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1 ltc3410b 3410bfa high efficiency: up to 96% 300ma output current at v in = 3v 380ma minimum peak switch current 2.5v to 5.5v input voltage range 2.25mhz constant frequency operation no schottky diode required low dropout operation: 100% duty cycle stable with ceramic capacitors 0.8v reference allows low output voltages shutdown mode draws < 1 a supply current 2% output voltage accuracy current mode operation for excellent line andload transient response overtemperature protected available in low profile sc70 package the ltc 3410b is a high efficiency monolithic synchro- nous buck regulator using a constant frequency, currentmode architecture. the device is available in adjustable and fixed output voltage versions. supply current during operation is only 200 a, dropping to <1 a in shutdown. the 2.5v to 5.5v input voltage range makes the ltc3410bideally suited for single li-ion battery-powered applica- tions. 100% duty cycle provides low dropout operation, extending battery life in portable systems. pwm pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. switching frequency is internally set at 2.25mhz, allowing the use of small surface mount inductors and capacitors. the ltc3410b is 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. low output voltages are easily supported with the 0.8v feed- back reference voltage. the ltc3410b is available in a tiny, low profile sc70 package. cellular telephones personal information appliances wireless and dsl modems digital still cameras mp3 players portable instruments 2.25mhz, 300ma synchronous step-down regulator in sc70 applicatio s u features typical applicatio u descriptio u efficiency and power loss vs output current v in c in 2.2 f cer v in 2.7v to 5.5v ltc3410b run 4.7 h 10pf 232k 464k 3410 ta01 sw v fb gnd c out 2.2 f cer v out 1.2v power loss (w) 10.1 0.01 0.001 0.0001 output current (ma) 1 40 efficiency (%) 50 60 70 80 10 100 1000 3410 ta01b 30 2020 0 90 100 efficiency power loss v in = 2.7v v in = 3.6v v in = 4.2v , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents, including 5481178, 5994885, 6580258, 6304066, 6127815, 6498466, 6611131. downloaded from: http:///
2 ltc3410b 3410bfa input supply voltage .................................. 0.3v to 6v run, v fb voltages ..................................... 0.3v to v in sw voltage (dc) ......................... 0.3v to (v in + 0.3v) p-channel switch source current (dc) ............. 500ma n-channel switch sink current (dc) ................. 500ma absolute axi u rati gs w ww u 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 (note 1) ltc3410besc6 order part number sc6 part marking consult ltc marketing for parts specified with wider operating temperature ranges. package/order i for atio uu w t jmax = 125 c, ja = 250 c/ w order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbflead free part marking: http://www.linear.com/leadfree/ lbzy t jmax = 125 c, ja = 250 c/ w ltc3410besc6-1.2ltc3410besc6-1.5 ltc3410besc6-1.8 ltc3410besc6-1.875 order part number sc6 part marking lcmxlcmy lcmz lchz run 1gnd 2 sw 3 6 v fb 5 gnd4 v in top view sc6 package 6-lead plastic sc70 run 1gnd 2 sw 3 6 v out 5 gnd4 v in top view sc6 package 6-lead plastic sc70 symbol parameter conditions min typ max units i vfb feedback current adjustable output voltage 30 na i vout output voltage feedback current fixed output voltage 3.3 6 a i pk peak inductor current v in = 3v, v fb = 0.7v or v out = 90%, duty cycle < 35% 380 490 600 ma v fb regulated feedback voltage adjustable output voltage (ltc3410be) 0.784 0.8 0.816 v ? v fb reference voltage line regulation v in = 2.5v to 5.5v 0.04 0.4 %/v v out regulated output voltage ltc3410b-1.2, i out = 100ma 1.176 1.2 1.224 v ltc3410b-1.5, i out = 100ma 1.47 1.5 1.53 v ltc3410b-1.8, i out = 100ma 1.764 1.8 1.836 v ltc3410b-1.875, i out = 100ma 1.837 1.875 1.913 v ? v out output voltage line regulation v in = 2.5v to 5.5v 0.04 0.4 %/v v loadreg output voltage load regulation i load = 50ma to 250ma 0.5 % v in input voltage range 2.5 5.5 v v uvlo undervoltage lockout threshold v in rising 2.0 2.3 v v in falling 1.94 v 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. electrical characteristics downloaded from: http:///
3 ltc3410b 3410bfa typical perfor a ce characteristics uw efficiency vs input voltage efficiency vs output current (from figure 1 except for the resistive divider resistor values) input voltage (v) 2.5 efficiency (%) 50 60 70 4 5 3410 g01 40 30 20 3 3.5 4.5 80 90 100 5.5 i out = 250ma i out = 10ma i out = 1ma v out = 1.2v i out = 100ma reference voltage vstemperature temperature ( c) ?0 reference voltage (v) 0.804 0.809 0.814 25 75 3410 g03 0.799 0.794 ?5 0 50 100 125 0.789 0.784 v in = 3.6v output current (ma) 1 40 efficiency (%) 50 60 70 80 10 100 1000 3410 g02 30 2010 0 90 100 v out = 1.8v v in = 2.7v v in = 3.6v v in = 4.2v symbol parameter conditions min typ max units i s input dc bias current (note 4) operating v fb = 0.83v or v out = 104%, i load = 0a 200 300 a shutdown v run = 0v 0.1 1 a f osc oscillator frequency v fb = 0.8v or v out = 100% 1.8 2.25 2.7 mhz v fb = 0v or v out = 0v 310 khz r pfet r ds(on) of p-channel fet i sw = 100ma 0.75 0.9 ? r nfet r ds(on) of n-channel fet i sw = 100ma 0.55 0.7 ? 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 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. electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolutemaximum rating condition for extended periods may affect device reliability and lifetime. note 2: the ltc3410be is guaranteed to meet performance specifications from 0 c to 85 c. specifications over the ?0 c to 85 c operating temperature range are assured by design, characterization and correlationwith 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: ltc3410b: 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.note 5: this ic includes overtemperature protection that is intended to protect the device during momentary overload conditions. junctiontemperature will exceed 125 c when overtemperature protection is active. continuous operation above the specified maximum operating junctiontemperature may impair device reliability. downloaded from: http:///
4 ltc3410b 3410bfa typical perfor a ce characteristics uw (from figure 1 except for the resistive divider resistor values) r ds(on ) vs input voltage switch leakage vs temperature dynamic supply currentvs temperature dynamic supply current vs v in r ds(on) vs temperature input voltage (v) 1 r ds (on) ( ? ) 0.4 1.0 1.1 1.2 3 5 6 3410 g07 0.2 0.8 0.6 0.3 0.90.1 0 0.7 0.5 2 4 7 main switch synchronous switch v in (v) 1 dynamic supply current ( a) 220 260 300 5 3410 g09 180 140 100 2 3 4 6 v out = 1.2v i load = 0a temperature ( c) 50 ?5 150 dynamic supply current ( a) 190 250 0 50 75 3410 g10 170 230 210 25 100 125 v out = 1.2v i load = 0a temperature ( c) ?0 switch leakage (na) 30 90 100 110 0 50 75 3410 g11 10 70 50 20 80 0 60 40 ?5 25 100 125 v in = 5.5v run = 0v synchronous switch main switch temperature ( c) ?0 0 r ds (on) ( ? ) 0.2 0.6 0.8 1.0 ?0 30 50 130 3410 g08 0.4 ?0 10 70 90 110 1.2 v in = 2.7v v in = 3.6v v in = 4.2v v in = 2.7v v in = 3.6v v in = 4.2v synchronous switch main switch oscillator frequency vssupply voltage output voltage vs load current oscillator frequency vstemperature load current (ma) 0 v out error (%) ?.6 0.2 1.0 400 3410 g06 ?.4?.2 ?.0 ?.2 0.6 ?.8?.6 ?.0 100 200 300 500 v in = 3.6v v out = 1.8v temperature ( c) ?0 1.8 oscillator frequency (mhz) 1.9 2.1 2.2 2.3 50 2.7 3410 g04 2.0 0 ?5 75 100 25 125 2.4 2.5 2.6 v in = 3.6v supply voltage (v) 2 1.8 oscillator frequency (mhz) 1.9 2.1 2.2 2.3 4 6 2.7 3410 g05 2.0 35 2.4 2.5 2.6 downloaded from: http:///
5 ltc3410b 3410bfa typical perfor a ce characteristics uw (from figure 1 except for the resistive divider resistor values) start-up from shutdown load step load step switch leakage vs input voltage pulse skipping input voltage (v) 0 leakage current (pa) 200 500 550 600 2 4 5 3410 g12 100 400 300 150 450 50 0 350 250 1 3 6 main switch synchronous switch 1 s/div v out 10mv/div ac coupled v in = 3.6v v out = 1.8v i load = 2ma i l 100ma/div sw 2v/div 3410 g13 100 s/div run 2v/div v in = 3.6v v out = 1.8v i load = 128ma i l 200ma/div v out 1v/div 3410 g14 4 s/div v out 100mv/div ac coupled v in = 3.6v v out = 1.8v i load = 0ma to 300ma i load 200ma/div i l 200ma/div 3410 g15 4 s/div v out 100mv/div ac coupled v in = 3.6v v out = 1.8v i load = 30ma to 300ma i load 200ma/div i l 200ma/div 3410 g16 downloaded from: http:///
6 ltc3410b 3410bfa 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 shutsdown the device. in shutdown, all functions are disabled drawing <1 a supply current. do not leave run floating. gnd (pins 2, 5): 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 fb (pin 6 on adjustable version): feedback pin. re- ceives the feedback voltage from an external resistivedivider across the output. v out (pin 6 on fixed voltage versions): output voltage feedback pin. an internal resistive divider divides theoutput voltage down for comparison to the internal refer- ence voltage. fu ctio al diagra u u w + + ea + i rcmp + i comp 6 1 run osc slope comp osc freq shift 0.8v 0.8v ref shutdown v in v fb /v out v in s r rs latch switching logic and blanking circuit anti- shoot- thru q q 5 4 sw 3 5 gnd 3410 bd 2 r1*r2 240k *r1 = 240k ?1 v out 0.8 () downloaded from: http:///
7 ltc3410b 3410bfa operatio u (refer to functional diagram) main control loopthe ltc3410b uses a constant frequency, current mode step-down architecture. both the 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 com- parator, 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. the v fb pin, described in the pin functions section, allows ea to receive an outputfeedback voltage from an external resistive divider. when the load current increases, it causes a slight decrease in the feedback voltage relative to the 0.8v reference, which in turn, causes the ea amplifier? output voltage to in- crease 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. pulse skipping mode operationat light loads, the inductor current may reach zero or re- verse on each pulse. the bottom mosfet is turned off by the current reversal comparator, i rcmp , and the switch voltage will ring. this is discontinuous mode operation,and is normal behavior for the switching regulator. at very light loads, the ltc3410b will automatically skip pulses in pulse skipping mode operation to maintain output regula- tion. refer to ltc3410 data sheet if burst mode operation is preferred.short-circuit protection when the output is shorted to ground, the frequency of the oscillator is reduced to about 310khz, 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 2.25mhz when v fb rises above 0v. dropout operationas the input supply voltage decreases to a value approach- ing the output voltage, the duty cycle increases toward the maximum on-time. further reduction of the supply volt- age forces the main switch to remain on for more than one cycle until it reaches 100% duty cycle. the output voltage will then be determined by the input voltage minus the voltage drop across the p-channel mosfet and the inductor. another important detail to remember is that at low input supply voltages, the r ds(on) of the p-channel switch increases (see typical performance characteristics).therefore, the user should calculate the power dissipation when the ltc3410b is used at 100% duty cycle with low input voltage (see thermal considerations in the applica- tions information section). 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 ltc3410b uses a patented scheme that counteracts this compensating ramp, which allows the maximum inductor peak current to remain unaffected throughout all duty cycles. burst mode is a registered trademark of linear technology corporation. downloaded from: http:///
8 ltc3410b 3410bfa the basic ltc3410b application circuit is shown in fig- ure 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 selectionfor most applications, the value of the inductor will fall in the range of 2.2 h to 4.7 h. its value is chosen based on the desired ripple current. large value inductors lowerripple 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 pointfor 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 leastequal 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. applicatio s i for atio wu uu inductor core selectiondifferent 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 ltc3410b requires to operate. table 1 shows some typical surface mount inductors that work well in ltc3410b applications. table 1. representative surface mount inductors max dc manufacturer part number value current dcr height taiyo yuden cb2016t2r2m 2.2 h 510ma 0.13 ? 1.6mm cb2012t2r2m 2.2 h 530ma 0.33 ? 1.25mm lbc2016t3r3m 3.3 h 410ma 0.27 ? 1.6mm panasonic elt5kt4r7m 4.7 h 950ma 0.2 ? 1.2mm sumida cdrh2d18/ld 4.7 h 630ma 0.086 ? 2mm murata lqh32cn4r7m23 4.7 h 450ma 0.2 ? 2mm taiyo yuden nr30102r2m 2.2 h 1100ma 0.1 ? 1mm nr30104r7m 4.7 h 750ma 0.19 ? 1mm fdk fdkmipf2520d 4.7 h 1100ma 0.11 ? 1mm fdkmipf2520d 3.3 h 1200ma 0.1 ? 1mm fdkmipf2520d 2.2 h 1300ma 0.08 ? 1mm c in and c out selection in continuous mode, the source current of the top mos-fet is a square wave of duty cycle v out /v in . to prevent large voltage transients, a low esr input capacitor sizedfor the maximum rms current must be used. the maxi- mum rms capacitor current is given by: ci vvv in omax out in out required i rms ? ? () ? ? ? ? 1/ 22 v in figure 1. high efficiency step-down converter v in c in 2.2 f cer v in 2.7v to 5.5v ltc3410b run 4.7 h 10pf232k 464k 3410 f01 sw v fb gnd c out 2.2 f cer v out 1.2v downloaded from: http:///
9 ltc3410b 3410bfa using ceramic input and output capacitorshigher 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 ltc3410b? 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. however, 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. atworst, 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. output voltage programming (ltc3410b only) the output voltage is set by a resistive divider according to the following formula: vv r r out =+ ? ? ? ? ? ? 08 1 2 1 . (2) the external resistive divider is connected to the output,allowing remote voltage sensing as shown in figure 2. 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 deviationsdo 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 inputvoltage since ? i l increases with input voltage. if tantalum capacitors are used, it is critical that thecapacitors 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. applicatio s i for atio wu uu figure 2. setting the ltc3410b output voltage v fb gnd ltc3410b 0.8v v out 5.5v r2 r1 3410 f02 downloaded from: http:///
10 ltc3410b 3410bfa applicatio s i for atio wu uu efficiency considerationsthe 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 + ...) where l1, l2, etc. are the individual losses as a percentageof input power. although all dissipative elements in the circuit produce losses, two main sources usually account for most of the losses in ltc3410b 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 loadcurrents. in a typical efficiency plot, the efficiency curve at very low load currents can be misleading since the actual power lost is of no consequence as illustrated in figure 3. 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 bottomswitches. both the dc bias and gate charge losses are proportional to v in and thustheir effectswill be more pronounced at higher supply voltages. 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 flowingthrough 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 charateristicscurves. 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 lessthan 2% total additional loss. figure 3. power lost vs load current load current (ma) 0.1 1 0.0001 power lost (w) 0.01 1 10 100 1000 3410 f03 0.001 0.1 v out = 1.2v v out = 1.8v v out = 2.5v downloaded from: http:///
11 ltc3410b 3410bfa applicatio s i for atio wu uu thermal considerations in most applications the ltc3410b does not dissipatemuch heat due to its high efficiency. but, in applications where the ltc3410b is running at high ambient temperature 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 nodewill become high impedance. to avoid the ltc3410b from exceeding the maximumjunction 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 ltc3410b in dropout at aninput voltage of 2.7v, a load current of 300ma 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 1.0 ? . therefore, power dissipated by the part is: p d = i load 2 ?r ds(on) = 90mw for the sc70 package, the ja is 250 c/ w. thus, the junction temperature of the regulator is: t j = 70 c + (90)(250) = 92.5 c which is well below the maximum junction temperatureof 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 stabilityproblem. for a detailed explanation of switching control loop theory, see application note 76. a second, more severe transient is caused by switching in loads with large (>1 f) supply bypass capacitors. the discharged bypass capacitors are effectively put in parallelwith c out , causing a rapid drop in v out . no regulator can deliver enough current to prevent this problem if the loadswitch resistance is low and it is driven quickly. the only solution is to limit the rise time of the switch drive so that the load rise time is limited to approximately (25 ?c load ). thus, a 10 f capacitor charging to 3.3v would require a 250 s rise time, limiting the charging current to about 130ma. downloaded from: http:///
12 ltc3410b 3410bfa applicatio s i for atio wu uu pc board layout checklistwhen laying out the printed circuit board, the following checklist should be used to ensure proper operation of the ltc3410b. 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 v fb pin connect directly to the feedback resistors? the resistive divider r1/r2 must be con-nected between the (+) plate of c out and ground. 3. does the (+) plate of c in connect to v in as closely as possible? this capacitor provides the ac current to theinternal power mosfets. 4. keep the (? plates of c in and c out as close as possible. 5. keep the switching node, sw, away from the sensitive v fb node. figure 4a. ltc3410b layout diagram figure 5a. ltc3410b suggested layout run ltc3410b gnd sw l1 r2 r1 c fwd bold lines indicate high current paths v in v out 3410b f04a 4 6 5 13 + 2 v fb v in c in c out ltc3410b gnd 3410b f05a pin 1 v out v in via to v out sw via to v in via to gnd c out c in l1 r2 c fwd r1 run ltc3410b-1.875 gnd sw l1 bold lines indicate high current paths v in v out 3410b f04b 4 6 5 13 + 2 v out v in c in c out figure 4b. ltc3410b-1.875 layout diagram ltc3410b- 1.875 3410b f05b pin 1 v out v in sw via to v in c out c in l1 figure 5b. ltc3410b fixed output voltagesuggested layout downloaded from: http:///
13 ltc3410b 3410bfa applicatio s i for atio wu uu design example as a design example, assume the ltc3410b is used in asingle 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 requirementis a maximum of 0.3a 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 2.5v. 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 = 2.5v, v in = 4.2v, ? i l = 100ma and f = 2.25mhz in equation (3) gives: l v mhz ma v v h = ? ? ? ? ? ? ? = 25 2 25 100 1 25 42 45 . .( ) . . . for best efficiency choose a 300ma or greater inductorwith 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 ceramic capacitor will satisfy this requirement.for the feedback resistors, choose r1 = 412k. r2 can then be calculated from equation (2) to be: r v r k use out 2 08 1 1 875 5 8 = ? ? ? ? ? ? ? = . . ; 87k figure 6 shows the complete circuit along with itsefficiency curve. figure 6a figure 6b figure 6c v in c in ? 2.2 f cer v in 2.7v to 4.2v ltc3410b run 3 4.7 h* 10pf887k 412k 3410 f07a 6 41 2, 5 sw v fb gnd c out ? 2.2 f cer v out 2.5v ? taiyo yuden jmk212bj225 *murata lqh32cn4r7m23 output current (ma) 1 40 efficiency (%) 50 60 70 80 10 100 1000 3410 f07b 30 2010 0 90 100 v in = 2.7v v in = 3.6v v in = 4.2v 4 s/div v out 100mv/div ac coupled v in = 3.6v v out = 2.5v i load = 100ma to 300ma i load 200ma/div i l 200ma/div 3410 f07c downloaded from: http:///
14 ltc3410b 3410bfa u typical applicatio v in c in ? 2.2 f v in 2.7v to 4.2v ltc3410b run 3 4.7 h* 10pf402k 464k 3410 ta02 6 41 2, 5 sw v fb gnd c out ? 2.2 f v out 1.5v ? taiyo yuden jmk212bj225 *murata lqh32cn4r7m23 4 s/div v out 100mv/div ac coupled v in = 3.6v v out = 1.5v i load = 100ma to 250ma i load 200ma/div il 200ma/div 3410 ta04 3410 ta03 output current (ma) 1 40 efficiency (%) 50 60 70 80 10 100 1000 30 2010 0 90 100 v in = 2.7v v in = 3.6v v in = 4.2v downloaded from: http:///
15 ltc3410b 3410bfa 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. u package descriptio sc6 package 6-lead plastic sc70 (reference ltc dwg # 05-08-1638) 1.15 ?1.35 (note 4) 1.80 ?2.40 0.15 ?0.30 6 plcs (note 3) sc6 sc70 1205 rev b 1.80 ?2.20 (note 4) 0.65 bsc pin 1 0.80 ?1.00 1.00 max 0.00 ?0.10 ref note:1. dimensions are in millimeters 2. drawing not to scale 3. dimensions are inclusive of plating4. dimensions are exclusive of mold flash and metal burr 5. mold flash shall not exceed 0.254mm 6. details of the pin 1 identifier are optional, but must be located within the index area 7. eiaj package reference is eiaj sc-70 8. jedec package reference is mo-203 variation ab 2.8 bsc 0.47 max 0.65 ref recommended solder pad layout per ipc calculator 1.8 ref 1.00 ref index area(note 6) 0.10 ?0.18 (note 3) 0.26 ?0.46 gauge plane 0.15 bsc 0.10 ?0.40 downloaded from: http:///
16 ltc3410b 3410bfa part number description comments lt1616 500ma (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 converter i sd = <1 a, thinsot package ltc1877 600ma (i out ), 550khz, synchronous step-down 95% efficiency, v in = 2.7v to 10v, v out(min) = 0.8v, i q = 10 a, dc/dc converter i sd = <1 a, ms8 package ltc1878 600ma (i out ), 550khz, synchronous step-down 95% efficiency, v in = 2.7v to 6v, v out(min) = 0.8v, i q = 10 a, dc/dc converter i sd = <1 a, ms8 package ltc1879 1.2a (i out ), 550khz, synchronous step-down 95% efficiency, v in = 2.7v to 10v, v out(min) = 0.8v, i q = 15 a, dc/dc converter i sd = <1 a, tssop-16 package ltc3403 600ma (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 = 20 a, i sd = <1 a, dfn package ltc3404 600ma (i out ), 1.4mhz, synchronous step-down 95% efficiency, v in = 2.7v to 6v, v out(min) = 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 96% efficiency, v in = 2.5v to 5.5v, v out(min) = 0.8v, i q = 20 a, dc/dc converter i sd = <1 a, thinsot package ltc3406 600ma (i out ), 1.5mhz, synchronous step-down 96% efficiency, v in = 2.5v to 5.5v, v out(min) = 0.6v, i q = 20 a, dc/dc converter i sd = <1 a, thinsot package ltc3407/ltc3407-2 dual 600ma/800ma (i out ), 1.5mhz/2.25mhz, 95% efficiency, v in = 2.5v to 5.5v, v out(min) = 0.6v, i q = 40 a, synchronous step-down dc/dc converter i sd = <1 a, dfn, ms10e packages ltc3409 600ma (i out ), 1.5mhz/2.25mhz, synchronous 95% efficiency, v in = 1.6v to 5.5v, v out(min) = 0.613v, i q = 65 a, step-down dc/dc converter dd8 package ltc3410 300ma (i out ), 2.25mhz, synchronous step-down 96% efficiency, v in = 2.5v to 5.5v, v out(min) = 0.8v, i q = 26 a, dc/dc converter with burst mode operation i sd = <1 a, sc7o package ltc3411 1.25a (i out ), 4mhz, synchronous step-down 95% efficiency, v in = 2.5v to 5.5v, v out(min) = 0.8v, i q = 60 a, dc/dc converter i sd = <1 a, ms package ltc3412/ltc3412a 2.5a/3a (i out ), 4mhz, synchronous step-down 95% efficiency, v in = 2.5v to 5.5v, v out(min) = 0.8v, i q = 60 a, dc/dc converter i sd = <1 a, tssop-16e package ltc3440 600ma (i out ), 2mhz, synchronous buck-boost 95% efficiency, v in = 2.5v to 5.5v, v out(min) = 2.5v to 5v, dc/dc converter i q = 25 a, i sd = <1 a, ms package ltc3548 dual 400ma/800ma (i out ), 2.25mhz, 95% efficiency, v in = 2.5v to 5.5v, v out(min) = 0.6v, i q = 40 a, synchronous step-down dc/dc converter i sd = <1 a, dfn, ms10e packages linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com lt 0706 rev a ?printed in usa ? linear technology corporation 2005 related parts u typical applicatio using low profile components, <1mm height 3410b ta06a c in ? 4.7 f 3 4.7 h* 6 41 2, 5 c out ? 4.7 f cer ? taiyo yuden jmk212bj475 *fdk mipf2520d v in v in 2.7v to 4.2v ltc3410b-1.875 run sw v out gnd v out 1.875v downloaded from: http:///

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