TIGER ELECTRONIC CO.,LTD 3A Step-Down Voltage Regulator LM2576BM DESCRIPITION The LM2576BM series of regulators are monolithic in tegrated circuits that provide all th e active functions for a step-down (buck) switching regulator, capable of driving 3A load with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5V, 12V and an ADJ output version. Requiring a minimu m number of external components, these regulators are simple to use and include internal frequency compensation and a fixed-frequency oscillator. The LM2576BM series offers a high-efficiency replacement for popular three-terminal linear regulators. It substantially reduces the size of the heat sink, and in so me cases no heat sink is required. A standard series of inducto rs optimized for use with the LM2576BM are available fro m several different manufacturers. This feature greatly si mplifies the design of switch-mode power supplies. Other features include a guaranteed ±4% tolerance on output voltage within specified input voltages and output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring 50 µA (typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as ther mal shutdown for full protection under fault conditions. FEATURES z 3.3V, 5V, 12V and adjustable output versions z Guaranteed 3A output current z Adjustable version output voltage range,1.23V to APPLICATIONS z step-down (buck) regulator z 37V±4% max over line and lo ad cond itions z 52 kHz fixed frequency internal oscillator z TTL shutdown capability, low power standby mode z High efficiency z Uses readily available standard inducto rs z Thermal shutdown and current limit protection z Wide input voltage range up to 40V z Requires on ly 4 ex tern al co mponents Si mple high-efficiency Efficient pre-regulator for linear regulators z On-card switching regu lato rs z Positive to negative conv erter (Buck-Boost) 1/9 LM2576BM CONNECTION DIAGRAMS ESOP-8L XX: Weekly LM2576BM YY: Output Voltage ORDERING INFORMATION Ordering LM2576BM-ADJ LM2576BM-3.3 LM2576BM-5.0 LM2576BM-12 Output Voltage Adj. 3.3V 5.0V 12V Package ESOP-8L ESOP-8L ESOP-8L ESOP -8L ESOP-8L BLOCK DIAGRAM 3.3V R2 =1.7 K 5V R2 =3.1 K For ADJ Version R1=open, R2=0Ω 2/9 LM2576BM PIN FUNCTIONS +VIN —This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator. Ground —Circuit ground. Output —Internal switch, the voltage at this pin switches between (+VIN VSAT) and approximat ely -0.5V. To mini mize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept to a minimu m. FeedBack —Senses the regulated output voltage to co mp lete the feedback lo op. —Allows the switching regulator circuit to be shut down using logic level signals. Pulling this pin below a threshold voltage of approximately 1.5V turns the regulator on, and shutdown feature is not needed, the ON/OFF pin can be wired to the ground pin or it can be left open, in eith er case the regulator will be in th e ON condition. ABSOLUTE MAXIMUM RATINGS (Ta=25 °C) * Characteristic Value Unit 45 V -0.3V≤V≤+V I N V -1 V Maximu m supply voltage ON /OFF pin input voltage Output voltage to ground(steady state) Power dissipation Internally li mited Storage temperature range -65~+150 Maximu m junction temp erature kV 2 ESD susceptibility (Human Body Model) °C °C 150 RECOMMENDED OPERATING CONDITIONS Characteristic Supply Vo ltage Operating te mp erature range Symbol Value Unit VCC 6～ 40 V -40 ～ +1 25 °C 3/9 LM2576BM ELECTRICAL CHARACTERISTICS (Specifications with standard type face are for Para meter T J = 25°C,) Min. *2 S y mb o l Condition Ib Adjustable version only, V O U T =5V fO *8 VSAT I O U T =3A *4 Max. duty cycle(ON) DC *5 93 98 Current li mit ICL *4,8 4.2 5.8 Output current IL Device Pa ra meters Feedback bias current Oscillator frequency VSAT saturation voltage leakage Quiescent cu rrent Standby quiescent current Output=0V *6,7 *6 ON/OF F Max. Unit 50 100 nA 52 58 kHz 1.4 1.8 V P I N =5V % 6.9 A 2.3 mA 30 mA 5 10 mA 50 200 µA 7.5 Output=-1VV *10 IQ ISTBY 47 Typ. ON/OF F Control ON/OF F pin logic input level ON/OF F pin input current VIH IIH V O U T =0V V O U T = n o mi n a l o u tp u t voltage ON/OFF pin=5V(OFF) IIL ON/OFF pin=0V(ON) VIL V 0.8 V 4 30 µA 0.01 10 µA 3.3 3.366 V LM2576BM 3.3V System Pa ra mete rs Output voltagde Efficiency VOUT η *3 6 V≤V I N ≤40V 0.5A≤I L O A D ≤3 A V I N =12V,I L O A D =3A 2.0 73 % LM2576BM 5.0V System Pa ra mete rs Output voltagde Efficiency VOUT η *3 8 V≤V I N ≤40V 0.5A≤I L O A D ≤3 A V I N =12V,I L O A D =3A 3.234 5.0 5.2 77 V % LM2576BM 12V System Pa ra mete rs Output voltagde Efficiency VOUT η *3 1 5 V≤V I N ≤40V 0.5A≤I L O A D ≤3 A V I N =15V,I L O A D =3A 4.8 12.0 12.48 88 V % LM2576BM ADJ Syste m Pa ra mete rs Output voltagde Efficiency VOUT η *3 8 V≤V I N ≤40V 0.5A≤I L O A D ≤3A V O U T =5V V I N =12V,I L O A D =3A V O U T =5V 11.52 1.193 1.230 1.267 77 V % * 1 Absolute Maxi mu m Ratings indicates limits beyond which dama ge to the device may occur. Operating Ratings indicate conditions for which the device is intended to be 4/9 LM2576BM functional, but specific performance is not guaranteed. For guaranteed specifications and the best conditions, see the Electrical Characteristics. * 2 All limi ts guaranteed at room te mperature (standard type face) and at temperature extremes(bold type face). All room temperature limits are 100% production tested. All li mits at temp erature extre mes are guaranteed via co rrelation using standard Statistical Quality Control (SQC) methods. * 3 External components such as th e catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. * 4 Output pin sourcing current. No diode, inductor or capacitor connected to output pin. * 5 Feedback pin removed fro m output and connected to 0V. * 6 Feedback pin removed fro m output and connected to +12V for the 3.3V, 5V, and the ADJ version, to force the output transistor switch OFF. * 7 V I N = 40V * 8 Th e oscillato r frequency reduces to approximately 11 KHz in the even t of an output short or an overload wh ich causes the regulated output voltage to drop approximately 40% fro m the nominal output voltage. The self-pro tection feature lo wers the av erag e power dissipation of the minimu m duty cycle fro m 5 % down to approximately 2%. TEST CIRCUIT LM2576BM LM2576BM-ADJ 5/9 LM2576BM APPLICATION CIRCUIT Ty pica l LM2576BM Low Noise LM2576BM APPLICATION INFORMATION Careful layout is impo rtant with an y switching regulator. Rapidly switching currents associated with wiring inductan ce generate vo ltage transients which can cause problems. To minimize inductance and ground loops, the lengths of the lead s indicated by heavy lines in Figure 1 below should be kept as short as possible. Single point grounding or ground plan e construction should be used for best results. When using the Adjustable version, place the programmi ng resistors as close as possible to LM2576BM, to keep the sensitive feedback wiring short. INPUT CA PACITOR C I N A low ESR aluminu m o r tantalum bypass capacitor is needed between the input pin and ground pin. It must be located near the regulator using short leads. This capacitor prevents large voltage transients fro m appearing at the input, and provides the instantaneous current needed each time the switch turns on. Selecting an input capacitor requires consulting the manufacturers data sheet for maximu m allowable RMS ripple current. For a maximu m ambient temperature of 40°C, a general guideline would be to select a capacitor with a ripple current rating of approximately 50% of the DC load current. For ambient 6/9 LM2576BM temperatures up to 70°C, a current rating of 75% of the DC load current would be a good choice for a conservative design. The capacitor voltage rating must be at least 1.25 times greater than the maximu m input voltage, and often a much higher voltage capacitor is needed to satisfy the RMS current requireme nts. OUTPUT CAPA CIT OR C O U T An output capacitor is required to filter the ou tput and provide regulator lo op stability. Low impedance or low ESR Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used. When selecting an output capacitor, the important capacitor para meters a re; the 100 kHz Equivalent Series resistance (ESR), the RMS ripples current rating, voltage rating, and capacitance value. For the output capacitor, the ESR value is th e mo st i mportant para meter. The output capacitor requires an ESR value that has an upper and lower limit. For low output ripple voltage, a low ESR value is needed. This value is determined by the maximu m allow ab le output ripple vo ltage, typically 1% to 2% of the output voltage. But if the selected capacitor’s ESR is extremely low, there is a possibility of an unstab le feedback loop, resulting in an oscillation at the output. CATCH DI ODE D1 Buck regulators require a diode to provide a return path for the inductor current when the switch turns off. This must be a fast diode and must be located close to the LM2576BM using short leads and short printed ci rcuit traces. Because of their very fast switching speed and low forward voltage drop, Schottky diodes provide the best performance, especially in low output voltage applications (5V and lower). Ultra fast recovery, or High-Efficiency rectifiers are also a good choice, but so me types with an abrupt turnoff characteristic ma y cause instability or EMI problems. INDUCTOR SELECTION L All switching regulators have two basic modes of operation; continuous and discontin uo us. The difference between the two types relates to th e in ductor cu rrent, whether it is flowing continuously, or if it drops to zero for a period of time i n the normal switching cycle. Each mode has distinctively different operating characteristics, which can affect the regulators performance and require ments. Most switcher designs will operate in the discontinuous mode when the load current is low. The LM2576BM (or any of the Si mple Switcher family) can be used for both continuous and discontinuous modes of operation. There is a formula for general applications: (Note The unit of vo ltage is V, th e un it of cu rrent is A) 7/9 LM2576BM CHARACTERISTICS CURVE 8/9 LM2576BM OUTLINE DRAWING Unit:mm ESOP-8L LM2576BM 9/9