LM2577T-ADJ

LM1577/LM2577 SIMPLE SWITCHER Step-Up Voltage Regulator April 2005 LM1577/LM2577 SIMPLE SWITCHER ® Step-Up Voltage Regulator General Description 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. 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. Features 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 n n n n Typical Applications 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 01146805 Top View Order Number LM2577T-12, LM2577T-15, or LM2577T-ADJ See NS Package Number T05A 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 Connection Diagrams (Continued) 24-Lead Surface Mount (M) 16-Lead DIP (N) 01146806 *No internal Connection Top View Order Number LM2577N-12, LM2577N-15, or LM2577N-ADJ See NS Package Number N16A *No internal Connection 01146807 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 01146832 Top View 4-Lead TO-3 (K) Side View Order Number LM2577S-12, LM2577S-15, or LM2577S-ADJ See NS Package Number TS5B 01146808 Bottom View Order Number LM1577K-12/883, LM1577K-15/883, or LM1577K-ADJ/883 See NS Package Number K04A www.national.com 2 LM1577/LM2577 Ordering Information Temperature Range −40˚C ≤ TA ≤ +125˚C Package Type 24-Pin Surface Mount 16-Pin Molded DIP 5-Lead Surface Mount 5-Straight Leads 5-Bent Staggered Leads −55˚C ≤ TA ≤ +150˚C 4-Pin TO-3 Output Voltage 12V LM2577M-12 LM2577N-12 LM2577S-12 LM2577T-12 LM2577T-12 Flow LB03 15V LM2577M-15 LM2577N-15 LM2577S-15 LM2577T-15 LM2577T-15 Flow LB03 ADJ LM2577M-ADJ LM2577N-ADJ LM2577S-ADJ LM2577T-ADJ LM2577T-ADJ Flow LB03 LM1577KADJ/883 K04A TO-3 NSC Package Drawing M24B N16A TS5B T05A T05D SO N TO-263 TO-220 TO-220 Package LM1577K-12/883LM1577K-15/883 Typical Application 01146801 Note: Pin numbers shown are for TO-220 (T) package. 3 www.national.com LM1577/LM2577 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Output Switch Voltage Output Switch Current (Note 2) Power Dissipation Storage Temperature Range Lead Temperature (Soldering, 10 sec.) Maximum Junction Temperature 260˚C 150˚C 45V 65V 6.0A Internally Limited −65˚C to +150˚C Minimum ESD Rating (C = 100 pF, R = 1.5 kΩ) 2 kV Operating Ratings Supply Voltage Output Switch Voltage Output Switch Current Junction Temperature Range LM1577 LM2577 −55˚C ≤ TJ ≤ +150˚C −40˚C ≤ TJ ≤ +125˚C 3.5V ≤ VIN ≤ 40V 0V ≤ VSWITCH ≤ 60V ISWITCH ≤ 3.0A 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. LM1577-12 Symbol Parameter Conditions Typical Limit (Notes 3, 4) SYSTEM PARAMETERS Circuit of Figure 1 (Note 6) VOUT Output Voltage VIN = 5V to 10V ILOAD = 100 mA to 800 mA (Note 3) Line Regulation VIN = 3.5V to 10V ILOAD = 300 mA Load Regulation VIN = 5V ILOAD = 100 mA to 800 mA η IS Efficiency Input Supply Current VIN = 5V, ILOAD = 800 mA VFEEDBACK = 14V (Switch Off) ISWITCH = 2.0A VCOMP = 2.0V (Max Duty Cycle) VUV Input Supply Undervoltage Lockout fO Oscillator Frequency Measured at Switch Pin ISWITCH = 100 mA VREF Output Reference Voltage Output Reference Voltage Line Regulator RFB GM Feedback Pin Input Resistance Error Amp Transconductance ICOMP = −30 µA to +30 µA VCOMP = 1.0V 370 225/145 515/615 225/145 515/615 µmho µmho(min) µmho(max) 9.7 kΩ Measured at Feedback Pin VIN = 3.5V to 40V VCOMP = 1.0V VIN = 3.5V to 40V 7 12 11.76/11.64 12.24/12.36 11.76/11.64 12.24/12.36 52 48/42 56/62 48/42 56/62 ISWITCH = 100 mA 2.90 2.70/2.65 3.10/3.15 2.70/2.65 3.10/3.15 80 7.5 10.0/14.0 25 50/85 50/85 10.0/14.0 DEVICE PARAMETERS mA mA(max) mA mA(max) V V(min) V(max) kHz kHz(min) kHz(max) V V(min) V(max) mV 20 50/100 50/100 20 50/100 50/100 12.0 11.60/11.40 12.40/12.60 11.60/11.40 12.40/12.60 V V(min) V(max) mV mV(max) mV mV(max) % LM2577-12 Limit (Note 5) Units (Limits) www.national.com 4 LM1577/LM2577 Electrical Characteristics—LM1577-12, LM2577-12 (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. LM1577-12 Symbol Parameter Conditions Typical Limit (Notes 3, 4) LM2577-12 Limit (Note 5) V/V 50/25 2.4 2.2/2.0 0.3 0.40/0.55 0.40/0.55 2.2/2.0 50/25 V/V(min) V V(min) V V(max) µA µA(min) µA(max) µA 2.5/1.5 7.5/9.5 95 93/90 12.5 93/90 2.5/1.5 7.5/9.5 µA(min) µA(max) % %(min) A/V Units (Limits) DEVICE PARAMETERS AVOL Error Amp Voltage Gain Error Amplifier Output Swing VCOMP = 1.1V to 1.9V RCOMP = 1.0 MΩ (Note 7) Upper Limit VFEEDBACK = 10.0V Lower Limit VFEEDBACK = 15.0V Error Amplifier Output Current ISS Soft Start Current VFEEDBACK = 10.0V to 15.0V VCOMP = 1.0V VFEEDBACK = 10.0V VCOMP = 0V D Maximum Duty Cycle Switch Transconductance IL VSAT Switch Leakage Current Switch Saturation Voltage NPN Switch Current Limit VSWITCH = 65V VFEEDBACK = 15V (Switch Off) ISWITCH = 2.0A VCOMP = 2.0V (Max Duty Cycle) 4.5 3.7/3.0 5.3/6.0 3.7/3.0 5.3/6.0 0.5 0.7/0.9 0.7/0.9 VCOMP = 1.5V ISWITCH = 100 mA 5.0 80 ± 200 ± 130/ ± 90 ± 300/ ± 400 ± 130/ ± 90 ± 300/ ± 400 10 300/600 300/600 µA µA(max) V V(max) A A(min) A(max) 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. LM1577-15 Symbol Parameter Conditions Typical Limit (Notes 3, 4) SYSTEM PARAMETERS Circuit of Figure 2 (Note 6) VOUT Output Voltage VIN = 5V to 12V ILOAD = 100 mA to 600 mA (Note 3) Line Regulation VIN = 3.5V to 12V ILOAD = 300 mA Load Regulation VIN = 5V ILOAD = 100 mA to 600 mA η Efficiency VIN = 5V, ILOAD = 600 mA 80 20 50/100 50/100 20 50/100 50/100 15.0 14.50/14.25 15.50/15.75 14.50/14.25 15.50/15.75 V V(min) V(max) mV mV(max) mV mV(max) % LM2577-15 Limit (Note 5) Units (Limits) 5 www.national.com 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. LM1577-15 Symbol Parameter Conditions Typical Limit (Notes 3, 4) LM2577-15 Limit (Note 5) mA 10.0/14.0 25 50/85 2.90 2.70/2.65 3.10/3.15 Measured at Switch Pin ISWITCH = 100 mA 52 48/42 56/62 48/42 56/62 14.70/14.55 15.30/15.45 2.70/2.65 3.10/3.15 50/85 10.0/14.0 mA(max) mA mA(max) V V(min) V(max) kHz kHz(min) kHz(max) V 15 10 14.70/14.55 15.30/15.45 V(min) V(max) mV kΩ µmho 170/110 420/500 65 40/20 2.4 2.2/2.0 0.3 0.4/0.55 0.40/0.55 2.2/2.0 40/20 170/110 420/500 µmho(min) µmho(max) V/V V/V(min) V V(min) V V(max) µA µA(min) µA(max) µA 2.5/1.5 7.5/9.5 95 93/90 12.5 93/90 2.5/1.5 7.5/9.5 µA(min) µA(max) % %(min) A/V Units (Limits) DEVICE PARAMETERS IS Input Supply Current VFEEDBACK = 18.0V (Switch Off) ISWITCH = 2.0A VCOMP = 2.0V (Max Duty Cycle) VUV Input Supply Undervoltage Lockout fO Oscillator Frequency ISWITCH = 100 mA 7.5 VREF Output Reference Voltage Output Reference Voltage Line Regulation Measured at Feedback Pin VIN = 3.5V to 40V VCOMP = 1.0V VIN = 3.5V to 40V RFB GM Feedback Pin Input Voltage Line Regulator Error Amp Transconductance ICOMP = −30 µA to +30 µA VCOMP = 1.0V VCOMP = 1.1V to 1.9V RCOMP = 1.0 MΩ (Note 7) Error Amplifier Output Swing Upper Limit VFEEDBACK = 12.0V Lower Limit VFEEDBACK = 18.0V Error Amp Output Current VFEEDBACK = 12.0V to 18.0V VCOMP = 1.0V VFEEDBACK = 12.0V VCOMP = 0V 12.2 300 AVOL Error Amp Voltage Gain ± 200 ± 130/ ± 90 ± 300/ ± 400 5.0 ± 130/ ± 90 ± 300/ ± 400 ISS Soft Start Current D Maximum Duty Cycle Switch Transconductance VCOMP = 1.5V ISWITCH = 100 mA IL Switch Leakage Current VSWITCH = 65V VFEEDBACK = 18.0V (Switch Off) ISWITCH = 2.0A VCOMP = 2.0V (Max Duty Cycle) 10 300/600 0.5 0.7/0.9 0.7/0.9 300/600 µA µA(max) V V(max) VSAT Switch Saturation Voltage www.national.com 6 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. LM1577-15 Symbol Parameter Conditions Typical Limit (Notes 3, 4) LM2577-15 Limit (Note 5) A 3.7/3.0 5.3/6.0 3.7/3.0 5.3/6.0 A(min) A(max) Units (Limits) DEVICE PARAMETERS NPN Switch Current Limit VCOMP = 2.0V 4.3 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 Limit (Notes 3, 4) SYSTEM PARAMETERS Circuit of Figure 3 (Note 6) VOUT Output Voltage VIN = 5V to 10V ILOAD = 100 mA to 800 mA (Note 3) ∆VOUT/ ∆VIN ∆VOUT/ ∆ILOAD η IS Efficiency Input Supply Current DEVICE PARAMETERS VFEEDBACK = 1.5V (Switch Off) ISWITCH = 2.0A VCOMP = 2.0V (Max Duty Cycle) VUV Input Supply Undervoltage Lockout fO Oscillator Frequency Measured at Switch Pin ISWITCH = 100 mA VREF Reference Voltage ∆VREF/ ∆VIN IB GM Reference Voltage Line Regulation Error Amp Input Bias Current Error Amp Transconductance AVOL Error Amp Voltage Gain ICOMP = −30 µA to +30 µA VCOMP = 1.0V VCOMP = 1.1V to 1.9V RCOMP = 1.0 MΩ (Note 7) 800 500/250 500/250 3700 2400/1600 4800/5800 2400/1600 4800/5800 VCOMP = 1.0V 100 300/800 300/800 nA nA(max) µmho µmho(min) µmho(max) V/V V/V(min) Measured at Feedback Pin VIN = 3.5V to 40V VCOMP = 1.0V VIN = 3.5V to 40V 0.5 1.230 1.214/1.206 1.246/1.254 1.214/1.206 1.246/1.254 52 48/42 56/62 48/42 56/62 ISWITCH = 100 mA 2.90 2.70/2.65 3.10/3.15 2.70/2.65 3.10/3.15 7.5 10.0/14.0 25 50/85 50/85 10.0/14.0 mA mA(max) mA mA(max) V V(min) V(max) kHz kHz(min) kHz(max) V V(min) V(max) mV Load Regulation Line Regulation VIN = 3.5V to 10V ILOAD = 300 mA VIN = 5V ILOAD = 100 mA to 800 mA VIN = 5V, ILOAD = 800 mA 80 20 50/100 50/100 20 50/100 50/100 12.0 11.60/11.40 12.40/12.60 11.60/11.40 12.40/12.60 V V(min) V(max) mV mV(max) mV mV(max) % Limit (Note 5) Units (Limits) 7 www.national.com 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 (Notes 3, 4) Limit (Note 5) V 2.2/2.0 0.3 0.40/0.55 0.40/0.55 2.2/2.0 V(min) V V(max) µA µA(min) µA(max) µA 2.5/1.5 7.5/9.5 95 93/90 12.5 VSWITCH = 65V VFEEDBACK = 1.5V (Switch Off) ISWITCH = 2.0A VCOMP = 2.0V (Max Duty Cycle) VCOMP = 2.0V 4.3 3.7/3.0 5.3/6.0 3.7/3.0 5.3/6.0 0.5 0.7/0.9 0.7/0.9 10 300/600 300/600 93/90 2.5/1.5 7.5/9.5 µA(min) µA(max) % %(min) A/V µA µA(max) V V(max) A A(min) A(max) Units (Limits) DEVICE PARAMETERS Error Amplifier Output Swing Upper Limit VFEEDBACK = 1.0V Lower Limit VFEEDBACK = 1.5V Error Amp Output Current ISS Soft Start Current VFEEDBACK = 1.0V to 1.5V VCOMP = 1.0V VFEEDBACK = 1.0V VCOMP = 0V D ∆ISWITCH/ ∆VCOMP IL VSAT Maximum Duty Cycle Switch Transconductance Switch Leakage Current Switch Saturation Voltage NPN Switch Current Limit THERMAL PARAMETERS (All Versions) θJA θJC θJA θJC θJA θJA θJA Thermal Resistance K Package, Junction to Ambient K Package, Junction to Case T Package, Junction to Ambient T Package, Junction to Case N Package, Junction to Ambient (Note 8) M Package, Junction to Ambient (Note 8) S Package, Junction to 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. 2.4 ± 200 ± 130/ ± 90 ± 300/ ± 400 5.0 ± 130/ ± 90 ± 300/ ± 400 VCOMP = 1.5V ISWITCH = 100 mA 35 1.5 65 2 85 100 37 ˚C/W www.national.com 8 LM1577/LM2577 Electrical Characteristics—LM1577-ADJ, LM2577-ADJ (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 Temperature ∆ Reference Voltage vs Supply Voltage 01146836 01146837 ∆ Reference Voltage vs Supply Voltage ∆ Reference Voltage vs Supply Voltage 01146838 01146839 9 www.national.com LM1577/LM2577 Typical Performance Characteristics Error Amp Transconductance vs Temperature (Continued) Error Amp Transconductance vs Temperature 01146840 01146841 Error Amp Transconductance vs Temperature Error Amp Voltage Gain vs Temperature 01146842 01146843 Error Amp Voltage Gain vs Temperature Error Amp Voltage Gain vs Temperature 01146844 01146845 www.national.com 10 LM1577/LM2577 Typical Performance Characteristics Quiescent Current vs Temperature (Continued) Quiescent Current vs Switch Current 01146846 01146847 Current Limit vs Temperature Current Limit Response Time vs Overdrive 01146848 01146849 Switch Saturation Voltage vs Switch Current Switch Transconductance vs Temperature 01146850 01146851 11 www.national.com LM1577/LM2577 Typical Performance Characteristics Feedback Pin Bias Current vs Temperature (Continued) Oscillator Frequency vs Temperature 01146852 01146853 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 Average Inductor Current Inductor Current Ripple Peak Inductor Current Peak Switch Current Switch Voltage When Off Diode Reverse Voltage Average Diode Current Peak Diode Current Power Dissipation of LM1577/2577 D 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. 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). 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. Voltage and current waveforms for this circuit are shown in Figure 5, and formulas for calculating them are given in Figure 6. IIND(AVE) ∆IIND IIND(PK) ISW(PK) VSW(OFF) VOUT + VF VR VOUT − VSAT ID(AVE) ID(PK) ILOAD PD VF = Forward Biased Diode Voltage ILOAD = Output Load Current 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 (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): 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. 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 Code L47 L68 L100 L150 L220 L330 L470 L680 H150 H220 H330 H470 H680 H1000 H1500 H2200 (Continued) C. Calculate the minimum value of CC . Manufacturer’s Part Number Schott 67126980 67126990 67127000 67127010 67127020 67127030 67127040 67127050 67127060 67127070 67127080 67127090 67127100 67127110 67127120 67127130 Pulse PE - 53112 PE - 92114 PE - 92108 PE - 53113 PE - 52626 PE - 52627 PE - 53114 PE - 52629 PE - 53115 PE - 53116 PE - 53117 PE - 53118 PE - 53119 PE - 53120 PE - 53121 PE - 53122 Renco RL2442 RL2443 RL2444 RL1954 RL1953 RL1952 RL1951 RL1950 RL2445 RL2446 RL2447 RL1961 RL1960 RL1959 RL1958 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. 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. FIGURE 10. Table of Standardized Inductors and Manufacturer’s Part Numbers 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 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. 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. The larger of these two values is the minimum value that ensures stability. www.national.com 18 LM1577/LM2577 Application Hints (Continued) 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. 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 If the LM1577 is located far from the supply source filter capacitors, an additional large electrolytic capacitor (e.g. 47 µF) is often required. 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. VOUT Schottky 1A 1N5817 MBR120P 1N5818 30V MBR130P 11DQ03 1N5819 40V MBR140P 11DQ04 MBR150 50V 100V 11DQ05 3A 1N5820 MBR320P 1N5821 MBR330P 31DQ03 1N5822 MBR340P 31DQ04 MBR350 31DQ05 1N4933 MUR105 1N4934 HER102 MUR110 10DL1 FIGURE 12. Diode Selection Chart MR851 30DL1 MR831 HER302 Fast Recovery 1A 3A 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. Cornell Dublier — Types 239, 250, 251, UFT, 300, or 350 P.O. Box 128, Pickens, SC 29671 (803) 878-6311 Nichicon — Types PF, PX, or PZ 927 East Parkway, Schaumburg, IL 60173 (708) 843-7500 Sprague — Types 672D, 673D, or 674D Box 1, Sprague Road, Lansing, NC 28643 (919) 384-2551 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 (max) 20V 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. 19 www.national.com 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 01146815 A: Switch pin voltage, 10 V/div B: Switch pin current, 2 A/div C: Inductor current, 2 A/div D: Output ripple voltage, 100 mV/div (AC-coupled) Horizontal: 5 µs/div A: Output Voltage Change, 100 mV/div. (AC-coupled) B: Load current, 0.2 A/div Horizontal: 5 ms/div FIGURE 15. Load Transient Response of Step-Up Regulator of Figure 13 FIGURE 16. Switching Waveforms of Step-Up Regulator of Figure 13 www.national.com 20 LM1577/LM2577 Application Hints FLYBACK REGULATOR (Continued) A. First, calculate the maximum value for RC. 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. Voltage and current waveforms for this circuit are shown in Figure 17, and formulas for calculating them are given in Figure 19. 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. 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. The larger of these two values must be used to ensure regulator stability. 01146817 FIGURE 17. Flyback Regulator Waveforms 21 www.national.com 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 Duty Cycle (Continued) D Primary Current Variation ∆IP Peak Primary Current IP(PK) Switch Voltage when Off VSW(OFF) Diode Reverse Voltage Average Diode Current Peak Diode Current ID(PK) Short Circuit Diode Current VR ID(AVE) VOUT+ N (VIN− VSAT) ILOAD Power Dissipation of LM1577/LM2577 PD 01146878 FIGURE 19. Flyback Regulator Formulas C. Calculate the minimum value of CC 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 D. Calculate the maximum ESR of the +VOUT and −VOUT output capacitors in parallel. 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 23 4. Diode Selection The switching diode in a flyback converter must withstand the reverse voltage specified by the following equation. 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 www.national.com LM1577/LM2577 Application Hints (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 Type LP = 100 µH 1 N=1 Input Voltage 5V 5V 5V 10V 10V 2 LP = 200 µH N = 0.5 10V 12V 12V 12V 3 LP = 250 µH N = 0.5 15V 15V 15V Transformer Type 1 2 3 Dual Output Voltage Maximum Output Current 325 mA 275 mA 225 mA 700 mA 575 mA 500 mA 800 mA 700 mA 575 mA 900 mA 825 mA 700 mA 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; ± 10V ± 12V ± 15V ± 10V ± 12V ± 15V ± 10V ± 12V ± 15V ± 10V ± 12V ± 15V Power dissipation (and power rating) of the resistor is; The fast recovery diode must have a reverse voltage rating greater than VCLAMP. Manufacturers’ Part Numbers AIE 326-0637 330-0202 330-0203 Pulse PE-65300 PE-65301 PE-65302 Renco RL-2580 RL-2581 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. 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- 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. 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 01146822 FIGURE 26. Load Transient Response of Flyback Regulator of Figure 22, −15V Output 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 unless otherwise noted inches (millimeters) 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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