View LTC3405A-18-15_8599897.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

1 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa high efficiency: up to 93% very low quiescent current: only 20 a during operation 300ma output current at v in = 3v 2.5v to 5.5v input voltage range 1.5mhz constant frequency operation no schottky diode required low dropout operation: 100% duty cycle stable with ceramic capacitors shutdown mode draws < 1 a supply current 3% output voltage accuracy current mode operation for excellent line and load transient response overtemperature protected low profile (1mm) thinsot tm package the ltc 3405a-1.5/ltc3405a-1.8 are high efficiency monolithic synchronous buck regulators using a constant frequency, current mode architecture. supply current during operation is only 20 a and drops to <1 a in shutdown. the 2.5v to 5.5v input voltage range makes the ltc3405a-1.5/ltc3405a-1.8 ideally suited for single li-ion battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. switching frequency is internally set at 1.5mhz, allowing the use of small surface mount inductors and capacitors. the ltc3405a-1.5/ltc3405a-1.8 are specifically designed to work well with ceramic output capacitors, achieving very low output voltage ripple and a small pcb footprint. the internal synchronous switch increases efficiency and eliminates the need for an external schottky diode. the ltc3405a-1.5/ltc3405a-1.8 are available in a low profile (1mm) thinsot package. for adjustable output voltage, refer to the ltc3405a data sheet. cellular telephones personal information appliances wireless and dsl modems digital still cameras mp3 players portable instruments figure 1a. high efficiency step-down converter 1.5v, 1.8v, 1.5mhz, 300ma synchronous step-down regulators in thinsot figure 1b. efficiency vs load current , ltc and lt are registered trademarks of linear technology corporation. thinsot is a trademark of linear technology corporation. protected by u.s. patents, including 6580258, 5481178. v in c in ** 4.7 f cer v in 2.7v to 5.5v * ** ltc3405a-1.8 run mode 3 4.7 h* 3405a1518 f01 murata lqh3c4r7m34 taiyo yuden jmk212bj475mg 5 4 6 1 2 sw v out gnd c out ** 4.7 f cer v out 1.8v 300ma descriptio u features applicatio s u typical applicatio u output current (ma) 0.1 efficiency (%) 10 1000 100 90 80 70 60 50 40 3405a1518 f01b 1 100 v in = 2.7v v in = 5.5v v in = 4.2v v in = 3.6v
2 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa symbol parameter conditions min typ max units i pk peak inductor current v in = 3v, v out = 90%, duty cycle < 35% 375 500 625 ma v out regulated output voltage ltc3405a-1.5, mode = 3.6v 1.455 1.500 1.545 v ltc3405a-1.8, mode = 3.6v 1.746 1.800 1.854 v ? v ovl ? output overvoltage lockout ? v ovl = v ovl ?v out 2.5 7.8 13 % ? v out output voltage line regulation v in = 2.5v to 5.5v 0.04 0.4 %/v v loadreg output voltage load regulation 0.5 % v in input voltage range 2.5 5.5 v i s input dc bias current (note 4) pulse skipping mode v out = 90%, mode = 3.6v, i load = 0a 300 400 a burst mode operation v out = 103%, mode = 0v, i load = 0a 20 35 a shutdown v run = 0v, v in = 4.2v 0.1 1 a f osc oscillator frequency v out = 100% 1.2 1.5 1.8 mhz v out = 0v 170 khz r pfet r ds(on) of p-channel fet i sw = 100ma 0.7 0.85 ? r nfet r ds(on) of n-channel fet i sw = 100ma 0.6 0.90 ? i lsw sw leakage v run = 0v, v sw = 0v or 5v, v in = 5v 0.01 1 a v run run threshold 0.3 1 1.5 v i run run leakage current 0.01 1 a v mode mode threshold 0.3 1.5 2 v i mode mode leakage current 0.01 1 a ltc3405aes6-1.5 ltc3405aes6-1.8 t jmax = 125 c, ja = 250 c/ w order part number (note 1) input supply voltage .................................. 0.3v to 6v mode, run, v out voltages....................... 0.3v to v in sw voltage .................................. 0.3v to (v in + 0.3v) p-channel switch source current (dc) ............. 400ma n-channel switch sink current (dc) ................. 400ma peak sw sink and source current .................... 630ma operating temperature range (note 2) .. 40 c to 85 c junction temperature (note 3) ............................ 125 c storage temperature range ................ 65 c to 150 c lead temperature (soldering, 10 sec)................. 300 c s6 part marking consult ltc marketing for parts specified with wider operating temperature ranges. the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c. v in = 3.6v unless otherwise specified. ltzq ltzp absolute axi u rati gs w ww u package/order i for atio uu w electrical characteristics run 1 gnd 2 sw 3 6 mode 5 v out 4 v in top view s6 package 6-lead plastic tsot-23 burst mode is a registered trademark of linear technology corporation. note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the ltc3405ae is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the ?0 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical process controls. note 3: t j is calculated from the ambient temperature t a and power dissipation p d according to the following formula: ltc3405a: t j = t a + (p d )(250 c/w) note 4: dynamic supply current is higher due to the gate charge being delivered at the switching frequency.
3 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa input voltage (v) 2.5 3.0 4.0 5.0 efficiency (%) 4.5 95 90 85 80 75 70 65 60 55 50 3405a1518 g02 3.5 5.5 burst mode operation v out = 1.8v i out = 0.1ma i out = 250ma i out = 100ma i out = 10ma i out = 1ma output current (ma) 0.1 efficiency (%) 10 1000 100 90 80 70 60 50 40 30 20 10 0 3405a1518 g03 1 100 v in = 3.6v v in = 4.2v v in = 3.6v v in = 4.2v v out = 1.8v pulse skipping mode burst mode operation output current (ma) 0.1 efficiency (%) 10 1000 100 90 80 70 60 50 40 3405a1518 g04 1 100 v in = 2.7v v in = 5.5v v in = 4.2v v in = 3.6v v out = 1.8v typical perfor a ce characteristics uw output current (ma) 60 efficiency (%) 80 100 50 70 90 0.1 10 100 1000 3405a1518 g05 40 1 v in = 2.7v v in = 4.2v v out = 1.5v v in = 3.6v efficiency vs input voltage efficiency vs output current efficiency vs output current efficiency vs output current oscillator frequency vs temperature oscillator frequency vs supply voltage output voltage vs load current r ds(on ) vs input voltage temperature ( c) ?0 frequency (mhz) 1.70 1.65 1.60 1.55 1.50 1.45 1.40 1.35 1.30 25 75 ?5 0 50 100 125 v in = 3.6v 3405a1518 g07 supply voltage (v) 2 oscillator frequency (mhz) 1.8 1.7 1.6 1.5 1.4 1.3 1.2 34 56 3405a1518 g08 load current (ma) 0 output voltage (v) 1.834 1.824 1.814 1.804 1.794 1.784 1.774 100 200 300 400 3405a1518 g09 500 600 burst mode operation pulse skipping mode input voltage (v) 0 r ds(0n) ( ? ) 2 4 5 3405a1518 g10 13 6 7 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 main switch synchronous switch (from figure1a) r ds(on) vs temperature temperature ( c) ?0 r ds(on) ( ? ) 1.2 1.0 0.8 0.6 0.4 0.2 0 25 75 ?5 0 50 100 125 3405f g11 synchronous switch main switch v in = 2.7v v in = 3.6v v in = 4.2v
4 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa dynamic supply current vs supply voltage dynamic supply current vs temperature switch leakage vs temperature switch leakage vs input voltage supply voltage (v) 2 0 supply current ( a) 200 600 800 1000 4 1800 3405a1518 g12 400 3 2.5 4.5 5 3.5 5.5 1200 1400 1600 pulse skipping mode burst mode operation v out = 1.8v i load = 0a temperature ( c) ?0 switch leakage (na) 160 140 120 100 80 60 40 20 0 25 75 ?5 0 50 100 125 v in = 5.5v run = 0v 3405f g14 main switch synchronous switch input voltage (v) 0 switch leakage (pa) 60 50 40 30 20 10 0 1 234 3405f g15 56 run = 0v main switch synchronous switch sw 5v/div v out 100mv/div ac coupled i l 100ma/div 3405a1518 g16 5 s/div v in = 3.6v v out = 1.8v i load = 20ma sw 5v/div v out 10mv/div ac coupled i l 100ma/div 3405a1518 g17 500ns/div v in = 3.6v v out = 1.8v i load = 20ma run 2v/div v out 1v/div i l 200ma/div 3405a1518 g18 100 s/div v in = 3.6v v out = 1.8v i load = 250ma 3405a1518 g19 v out 100mv/div ac coupled i load 200ma/div i l 200ma/div 40 s/div v in = 3.6v v out = 1.8v i load = 0ma to 250ma pulse skipping mode typical perfor a ce characteristics uw (from figure 1a) burst mode operation pulse skipping mode operation start-up from shutdown load step temperature ( c) ?0 300 340 25 75 3405a1518 g13 260 ?5 0 50 100 125 220 180 140 100 60 20 0 supply current ( a) v in = 3.6v v out = 1.8v i load = 0a pulse skipping mode burst mode operation
5 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa uu u pi fu ctio s run (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 <1 a 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 2.2 f or greater ceramic capacitor. v out (pin 5): output voltage feedback pin. an internal resistive divider divides the output voltage down for com- parison to the internal 1.2v reference voltage. mode (pin 6): mode select input. to select pulse skip- ping mode, tie to v in . grounding this pin selects burst mode operation. do not leave this pin floating. 3405a1518 g20 v out 100mv/div ac coupled i load 200ma/div i l 200ma/div 40 s/div v in = 3.6v v out = 1.8v i load = 20ma to 250ma pulse skipping mode v out 100mv/div ac coupled i load 200ma/div i l 200ma/div 3405a1518 g21 40 s/div v in = 3.6v v out = 1.8v i load = 20ma to 250ma burst mode operation 3405a1518 g22 40 s/div v in = 3.6v v out = 1.8v i load = 0ma to 250ma burst mode operation v out 100mv/div ac coupled i load 200ma/div i l 200ma/div typical perfor a ce characteristics uw load step load step load step (from figure 1a)
6 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa fu ctio al diagra u u w operatio u (refer to functional diagram) main control loop the ltc3405a fixed output voltage series parts use a constant frequency, current mode step-down architec- ture. their main (p-channel mosfet) and synchronous (n-channel mosfet) switches are internal. during normal operation, the internal top power mosfet is turned on each cycle when the oscillator sets the rs latch, and turned off when the current comparator, i comp , resets the rs latch. the peak inductor current at which i comp resets the rs latch, is controlled by the output of error amplifier ea. when the load current increases, the output voltage de- creases which causes a slight decrease in v fb relative to the 1.2v reference, which in turn, causes the ea amplifier? output voltage to increase until the average inductor current matches the new load current. while the top mosfet is off, the bottom mosfet is turned on until either the inductor current starts to reverse, as indicated by the current reversal comparator i rcmp , or the beginning of the next clock cycle. comparator ovdet guards against transient overshoots > 7.8% by turning the main switch off and keeping it off until the fault is removed. burst mode operation the ltc3405a series parts are capable of burst mode operation in which the internal power mosfets operate intermittently based on load demand. to enable burst mode operation, simply connect the mode pin to gnd. to disable burst mode operation and enable pwm pulse skipping mode, connect the mode pin to v in or drive it with a logic high (v mode > 1.5v). in this mode, the efficiency is lower at light loads, but becomes comparable to burst mode operation when the output load exceeds 25ma. the advantage of pulse skipping mode is lower output ripple and less interference to audio circuitry. + + + + ovdet ea + i rcmp + i comp 5 1 run osc slope comp osc freq shift 1.2v r1 ltc3405a-1.5 r1 = 110k r2 = 440k ltc3405a-1.8 r1 = 180k r2 = 360k r2 1.294v 1.2v ref shutdown ov 0.4v 0.65v sleep v in v out 6 mode en burst v in s r rs latch switching logic and blanking circuit anti- shoot- thru q q 5 ? 4 sw 3 gnd 3405a1518 bd 2 v fb
7 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa operatio u (refer to functional diagram) when the converter is in burst mode operation, the peak current of the inductor is set to approximately 100ma re- gardless of the output load. each burst event can last from a few cycles at light loads to almost continuously cycling with short sleep intervals at moderate loads. in between these burst events, the power mosfets and any unneeded circuitry are turned off, reducing the quiescent current to 20 a. in this sleep state, the load current is being supplied solely from the output capacitor. as the output voltage droops, the ea amplifier? output rises above the sleep threshold signaling the burst comparator to trip and turn the top mosfet on. this process repeats at a rate that is dependent on the load demand. short-circuit protection when the output is shorted to ground, the frequency of the oscillator is reduced to about 210khz, 1/7 the nominal frequency. this frequency foldback ensures that the in- ductor current has more time to decay, thereby preventing runaway. the oscillator? frequency will progressively increase to 1.5mhz when v out rises above 0v. low supply operation the ltc3405a series parts will operate with input supply voltages as low as 2.5v, but the maximum allowable output current is reduced at this low voltage. figure 2 shows the reduction in the maximum output current as a function of input voltage for both fixed output voltages. figure 2. maximum output current vs input voltage supply voltage (v) 2.5 maximum output current (ma) 600 500 400 300 200 100 0 3.0 3.5 4.0 4.5 3405a1518 f02 5.0 5.5 v out = 1.8v v out = 1.5v slope compensation and inductor peak current slope compensation provides stability in constant fre- quency architectures by preventing subharmonic oscilla- tions at high duty cycles. it is accomplished internally by adding a compensating ramp to the inductor current signal at duty cycles in excess of 40%. normally, this results in a reduction of maximum inductor peak current for duty cycles > 40%. however, the ltc3405a series parts use a patent-pending scheme that counteracts this compensating ramp, which allows the maximum inductor peak current to remain unaffected throughout all duty cycles.
8 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa applicatio s i for atio wu uu table 1. representative surface mount inductors max dc manufacturer part number value current dcr height taiyo yuden lb2016t2r2m 2.2 h 315ma 0.13 ? 1.6mm lb2012t2r2m 2.2 h 240ma 0.23 ? 1.25mm lb2016t3r3m 3.3 h 280ma 0.2 ? 1.6mm panasonic elt5kt4r7m 4.7 h 950ma 0.2 ? 1.2mm murata lqh32cn2r2m33 4.7 h 450ma 0.2 ? 2mm taiyo yuden lb2016t4r7m 4.7 h 210ma 0.25 ? 1.6mm panasonic elt5kt6r8m 6.8 h 760ma 0.3 ? 1.2mm panasonic elt5kt100m 10 h 680ma 0.36 ? 1.2mm sumida cmd4d116r8mc 6.8 h 620ma 0.23 ? 1.2mm the basic ltc3405a series parts application circuit is shown in figure 1. external component selection is driven by the load requirement and begins with the selection of l followed by c in and c out . inductor selection for most applications, the inductor value will fall in the range of 2.2 h to 10 h. its value is determined by 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 = 120ma (40% of 300ma). ? = ()( ) ? ? ? ? ? ? ? i fl v v v l out out in 1 1 (1) the dc current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. thus, a 360ma rated inductor should be enough for most applications (300ma + 60ma). for better efficiency, choose a low dc-resistance inductor. the inductor value also has an effect on burst mode operation. the transition to low current operation begins when the inductor current peaks fall to approximately 100ma. lower inductor values (higher ? i l ) will cause this to occur at lower load currents, which can cause a dip in efficiency in the upper range of low current operation. in burst mode operation, lower inductance values will cause the burst frequency to increase. inductor core selection different core materials and shapes will change the size/ current and price/current relationship of an inductor. tor- oid or shielded pot cores in ferrite or permalloy materials are small and don? radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. the choice of which style induc- tor to use often depends more on the price vs size require- ments and any radiated field/emi requirements than on what the ltc3405a series parts require to operate. table 1 shows some typical surface mount inductors that work well in ltc3405a series parts applications. c in and c out selection in 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: ci vvv v in omax out in out in required i rms ? ? () [] 12 / this 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? 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 require- ment 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 determined by: ??? + ? ? ? ? ? ? v i esr fc out l out 1 8 where f = operating frequency, c out = output capacitance and ? 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.
9 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa applicatio s i for atio wu uu where l1, l2, etc. are the individual losses as a percentage of input power. although all dissipative elements in the circuit produce losses, two main sources usually account for most of the losses in ltc3405a series parts circuits: v in quiescent current and i 2 r losses. the v in quiescent current loss dominates the efficiency loss at very low load currents whereas the i 2 r loss dominates the efficiency loss at medium to high load currents. in a typical efficiency plot, the efficiency curve at very low load currents can be misleading since the actual power lost is of no conse- quence as illustrated in figure 3. aluminum electrolytic and dry tantalum capacitors are both available in surface mount configurations. in the case of tantalum, it is critical that the capacitors are surge tested for use in switching power supplies. an excellent choice is the avx tps series of surface mount tantalum. these are specially constructed and tested for low esr so they give the lowest esr for a given volume. other capacitor types include sanyo poscap, kemet t510 and t495 series, and sprague 593d and 595d series. consult the manufacturer for other specific recommendations. using ceramic input and output capacitors higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. their high ripple current, high voltage rating and low esr make them ideal for switching regulator applications. because the ltc3405a series?control loop does not depend on the output capacitor? esr for stable operation, ceramic capacitors can be used freely to achieve very low output ripple and small circuit size. care must be taken when ceramic capacitors are used at the input and the output. when a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, v in . at best, this ringing can couple to the output and be mistaken as loop instability. at worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at v in , large enough to damage the part. when choosing the input and output ceramic capacitors, choose the x5r or x7r dielectric formulations. these dielectrics have the best temperature and voltage charac- teristics of all the ceramics for a given value and size. efficiency considerations the efficiency of a switching regulator is equal to the output power divided by the input power times 100%. it is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. efficiency can be expressed as: efficiency = 100% ?(l1 + l2 + l3 + ...) figure 3. power lost vs load current load current (ma) 0.1 power lost (w) 10 1000 1 0.1 0.01 0.001 0.0001 3405a1518 f03 1 100 v out = 1.8v v in = 3.6v v out = 1.5v 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.
10 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa applicatio s i for atio wu uu 2. i 2 r 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 ?hopped?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 2 r 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 esr dissipative losses and inductor core losses generally account for less than 2% total additional loss. thermal considerations in most applications, the ltc3405a series parts do not dissipate much heat due to their high efficiency. but, in applications where they run at high ambient temperature with low supply voltage, 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 keep the ltc3405a series parts 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 )( ja ) where p d is the power dissipated by the regulator and ja 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 r where t a is the ambient temperature. as an example, consider the ltc3405a-1.8 with an input voltage of 2.7v, a load current of 300ma and an ambient temperature of 70 c. from the typical performance graph of switch resistance, the r ds(on) of the p-channel switch at 70 c is approximately 0.94 ? and the r ds(on) of the n-channel synchronous switch is approximately 0.75 ? . the series resistance looking into the sw pin is: r sw = 0.95 ? (0.67) + 0.75 ? (0.33) = 0.88 ? therefore, power dissipated by the part is: p d = i load 2 ?r sw = 79.2mw for the sot-23 package, the ja is 250 c/ w. thus, the junction temperature of the regulator is: t j = 70 c + (0.0792)(250) = 89.8 c which is well 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 response the 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.
11 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa applicatio s i for atio wu uu figure 4. ltc3405a-1.8 layout diagram figure 5. ltc3405a-1.8 suggested layout run ltc3405a-1.8 gnd sw 6 l1 bold lines indicate high current paths v in v out 3405a1518 f04 4 5 1 3 + 2 mode v out v in c in c out ltc3405a-1.8 gnd 3405a1518 f05 pin 1 v out v in sw via to v in c out c in l1 pc board layout checklist when laying out the printed circuit board, the following checklist should be used to ensure proper operation of the ltc3405a series parts. these items are also illustrated graphically in figures 4 and 5. check the following in your layout: 1. the power traces, consisting of the gnd trace, the sw trace and the v in trace should be kept short, direct and wide. 2. does the (+) plate of c in connect to v in as closely as possible? this capacitor provides the ac current to the internal power mosfets. 3. keep the (? plates of c in and c out as close as possible. design example as a design example, assume the ltc3405a-1.8 is used in a single lithium-ion battery-powered cellular phone application. the v in will be operating from a maximum of 4.2v down to about 2.7v. the load current requirement is a maximum of 0.25a but most of the time it will be in standby mode, requiring only 2ma. efficiency at both low and high load currents is important. output voltage is 1.8v. with this information we can calculate l using equation (1), l fi v v v l out out in = () ? () ? ? ? ? ? ? ? 1 1 (3) substituting v out = 1.8v, v in = 4.2v, ? i l = 100ma and f = 1.5mhz in equation (3) gives: l v mhz ma v v h = ? ? ? ? ? ? ? ? 18 1 5 100 1 18 42 68 . .( ) . . . for best efficiency choose a 300ma or greater inductor with less than 0.3 ? series resistance. c in will require an rms current rating of at least 0.125a ? i load(max) /2 at temperature and c out will require an esr of less than 0.5 ? . in most cases, a tantalum capacitor will satisfy this requirement. figure 6 shows the complete circuit along with its effi- ciency curve.
12 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa v out 100mv/div ac coupled i l 200ma/div i l 200ma/div 3405a1518 f06c 20 s/div v in = 3.6v v out = 1.8v i load = 100ma to 300ma applicatio s i for atio wu uu output current (ma) 50 efficiency (%) 70 90 100 0.1 10 100 1000 3405a1518 f06b 30 1 60 60 40 v in = 2.7v v in = 4.2v v in = 3.6v v in c in ** 4.7 f cer v in 2.7v to 4.2v ltc3405a-1.8 run mode 3 6.8 h* 3405a1518 f06a 5 4 6 1 2 sw v out gnd c out ** 4.7 f cer v out 1.8v *sumida cmd4d11-6r8mc ** taiyo yuden jmk212bj475mg figure 6a. figure 6b. figure 6c.
13 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa typical applicatio s u single li-ion to 1.5v/300ma regulator for high efficiency and small footprint v in c in ** 4.7 f cer v in 2.7v to 4.2v ltc3405a-1.5 run mode 3 4.7 h* 3405a1518 ta02a 5 4 6 1 2 sw v out gnd c out1 ** 4.7 f cer v out 1.5v * ** murata lqh32cn4r7m33 taiyo yuden ceramic jmk212bj475mg output current (ma) 50 efficiency (%) 70 90 100 0.1 10 100 1000 3405a1518 ta02b 30 1 60 60 40 v in = 2.7v v in = 4.2v v in = 3.6v v out 100mv/div ac coupled i l 200ma/div i l 200ma/div 3405a1518 ta02c 20 s/div v in = 3.6v v out = 1.5v i load = 100ma to 300ma
14 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa typical applicatio s u v in c in ** 2.2 f cer v in 2.7v to 4.2v ltc3405a-1.5 run mode 3 2.2 h* 3405a1518 ta03a 5 4 6 1 2 sw v out gnd c out1 ** 2.2 f cer v out 1.5v * ** taiyo yuden lb2012t2r2m taiyo yuden ceramic lmk212bj225mg output current (ma) 0.1 efficiency (%) 10 1000 90 80 70 60 50 40 30 3405a1518 ta03b 1 100 v in = 2.7v v in = 4.2v v out = 1.5v v in = 3.6v v out 100mv/div ac coupled i l 100ma/div i l 200ma/div 3405a1518 ta03c 20 s/div v in = 3.6v v out = 1.5v i load = 50ma to 150ma single li-ion to 1.5v/150ma regulator using all ceramic capacitors optimized for smallest footprint
15 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa u package descriptio 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. s6 package 6-lead plastic tsot-23 (reference ltc dwg # 05-08-1636) 1.50 ?1.75 (note 4) 2.80 bsc 0.30 ?0.45 6 plcs (note 3) datum ? 0.09 ?0.20 (note 3) s6 tsot-23 0302 2.90 bsc (note 4) 0.95 bsc 1.90 bsc 0.80 ?0.90 1.00 max 0.01 ?0.10 0.20 bsc 0.30 ?0.50 ref pin one id note: 1. dimensions are in millimeters 2. drawing not to scale 3. dimensions are inclusive of plating 4. dimensions are exclusive of mold flash and metal burr 5. mold flash shall not exceed 0.254mm 6. jedec package reference is mo-193 3.85 max 0.62 max 0.95 ref recommended solder pad layout per ipc calculator 1.4 min 2.62 ref 1.22 ref
16 ltc3405a-1.5/ltc3405a-1.8 3405a1518fa related parts part number description comments lt1616 500ma (i out ), 1.4mhz, high efficiency step-down 90% efficiency, v in = 3.6v to 25v, v out = 1.25v, i q = 1.9ma dc/dc converter i sd = <1 a, thinsot package lt1676 450ma (i out ), 100khz, high efficiency step-down 90% efficiency, v in = 7.4v to 60v, v out = 1.24v, i q = 3.2ma dc/dc converter i sd = 2.5 a, s8 package lt1765 25v, 2.75a (i out ), 1.25mhz, high efficiency step-down 90% efficiency, v in = 3.0v to 25v, v out = 1.20v, i q = 1ma dc/dc converter i sd = 15 a, s8, tssop16e packages lt1776 500ma (i out ), 200khz, high efficiency step-down 90% efficiency, v in = 7.4v to 40v, v out = 1.24v, i q = 3.2ma dc/dc converter i sd = 30 a, n8,s8 packages ltc1878 600ma (i out ), 550khz, synchronous step-down 95% efficiency, v in = 2.7v to 6v, v out = 0.8v, i q = 10 a dc/dc converter i sd = <1 a, ms8 package ltc1879 1.20a (i out ), 550khz, synchronous step-down 95% efficiency, v in = 2.7v to 10v, v out = 0.8v, i q = 15 a dc/dc converter i sd = <1 a, tssop16 package ltc3404 600ma (i out ), 1.4mhz, synchronous step-down 95% efficiency, v in = 2.7v to 6v, v out = 0.8v, i q = 10 a dc/dc converter i sd = <1 a, ms8 package ltc3405/ltc3405a 300ma (i out ), 1.5mhz, synchronous step-down 95% efficiency, v in = 2.7v to 6v, v out = 0.8v, i q = 20 a dc/dc converter i sd = <1 a, thinsot package ltc3406/ltc3406b 600ma (i out ) 1.5mhz, synchronous step-down 95% efficiency, v in = 2.5v to 5.5v, v out = 0.6v, i q = 20 a dc/dc converter i sd = <1 a, thinsot package ltc3411 1.25a (i out ), 4mhz, synchronous step-down 95% efficiency, v in = 2.5v to 5.5v, v out = 0.8v, i q = 60 a dc/dc converter i sd = <1 a, ms10 package ltc3412 2.5a (i out ), 4mhz, synchronous step-down 95% efficiency, v in = 2.5v to 5.5v, v out = 0.8v, i q = 60 a dc/dc converter i sd = <1 a, tssop16e package ltc3413 3a (i out ), sink/source, 2mhz, monolithic synchronous 90% efficiency, v in = 2.25v to 5.5v, v out = v ref/2 , i q = 280 a regulator for ddr/qdr memory termination i sd = <1 a, tssop16e package lt3430 60v, 2.75a (i out ), 200khz, high efficiency step-down 90% efficiency, v in = 5.5v to 60v, v out = 1.20v, i q = 2.5ma dc/dc converter i sd = 25 a, tssop16e package ltc3440 600ma (i out ), 2mhz, synchronous buck-boost 95% efficiency, v in = 2.5v to 5.5v, v out = 2.5v, i q = 25 a dc/dc converter i sd = <1 a, ms package linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com lt/tp 0604 1k rev a ? printed in usa ? linear technology corporation 2002

▲Up To Search▲

Price & Availability of LTC3405A-18-15

	To Download LTC3405A-18-15 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .