LTC3406B-2ES5#TRM,LTC3406B-2ES5#TRMPBF,LTC3406B-2ES5#TR,LTC3406B-2ES5#TRPBF, 规格书,Datasheet 资料
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1芯天下--/2芯天下--/3芯天下--/4sn3406b2 3406b2fs1µs/DIVV IN = 3.6V V OUT = 1.8V I LOAD = 50mA3406B G15Load Step40µs/DIV V IN = 3.6V V OUT = 1.8VI LOAD = 600mA (LOAD: 3Ω RESISTOR)3406B G1620µs/DIV V IN = 3.6V V OUT = 1.8VI LOAD = 0mA TO 600mA3406B G1720µs/DIV V IN = 3.6V V OUT = 1.8VI LOAD = 50mA TO 600mA3406B G18芯天下--/5sn3406b2 3406b2fsTYPICAL PERFOR A CE CHARACTERISTICSU W(From Figure 1a Except for the Resistive Divider Resistor Values)Load StepLoad StepU U UPI FU CTIO SRUN (Pin 1): Run Control Input. Forcing this pin above 1.5V enables the part. Forcing this pin below 0.3V shuts down the device. In shutdown, all functions are disabled drawing <1µA supply current. Do not leave RUN floating.GND (Pin 2): Ground Pin.SW (Pin 3): Switch Node Connection to Inductor. This pin connects to the drains of the internal main and synchro-nous power MOSFET switches.V IN (Pin 4): Main Supply Pin. Must be closely decoupled to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.V FB (Pin 5):Feedback Pin. Receives the feedback voltage from an external resistive divider across the output.V OUT 100mV/DIV AC COUPLED I L500mA/DIV I LOAD 500mA/DIV20µs/DIV V IN = 3.6V V OUT = 1.8VI LOAD = 100mA TO 600mA3406B G19V OUT 100mV/DIV AC COUPLED I L500mA/DIV I LOAD 500mA/DIV20µs/DIV V IN = 3.6V V OUT = 1.8VI LOAD = 200mA TO 600mA3406B G20芯天下--/6芯天下--/7芯天下--/8sn3406b2 3406b2fsAPPLICATIO S I FOR ATIOW UUU The basic LTC3406B-2 application circuit is shown in Figure 1. External component selection is driven by the load requirement and begins with the selection of L fol-lowed by C IN and C OUT .Inductor SelectionFor most applications, the value of the inductor will fall in the range of 1µH to 4.7µH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or V OUT also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is ∆I L = 240mA (40% of 600mA).∆=()()−⎛⎝⎜⎞⎠⎟I f LV V V L OUT OUT IN 11(1)The DC current rating of the inductor should be at leastequal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 720mA rated inductor should be enough for most applications (600mA + 120mA). For better efficiency, choose a low DC-resis-tance inductor.Inductor Core SelectionDifferent core materials and shapes will change the size/current and price/current relationship of an inductor.Toroid or shielded pot cores in ferrite or permalloy mate-rials are small and don’t radiate much energy, but gener-ally cost more than powdered iron core inductors with similar electrical characteristics. The choice of which style inductor to use often depends more on the price vs size requirements and any radiated field/E MI requirements than on what the LTC3406B-2 requires to operate. Table 1shows some typical surface mount inductors that work well in LTC3406B-2 applications.C IN and C OUT SelectionIn continuous mode, the source current of the top MOSFET is a square wave of duty cycle V OUT /V IN . To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by:C I V VV V IN OMAXOUTIN OUTINrequired I RMS ≅−()[]12/Table 1. Representative Surface Mount InductorsPart Value DCR MAX DC Size Number (µH)(ΩMAX)Current (A)WxLxH (mm 3)Sumida 1.50.0680.90 3.2 x 3.2 x 1.2CDRH2D11 2.20.0980.783.30.1230.60Sumida2.20.0410.853.2 x 3.2 x 2.0CDRH2D18/LD 3.30.0540.754.70.0780.63Sumida 2.20.1160.95 3.5 x 4.1 x 0.8CMD4D06 3.30.1740.774.70.2160.75Murata 1.00.060 1.00 2.5 x 3.2 x 2.0LQH32C 2.20.0970.794.70.1500.65Taiyo Yuden 1.00.0800.78 1.8 x 2.5 x 1.8LQLBC2518 1.50.1100.662.20.1300.60Toko 2.20.14 1.14 4.6 x 4.6 x 1.2D412F3.30.200.904.70.220.80This formula has a maximum at V IN = 2V OUT , where I RMS = I OUT /2. This simple worst-case condition is com-monly used for design because even significant deviations do not offer much relief. Note that the capacitor manufacturer’s ripple current ratings are often based on 2000 hours of life. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Always consult the manufac-turer if there is any question.The selection of C OUT is driven by the required effective series resistance (ESR).Typically, once the ESR requirement for C OUT has been met, the RMS current rating generally far exceeds the I RIPPLE(P-P) requirement. The output ripple ∆V OUT is deter-mined by:∆≅∆+⎛⎝⎜⎞⎠⎟V I ESR fC OUT L OUT 18where f = operating frequency, C OUT = output capacitanceand ∆I L = ripple current in the inductor. For a fixed output voltage, the output ripple is highest at maximum input voltage since ∆I L increases with input voltage.芯天下--/9芯天下--/10sn3406b2 3406b2fsAPPLICATIO S I FOR ATIOW UUU 1. The V IN quiescent current is due to two components:the DC bias current as given in the electrical character-istics and the internal main switch and synchronous switch gate charge currents. The gate charge current results from switching the gate capacitance of the internal power MOSFET switches. Each time the gate is switched from high to low to high again, a packet of charge, dQ, moves from V IN to ground. The resulting dQ/dt is the current out of V IN that is typically larger than the DC bias current. In continuous mode, I GATECHG =f(Q T + Q B ) where Q T and Q B are the gate charges of the internal top and bottom switches. Both the DC bias and gate charge losses are proportional to V IN and thus their effects will be more pronounced at higher supply voltages.2. I 2R losses are calculated from the resistances of the internal switches, R SW , and external inductor R L . In continuous mode, the average output current flowing through inductor L is “chopped” between the main switch and the synchronous switch. Thus, the series resistance looking into the SW pin is a function of both top and bottom MOSFET R DS(ON) and the duty cycle (DC) as follows:R SW = (R DS(ON)TOP )(DC) + (R DS(ON)BOT )(1 – DC)The R DS(ON) for both the top and bottom MOSFETs can be obtained from the Typical Performance Charateristics curves. Thus, to obtain I 2R losses, simply add R SW to R L and multiply the result by the square of the average output current.Other losses including C IN and C OUT E SR dissipative losses and inductor core losses generally account for less than 2% total additional loss.Thermal ConsiderationsIn most applications the LTC3406B-2 does not dissipate much heat due to its high efficiency. But, in applications where the LTC3406B-2 is running at high ambient tem-perature with low supply voltage and high duty cycles,such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 150°C, both power switches will be turned off and the SW node will become high impedance.To avoid the LTC3406B-2 from exceeding the maximum junction temperature, the user will need to do some thermal analysis. The goal of the thermal analysis is to determine whether the power dissipated exceeds the maximum junction temperature of the part. The tempera-ture rise is given by:T R = (P D )(θJA )where P D is the power dissipated by the regulator and θJA is the thermal resistance from the junction of the die to the ambient temperature.The junction temperature, T J , is given by:T J = T A + T Rwhere T A is the ambient temperature.As an example, consider the LTC3406B-2 in dropout at an input voltage of 2.7V, a load current of 600mA and an ambient temperature of 70°C. From the typical perfor-mance graph of switch resistance, the R DS(ON) of the P-channel switch at 70°C is approximately 0.52Ω. There-fore, power dissipated by the part is:P D = I LOAD 2 • R DS(ON) = 187.2mWFor the SOT-23 package, the θJA is 250°C/W. Thus, the junction temperature of the regulator is:T J = 70°C + (0.1872)(250) = 116.8°Cwhich is below the maximum junction temperature of 125°C.Note that at higher supply voltages, the junction tempera-ture is lower due to reduced switch resistance (R DS(ON)).Checking Transient ResponseThe regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, V OUT immediately shifts by an amount equal to (∆I LOAD • ESR), where ESR is the effective series resistance of C OUT . ∆I LOAD also begins to charge or discharge C OUT , which generates a feedback error signal.The regulator loop then acts to return V OUT to its steady-state value. During this recovery time V OUT can be moni-tored for overshoot or ringing that would indicate a stability problem. For a detailed explanation of switching control loop theory, see Application Note 76.芯天下--/11芯天下--/12芯天下--/13Load Step20µs/DIV V IN = 3.6V V OUT = 1.2VI LOAD = 0mA TO 600mA3406B TA1120µs/DIV V IN = 3.6V V OUT = 1.2VI LOAD = 100mA TO 600mA3406B TA12芯天下--/14Load Step20µs/DIV V IN = 3.6V V OUT = 3.3VI LOAD = 0mA TO 600mA3406B TA1520µs/DIV V IN = 3.6V V OUT = 3.3VI LOAD = 100mA TO 600mA3406B TA16芯天下--/Information furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.芯天下--/1516sn3406b2 3406b2fsRELATED PARTSPART NUMBER DESCRIPTIONCOMMENTSLT1616500mA (I OUT ), 1.4MHz, High Efficiency Step-Down 90% Efficiency, V IN : 3.6V to 25V, V OUT(MIN) = 1.25V, I Q = 1.9mA,DC/DC ConverterI SD < 1µA, ThinSOT PackageLT1676450mA (I OUT ), 100kHz, High Efficiency Step-Down 90% Efficiency, V IN : 7.4V to 60V, V OUT(MIN) = 1.24V, I Q = 3.2mA,DC/DC ConverterI SD = 2.5µA, S8 PackageLTC1877600mA (I OUT ), 550kHz, Synchronous Step-Down 95% Efficiency, V IN : 2.7V to 10V, V OUT(MIN) = 0.8V, I Q = 10µA,DC/DC ConverterI SD < 1µA, MS8 PackageLTC1878600mA (I OUT ), 550kHz, Synchronous Step-Down 95% Efficiency, V IN : 2.7V to 6V, V OUT(MIN) = 0.8V, I Q = 10µA,DC/DC ConverterI SD < 1µA, MS8 PackageLTC1879 1.2A (I OUT ), 550kHz, Synchronous Step-Down 95% Efficiency, V IN : 2.7V to 10V, V OUT(MIN) = 0.8V, I Q = 15µA,DC/DC ConverterI SD < 1µA, TSSOP-16 PackageLTC3403600mA (I OUT ), 1.5MHz, Synchronous Step-Down 96% Efficiency, V IN : 2.5V to 5.5V, V OUT(MIN) = Dynamically DC/DC Converter with Bypass Transistor Adjustable, I Q = 20µA, I SD < 1µA, DFN PackageLTC3404600mA (I OUT ), 1.4MHz, Synchronous Step-Down 95% Efficiency, V IN : 2.7V to 6V, V OUT(MIN) = 0.8V, I Q = 10µA,DC/DC ConverterI SD < 1µA, MS8 PackageLTC3405/LTC3405A 300mA (I OUT ), 1.5MHz, Synchronous Step-Down 96% Efficiency, V IN : 2.5V to 5.5V, V OUT(MIN) = 0.8V, I Q = 20µA,DC/DC ConverterI SD < 1µA, ThinSOT PackageLTC3406/LTC3406B 600mA (I OUT ), 1.5MHz, Synchronous Step-Down 96% Efficiency, V IN : 2.5V to 5.5V, V OUT(MIN) = 0.6V, I Q = 20µA,DC/DC ConverterI SD < 1µA, ThinSOT PackageLTC3407Dual Output (600mA × 2) 1.5MHz Synchronous 95% Efficiency V IN : 2.5V to 5.5V, V OUT(MIN) = 0.6V, I Q = 40µA,Step-Down DC/DC ConverterMS10E PackageLTC3408600mA (I OUT ), 1.5MHz Synchronous Step-Down 96% Efficiency, V IN : 2.5V to 5.5V, V OUT(MIN) = Dynamically DC/DC Converter with 0.08Ω Bypass Transistor Adjustable, I Q = 1.5mA, I SD < 1µA, DFN PackageLTC3411 1.25A (I OUT ), 4MHz, Synchronous Step-Down 95% Efficiency, V IN : 2.5V to 5.5V, V OUT(MIN) = 0.8V, I Q = 60µA,DC/DC ConverterI SD < 1µA, MS PackageLTC3412 2.5A (I OUT ), 4MHz, Synchronous Step-Down 95% Efficiency, V IN : 2.5V to 5.5V, V OUT(MIN) = 0.8V, I Q = 60µA,DC/DC ConverterI SD < 1µA, TSSOP-16E PackageLTC34144A (I OUT ), 4MHz, Synchronous Step-Down 95% Efficiency, V IN : 2.25V to 5.5V, V OUT(MIN) = 0.8V, I Q = 64µA,DC/DC ConverterTSSOP-20E PackageLTC3440600mA (I OUT ), 2MHz, Synchronous Buck-Boost 95% Efficiency, V IN : 2.5V to 5.5V, V OUT : 2.5V to 5.5V, I Q = 25µA,DC/DC ConverterI SD < 1µA, MS PackageLTC34411A (I OUT ), 1MHz, Synchronous Buck-Boost 95% Efficiency, V IN : 2.5V to 5.5V, V OUT : 2.4V to 5.25V, I Q = 25µA,DC/DC ConverterDFN PackageLinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 ●FAX: (408) 434-0507 ● © LINEAR TECHNOLOGY CORPORA TION 2003LT/TP 0204 1K • PRINTED IN USA芯天下--/。
