UC2577-ADJ Simple Step-Up Voltage Regulator FEATURES DESCRIPTION • Requires Few External Components • NPN Output Switches 3.0A, 65V(max) • Extended Input Voltage Range: 3.0V to 40V • Current Mode Operation for Improved Transient Response, Line Regulation, and Current Limiting The UC2577-ADJ device provides all the active functions necessary to implement step-up (boost), flyback, and forward converter switching regulators. Requiring only a few components, these simple regulators efficiently provide up to 60V as a step-up regulator, and even higher voltages as a flyback or forward converter regulator. • Soft Start Function Provides Controlled Startup • 52kHz Internal Oscillator • Output Switch Protected by Current Limit, Undervoltage Lockout and Thermal Shutdown • Improved Replacement for LM2577-ADJ Series TYPICAL APPLICATIONS • Simple Boost and Flyback Converters • SEPIC Topology Permits Input Voltage to be Higher or Lower than Output Voltage • Transformer Coupled Forward Regulators • Multiple Output Designs BLOCK DIAGRAM The UC2577-ADJ features a wide input voltage range of 3.0V to 40V and an adjustable output voltage. An on-chip 3.0A NPN switch is included with undervoltage lockout, thermal protection circuitry, and current limiting, as well as soft start mode operation to reduce current during startup. Other features include a 52kHz fixed frequency on-chip oscillator with no external components and current mode control for better line and load regulation. A standard series of inductors and capacitors are available from several manufacturers optimized for use with these regulators and are listed in this data sheet. CONNECTION DIAGRAM 5-Pin TO-220 (Top View) T Package Also available in TO-263 Package (TD). UDG-94034 3/97 Powered by ICminer.com Electronic-Library Service CopyRight 2003 UC2577-ADJ ABSOLUTE MAXIMUM RATINGS (Note 1) RECOMMENDED OPERATING RANGE Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45V Output Switch Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65V Output Switch Current (Note 2) . . . . . . . . . . . . . . . . . . . . . 6.0A Power Dissipation . . . . . . . . . . . . . . . . . . . . . . Internally Limited Storage Temperature Range . . . . . . . . . . . . . −65°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . . 260°C Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . 150°C Minimum ESD Rating (C = 100pF, R = 15kΩ) . . . . . . . . . . . 2kV Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . 3.0V ≤ VIN ≤ 40V Output Switch Voltage . . . . . . . . . . . . . . . 0V ≤ VSWITCH ≤ 60V Output Switch Current . . . . . . . . . . . . . . . . . . . . ISWITCH ≤ 3.0A Junction Temperature Range . . . . . . . . . . −40°C ≤ TJ ≤ +125°C ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for TA = −40°C to +125°C, VIN = 5V, VFB = VREF, ISWITCH = 0, and TA =TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 12.0 12.60 V System Parameters Circuit Figure 1 (Note 3) Output Voltage VIN = 5V to 10V, ILOAD = 100mA to 800mA 11.40 TJ = 25°C 11.60 Line Regulation VIN = 3.0V to 10V, ILOAD = 300mA 20 TJ = 25°C Load Regulation VIN = 5V, ILOAD = 100mA to 800mA 20 TJ = 25°C Efficiency VIN = 5V, ILOAD = 800mA 80 VFB = 1.5V (Switch Off) 7.5 12.40 V 100 mV 50 mV 100 mV 50 mV % Device Parameters Input Supply Current TJ = 25°C ISWITCH = 2.0A, VCOMP = 2.0V (Max Duty Cycle) 45 TJ = 25°C Input Supply UVLO ISWITCH = 100mA 2.70 TJ = 25°C Oscillator Frequency Reference Voltage Measured at SWITCH Pin, ISWITCH = 100mA 42 TJ = 25°C 48 Measured at FB Pin, VIN = 3.0V to 40V, VCOMP = 1.0V 1.206 TJ = 25°C 1.214 52 1.230 Reference Voltage Line Regulation VIN = 3.0V to 40V 0.5 Error Amp Input Bias Current VCOMP = 1.0V 100 TJ = 25°C Error Amp Transconductance Error Amp Voltage Gain Error Amplifier Output Swing ICOMP = −30µA to +30µA, VCOMP = 1.0V 1600 TJ = 25°C 2400 VCOMP = 0.8V to 1.6V, RCOMP = 1.0MW (Note 4) 250 TJ = 25°C 500 Upper Limit VFB = 1.0V 2.0 TJ = 25°C 2.2 Lower Limit VFB = 1.5V 3700 VFB = 1.0V to 1.5V, VCOMP = 1.0V ±90 TJ = 25°C ±130 Soft Start Current VFB = 1.0V, VCOMP = 0.5V 1.5 TJ = 25°C 2.5 Maximum Duty Cycle VCOMP = 1.5V, ISWITCH = 100mA 90 TJ = 25°C 93 Powered by ICminer.com Electronic-Library Service CopyRight 2003 2 mA 10 mA 85 mA 70 mA 2.95 V 2.85 V 62 kHz 56 kHz 1.254 V 1.246 V mV 800 nA 300 nA 5800 µmho 4800 µmho 800 V/V V/V 2.4 V V 0.3 0.55 0.40 V ±200 ±400 µA ±300 µA 9.5 µA 7.5 µA TJ = 25°C Error Amp Output Current 14 5.0 95 V % % UC2577-ADJ ELECTRICAL CHARACTERISTICS Unless otherwise stated, these specifications apply for TA = −40°C to +125°C, VIN = 5V, VFB = VREF, ISWITCH = 0, and TA =TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Device Parameters (cont.) Switch Transconductance Switch Leakage Current 12.5 VSWITCH = 65V, VFB = 1.5V (Switch Off) 10 TJ = 25°C Switch Saturation Voltage ISWITCH = 2.0A, VCOMP = 2.0V (Max Duty Cycle) 0.5 TJ = 25°C NPN Switch Current Limit VCOMP = 2.0V Thermal Resistance Junction to Ambient 65 Junction to Case 2 VCOMP = 0 25 COMP Pin Current 3.0 TJ = 25°C 4.3 A/V 600 µA 300 µA 0.9 V 0.7 V 6.0 A °C/W °C/W 50 µA 40 µA Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions during 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: Output current cannot be internally limited when the UC2577 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 UC2577 is used as a flyback or forward converter regulator. Note 3. External components such as the diode, inductor, input and output capacitors can affect switching regulator performance. When the UC2577 is used as shown in the Test Circuit, system performance will be as specified by the system parameters. Note 4: A 1.0MΩ 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 ≥ 10MΩ, resulting in AVOL that is typically twice the guaranteed minimum limit. UDG-94035 L = 415-0930 (AIE) D = any manufacturer COUT = Sprague Type 673D Electrolytic 680µF, 20V R1 = 48.7k in series with 511Ω (1%) R2 = 5.62k (1%) Figure 1. Circuit Used to Specify System Parameters Powered by ICminer.com Electronic-Library Service CopyRight 2003 3 UC2577-ADJ APPLICATIONS INFORMATION Step-up (Boost) Regulator The Block Diagram shows a step-up switching regulator utilizing the UC2577. The regulator produces an output voltage higher than the input voltage. The UC2577 turns its switch on and off at a fixed frequency of 52kHz, thus storing energy in the inductor (L). When the NPN switch is on, the inductor current is charged at a rate of VIN/L. When the switch is off, the voltage at the SWITCH terminal of the inductor rises above VIN, discharging the stored current through the output diode (D) into the output capacitor (COUT) at a rate of (VOUT - VIN)/L. The energy stored in the inductor is thus transferred to the output. D VOUT + VF − VIN VOUT − VIN ≈ VOUT VOUT + VF − VSAT Avg. Inductor Current IIND(AVG) ILOAD 1−D Inductor Current Ripple ∆IIND Peak Inductor Current IIND(PK) ILOAD ∆IIND + 2 1−D Peak Switch Current ISW(PK) ILOAD ∆IIND + 2 1−D Duty Cycle The output voltage is controlled by the amount of energy transferred, which is controlled by modulating the peak inductor current. This modulation is accomplished by feeding a portion of the output voltage to an error amplifier which amplifies the difference between the feedback voltage and an internal 1.23V precision reference voltage. The output of the error amplifier is then compared to a voltage proportional to the switch current, or the inductor current, during the switch on time. A comparator terminates the switch on time when the two voltages are equal and thus controls the peak switch current to maintain a constant output voltage. Figure 2 shows voltage and current waveforms for the circuit. Formulas for calculation are shown in Figure 3. VIN − VSAT L Switch Voltage VSW(OFF) when Off Diode Reverse Voltage • D 52,000 VOUT + VF VR VOUT - VSAT Avg. Diode Current ID(AVG) ILOAD Peak Diode Current ID(PK) ILOAD ∆IIND + . 2 1−D STEP-UP REGULATOR DESIGN PROCEDURE Power Dissipation PD Refer to the Block Diagram Given: VINmin = Minimum input supply voltage VOUT = Regulated output voltage ILOAD • D • VIN ILOAD D+ 0.25Ω 50 (1−D) 1−D VF = Forward Biased Diode Voltage, ILOAD = Output Load 2 Figure 3. Step-up Regulator Formulas First, determine if the UC2577 can provide these values of VOUT and ILOADmax when operating with the minimum value of VIN. The upper limits for VOUT and ILOADmax are given by the following equations. VOUT ≤ 60V and VOUT ≤ 10 • VINmin 2.1A • VINmin ILOADmax ≤ VOUT These limits must be greater than or equal to the values specified in this application. 1. Output Voltage Section Resistors R1 and R2 are used to select the desired output voltage. These resistors form a voltage divider and present a portion of the output voltage to the error amplifier which compares it to an internal 1.23V reference. Select R1 and R2 such that: R1 VOUT = −1 R2 1.23V Figure 2. Step-up Regulator Waveforms Powered by ICminer.com Electronic-Library Service CopyRight 2003 4 UC2577-ADJ APPLICATIONS INFORMATION (cont.) 2. Inductor Selection (L) A. Preliminary Calculations To select the inductor, the calculation of the following three parameters is necessary: If Lmin is smaller than the inductor values 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: Dmax, 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. Dmax = VOUT + VF − VINmin VOUT + VF − 0.6V where typically VF = 0.5V for Schottky diodes and VF = 0.8V for fast recovery diodes. E • T, the product of volts • time that charges the inductor: E•T= C. Inductor Selection Select an inductor from the table of Figure 5 which cross references the inductor codes to the part numbers of the three different manufacturers. The inductors listed in this table have the following characteristics: Dmax • (VINmin − 0.6V)106 (V• µs) 52,000Hz IIND, DC, the average inductor current under full load: IIND, DC = AIE (ferrite, pot-core inductors): Benefits of this type are low etectromagnetic interference (EMI), small physical size, and very low power dissipation (core loss). 1.05 • ILOADmax 1 − Dmax B. Identify Inductor Value: 1. From Figure 4, 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 90Vµs (L) or 250Vµs (H). 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. 2. If D < 0.85, go to step C. If D ≥ 0.85, calculate the minimum inductance needed to ensure the switching regulator’s stability: 200 H2200 150 H1500 H1000 H680 H470 H330 H220 100 90 H150 E·T (V·µs) 80 70 L680 60 50 45 40 L470 L330 L220 L150 L100 L68 35 30 L47 25 20 0.3 0.35 0.4 0.45 0.5 0.6 0.7 0.8 0.9 1.0 1.5 2.0 2.5 3.0 IIND, DC (A) Note: This chart assumes 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 4. Inductor Selection Graph Powered by ICminer.com Electronic-Library Service CopyRight 2003 5 UC2577-ADJ APPLICATIONS INFORMATION (cont.) Inductor Code L47 L68 L100 L150 L220 L330 L470 L680 H150 H220 H330 H470 H680 H1000 H1500 H2200 Manufacturer’s Part Number AIE Pulse Renco 415 - 0932 PE - 53112 RL2442 415 - 0931 PE - 92114 RL2443 415 - 0930 PE - 92108 RL2444 415 - 0953 PE - 53113 RL1954 415 - 0922 PE - 52626 RL1953 415 - 0926 PE - 52627 RL1952 415 - 0927 PE - 53114 RL1951 415 - 0928 PE - 52629 RL1950 415 - 0936 PE - 53115 RL2445 430 - 0636 PE - 53116 RL2446 430 - 0635 PE - 53117 RL2447 430 - 0634 PE - 53118 RL1961 415 - 0935 PE - 53119 RL1960 415 - 0934 PE - 53120 RL1959 415 - 0933 PE - 53121 RL1958 415 - 0945 PE - 53122 RL2448 COUT ≥ C. Calculate the minimum value of CC. CC ≥ RC2 • VINmin Figure 6 lists several types of aluminum electrolytic capacitors which could be used for the output filter. Use the following parameters to select the 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: 3. Compensation Network (RC, CC) and Output Capacitor (COUT) Selection The compensation network consists of resistor RC and capacitor CC which form a simple pole-zero network and stabilize the regulator. The values of RC and CC depend upon the voltage gain of the regulator, ILOADmax, the inductor L, and output capacitance COUT. A procedure to calculate and select the values for RC, CC, and COUT which ensures stability is described below. It should be noted, however, that this may not result in optimum compensation. To guarantee optimum compensation a standard procedure for testing loop stability is recommended, such as measuring VOUT transient responses to pulsing ILOAD. IRIPPLErms = ILOADmax • Dmax 1 − Dmax Choose a capacitor that is rated at least 50% higher than this value at 52kHz. 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 the ESR does not exceed the maximum value specified by the following equations. ESR ≤ A. Calculate the maximum value for R C. 750 • ILOADmax • VOUT2 8.7 • 10−3 • VIN 0.01 • 15V and ≤ where IRIPPLE(P−P) ILOADmax IRIPPLE(P−P) = VINmin2 Select a resistor less than or equal to this value, not to exceed 3kΩ. 1.15 • ILOADmax 1 − Dmax Select a capacitor with an ESR, at 52kHz, that is less than or equal to the lower value calculated. Most electrolytic capacitors specify ESR at 120kHz which is 15% to 30% higher than at 52kHz. Also, note that ESR increases by a factor of 2 when operating at −20°C. B. Calculate the minimum value for COUT using the following two equations. 0.19 • L • RC • ILOADmax and VINmin • VOUT Powered by ICminer.com Electronic-Library Service CopyRight 2003 58.5 • VOUT2 • COUT The compensation capacitor is also used in the soft start function of the regulator. When the input voltage is applied to the part, the switch duty cycle is increased slowly at a rate defined by the compensation capacitor and the soft start current, thus eliminating high input currents. Without the soft start circuitry, the switch duty cycle would instantly rise to about 90% and draw large currents from the input supply. For proper soft starting, the value for C C should be equal or greater than 0.22µF. Figure 5. Table of Standardized Inductors and Manufacturer’s Part Numbers COUT ≥ 487,800 • VOUT3 The larger of these two values is the minimum value that ensures stability. AIE Magnetics, Div. Vernitron Corp., (813)347-2181 2801 72nd Street North, St. Petersburg, FL 33710 Pulse Engineering, (619)674-8100 12220 World Trade Drive, San Diego, CA 92128 Renco Electronics, Inc., (516)586-5566 60 Jeffryn Blvd. East, Deer Park, NY 11729 RC ≤ VINmin • RC • (VINmin + (3.74 • 105 • L)) In general, low values of ESR are achieved by using large value capacitors (C ≥ 470µF), and capacitors with high WVDC, or by paralleling smaller value capacitors. 6 UC2577-ADJ APPLICATIONS INFORMATION (cont.) 4. Input Capacitor Selection (CIN) To reduce noise on the supply voltage caused by the switching action of a step-up regulator (ripple current noise), VIN should be bypassed to ground. A good quality 0.1µF capacitor with low ESR should provide sufficient decoupling. If the UC2577 is located far from the supply source filter capacitors, an additional electrolytic (47µF, for example) is required. VOUTmax 20V 30V 40V Nichicon - Types PF, PX, or PZ 927 East StateParkway, Schaumburg, IL 60173 (708)843-7500 50V United Chemi-CON - Types LX, SXF, or SXJ 9801 West Higgens, Rosemont, IL 60018 (708)696-2000 100V Figure 6. Aluminum Electrolytic Capacitors Recommended for Switching Regulators Fast Recovery 1A 3A 1N4933 MUR105 1N4934 MUR110 10DL1 MR851 30DL1 MR831 MBRxxx and MURxxx are manufactured by Motorola. 1DDxxx, 11Cxx and 31Dxx are manufactured by International Rectifier 5. Output Diode Selection (D) In the step-up regulator, the switching diode must withstand a reverse voltage and be able to conduct the peak output current of the UC2577. Therefore a suitable diode must have a minimum reverse breakdown voltage greater than the circuit output voltage, and should also be rated for average and peak current greater than ILOADmax and IDpk. Because of their low forward voltage drop (and thus higher regulator efficiencies), Schottky barrier diodes are often used in switching regulators. Refer to Figure 7 for recommended part numbers and voltage ratings of 1A and 3A diodes. Figure 7. Diode Selection Chart ORDERING INFORMATION Unitrode Type Number UC2577T-ADJ 5 Pin TO-220 Plastic Package UC2577TD-ADJ 5 Pin TO-263 Plastic Package UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 • FAX (603) 424-3460 Powered by ICminer.com Electronic-Library Service CopyRight 2003 Schottky 1A 3A 1N5817 1N5820 MBR120P MBR320P 1N5818 1N5821 MBR130P MBR330P 11DQ03 31DQ03 1N5819 1N5822 MBR140P MBR340P 11DQ04 31DQ04 MBR150 MBR350 11DQ05 31DQ05 7 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. 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INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER’S RISK. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI’s publication of information regarding any third party’s products or services does not constitute TI’s approval, warranty or endorsement thereof. Copyright 1999, Texas Instruments Incorporated Powered by ICminer.com Electronic-Library Service CopyRight 2003