1 lt3463/LT3463A 3463f dual micropower dc/dc converters with schottky diodes , ltc and lt are registered trademarks of linear technology corporation. ccd bias supply (15v, C8v) efficiency and power loss the lt ? 3463/LT3463A are dual micropower dc/dc con- verters with internal schottky diodes in a 10-lead 3mm 3mm dfn package. negative and positive lt3463 con- verters have a 250ma current limit. the LT3463A positive converter also has a 250ma limit, while the negative converter has a 400ma limit. both devices have an input voltage range of 2.4v to 15v, making them ideal for a wide variety of applications. each converter features a quies- cent current of only 20 m a, which drops to under 1 m a in shutdown. a current limited, fixed off-time control scheme conserves operating current, resulting in high efficiency over a broad range of load current. the 42v switch enables high voltage outputs up to 40v to be easily generated without the use of costly transformers. the low 300ns off- time permits the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space-con- scious portable applications. n generates well-regulated positive and negative outputs n low quiescent current: 20 m a (per converter) in active mode <1 m a in shutdown mode n internal 42v power switches n internal 42v schottky diodes n low v cesat switch: 180mv at 150ma n input voltage range: 2.4v to 15v n high output voltages: up to 40v n low profile (0.8mm) 3mm x 3mm dfn package n ccd bias n lcd bias n handheld computers n digital cameras descriptio u features applicatio s u typical applicatio u v in v ref v out1 v out1 15v 10ma v out2 ?v 50ma sw1 fb2 LT3463A 10 h shdn2 2.2 f v in 2.7v to 5v 3463 ta01a gnd sw2 d2 1 f 4.7 f fb1 shdn1 1m 1m 10pf 154k 90.9k 4.7 f 10 h load current (ma) 0.1 50 efficiency (%) power loss (mw) 70 75 80 1 10 100 3463 ta01b 65 ?v loss 60 55 0 160 200 240 120 80 40 v in = 3.6v 15v efficiency ?v efficiency 15v loss
2 lt3463/LT3463A 3463f absolute axi u rati gs w ww u package/order i for atio uu w (note 1) v in , shdn1, shdn2 voltage ................................... 15v sw1, sw2, v out1 voltage ....................................... 42v d2 voltage ............................................................. C42v fb1, fb2 voltage range .............................. C0.3v to 2v junction temperature ........................................... 125 c operating ambient temperature range (note 2) .............................................. C 40 c to 85 c storage temperature range ................. C 65 c to 125 c order part number lt3463edd LT3463Aedd dd part marking electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 2.5v, v shdn = 2.5v unless otherwise noted. parameter conditions min typ max units minimum input voltage 2.2 2.4 v total quiescent current for both switchers, not switching 40 60 m a shutdown current v shdn1 = v shdn2 = 0v 0.1 1 m a v ref pin voltage with 124k w to gnd l 1.23 1.25 1.27 v v ref pin voltage line regulation with 124k w to gnd 0.05 0.10 %/v fb1 comparator trip voltage high to low transition l 1.225 1.25 1.275 v fb1 comparator hysteresis 8mv fb1 line regulation 2.5v < v in < 15v 0.05 0.10 %/v fb1 pin bias current (note 3) v fb1 = 1.3v l 20 50 na fb2 comparator trip voltage low to high transition l 0312mv fb2 comparator hysteresis 8mv fb2 line regulation (v ref C v fb2 ) 2.5v < v in < 15v 0.05 0.10 %/v fb2 pin bias current (note 4) v fb2 = C0.1v l 20 50 na sw1 switch off time v out1 C v in = 4v 300 ns v out1 C v in = 0v 1.5 m s sw2 switch off time v fb2 < 0.1v 300 ns v fb2 = 1v 1.5 m s switch v cesat (sw1, sw2) i sw = 150ma 180 mv switch current limit (sw1) 180 250 320 ma switch current limit (sw2) lt3463 180 250 320 ma LT3463A 320 400 460 ma swith leakage current (sw1, sw2) switch off, v sw = 42v 0.01 1 m a schottky forward voltage (v out1 , d2) i d = 150ma 750 mv schottky reverse leakage current v out1 C v sw = 42v 1 5 m a v d2 = C42v 1 5 m a shdn1 pin current v shdn1 = 2.5v 4 10 m a shdn2 pin current v shdn2 = 2.5v 4 10 m a shdn1/shdn2 start-up threshold 0.3 1 1.5 v note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: the lt3463/LT3463A are guaranteed to meet performance specifications from 0 c to 70 c. specifications over the C40 c to 85 c t jmax = 125 c, q ja = 43 c/w, q jc = 3 c/w exposed pad (pin 11) is gnd and must be soldered to pcb lafc lbjk consult ltc marketing for parts specified with wider operating temperature ranges. top view dd package 10-lead (3mm 3mm) plastic dfn 10 9 6 7 8 4 5 3 2 1 fb1 shdn1 shdn2 v ref fb2 v out1 sw1 v in sw2 d2 11 operating ambient temperature range are assured by design, characterization and correlation with statistical process controls. note 3: bias current flows into the fb1 pin. note 4: bias current flows out of the fb2 pin.
3 lt3463/LT3463A 3463f typical perfor a ce characteristics uw pi fu ctio s uuu v out1 (pin 1): output voltage switcher 1. this is the cathode of an internal schottky diode whose anode is connected to the sw1 pin. sw1 (pin 2): switch pin for switcher 1. this is the collector of the internal npn switch. minimize the metal trace area connected to this pin to minimize emi. v in (pin 3): input supply pin. bypass this pin with a capacitor as close to the device as possible. sw2 (pin 4): switch pin for switcher 2. this is the collector of the internal npn switch. minimize the metal trace area connected to this pin to minimize emi. d2 (pin 5): diode for switcher 2. this is the anode of an internal schottky diode whose cathode connected to the gnd pin. fb2 (pin 6): feedback pin for switcher 2. set the output voltage by selecting values for r3 and r4. v ref (pin 7): voltage reference pin (1.25v). this pin is used along with fb2 to set the negative output voltage for switcher 2. shdn2 (pin 8): shutdown pin for switcher 2. pull this pin above 1.5v to enable switcher 2. pull below 0.3v to turn it off. do not leave this pin floating. v cesat and v diode voltage v ref and v fb1 voltage v fb2 voltage switch off time switch current limit quiescent current v cesat and v diode voltage (v) 900 800 700 600 500 400 300 200 100 0 3463 g01 temperature ( c) 50 100 050 25 25 75 125 i diode = 150ma i switch = 150ma for both switchers v ref and v fb1 voltage (v) 1.27 1.26 1.25 1.24 1.23 1.22 3463 g02 temperature ( c) 50 100 050 25 25 75 125 v ref v fb1 v fb2 voltage (mv) 10 8 6 4 2 0 3463 g03 temperature ( c) ?0 25 75 ?5 0 50 100 125 temperature ( c) ?0 switch off time (ns) 100 3463 g04 050 400 350 300 250 200 150 100 50 0 25 25 75 125 temperature ( c) ?0 switch current limit (ma) 100 3463 g05 050 450 400 350 300 250 200 150 100 50 0 25 25 75 125 lt3463 sw1, sw2 LT3463A sw1 LT3463A sw2 temperature ( c) ?0 quiescent current ( a) 60 50 40 30 20 10 0 25 75 3463 g06 ?5 0 50 100 125 not switching v fb1 = 1.3v v fb2 = 0.1v
4 lt3463/LT3463A 3463f block diagra w figure 1. block diagram operatio u the lt3463 uses a constant off-time control scheme to provide high efficiency over a wide range of output cur- rent. operation can be best understood by referring to the block diagram in figure 1. when the voltage at the fb1 pin is slightly above 1.25v, comparator a1 disables most of the internal circuitry. output current is then provided by capacitor c2, which slowly discharges until the voltage at the fb1 pin goes below the hysteresis point of a1 (typical hysteresis at the fb1 pin is 8mv). a1 then enables the internal circuitry, turns on power switch q1, and the current in inductor l1 begins ramping up. once the switch current reaches 250ma, comparator a2 resets the one- shot, which turns off q1 for 300ns. q1 turns on again and the inductor currents ramp back up to 250ma, then a2 again resets the one-shot. this switching action continues until the output voltage is charged up (until the fb1 pin reaches 1.25v), then a1 turns off the internal circuitry and the cycle repeats. the second switching regulator is an inverting converter (which generates a negative output) but the basic operation is the same. shdn1 (pin 9): shutdown pin for switcher 1. pull this pin above 1.5v to enable switcher 1. pull below 0.3v to turn it off. do not leave this pin floating. fb1 (pin 10): feedback pin for switcher 1. set the output voltage by selecting values for r1 and r2. gnd (pin 11): exposed pad. solder this exposed pad directly to the local ground plane. this pad must be electrically connected for proper operation. uu u pi fu ctio s + + + 3 300ns one-shot 25mv lt3463: r s1 = r s2 = 0.1 LT3463A: r s1 = 0.1 , r s2 = 0.063 25mv 1.25v 1.25v a2 a1 q1 10 v in fb1 fb2 1 v out1 v out1 sw1 3463 f01 l1 v in v in r1 r2 v out1 v out2 v ref r4 r3 c1 c2 v out2 c3 + 300ns one-shot a4 a3 q2 11 8 4 7 6 5 sw2 gnd d2 d2 d1 d3 switcher 1 switcher 2 l2 2 c4 shdn2 shdn2 9 shdn1 shdn1 r s1 r s2
5 lt3463/LT3463A 3463f choosing an inductor several recommended inductors that work well with the lt3463 are listed in table 1, although there are many other manufacturers and devices that can be used. consult each manufacturer for more detailed information and for their entire selection of related parts. many different sizes and shapes are available. use the equations and recommenda- tions in the next few sections to find the correct inductance value for your design. table 1. recommended inductors max max height part l ( m h) i dc (ma) dcr( w ) (mm) manufacturer cmd4d06 4.7 750 0.22 0.8 sumida 10 500 0.46 (847) 956-0666 22 310 1.07 www.sumida.com cdrh3d16 10 500 0.19 1.8 sumida 22 310 0.36 lpo4812 4.7 600 0.16 1.2 coilcraft 10 400 0.30 (847) 639-6400 22 280 0.64 www.coilcraft.com lqh32c 10 450 0.39 1.8 murata 15 300 0.75 (714) 852-2001 22 250 0.92 www.murata.com lqh31c 4.7 340 0.85 1.8 murata inductor selectionboost regulator the formula below calculates the appropriate inductor value to be used for a boost regulator using the lt3463 (or at least provides a good starting point). this value pro- vides a good tradeoff in inductor size and system perfor- mance. pick a standard inductor close to this value. a larger value can be used to slightly increase the available output current, but limit it to around twice the value calculated below, as too large of an inductance will in- crease the output voltage ripple without providing much additional output current. a smaller value can be used (especially for systems with output voltages greater than 12v) to give a smaller physical size. inductance can be calculated as: l vv v i t out in min d lim off = -+ () where v d = 0.5v (schottky diode voltage), i lim = 250ma (or 400ma) and t off = 300ns; for designs with varying v in applicatio s i for atio wu u u such as battery powered applications, use the minimum v in value in the above equation. for most regulators with output voltages below 7v, a 4.7 m h inductor is the best choice, even though the equation above might specify a smaller value. for higher output voltages, the formula above will give large inductance values. for a 3v to 20v converter (typical lcd bias application), a 21 m h inductor is called for with the above equation, but a 10 m h inductor could be used without much reduction in the maximum output current. inductor selectioninverting regulator the formula below calculates the appropriate inductor value to be used for an inverting regulator using the lt3463 (or at least provides a good starting point). this value provides a good tradeoff in inductor size and system performance. pick a standard inductor close to this value (both inductors should be the same value). a larger value can be used to slightly increase the available output current, but limit it to around twice the value calculated below, as too large of an inductance will increase the output voltage ripple without providing much additional output current. a smaller value can be used (especially for systems with output voltages greater than 12v) to give a smaller physical size. inductance can be calculated as: l vv i t out d lim off = + ? ? ? ? ? 2 where v d = 0.5v (schottky diode voltage), i lim = 250ma (or 400ma) and t off = 300ns. for higher output voltages, the formula above will give large inductance values. for a 3v to 20v converter (typical lcd bias application), a 49 m h inductor is called for with the above equation, but a 10 m h or 22 m h inductor could be used without much reduction in the maximum output current. inductor selectioninverting charge pump regulator for the inverting regulator, the voltage seen by the internal power switch is equal to the sum of the absolute value of the input and output voltages, so that generating high
6 lt3463/LT3463A 3463f inrush current include a larger more abrupt voltage step at v in , a larger output capacitor tied to the outputs, and an inductor with a low saturation current. while the internal diode is designed to handle such events, the inrush current should not be allowed to exceed 1 amp. for circuits that use output capacitor values within the recommended range and have input voltages of less than 5v, inrush current remains low, posing no hazard to the device. in cases where there are large steps at v in and/or a large capacitor is used at the outputs, inrush current should be measured to ensure safe operation. setting the output voltages the output voltages are programmed using two feedback resistors. as shown in figure 1, resistors r1 and r2 program the positive output voltage (for switcher 1), and resistors r3 and r4 program the negative output voltage (for switcher 2) according to the following formulas: vv r r vv r r out out 1 2 125 1 2 1 125 4 3 =+ ? ? ? ? = ? ? ? ? . . r1 and r3 are typically 1% resistors with values in the range of 50k to 250k. board layout considerations as 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 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 rising and falling edges. minimize the length and area of all traces connected 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. applicatio s i for atio wu u u output voltages from a high input voltage source will often exceed the 50v maximum switch rating. for instance, a 12v to C 40v converter using the inverting topology would generate 52v on the sw pin, exceeding its maximum rating. for this application, an inverting charge pump is the best topology. the formula below calculates the approximate inductor value to be used for an inverting charge pump regulator using the lt3463. as for the boost inductor selection, a larger or smaller value can be used. for designs with varying v in such as battery powered applications, use the minimum v in value in the equation below. l vv v i t out in min d lim off = -+ () capacitor selection the small size and low esr of ceramic capacitors makes them ideal for lt3463 applications. use only x5r and x7r types because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. a 1 m f input capacitor and a 0.22 m f or 0.47 m f output capacitor are sufficient for most applications. table 2 shows a list of several ceramic capacitor manufacturers. consult the manufacturers for more detailed information on their entire selection of ceramic capacitors. for appli- cations needing very low output voltage ripple, larger output capacitor values can be used. table 2. recommended ceramic capacitor manufacturers manufacturer phone url avx 843-448-9411 www.avxcorp.com kemet 408-986-0424 www.kemet.com murata 814-237-1431 www.murata.com taiyo yuden 408-573-4150 www.t-yuden.com inrush current when v in is increased from ground to operating voltage while the output capacitor is discharged, an inrush current will flow through the inductor and integrated schottky diode into the output capacitor. conditions that increase
7 lt3463/LT3463A 3463f package descriptio u dd package 10-lead plastic dfn (3mm 3mm) (reference ltc dwg # 05-08-1699) 3.00 0.10 (4 sides) note: 1. drawing to be made a jedec package outline m0-229 variation of (weed-2). check the ltc website data sheet for current status of variation assignment 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 0.38 0.10 bottom view?xposed pad 1.65 0.10 (2 sides) 0.75 0.05 r = 0.115 typ 2.38 0.10 (2 sides) 1 5 10 6 pin 1 top mark (see note 6) 0.200 ref 0.00 ?0.05 (dd10) dfn 1103 0.25 0.05 2.38 0.05 (2 sides) recommended solder pad pitch and dimensions 1.65 0.05 (2 sides) 2.15 0.05 0.50 bsc 0.675 0.05 3.50 0.05 package outline 0.25 0.05 0.50 bsc 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package typical applicatio u v in v ref v out1 v out1 20v 9ma v out2 20v 9ma sw1 fb2 lt3463 8 11 l1 10 h shdn2 c2 0.47 f v in 2.7v to 5v 3463 ta02 gnd 4 sw2 5 321 d2 c4 0.1 f d1 c1 1 f fb1 9 6 7 10 shdn1 r2 1m r4 1m r3 61.9k r1 66.5k c3 0.47 f l2 10 h dual output 20v converter 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.
8 lt3463/LT3463A 3463f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear.com ? linear technology corporation 2003 lt/tp 0404 1k ? printed in usa related parts part number description comments lt1615/lt1615-1 300ma/80ma (i sw ), high efficiency step-up dc/dc converters v in : 1v to 15v, v out(max) : 34v, i q : 20 m a, i sd : <1 m a, thinsot package lt1944 dual output 350ma (i sw ), constant off-time, v in : 1.2v to 15v, v out(max) : 34v, i q : 20 m a, i sd : <1 m a, high efficiency step-up dc/dc converter ms package lt1944-1 dual output 150ma (i sw ), constant off-time, v in : 1.2v to 15v, v out(max) : 34v, i q : 20 m a, i sd : <1 m a, high efficiency step-up dc/dc converter ms package lt1945 dual output, pos/neg, 350ma (i sw ), v in : 1.2v to 15v, v out(max) : 34v, i q : 20 m a, i sd : <1 m a, constant off-time, high efficiency step-up dc/dc converter ms package lt3464 85ma (i sw ), high efficiency step-up dc/dc converter v in : 2.3v to 10v, v out(max) : 34v, i q : 25 m a, i sd : <1 m a, with integrated schottky and pnp disconnect thinsot package ccd bias supply u typical applicatio v in v ref v out1 v out1 15v 10ma v out2 ?v 50ma sw1 fb2 LT3463A 8 11 l1 10 h shdn2 c2 2.2 f v in 2.7v to 5v 3463 ta01a gnd 4 sw2 5 321 d2 c4 1 f d1 c1 4.7 f fb1 9 6 7 10 shdn1 r2 1m r4 1m c5 10pf c1: taiyo yuden jmk212bj475mg c2: taiyo yuden emk316bj225ml c3: taiyo yuden lmk316bj475ml c4: taiyo yuden emk212bj105mg c5: avx 06035a100kat2a d1: diodes, inc b0540w l1, l2: murata lqh32cn100k53 r3 154k r1 90.9k c3 4.7 f l2 10 h typical waveforms for 15v output typical waveforms for C8v output v sw1 10v/div v out1 ac-coupled 50mv/div i l1 200ma/div 2 m s/div 3463 ta04 v sw2 5v/div v out2 ac-coupled 50mv/div i l2 200ma/div 2 m s/div 3463 ta05
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