LM2576BM

TIGER ELECTRONIC CO.,LTD 3A Step-Down Voltage Regulator L M 2576BM D ESCRIPITION T he L M 2576BM 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 L M 2576BM 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 L M 2576BM 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. F EATURES 3 .3V, 5V, 12V and adjustable output versions G uaranteed 3A output current A djustable version output voltage range,1.23V to 37V ± 4% max over line and lo ad cond itions 5 2 kHz fixed frequency internal oscillator T TL shutdown capability, low power standby mode H igh efficiency U ses readily available standard inducto rs T hermal shutdown and current limit protection W ide input voltage range up to 40V R equires on ly 4 ex tern al co mponents APPLICATIONS S i mple high-efficiency step-down (buck) regulator E fficient pre-regulator for linear regulators O n-card switching regu lato rs P ositive to negative conv erter (Buck-Boost) 1/9 LM2576BM C ONNECTION DIAGRAMS E SOP-8L X X: Weekly LM2576BM Y Y: Output Voltage O RDERING INFORMATION O rdering L M 2576BM - AD J L M 2576BM - 3 . 3 LM 2576BM - 5 . 0 L M 2576BM - 12 O utput Voltage A dj. 3.3V 5.0V 12V P ackage E SOP-8L ESOP-8L E SOP-8L ESOP -8L ESOP-8L B LOCK DIAGRAM 3 .3V R2 =1.7 K 5V R2 =3.1 K For ADJ Version R1=open, R2=0 Ω 2/9 LM2576BM P IN 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. G round — Circuit ground. O utput — 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. F eedBack — 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 s hutdown 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. A BSOLUTE MAXIMUM RATINGS ( Ta=25 ° C) * C haracteristic M aximu m supply voltage O N /OFF pin input voltage O utput voltage to ground(steady state) P ower dissipation S torage temperature range M aximu m junction temp erature E SD susceptibility (Human Body Model) Value 45 -0.3V ≤ V ≤ +V I N -1 Internally li mited -65~+150 2 150 °C kV °C Unit V V V R ECOMMENDED OPERATING CONDITIONS C haracteristic S upply Vo ltage O perating te mp erature range Symbol VCC Value 6～ 40 -40 ～ +1 25 Unit V °C 3/9 LM2576BM E LECTRICAL CHARACTERISTICS ( Specifications with standard type face are for Para meter D evice Pa ra meters F eedback bias current O scillator frequency VSAT saturation voltage Max. duty cycle(ON) C urrent li mit O utput current leakage S y mb o l T J = 2 5°C,) Min. *2 Typ. Max. Unit C ondition A djustable version only, V O U T =5V *8 I O U T =3A *4 *5 * 4,8 O utput=0V *6,7 O utput=-1VV *10 *6 O N/OF F P I N =5V Ib fO VSAT DC ICL IL IQ ISTBY 50 47 52 1.4 93 4.2 98 5.8 7.5 5 50 100 58 1.8 6.9 2.3 30 10 200 nA kHz V % A mA mA mA µA Q uiescent cu rrent S tandby quiescent current O N/OF F Control O N/OF F pin logic input level O N/OF F pin input current VIH VIL IIH IIL V O U T =0V V O U T = n o mi n a l o u tp u t voltage O N/OFF pin=5V(OFF) O N/OFF pin=0V(ON) *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 *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 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 *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 2.0 0.8 4 0.01 30 10 V V µA µA L M 2576BM 3.3V S ystem Pa ra mete rs Output voltagde Efficiency VOUT 3 .234 3.3 73 3.366 V % η VOUT L M 2576BM 5.0V S ystem Pa ra mete rs Output voltagde Efficiency 4 .8 5.0 77 5.2 V % η VOUT L M 2576BM 12V S ystem Pa ra mete rs Output voltagde Efficiency 1 1.52 12.0 88 12.48 V % η L M 2576BM ADJ S yste m Pa ra mete rs Output voltagde Efficiency VOUT 1 .193 1.230 77 1.267 V % η * 1 A bsolute Maxi mu m Ratings indicates limits beyond which dama ge to the device may o ccur. Operating Ratings indicate conditions for which the device is intended to be 4/9 LM2576BM f unctional, but specific performance is not guaranteed. For guaranteed specifications and the best conditions, see the Electrical Characteristics. * 2 A ll 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 E xternal components such as th e catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. * 4 O utput pin sourcing current. No diode, inductor or capacitor connected to output pin. * 5 F eedback pin removed fro m output and connected to 0V. * 6 F eedback 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 = 4 0V * 8 T h 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%. T EST CIRCUIT LM2576BM LM2576BM-ADJ 5/9 LM2576BM A PPLICATION CIRCUIT Ty pica l L M 2576BM L ow Noise L M 2576BM A PPLICATION INFORMATION C areful 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 L M 2576BM, to keep the sensitive feedback wiring short. I NPUT CA PACITOR C I N A l ow ESR aluminu m o r tantalum bypass capacitor is needed between the input pin and ground pin . I t 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. O UTPUT CAPA CIT OR C O U T A n 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. C ATCH DI ODE D 1 B uck 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 L M 2576BM 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. I NDUCTOR SELECTION L A ll 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 L M 2576BM (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 C HARACTERISTICS CURVE 8/9 LM2576BM O UTLINE DRAWING E SOP-8L U nit:mm LM2576BM 9/9