(max) V VCOMP = 1.0V Output Reference mA(max) 52 ISWITCH = 100 mA VREF 10.0/14.0 2.90 Undervoltage Lockout fO 10.0/14.0 11.76/11.64 11.76/11.64 V(min) 12.24/12.36 12.24/12.36 V(max) 7 mV 9.7 kΩ Voltage Line Regulator RFB Feedback Pin Input Resistance GM www.national.com Error Amp ICOMP = −30 µA to +30 µA Transconductance VCOMP = 1.0V 4 370 µmho 225/145 225/145 µmho(min) 515/615 515/615 µmho(max) (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, and ISWITCH = 0. Symbol Parameter Conditions Typical LM1577-12 LM2577-12 Units Limit Limit (Limits) (Notes 3, 4) (Note 5) DEVICE PARAMETERS AVOL Error Amp Voltage Gain VCOMP = 1.1V to 1.9V 80 RCOMP = 1.0 MΩ V/V 50/25 50/25 V/V(min) 2.2/2.0 2.2/2.0 V(min) 0.40/0.55 0.40/0.55 V(max) (Note 7) Error Amplifier Upper Limit Output Swing VFEEDBACK = 10.0V 2.4 Lower Limit 0.3 VFEEDBACK = 15.0V ISS Error Amplifier VFEEDBACK = 10.0V to 15.0V Output Current VCOMP = 1.0V Soft Start Current Maximum Duty Cycle VFEEDBACK = 10.0V ± 130/ ± 90 ± 300/ ± 400 5.0 VCOMP = 1.5V 2.5/1.5 2.5/1.5 µA(min) 7.5/9.5 7.5/9.5 µA(max) 93/90 93/90 %(min) % 12.5 Switch Leakage VSWITCH = 65V Current VFEEDBACK = 15V (Switch Off) Switch Saturation ISWITCH = 2.0A Voltage VCOMP = 2.0V (Max Duty Cycle) A/V 10 µA 300/600 300/600 0.5 NPN Switch µA(max) V 0.7/0.9 0.7/0.9 V(max) 3.7/3.0 3.7/3.0 A(min) 5.3/6.0 5.3/6.0 A(max) 4.5 Current Limit µA(min) µA(max) µA 95 Switch Transconductance VSAT µA ± 130/ ± 90 ± 300/ ± 400 ISWITCH = 100 mA IL V ± 200 VCOMP = 0V D V A Electrical Characteristics—LM1577-15, LM2577-15 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, and ISWITCH = 0. Symbol Parameter Conditions Typical LM1577-15 LM2577-15 Units Limit Limit (Limits) (Notes 3, 4) (Note 5) SYSTEM PARAMETERS Circuit of Figure 2 (Note 6) VOUT Output Voltage Line Regulation VIN = 5V to 12V 15.0 ILOAD = 100 mA to 600 mA 14.50/14.25 14.50/14.25 V(min) (Note 3) 15.50/15.75 15.50/15.75 V(max) 50/100 50/100 50/100 50/100 VIN = 3.5V to 12V 20 ILOAD = 300 mA Load Regulation VIN = 5V Efficiency mV 20 ILOAD = 100 mA to 600 mA η V VIN = 5V, ILOAD = 600 mA 5 80 mV(max) mV mV(max) % www.national.com LM1577/LM2577 Electrical Characteristics—LM1577-12, LM2577-12 LM1577/LM2577 Electrical Characteristics—LM1577-15, LM2577-15 (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, and ISWITCH = 0. Symbol Parameter Conditions Typical LM1577-15 LM2577-15 Units Limit Limit (Limits) (Notes 3, 4) (Note 5) DEVICE PARAMETERS IS Input Supply Current VFEEDBACK = 18.0V 7.5 (Switch Off) mA 10.0/14.0 10.0/14.0 mA(max) 50/85 50/85 mA(max) Undervoltage 2.70/2.65 2.70/2.65 V(min) Lockout 3.10/3.15 3.10/3.15 V(max) 48/42 48/42 kHz(min) 56/62 56/62 kHz(max) 14.70/14.55 14.70/14.55 V(min) 15.30/15.45 15.30/15.45 V(max) ISWITCH = 2.0A 25 VCOMP = 2.0V mA (Max Duty Cycle) VUV fO Input Supply Oscillator Frequency ISWITCH = 100 mA 2.90 Measured at Switch Pin 52 ISWITCH = 100 mA VREF Output Reference Measured at Feedback Pin Voltage VIN = 3.5V to 40V Output Reference VIN = 3.5V to 40V V kHz V 15 VCOMP = 1.0V 10 mV 12.2 kΩ 300 µmho Voltage Line Regulation RFB Feedback Pin Input Voltage Line Regulator GM AVOL Error Amp ICOMP = −30 µA to +30 µA Transconductance VCOMP = 1.0V Error Amp VCOMP = 1.1V to 1.9V Voltage Gain RCOMP = 1.0 MΩ 170/110 170/110 µmho(min) 420/500 420/500 µmho(max) 65 V/V 40/20 40/20 V/V(min) 2.2/2.0 2.2/2.0 V(min) 0.4/0.55 0.40/0.55 V(max) ± 130/ ± 90 ± 300/ ± 400 ± 130/ ± 90 ± 300/ ± 400 µA(max) 2.5/1.5 2.5/1.5 µA(min) 7.5/9.5 7.5/9.5 µA(max) 93/90 93/90 %(min) (Note 7) Error Amplifier Upper Limit Output Swing VFEEDBACK = 12.0V 2.4 Lower Limit 0.3 VFEEDBACK = 18.0V Error Amp Output Current ISS Soft Start Current VFEEDBACK = 12.0V to 18.0V VCOMP = 1.0V VFEEDBACK = 12.0V Maximum Duty VCOMP = 1.5V Cycle ISWITCH = 100 mA µA 5.0 % 12.5 Switch Leakage VSWITCH = 65V Current VFEEDBACK = 18.0V µA(min) µA 95 Switch Transconductance IL V ± 200 VCOMP = 0V D V A/V 10 µA 300/600 300/600 µA(max) 0.7/0.9 0.7/0.9 V(max) (Switch Off) VSAT Switch Saturation ISWITCH = 2.0A Voltage VCOMP = 2.0V 0.5 (Max Duty Cycle) www.national.com 6 V (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, and ISWITCH = 0. Symbol Parameter Conditions Typical LM1577-15 LM2577-15 Units Limit Limit (Limits) (Notes 3, 4) (Note 5) DEVICE PARAMETERS NPN Switch VCOMP = 2.0V 4.3 Current Limit A 3.7/3.0 3.7/3.0 A(min) 5.3/6.0 5.3/6.0 A(max) Electrical Characteristics—LM1577-ADJ, LM2577-ADJ 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, VFEEDBACK = VREF, and ISWITCH = 0. LM1577-ADJ LM2577-ADJ Symbol Parameter Conditions Typical Units Limit Limit (Notes 3, 4) (Note 5) (Limits) ILOAD = 100 mA to 800 mA 11.60/11.40 11.60/11.40 V(min) (Note 3) 12.40/12.60 12.40/12.60 V(max) 50/100 50/100 mV(max) 50/100 50/100 mV(max) SYSTEM PARAMETERS Circuit of Figure 3 (Note 6) VOUT ∆VOUT/ Output Voltage Line Regulation ∆VIN ∆VOUT/ 12.0 VIN = 3.5V to 10V Load Regulation VIN = 5V mV 20 ILOAD = 100 mA to 800 mA Efficiency V 20 ILOAD = 300 mA ∆ILOAD η VIN = 5V to 10V mV VIN = 5V, ILOAD = 800 mA 80 % VFEEDBACK = 1.5V (Switch Off) 7.5 mA ISWITCH = 2.0A 25 DEVICE PARAMETERS IS Input Supply Current VCOMP = 2.0V (Max Duty Cycle) VUV Input Supply ISWITCH = 100 mA Oscillator Frequency Measured at Switch Pin Reference Measured at Feedback Pin Voltage VIN = 3.5V to 40V ∆VREF/ Reference Voltage Line Regulation IB Error Amp 1.230 VIN = 3.5V to 40V 0.5 VCOMP = 1.0V 100 Input Bias Current GM AVOL 50/85 50/85 mA(max) mA V 2.70/2.65 2.70/2.65 V(min) 3.10/3.15 3.10/3.15 V(max) kHz 48/42 48/42 kHz(min) 56/62 56/62 kHz(max) V VCOMP = 1.0V ∆VIN mA(max) 52 ISWITCH = 100 mA VREF 10.0/14.0 2.90 Undervoltage Lockout fO 10.0/14.0 1.214/1.206 1.214/1.206 V(min) 1.246/1.254 1.246/1.254 V(max) mV nA 300/800 Error Amp ICOMP = −30 µA to +30 µA Transconductance VCOMP = 1.0V Error Amp VCOMP = 1.1V to 1.9V Voltage Gain RCOMP = 1.0 MΩ (Note 7) 300/800 3700 µmho 2400/1600 2400/1600 µmho(min) 4800/5800 4800/5800 µmho(max) 500/250 500/250 V/V(min) 800 7 nA(max) V/V www.national.com LM1577/LM2577 Electrical Characteristics—LM1577-15, LM2577-15 LM1577/LM2577 Electrical Characteristics—LM1577-ADJ, LM2577-ADJ (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, VFEEDBACK = VREF, and ISWITCH = 0. LM1577-ADJ LM2577-ADJ Symbol Parameter Conditions Typical Limit Limit (Notes 3, 4) (Note 5) Units (Limits) DEVICE PARAMETERS Error Amplifier Upper Limit Output Swing VFEEDBACK = 1.0V 2.4 Lower Limit Error Amp VFEEDBACK = 1.0V to 1.5V Output Current VCOMP = 1.0V Soft Start Current Maximum Duty Cycle ∆ISWITCH/ Switch ∆VCOMP Transconductance IL Switch Leakage V(min) 0.40/0.55 0.40/0.55 V(max) V µA ± 130/ ± 90 ± 300/ ± 400 VFEEDBACK = 1.0V ± 130/ ± 90 ± 300/ ± 400 5.0 VCOMP = 1.5V 2.5/1.5 2.5/1.5 µA(min) 7.5/9.5 7.5/9.5 µA(max) % 93/90 VSWITCH = 65V Current VFEEDBACK = 1.5V (Switch Off) Switch Saturation ISWITCH = 2.0A Voltage VCOMP = 2.0V (Max Duty Cycle) NPN Switch VCOMP = 2.0V µA(min) µA(max) µA 95 ISWITCH = 100 mA VSAT 2.2/2.0 ± 200 VCOMP = 0V D 2.2/2.0 0.3 VFEEDBACK = 1.5V ISS V 93/90 %(min) 12.5 A/V 10 µA 300/600 300/600 µA(max) 0.7/0.9 0.7/0.9 V(max) 3.7/3.0 3.7/3.0 A(min) 5.3/6.0 5.3/6.0 A(max) 0.5 V 4.3 Current Limit A THERMAL PARAMETERS (All Versions) θJA K Package, Junction to Ambient 35 θJC Thermal Resistance K Package, Junction to Case 1.5 θJA T Package, Junction to Ambient 65 θJC T Package, Junction to Case 2 θJA N Package, Junction to 85 Ambient (Note 8) θJA M Package, Junction ˚C/W 100 to Ambient (Note 8) θJA S Package, Junction to 37 Ambient (Note 9) Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions 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: Due to timing considerations of the LM1577/LM2577 current limit circuit, output current cannot be internally limited when the LM1577/LM2577 is used as a step-up regulator. To prevent damage to the switch, its current must be externally limited to 6.0A. However, output current is internally limited when the LM1577/LM2577 is used as a flyback or forward converter regulator in accordance to the Application Hints. Note 3: All limits guaranteed at room temperature (standard type face) and at temperature extremes (boldface type). All limits are used to calculate Outgoing Quality Level, and are 100% production tested. Note 4: A military RETS electrical test specification is available on request. At the time of printing, the LM1577K-12/883, LM1577K-15/883, and LM1577K-ADJ/883 RETS specifications complied fully with the boldface limits in these columns. The LM1577K-12/883, LM1577K-15/883, and LM1577K-ADJ/883 may also be procured to Standard Military Drawing specifications. Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (boldface type). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. Note 6: External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the LM1577/LM2577 is used as shown in the Test Circuit, system performance will be as specified by the system parameters. Note 7: A 1.0 MΩ resistor is connected to the compensation pin (which is the error amplifier’s output) to ensure accuracy in measuring AVOL. In actual applications, this pin’s load resistance should be ≥10 MΩ, resulting in AVOL that is typically twice the guaranteed minimum limit. www.national.com 8 (Continued) Note 8: Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper area will lower thermal resistance further. See thermal model in “Switchers Made Simple” software. Note 9: If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package. Using 0.5 square inches of copper area, θJA is 50˚C/W; with 1 square inch of copper area, θJA is 37˚C/W; and with 1.6 or more square inches of copper area, θJA is 32˚C/W. Typical Performance Characteristics Reference Voltage vs Temperature Reference Voltage vs Temperature 01146834 01146835 ∆ Reference Voltage vs Supply Voltage Reference Voltage vs Temperature 01146836 01146837 ∆ Reference Voltage vs Supply Voltage ∆ Reference Voltage vs Supply Voltage 01146838 01146839 9 www.national.com LM1577/LM2577 Electrical Characteristics—LM1577-ADJ, LM2577-ADJ LM1577/LM2577 Typical Performance Characteristics (Continued) Error Amp Transconductance vs Temperature Error Amp Transconductance vs Temperature 01146841 01146840 Error Amp Transconductance vs Temperature Error Amp Voltage Gain vs Temperature 01146843 01146842 Error Amp Voltage Gain vs Temperature Error Amp Voltage Gain vs Temperature 01146844 www.national.com 01146845 10 LM1577/LM2577 Typical Performance Characteristics (Continued) Quiescent Current vs Temperature Quiescent Current vs Switch Current 01146846 01146847 Current Limit vs Temperature Current Limit Response Time vs Overdrive 01146849 01146848 Switch Saturation Voltage vs Switch Current Switch Transconductance vs Temperature 01146851 01146850 11 www.national.com LM1577/LM2577 Typical Performance Characteristics (Continued) Feedback Pin Bias Current vs Temperature Oscillator Frequency vs Temperature 01146853 01146852 Maximum Power Dissipation (TO-263) (Note 9) 01146831 www.national.com 12 LM1577/LM2577 LM1577-12, LM2577-12 Test Circuit 01146830 L = 415-0930 (AIE) D = any manufacturer COUT = Sprague Type 673D Electrolytic 680 µF, 20V Note: Pin numbers shown are for TO-220 (T) package FIGURE 1. Circuit Used to Specify System Parameters for 12V Versions LM1577-15, LM2577-15 Test Circuit 01146826 L = 415-0930 (AIE) D = any manufacturer COUT = Sprague Type 673D Electrolytic 680 µF, 20V Note: Pin numbers shown are for TO-220 (T) package FIGURE 2. Circuit Used to Specify System Parameters for 15V Versions 13 www.national.com LM1577/LM2577 LM1577-ADJ, LM2577-ADJ Test Circuit 01146809 L = 415-0930 (AIE) D = any manufacturer COUT = Sprague Type 673D Electrolytic 680 µF, 20V R1 = 48.7k in series with 511Ω (1%) R2 = 5.62k (1%) Note: Pin numbers shown are for TO-220 (T) package FIGURE 3. Circuit Used to Specify System Parameters for ADJ Versions Application Hints 01146810 Note: Pin numbers shown are for TO-220 (T) package *Resistors are internal to LM1577/LM2577 for 12V and 15V versions. FIGURE 4. LM1577/LM2577 Block Diagram and Boost Regulator Application www.national.com 14 LM1577/LM2577 Application Hints (Continued) Duty Cycle STEP-UP (BOOST) REGULATOR Figure 4 shows the LM1577-ADJ/LM2577-ADJ used as a Step-Up Regulator. This is a switching regulator used for producing an output voltage greater than the input supply voltage. The LM1577-12/LM2577-12 and LM1577-15/ LM2577-15 can also be used for step-up regulators with 12V or 15V outputs (respectively), by tying the feedback pin directly to the regulator output. Average Inductor Current A basic explanation of how it works is as follows. The LM1577/LM2577 turns its output switch on and off at a frequency of 52 kHz, and this creates energy in the inductor (L). When the NPN switch turns on, the inductor current charges up at a rate of VIN/L, storing current 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 the amount of energy transferred which, in turn, is controlled by modulating the peak inductor 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 voltage proportional to the switch current (i.e., inductor current during the switch on time). IIND(AVE) Inductor Current Ripple ∆IIND Peak Inductor Current IIND(PK) Peak Switch Current ISW(PK) Switch Voltage When Off VSW(OFF) VOUT + VF VR VOUT − VSAT Average Diode Current ID(AVE) ILOAD Peak Diode Current ID(PK) Diode Reverse Voltage Power Dissipation of LM1577/2577 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. D PD VF = Forward Biased Diode Voltage ILOAD = Output Load Current Voltage and current waveforms for this circuit are shown in Figure 5, and formulas for calculating them are given in Figure 6. FIGURE 6. Step-Up Regulator Formulas STEP-UP REGULATOR DESIGN PROCEDURE The following design procedure can be used to select the appropriate external components for the circuit in Figure 4, based on these system requirements. Given: VIN (min) = Minimum input supply voltage VOUT = Regulated output voltage ILOAD(max) = Maximum output load current Before proceeding any further, determine if the LM1577/ LM2577 can provide these values of VOUT and ILOAD(max) when operating with the minimum value of VIN. The upper limits for VOUT and ILOAD(max) are given by the following equations. VOUT ≤ 60V and VOUT ≤ 10 x VIN(min) 01146811 FIGURE 5. Step-Up Regulator Waveforms These limits must be greater than or equal to the values specified in this application. 1. Inductor Selection (L) A. Voltage Options: 1. For 12V or 15V output From Figure 7 (for 12V output) or Figure 8 (for 15V output), identify inductor code for region indicated by VIN (min) and ILOAD (max). The shaded region indicates con15 www.national.com LM1577/LM2577 Application Hints 1. Find the lowest value inductor that is greater than LMIN. 2. Find where E • T intersects this inductor value to determine if it has an L or H prefix. If E • T intersects both the L and H regions, select the inductor with an H prefix. (Continued) ditions for which the LM1577/LM2577 output switch would be operating beyond its switch current rating. The minimum operating voltage for the LM1577/LM2577 is 3.5V. From here, proceed to step C. 2. For Adjustable version Preliminary calculations: The inductor selection is based on the calculation of the following three parameters: D(max), the maximum switch duty cycle (0 ≤ D ≤ 0.9): where VF = 0.5V for Schottky diodes and 0.8V for fast recovery diodes (typically); E • T, the product of volts x time that charges the inductor: 01146827 FIGURE 7. LM2577-12 Inductor Selection Guide IIND,DC, the average inductor current under full load; B. Identify Inductor Value: 1. From Figure 9, identify the inductor code for the region indicated by the intersection of E • T and IIND,DC. This code gives the inductor value in microhenries. The L or H prefix signifies whether the inductor is rated for a maximum E • T of 90 V • µs (L) or 250 V • µs (H). 2. If D < 0.85, go on to step C. If D ≥ 0.85, then calculate the minimum inductance needed to ensure the switching regulator’s stability: 01146828 FIGURE 8. LM2577-15 Inductor Selection Guide If LMIN is smaller than the inductor value found in step B1, go on to step C. Otherwise, the inductor value found in step B1 is too low; an appropriate inductor code should be obtained from the graph as follows: www.national.com 16 LM1577/LM2577 Application Hints (Continued) 01146812 Note: These charts assume that the inductor ripple current inductor is approximately 20% to 30% of the average inductor current (when the regulator is under full load). Greater ripple current causes higher peak switch currents and greater output ripple voltage; lower ripple current is achieved with larger-value inductors. The factor of 20 to 30% is chosen as a convenient balance between the two extremes. FIGURE 9. LM1577-ADJ/LM2577-ADJ Inductor Selection Graph C. Select an inductor from the table of Figure 10 which cross-references the inductor codes to the part numbers of three different manufacturers. Complete specifications for these inductors are available from the respective manufacturers. The inductors listed in this table have the following characteristics: AIE: ferrite, pot-core inductors; Benefits of this type are low electro-magnetic interference (EMI), small physical size, and very low power dissipation (core loss). Be careful not to operate these inductors too far beyond their maximum ratings for E • T and peak current, as this will saturate the core. Pulse: powdered iron, toroid core inductors; Benefits are low EMI and ability to withstand E • T and peak current above rated value better than ferrite cores. Renco: ferrite, bobbin-core inductors; Benefits are low cost and best ability to withstand E • T and peak current above rated value. Be aware that these inductors generate more EMI than the other types, and this may interfere with signals sensitive to noise. 17 www.national.com LM1577/LM2577 Application Hints Inductor C. Calculate the minimum value of CC . (Continued) Manufacturer’s Part Number Code Schott Pulse Renco L47 67126980 PE - 53112 RL2442 RL2443 L68 67126990 PE - 92114 L100 67127000 PE - 92108 RL2444 L150 67127010 PE - 53113 RL1954 L220 67127020 PE - 52626 RL1953 L330 67127030 PE - 52627 RL1952 L470 67127040 PE - 53114 RL1951 L680 67127050 PE - 52629 RL1950 H150 67127060 PE - 53115 RL2445 H220 67127070 PE - 53116 RL2446 H330 67127080 PE - 53117 RL2447 H470 67127090 PE - 53118 RL1961 H680 67127100 PE - 53119 RL1960 H1000 67127110 PE - 53120 RL1959 H1500 67127120 PE - 53121 RL1958 H2200 67127130 PE - 53122 RL2448 The compensation capacitor is also part of the soft start circuitry. When power to the regulator is turned on, the switch duty cycle is allowed to rise at a rate controlled by this capacitor (with no control on the duty cycle, it would immediately rise to 90%, drawing huge currents from the input power supply). In order to operate properly, the soft start circuit requires CC ≥ 0.22 µF. The value of the output filter capacitor is normally large enough to require the use of aluminum electrolytic capacitors. Figure 11 lists several different types that are recommended for switching regulators, and the following parameters are used to select the proper capacitor. Working Voltage (WVDC): Choose a capacitor with a working voltage at least 20% higher than the regulator output voltage. Ripple Current: This is the maximum RMS value of current that charges the capacitor during each switching cycle. For step-up and flyback regulators, the formula for ripple current is Schott Corp., (612) 475-1173 1000 Parkers Lake Rd., Wayzata, MN 55391 Pulse Engineering, (619) 268-2400 P.O. Box 12235, San Diego, CA 92112 Renco Electronics Inc., (516) 586-5566 60 Jeffryn Blvd. East, Deer Park, NY 11729 Choose a capacitor that is rated at least 50% higher than this value at 52 kHz. FIGURE 10. Table of Standardized Inductors and Manufacturer’s Part Numbers Equivalent Series Resistance (ESR) : This is the primary cause of output ripple voltage, and it also affects the values of RC and CC needed to stabilize the regulator. As a result, the preceding calculations for CC and RC are only valid if ESR doesn’t exceed the maximum value specified by the following equations. 2. Compensation Network (RC, CC) and Output Capacitor (COUT) Selection RC and CC form a pole-zero compensation network that stabilizes the regulator. The values of RC and CC are mainly dependant on the regulator voltage gain, ILOAD(max), L and COUT. The following procedure calculates values for RC, CC, and COUT that ensure regulator stability. Be aware that this procedure doesn’t necessarily result in RC and CC that provide optimum compensation. In order to guarantee optimum compensation, one of the standard procedures for testing loop stability must be used, such as measuring VOUT transient response when pulsing ILOAD (see Figure 15). A. First, calculate the maximum value for RC. Select a capacitor with ESR, at 52 kHz, that is less than or equal to the lower value calculated. Most electrolytic capacitors specify ESR at 120 Hz which is 15% to 30% higher than at 52 kHz. Also, be aware that ESR increases by a factor of 2 when operating at −20˚C. In general, low values of ESR are achieved by using large value capacitors (C ≥ 470 µF), and capacitors with high WVDC, or by paralleling smaller-value capacitors. Select a resistor less than or equal to this value, and it should also be no greater than 3 kΩ. B. Calculate the minimum value for COUT using the following two equations. The larger of these two values is the minimum value that ensures stability. www.national.com 18 (Continued) If the LM1577 is located far from the supply source filter capacitors, an additional large electrolytic capacitor (e.g. 47 µF) is often required. 3. Output Voltage Selection (R1 and R2) This section is for applications using the LM1577-ADJ/ LM2577-ADJ. Skip this section if the LM1577-12/LM2577-12 or LM1577-15/LM2577-15 is being used. 5. Diode Selection (D) The switching diode used in the boost regulator must withstand a reverse voltage equal to the circuit output voltage, and must conduct the peak output current of the LM2577. A suitable diode must have a minimum reverse breakdown voltage greater than the circuit output voltage, and should be rated for average and peak current greater than ILOAD(max) and ID(PK). Schottky barrier diodes are often favored for use in switching regulators. Their low forward voltage drop allows higher regulator efficiency than if a (less expensive) fast recovery diode was used. See Figure 12 for recommended part numbers and voltage ratings of 1A and 3A diodes. With the LM1577-ADJ/LM2577-ADJ, the output voltage is given by VOUT = 1.23V (1 + R1/R2) Resistors R1 and R2 divide the output down so it can be compared with the LM1577-ADJ/LM2577-ADJ internal 1.23V reference. For a given desired output voltage VOUT, select R1 and R2 so that VOUT 4. Input Capacitor Selection (CIN) The switching action in the step-up regulator causes a triangular ripple current to be drawn from the supply source. This in turn causes noise to appear on the supply voltage. For proper operation of the LM1577, the input voltage should be decoupled. Bypassing the Input Voltage pin directly to ground with a good quality, low ESR, 0.1 µF capacitor (leads as short as possible) is normally sufficient. 1A 3A 20V 1N5817 1N5820 MBR120P MBR320P 40V P.O. Box 128, Pickens, SC 29671 (803) 878-6311 Fast Recovery (max) 30V Cornell Dublier — Types 239, 250, 251, UFT, 300, or 350 Schottky 50V Nichicon — Types PF, PX, or PZ 1N5818 1N5821 MBR130P MBR330P 11DQ03 31DQ03 1N5819 1N5822 MBR140P MBR340P 1A 11DQ04 31DQ04 MBR150 MBR350 1N4933 11DQ05 31DQ05 MUR105 1N4934 927 East Parkway, Schaumburg, IL 60173 (708) 843-7500 100V Sprague — Types 672D, 673D, or 674D 3A MR851 HER102 30DL1 MUR110 MR831 10DL1 HER302 FIGURE 12. Diode Selection Chart Box 1, Sprague Road, Lansing, NC 28643 (919) 384-2551 BOOST REGULATOR CIRCUIT EXAMPLE By adding a few external components (as shown in Figure 13), the LM2577 can be used to produce a regulated output voltage that is greater than the applied input voltage. Typical performance of this regulator is shown in Figure 14 and Figure 15. The switching waveforms observed during the operation of this circuit are shown in Figure 16. United Chemi-Con — Types LX, SXF, or SXJ 9801 West Higgins Road, Rosemont, IL 60018 (708) 696-2000 FIGURE 11. Aluminum Electrolytic Capacitors Recommended for Switching Regulators 19 www.national.com LM1577/LM2577 Application Hints LM1577/LM2577 Application Hints (Continued) 01146813 Note: Pin numbers shown are for TO-220 (T) package. FIGURE 13. Step-up Regulator Delivers 12V from a 5V Input 01146814 FIGURE 14. Line Regulation (Typical) of Step-Up Regulator of Figure 13 01146816 A: Switch pin voltage, 10 V/div 01146815 A: Output Voltage Change, 100 mV/div. (AC-coupled) B: Switch pin current, 2 A/div B: Load current, 0.2 A/div C: Inductor current, 2 A/div Horizontal: 5 ms/div D: Output ripple voltage, 100 mV/div (AC-coupled) Horizontal: 5 µs/div FIGURE 15. Load Transient Response of Step-Up Regulator of Figure 13 www.national.com FIGURE 16. Switching Waveforms of Step-Up Regulator of Figure 13 20 A. First, calculate the maximum value for RC. (Continued) FLYBACK REGULATOR A Flyback regulator can produce single or multiple output voltages that are lower or greater than the input supply voltage. Figure 18 shows the LM1577/LM2577 used as a flyback regulator with positive and negative regulated outputs. Its operation is similar to a step-up regulator, except the output switch contols the primary current of a flyback transformer. Note that the primary and secondary windings are out of phase, so no current flows through secondary when current flows through the primary. This allows the primary to charge up the transformer core when the switch is on. When the switch turns off, the core discharges by sending current through the secondary, and this produces voltage at the outputs. The output voltages are controlled by adjusting the peak primary current, as described in the step-up regulator section. Where ∑ILOAD(max) is the sum of the load current (magnitude) required from both outputs. Select a resistor less than or equal to this value, and no greater than 3 kΩ. B. Calculate the minimum value for ∑COUT (sum of COUT at both outputs) using the following two equations. Voltage and current waveforms for this circuit are shown in Figure 17, and formulas for calculating them are given in Figure 19. The larger of these two values must be used to ensure regulator stability. FLYBACK REGULATOR DESIGN PROCEDURE 1. Transformer Selection A family of standardized flyback transformers is available for creating flyback regulators that produce dual output voltages, from ± 10V to ± 15V, as shown in Figure 18. Figure 20lists these transformers with the input voltage, output voltages and maximum load current they are designed for. 2. Compensation Network (CC, RC) and Output Capacitor (COUT) Selection As explained in the Step-Up Regulator Design Procedure, CC, RC and COUT must be selected as a group. The following procedure is for a dual output flyback regulator with equal turns ratios for each secondary (i.e., both output voltages have the same magnitude). The equations can be used for a single output regulator by changing ∑ILOAD(max) to ILOAD(max) in the following equations. 01146817 FIGURE 17. Flyback Regulator Waveforms 21 www.national.com LM1577/LM2577 Application Hints LM1577/LM2577 Application Hints (Continued) 01146818 T1 = Pulse Engineering, PE-65300 D1, D2 = 1N5821 FIGURE 18. LM1577-ADJ/LM2577-ADJ Flyback Regulator with ± Outputs www.national.com 22 LM1577/LM2577 Application Hints (Continued) Duty Cycle D Primary Current Variation ∆IP Peak Primary Current IP(PK) Switch Voltage when Off VSW(OFF) Diode Reverse Voltage VR VOUT+ N (VIN− VSAT) Average Diode Current ID(AVE) ILOAD Peak Diode Current ID(PK) Short Circuit Diode Current Power Dissipation of LM1577/LM2577 PD 01146878 FIGURE 19. Flyback Regulator Formulas VOUT = 1.23V (1 + R1/R2) Resistors R1 and R2 divide the output voltage down so it can be compared with the LM1577-ADJ/LM2577-ADJ internal 1.23V reference. For a desired output voltage VOUT, select R1 and R2 so that C. Calculate the minimum value of CC D. Calculate the maximum ESR of the +VOUT and −VOUT output capacitors in parallel. 4. Diode Selection The switching diode in a flyback converter must withstand the reverse voltage specified by the following equation. This formula can also be used to calculate the maximum ESR of a single output regulator. At this point, refer to this same section in the Step-Up Regulator Design Procedurefor more information regarding the selection of COUT. 3. Output Voltage Selection This section is for applications using the LM1577-ADJ/ LM2577-ADJ. Skip this section if the LM1577-12/LM2577-12 or LM1577-15/LM2577-15 is being used. With the LM1577-ADJ/LM2577-ADJ, the output voltage is given by A suitable diode must have a reverse voltage rating greater than this. In addition it must be rated for more than the average and peak diode currents listed in Figure 19. 5. Input Capacitor Selection The primary of a flyback transformer draws discontinuous pulses of current from the input supply. As a result, a flyback regulator generates more noise at the input supply than a 23 www.national.com LM1577/LM2577 Application Hints ber consists of a fast recovery diode, and a parallel RC. The RC values are selected for switch clamp voltage (VCLAMP) that is 5V to 10V greater than VSW(OFF). Use the following equations to calculate R and C; (Continued) step-up regulator, and this requires a larger bypass capacitor to decouple the LM1577/LM2577 VIN pin from this noise. For most applications, a low ESR, 1.0 µF cap will be sufficient, if it is connected very close to the VIN and Ground pins. Transformer Input Type Voltage LP = 100 µH 5V N=1 5V 1 5V 10V 10V 2 LP = 200 µH 10V N = 0.5 12V 12V 12V 3 LP = 250 µH 15V N = 0.5 15V 15V Transformer Dual Maximum Output Output Voltage Current ± 10V ± 12V ± 15V ± 10V ± 12V ± 15V ± 10V ± 12V ± 15V ± 10V ± 12V ± 15V 325 mA 275 mA Power dissipation (and power rating) of the resistor is; 225 mA 700 mA 575 mA 500 mA The fast recovery diode must have a reverse voltage rating greater than VCLAMP. 800 mA 700 mA 575 mA 900 mA 825 mA 700 mA Manufacturers’ Part Numbers Type AIE Pulse Renco 1 326-0637 PE-65300 RL-2580 2 330-0202 PE-65301 RL-2581 3 330-0203 PE-65302 RL-2582 FIGURE 20. Flyback Transformer Selection Guide In addition to this bypass cap, a larger capacitor (≥ 47 µF) should be used where the flyback transformer connects to the input supply. This will attenuate noise which may interfere with other circuits connected to the same input supply voltage. 01146819 FIGURE 21. Snubber Circuit FLYBACK REGULATOR CIRCUIT EXAMPLE The circuit of Figure 22 produces ± 15V (at 225 mA each) from a single 5V input. The output regulation of this circuit is shown in Figure 23 and Figure 25, while the load transient response is shown in Figure 24 and Figure 26. Switching waveforms seen in this circuit are shown in Figure 27. 6. Snubber Circuit A “snubber” circuit is required when operating from input voltages greater than 10V, or when using a transformer with LP ≥ 200 µH. This circuit clamps a voltage spike from the transformer primary that occurs immediately after the output switch turns off. Without it, the switch voltage may exceed the 65V maximum rating. As shown in Figure 21, the snub- www.national.com 24 LM1577/LM2577 Application Hints (Continued) 01146820 T1 = Pulse Engineering, PE-65300 D1, D2 = 1N5821 FIGURE 22. Flyback Regulator Easily Provides Dual Outputs 01146823 A: Output Voltage Change, 100 mV/div B: Output Current, 100 mA/div 01146821 Horizontal: 10 ms/div FIGURE 23. Line Regulation (Typical) of Flyback Regulator of Figure 22, +15V Output FIGURE 24. Load Transient Response of Flyback Regulator of Figure 22, +15V Output 25 www.national.com LM1577/LM2577 Application Hints (Continued) 01146824 A: Output Voltage Change, 100 mV/div B: Output Current, 100 mA/div Horizontal: 10 ms/div FIGURE 26. Load Transient Response of Flyback Regulator of Figure 22, −15V Output 01146822 FIGURE 25. Line Regulation (Typical) of Flyback Regulator of Figure 22, −15V Output 01146825 A: Switch pin voltage, 20 V/div B: Primary current, 2 A/div C: +15V Secondary current, 1 A/div D: +15V Output ripple voltage, 100 mV/div Horizontal: 5 µs/div FIGURE 27. Switching Waveforms of Flyback Regulator of Figure 22, Each Output Loaded with 60Ω www.national.com 26 LM1577/LM2577 Physical Dimensions inches (millimeters) unless otherwise noted TO-3 Metal Can Package (K) Order Number LM1577K-12/883, LM1577K-15/883, or LM1577K-ADJ/883 NS Package Number K04A 0.300 Wide SO Package (M) Order Number LM2577M-12, LM2577M-15 or LM2577M-ADJ NS Package Number M24B 27 www.national.com LM1577/LM2577 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Molded Dual-In-Line Package (N) Order Number LM2577N-12, LM2577N-15, or LM2577N-ADJ NS Package Number N16A TO-220, Straight Leads (T) Order Number LM2577T-12, LM2577T-15, or LM2577T-ADJ NS Package Number TO5A www.national.com 28 LM1577/LM2577 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) TO-220, Bent Staggered Leads (T) Order Number LM2577T-12 Flow LB03, LM2577T-15 Flow LB03, or LM2577T-ADJ Flow LB03 NS Package Number T05D 29 www.national.com LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 5-Lead TO-263 (S) Order Number LM2577S-12, LM2577S-15 or LM2577S-ADJ NS Package Number TS5B 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. 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