lt3469 1 3469f amplifier current limit: 40ma typical input common mode range: 0v to 10v output voltage range: 1v to (v cc ?1v) differential gain stage with high impedance output(g m stage) quiescent current (from v cc ): 2ma unloaded gain: 30,000 typical switching regulator generates v cc up to 35v wide operating supply range: 2.5v to 16v high switching frequency: 1.3mhz internal schottky diode tiny external components current mode switcher with internal compensation low profile (1mm) sot-23 package piezo microactuator driver with boost regulator piezo speakers piezo microactuators varactor bias , ltc and lt are registered trademarks of linear technology corporation. + +in 35 62 4 1 8 7 gnd fb v cc sw lt3469 v in 453k16.5k 0.47 f 50v v out 1v to 33v piezoactuator 5nf < c < 300nf 10k + 9.09k 100k 47 h ?n out 3469 ta03 5v or 12v input 0v to 3v 1 f 16v the lt 3469 is a transconductance (g m ) amplifier that can drive outputs up to 33v from a 5v or 12v supply. aninternal switching regulator generates a boosted supply voltage for the g m amplifier. the amplifier can drive capacitive loads in the range of 5nf to 300nf. slew rate islimited only by the maximum output current. the 35v output voltage capability of the switching regulator, along with the high supply voltage of the amplifier, combine to allow the wide output voltage range needed to drive a piezoceramic microactuator. the lt3469 switching regulator switches at 1.3mhz, allowing the use of tiny external components. the output capacitor can be as small as 0.22 m f, saving space and cost versus alternative solutions.the lt3469 is available in a low profile thinsot tm package. thinsot is a trademark of linear technology corporation. piezo microactuator driver response driving a 33nf load i out 100ma/div v out 10v/div input 5v/div 50 m s/div 3469 ta04 features descriptio u applicatio s u typical applicatio u downloaded from: http:///
lt3469 2 3469f v in voltage ............................................................. 16v sw voltage ............................................................. 40v v cc voltage............................................................. 38v +in, ?n voltage ..................................................... 10v fb voltage ................................................................ 3v current into sw pin ................................................. 1a operating temperature range (note 2) .. 40 c to 85 c storage temperature range ................ 65 c to 150 c lead temperature (soldering, 10 sec)................. 300 c order part number (note 1) absolute axi u rati gs w ww u consult ltc marketing for parts specified with wider operating temperature ranges. lt3469ets8 t jmax = 125 c, q ja = 250 c/w the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. (note 2) v in = 5v, v cc = 35v, unless otherwise noted. electrical characteristics ts8 part marking ltaca out 1 fb 2 v in 3 gnd 4 8 in 7 +in 6 v cc 5 sw top view ts8 package 8-lead plastic tsot-23 parameter conditions min typ max units g m amplifier input offset voltage v out = v cc /2 31 0 m v input offset current 10 100 na input bias current 150 500 na input resistance?ifferential mode 1m w input resistance?ommon mode 200 m w common mode rejection ratio v cm = 0v to 10v 70 100 db power supply rejection ratio? in v in = 2.5v to 16v 80 120 db power supply rejection ratio? cc v cc = 15v to 35v 65 85 db gain no load, v out = 2v to 33v 15 30 v/mv r l = 200k, v out = 2v to 33v 10 20 v/mv transconductance i out = 100 m a 160 220 260 m a/mv 140 300 m a/mv maximum output current v out = v cc /2 30 40 55 ma 23 58 ma maximum output voltage, sourcing v cc = 35v, i out = 10ma 34.0 34.5 v v cc = 35v, i out = 0ma 34.5 34.9 v minimum output voltage, sinking i out = ?0ma 200 1000 mv i out = 0ma 10 500 mv output resistance v cc = 35v, v out = 2v to 33v 100 k w supply current? cc v cc = 35v 1.5 2 2.5 ma switching regulator minimum operating voltage 2.5 v maximum operating voltage 16 v feedback voltage 1.19 1.23 1.265 v fb pin bias current 45 200 na fb line regulation 2.5v < v in < 16v 0.03 %/v supply current? in 1.9 2.6 ma switching frequency 0.8 1.3 1.7 mhz maximum duty cycle 88 91 % switch current limit (note 3) 165 220 ma switch v cesat i sw = 100ma 350 500 mv package/order i for atio uu w downloaded from: http:///
lt3469 3 3469f parameter conditions min typ max units switch leakage current v sw = 5v 0.01 1 m a diode v f i d = 100ma 740 1100 mv diode reverse leakage current v r = 5v 0.1 1 m a the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. (note 2) v in = 5v, v cc = 35v, unless otherwise noted. electrical characteristics note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired.note 2: the lt3469e 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: current limit is guaranteed by design and/or correlation to static test. slope compensation reduces current limit at higher duty cycles. typical perfor a ce characteristics uw schottky forward voltage schottky reverse leakage forward voltage (mv) 200 schottky current (ma) 150 200 250 500 700 1000 3469 g07 100 50 0 300 400 600 800 900 100 c ?0 c 25 c temperature ( c) ?0 0 leakage current ( a) 5 10 15 20 25 ?5 02 55 0 3469 g09 75 100 v r = 5v switching frequency fb pin voltage and bias current temperature ( c) ?0 1.41.2 1.0 0.8 0.6 0.4 0.2 0 25 75 3469 g10 ?5 0 50 100 switching frequency (mhz) temperature ( c) ?0 1.175 fb voltage (v) fb bias current (na) 1.195 1.215 1.235 1.255 1.275 0 10 20 30 40 50 ?5 02 55 0 3469 g11 75 100 current voltage (switching regulator) v in (v) 0 i q (ma) 1.2 1.8 2.0 16 3469 g05 1.00.8 0 4 8 12 14 2 6 10 0.4 2.42.2 1.6 1.4 0.6 0.2 ?0 c 100 c 25 c duty cycle (%) 0 current limit (ma) 150 200 250 80 3469 g06 100 50 0 20 40 60 100 t a = 25 c v in quiescent current current limit vs duty cycle downloaded from: http:///
lt3469 4 3469f typical perfor a ce characteristics uw v cc quiescent current output currentvs differential input voltage v cc (v) 15 18 0 i q (ma) 1.0 2.5 21 27 30 3469 g01 0.5 2.0 100 c 25 c ?0 c 1.5 24 33 36 differential input voltage (mv) ?0 output current (ma) 0 10 20 30 30 3469 g02 ?0 ?0 ? 5 15 25 ?5 ?5 ?0 ?0 ?0 10 ?0 40 ?0 0 20 50 100 c ?0 c 25 c (g m amplifier) g m vs v cc v cc (v) 15 g m ( a/mv) 100 150 35 3469 g14 50 0 20 25 30 250200 ?0 c 25 c 100 c uu u pi fu ctio s out (pin 1): output of the g m amplifier. there must be at least 5nf of capacitive load at the output in a gain of 10configuration. capacitive loads up to 300nf can be con- nected to this pin. piezo actuators below 5nf can be driven if capacitance is placed in parallel to bring the total capacitance to 5nf. fb (pin 2): feedback pin. reference voltage is 1.23v. connect feedback resistor divider here.v in (pin 3): input supply pin. must be locally bypassed. gnd (pin 4): ground pin. connect directly to local ground plane.sw (pin 5): switch pin. connect inductor here. minimize trace area at this pin to reduce emi.v cc (pin 6): output of switching regulator and supply rail for g m amp. there must be 0.22 m f or more of capacitance here. +in (pin 7): noninverting terminal of the g m amplifier. in (pin 8): inverting terminal of the g m amplifier. block diagra w + sw 4 5 v cc 2 fb 1.23v 7 1 v in v cc +in ?n out gnd 3469 f01 q1 a1 switch controller 6 v in 3 + 8 g m figure 1. lt3469 block diagram downloaded from: http:///
lt3469 5 3469f operatio u g m amplifier the lt3469 is a wide output voltage range g m amplifier designed to drive capacitive loads. input common moderange extends from 10v to ground. the output current is proportional to the voltage difference across the input terminals. when the output voltage has settled, the input terminals will be at the same voltage; supply current of the amplifier will be low and power dissipation will be low. if presented with an input differential, however, the output current can increase significantly, up to the maximum output current (typically 40ma). the output voltage slew rate is determined by the maximum output current and the output capacitance, and can be quite high. with a 10nf load, the output slew rate will typically be 4v/ m s. the capacitive load compensates the g m amplifier and must be present for stable operation. the gain capacitance productof the amplifier must be at least 50nf. for example, if the amplifier is operated in a gain of 10 configuration, a minimum capacitance of 5nf is necessary. in a gain of 20 configuration, a minimum of 2.5nf is necessary. closed loop ?db bandwidth is set by the output capacitance. typical closed loop bandwidth is approximately: g ac m v out 2 p ? where g m = 200 m a/mv for example, an amplifier in a gain of 10 configuration with10nf of output capacitance will have a closed loop ?db bandwidth of approximately 300khz. figure 3 shows typi- cal bandwidth of a gain of 10 configuration per outputcapacitance. in applications where negative phase contributions below crossover frequency must be minimized, a phase boost capacitor can be added, as shown in figure 4. larger val- ues of c boost will further reduce the closed-loop negative phase con tri bution, however, the amplifier phase margin will be reduced. for an amplifier phase margin of approxi-mately 55 , select c boost as follows: c crr gr r boost out m = + () () 121 12 / || where g m = 200 m a/mv. in a gain of 10 configuration, choosing c boost as de- scribed will lead to nearly zero closed-loop negative phasecontribution at 3khz for values of c out from 10nf to 200nf. the phase boost capacitor should not be used ifc out is less than twice the minimum for stable operation. the gain capacitance product should therefore be higherthan 100nf if a phase boost capacitor is used. switching regulator the lt3469 uses a constant frequency, current mode control scheme to provide excellent line and load regula- tion. operation can be best understood by referring to the block diagram in figure 1. the switch controller sets the peak current in q1 proportional to its input. the input to the switch controller is set by the error amplifier, a1, and is figure 2. slew rate vs capacitance figure 3. closed loop ?db bandwidthvs capacitance in a gain of 10 configuration capacitance (nf) 2 0.1 slew rate (v/ s) 1 10 100 20 200 3469 f02 capacitance (nf) 2 bandwidth (khz) 10 100 1000 20 200 3469 f03 with phaseboost capacitor without phase boost capacitor downloaded from: http:///
lt3469 6 3469f operatio u transient response, however, more output capacitance canhelp limit the voltage droop on v cc during transients. table 2. recommended ceramic capacitor manufacturers manufacturer phone url taiyo yuden 408-573-4150 www.t-yuden.com avx 843-448-9411 www.avxcorp.com murata 814-237-1431 www.murata.com kemet 408-986-0424 www.kemet.com inrush current considerations when hot plugging when the supply voltage is applied to v in , the voltage difference between v in and v cc generates inrush current flowing from the input through the inductor, the sw pin,and the integrated schottky diode to charge the output capacitor. care should be taken not to exceed the lt3469 maximum sw pin current rating of 1a. worst-case inrush current occurs when the application circuit is hot plugged into a live supply with a large output capacitance. the typical application circuit will maintain a peak sw pin current below 1a when it is hot plugged into a 5v supply. to keep sw pin current below 1a during a hot plug into a 12v supply, 4.7 w must be added between the supply and the lt3469 input capacitor. during normal operation,the sw pin current remains significantly less than 1a. layout hintsas with all switching regulators, careful attention must be paid to the pcb board layout and component placement. to maximize efficiency, switch rise and fall times are made 3469 f04 + c boost r2 r1 v out g m input figure 4. boosting the bandwidth of the g m amplifier with capacitance on the inverting input simply an amplified version of the difference between thefeedback voltage and the reference voltage of 1.23v. in this manner, the error amplifier sets the correct peak current level to keep the output in regulation. if the error amplifier? output increases, more current is delivered to the output; if it decreases, less current is delivered. the switching regulator provides the boosted supply voltage for the g m amplifier. inductor selectiona 47 m h inductor is recommended for most lt3469 appli- cations. some suitable inductors with small size are listedin table 1. the efficiency comparison of different induc- tors is shown in figure 5. table 1. recommended inductors current dcr rating part number ( w ) (ma) manufacturer lqh32cn470 1.3 170 murata 814-237-1431www.murata.com cmd4d11-470 2.8 180 sumida 847-545-6700www.sumida.com lbc2518t470m 1.9 150 taiyo yuden 408-573-4150www.t-yuden.com capacitor selectionthe small size of ceramic capacitors makes them ideal for lt3469 applications. x5r and x7r types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as y5v or z5u. a 1 m f input capacitor is sufficient for most lt3469 appli- cations. a 0.22 m f output capacitor is sufficient for stable load current (ma) 0 40 efficiency (%) 50 60 70 5 10 15 20 3469 f05 25 80 90 45 55 65 75 85 30 v in = 12v v out = 35v murata lqh32cn470sumida cmd4011-470 taiyo yuden lbc2518t470m figure 5. efficiency comparison of different inductors downloaded from: http:///
lt3469 7 3469f as short as possible. to prevent electromagnetic interfer-ence (emi) problems, proper layout of the high frequency switching path is essential. the voltage signal of the sw pin has sharp rise and fall edges. the sw pin should be surrounded on three sides by metal connected to v cc to shield +in and in. minimize the area of all traces con- nected to the sw pin and always use a ground plane under the switching regulator to minimize interplane coupling. in addition, the ground connection for the feedback resistor r1 should be tied directly to the gnd pin and not shared with any other component, ensuring a clean, noise-free connection. the ground return of the piezoceramic microactuator should also have a direct and unshared connection to the gnd pin. the gnd connection to r5 should be tied directly to the ground of the source gener- ating the input signal to avoid error induced by voltage drops along the gnd line. recommended component placement is shown in figure 6. thermal considerations and power dissipation the lt3469 combines large output drive with a small package. because of the high supply voltage capability, it is possible to operate the part under conditions that exceed the maximum junction temperature. maximum junction temperature (t j ) is calculated from the ambient temperature (t a ) and power dissipation (p d ) as follows: t j = t a + (p d ?250 c/w) worst-case power dissipation occurs at maximum outputswing, frequency, capacitance and v cc . for a square wave input, power dissipation is calculated from the amplifierquiescent current (i q ), input frequency (f), output swing (v out(p-p) ), capacitive load (c l ), amplifier supply voltage (v cc ) and switching regulator efficiency ( h ) as follows: p if v cv d ql c c = + () () out(p-p) h example: lt3469 at t a = 70 c, v cc = 35v, c l = 200nf, f = 3khz, v out(p-p) = 4v, h = 80%: p ma khz v nf v mw t c mw c w c d j = + () ( ) = =+ () = 2 5 3 4 200 35 080 214 70 214 250 124 .? ? .? do not exceed the maximum junction temperature of125 c. figure 6. recommended component placement r4 input r5 r1 r3 r2 c1 c2 v in vias to ground plane piez0 actuator gnd l 3469 f06 operatio u piezo speaker driver + +in 35 62 4 1 8 7 gnd fb v cc sw lt3469 v in 294k17.4k c20.47 f 35v v out 1v to 20v c1, c2: x5r or x7r dielectricl1: murata lqh32cn470 sound pressure level: 87db at 750hz/10v p-p /10cm with a 55nf piezo speaker. i vin with v in = 3.3v: 24ma at 750hz/10v p-p with a 55nf piezo speaker piezospeaker 8nf < c < 300nf 20k + 16.9k 113k l1 47 h ?n out 3469 ta01 v in 3v to 6v input 0v to 3v c11 f u typical applicatio 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. downloaded from: http:///
lt3469 8 3469f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2003 lt/tp 0304 1k ? printed in usa related parts part number description comments lt1611 550ma i sw , 1.4mhz, high efficiency inverting dc/dc converter v in : 0.9v to 10v, v out(max) : 34v, i q : 3ma, i sd : <1 m a, thinsot lt1616 600ma i out , 1.4mhz, high efficiency step-down v in : 3.6v to 25v, v out(min) : 1.25v, i q : 1.9ma, i sd : <1 m a, thinsot dc/dc converter ltc1772b 550khz, current mode step-down dc/dc controller v in : 2.5v to 9.8v, v out(min) : 0.8v, i q : 270 m a, i sd : <8 m a, thinsot lt1931/lt1931a 1a i sw , 1.2mhz/2.2mhz, high efficiency inverting dc/dc v in : 2.6v to 16v, v out(max) : 34v, i q : 4.2ma, i sd : <1 m a, thinsot converter lt1940 (dual) dual output 1.4a i out , constant 1.1mhz, high efficiency v in : 3v to 25v, v out(min) : 1.2v, i q : 2.5ma, i sd : <1 m a, tssop-16e step-down dc/dc converter ltc3411 1.25a i out , 4mhz synchronous step-down dc/dc converter v in : 2.5v to 5.5v, v out(min) : 0.8v, i q : 60 m a, i sd : <1 m a, ms10, dfn lt3464 85ma i sw , constant off-time, high efficiency step-up dc/dc v in : 2.3v to 10v, v out(max) : 34v, i q : 25 m a, i sd : <0.5 m a, thinsot converter with integrated schottky and output disconnect u package descriptio ts8 package 8-lead plastic tsot-23 (reference ltc dwg # 05-08-1637) 1.50 ?1.75 (note 4) 2.80 bsc 0.22 ?0.36 8 plcs (note 3) datum ? 0.09 ?0.20 (note 3) ts8 tsot-23 0802 2.90 bsc (note 4) 0.65 bsc 1.95 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 3.85 max 0.52 max 0.65 ref recommended solder pad layout per ipc calculator 1.4 min 2.62 ref 1.22 ref 4. dimensions are exclusive of mold flash and metal burr5. mold flash shall not exceed 0.254mm 6. jedec package reference is mo-193 downloaded from: http:///
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