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1 lt1612 sn1612 1612fs operates from input voltage as low as 2v internal 0.7a synchronous switches uses ceramic input and output capacitors 620mv reference voltage 800khz fixed frequency switching programmable burst mode operation low quiescent current: 160 m a 8-lead msop or so package the lt 1612 is an 800khz, synchronous step-down dc/ dc converter that operates from an input voltage as lowas 2v. internal 0.45 w switches deliver output currents up to 500ma, and the 800khz switching frequency allows theuse of small, low value ceramic input and output capaci- tors. input voltage ranges from 5.5v down to 2v and output voltage can be set as low as the 620mv reference. the device features burst mode tm operation, keeping efficiency high at light loads. burst mode operation can bedefeated by pulling the mode pin high, enabling constant switching throughout the load range for low noise. no-load quiescent current is 160 m a and shutdown current is less than 1 m a. the device is available in 8-lead so and msop packages. portable devices lithium-ion step-down converters 5v to 3.3v conversion 2-cell alkaline step-down converters figure 1. 2v to 1.2v converter synchronous, step-down 800khz pwm dc/dc converter , ltc and lt are registered trademarks of linear technology corporation. burst mode is a trademark of linear technology corporation. v in 2v 0.1 f 33.2k r2 232k 1% r1 215k 1% l1 10 h 330pf c1 10 f c268 f 3.15v c1: taiyo-yuden jmk325bj106mnc2: panasonic eefcdof680r l1: sumida cd43-100 1612 f01a v out 1.2v500ma 100pf v in sw fb boost mode shdn v c gnd lt1612 load current (ma) efficiency (%) 9080 70 60 50 40 30 100 10 500 1612 ?f01b v in = 2v (linear) v in = 3v (linear) v in = 2v v in = 3v efficiency for lt1612 vs linear regulator v out = 1.2v applicatio s u features descriptio u typical applicatio n u downloaded from: http:///
2 lt1612 sn1612 1612fs symbol parameter conditions min typ max units i q quiescent current mode = 5v 12 m a mode = 0v, not switching 160 220 m a shdn = 0v 1 m a v fb fb voltage 0.605 0.62 0.635 v 0.60 0.62 0.635 v fb line regulation 0.02 0.15 %/v fb pin bias current (note 3) 75 0 n a g m error amplifier transconductance 250 m mhos min input voltage 2v max input voltage 5.5 v f osc oscillator frequency 700 800 900 khz 550 1100 khz f osc line regulation 1% / v maximum duty cycle 85 90 % 80 % shutdown threshold minimum voltage for active 2v maximum voltage for shutdown 0.2 v lt1612ems8 t jmax = 125 c, q ja = 200 c/ w order part number supply voltage (v in ) ............................................... 5.5v sw pin voltage ....................................................... 5.5v fb pin voltage ............................................... v in + 0.3v v c pin voltage ........................................................... 2v shdn pin voltage ................................................... 5.5v mode pin voltage .................................................. 5.5v (note 1) absolute m axi m u m ratings w ww u package/order i n for m atio n w u u electrical characteristics consult factory for parts specified with wider operating temperature ranges. boost pin voltage ....................................... v in + 5.5v junction temperature ........................................... 125 c 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 lt1612es8 order part number ms8 part marking t jmax = 125 c, q ja = 120 c/ w s8 part marking 1612 the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c, v in = v shdn = 3v v c fb v in gnd 12 3 4 87 6 5 shdnmode boost sw top view ms8 package 8-lead plastic msop top view shdnmode boost sw v c fb v in gnd s8 package 8-lead plastic so 12 3 4 87 6 5 ltms downloaded from: http:///
3 lt1612 sn1612 1612fs symbol parameter conditions min typ max units shdn pin current shdn = 2v 10 15 m a shdn = 5v 30 45 m a boost pin current boost = v in + 2v 4 ma switch current limit (note 4) duty cycle = 0% mode = ov 600 710 900 ma mode = 5v 550 650 900 ma burst mode operation current limit mode = 0v 180 ma switch voltage drop i sw = 500ma 200 280 mv rectifier voltage drop i rect = 500ma 300 400 mv sw pin leakage v sw = 5v, v shdn = 0v 1 m a note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired.note 2: the lt1612e is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the ?0 c to 85 c operating electrical characteristics the denotes specifications which apply over the full operating temperature range, otherwise specifications are t a = 25 c, v in = v shdn = 3v temperature range are assured by design, characterization and correlationwith statistical process controls. note 3: bias current flows out of the fb pin. note 4: duty cycle affects current limit due to slope compensation. typical perfor a ce characteristics uw fb voltage vs temperature quiescent current vs temperature fb pin bias current temperature ( c) 50 ?5 25 75 quiescent current ( a) 50 190180 170 160 150 140 130 120 110 100 1612 ? g02 0 100 mode = 0v temperature ( c) ?0 fb pin current (na) ?5 0 50 75 1612 ?g03 100 0 ?? ? ? ?0?2 ?4 ?6 ?8 ?0 25 temperature ( c) ?0 fb voltage (v) 0.640.63 0.62 0.61 0.60 0.59 ?5 02 55 0 1612 ?g01 75 100 downloaded from: http:///
4 lt1612 sn1612 1612fs typical perfor a ce characteristics uw shdn pin bias current switch current limit vstemperature oscillator frequency vstemperature maximum duty cycle vstemperature switch voltage drop rectifier voltage drop shdn pin voltage (v) 0 shdn pin current ( a) 3 5 1612 ?g04 12 4 8070 60 50 40 30 20 10 0 temperature ( c) ?0 switch current (ma) 800700 600 500 400 300 200 ?5 02 55 0 1612 ?g05 75 100 mode = 0v mode = 5v temperature ( c) ?0 oscillator frequency (khz) 1000 900800 700 600 500 400 ?5 02 55 0 1612 ?g06 75 100 temperature ( c) ?0 maximum duty cycle (%) 9490 86 82 78 74 70 ?5 02 55 0 1612 ?g07 75 100 switch current (ma) 0 switch voltage drop (mv) 600500 400 300 200 100 0 100 200 300 400 1612 ?g08 500 600 rectifier current (ma) 0 rectifier voltage drop (mv) 600500 400 300 200 100 0 100 200 300 400 1612 ?g09 500 600 downloaded from: http:///
5 lt1612 sn1612 1612fs v c (pin 1): compensation pin. this is the current sink/ source output of the error amplifier. by connecting an rcnetwork from this pin to ground, frequency response can be tuned for a wide range of circuit configurations. the voltage at this pin also sets the current limit, and if grounded, the switch will remain in the off state. fb (pin 2): feedback pin. this pin is the negative input to the error amplifier. connect the resistor divider tap to thispoint which sets v out according to: v out = 0.62v (1 + r1/r2) v in (pin 3): supply pin. bypass capacitor c1 must be right next to this pin.gnd (pin 4): ground pin. connect directly to local ground plane. pi n fu n ctio n s uuu sw (pin 5): switch pin. connect inductor and boost capacitor here. minimize trace area at this pin to keep emidown. boost (pin 6): this is the supply pin for the switch driver and must be above v in by 1.5v for proper switch opera- tion. connect the boost capacitor to this pin.mode (pin 7): burst mode operation disable pin. for continuous switching operation (low noise), pull this pinabove 2v. for burst mode operation which gives better light load efficiency, tie to ground. output ripple voltage in burst mode operation is typically 30mv p-p . see applica- tions section for more information about this function.shdn (pin 8): shutdown pin. pull this pin low for shut- down mode. tie to a voltage between 2v and 5.5v fornormal operation. block diagra w + r sense 0.08 + a1 v/i slopecompensation switch swgnd 1612 bd boost a3 enable + a2 0.62v 0.7v boost diode switch driver v in v c fb rectifier rectifier drive 3 12 5 4 6 mode 7 8 shdn shutdown oscillator rq s flip-flop downloaded from: http:///
6 lt1612 sn1612 1612fs figure 2. recommended component placement. tracescarrying high current are direct. trace area at fb pin and v c pin is kept low. lead length to battery should be kept short 12 87 34 65 l1 c2 r1 c3 lt1612 v out v in gnd shdn 1612 f02 mode multiple vias c1 r2 r c c c operatio u the lt1612 employs fixed frequency, current mode con-trol. this type of control uses two feedback loops. the main control loop sets output voltage and operates as follows: a load step causes v out and the fb voltage to be perturbed slightly. the error amplifier responds to thischange in fb by driving the v c pin either higher or lower. because switch current is proportional to the v c pin voltage, this change causes the switch current to beadjusted until v out is once again satisfied. loop compen- sation is taken care of by an rc network from the v c pin to ground.inside this main loop is another that sets current limit on a cycle-by-cycle basis. this loop utilizes current compara- tor a2 to control peak current. the oscillator runs at 800khz and issues a set pulse to the flip-flop at the beginning of each cycle, turning the switch on. with the switch now in the on state the sw pin is effectively connected to v in . current ramps up in the inductor linearly at a rate of (v in ?v out )/l. switch current is set by the v c pin voltage and when the voltage across r sense trips the current comparator, a reset pulse will be generated and theswitch will be turned off. since the inductor is now loaded up with current, the sw pin will fly low and trigger the rectifier to turn on. current will flow through the rectifier decreasing at a rate of v out /l until the oscillator issues a new set pulse, causing the cycle to repeat.if the load is light and v c decreases below a3? trip point, the device will enter the burst mode operation region (themode pin must be at ground or floating). in this state the oscillator and all other circuitry except the reference and comparator a3 are switched on and off at low frequency. this mode of operation increases efficiency at light loads but introduces low frequency voltage ripple at the output. for continuous switching and no low frequency output voltage ripple, pull the mode pin high. this will disable comparator a3 which forces the oscillator to run continuously. layout hintsthe lt1612 switches current at high speed, mandating careful attention to layout for proper performance. you will not get advertised performance with careless layout . figure 2 shows recommended component placement fora buck (step-down) converter. follow this closely in your pc layout. note the direct path of the switching loops. input capacitor c1 must be placed close (< 5mm) to the ic package. as little as 10mm of wire or pc trace from c in to v in will cause problems such as inability to regulate or oscillation.the ground terminal of input capacitor c1 should tie close to pin 4 of the lt1612. doing this reduces di/dt in the ground copper which keeps high frequency spikes to a minimum. the dc/dc converter ground should tie to the pc board ground plane at one place only, to avoid intro- ducing di/dt in the ground plane. downloaded from: http:///
7 lt1612 sn1612 1612fs operatio u figure 3. output voltage ripple is 20mv p-p for the circuit of figure 1 burst mode operation defeatto maintain high efficiency at light loads, the lt1612 will automatically shift into burst mode operation (mode = 0v or floating). in this mode of operation the oscillator and switch drive circuitry is alternately turned on and off, reducing quiescent current to 160 m a. this reduces power consumption but also adds low frequency voltage ripple tothe output. figure 3 shows switching waveforms for a 5v to 3.3v converter running in burst mode operation. output voltage ripple is approximately 20mv p-p . if the mode pin is pulled high, burst mode operation will be inhibited andthe oscillator runs continuously with no low frequency ripple at the output. see figures 4 and 5. figure 4. transient response for the circuit of figure 1with the mode pin tied to ground or floating figure 5. with the mode pin tied high, lowfrequency output voltage ripple is no longer present 1612 f03 v out 20mv/div ac coupled il 200ma/div 5 m s/div 1612 f04 v out 200mv/div ac coupled i load 10ma to 310ma 0.1ms/div i l 200ma/div 1612 f05 v out 200mv/div ac coupled i load 10ma to 300ma 0.1ms/div i l 200ma/div downloaded from: http:///
8 lt1612 sn1612 1612fs v in v in 2.7v to 4.2v sw fb boost mode shdn v c 0.1 f 30.1k 453k 1% 1m 1% l1 10 h 680pf 10 f ceramic gnd lt1612 22 f ceramic c1: taiyo-yuden lmk325bj106mnc2: taiyo-yuden lmk325bj226mn l1: sumida cd43-100 1612 ta02 v out 2v500ma 20pf load current (ma) 1 efficiency (%) 8580 75 70 65 60 55 50 10 100 1000 1612 ta04 v in = 2.8v v in = 4.2v v in = 3.5v single li-ion to 2v converter burst mode operation li-ion to 2v converter efficiency inrush current at start-up v out 2v/div v shdn 5v/div inrush current 200ma/div 0.2ms/div 1612 ta06 typical applicatio n s u 100 m s/div transient response 1612 ta03 v in = 4v v out = 2v mode = high load step 125ma to 300ma i l 200ma/div v out 50mv/div v out 20mv/div i l 100ma/div mode = low 1612 ta05 5 m s/div downloaded from: http:///
9 lt1612 sn1612 1612fs v in v in 5v sw fb boost mode shdn v c 0.1 f 30.1k 332k 1m l1 10 h 680pf c1 10 f ceramic gnd lt1612 c222 f ceramic c1: taiyo-yuden lmk325bj106mnc2: taiyo-yuden lmk325bj226mn l1: sumida cd43-100 1612 ta07 v out 2.5v500ma 20pf load current (ma) 1 efficiency (%) 8580 75 70 65 60 55 50 10 100 1000 1612 ta08 5v to 2.5v converter 5v to 2.5v converter efficiency typical applicatio n s u v in v in 2v sw fb boost mode shdn v c 0.1 f 33.2k r2 232k r1 105k l1 10 h 330pf c1 10 f gnd lt1612 c268 f 3.15v c1: taiyo-yuden jmk325bj106mnc2: panasonic eefcdof680r l1: sumida cd43-100 1612 ta09 v out 0.9v500ma 100pf load current (ma) 1 efficiency (%) 8070 60 50 40 30 20 10 10 100 1000 1612 ta10 v in = 2v v in = 2v (linear) v in = 3v (linear) v in = 3v 2v to 0.9v converter efficiency for lt1612 vs linear regulator. v out = 0.9v. downloaded from: http:///
10 lt1612 sn1612 1612fs ms8 package 8-lead plastic msop (ltc dwg # 05-08-1660) dimension in inches (millimeters) unless otherwise noted. package descriptio n u msop (ms8) 1100 * dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.006" (0.152mm) per side ** dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.006" (0.152mm) per side 0.021 0.006 (0.53 0.015) 0 ?6 typ seating plane 0.007 (0.18) 0.043 (1.10) max 0.009 ?0.015 (0.22 ?0.38) 0.005 0.002 (0.13 0.05) 0.034 (0.86) ref 0.0256 (0.65) bsc 12 3 4 0.193 0.006 (4.90 0.15) 8 7 6 5 0.118 0.004* (3.00 0.102) 0.118 0.004** (3.00 0.102) downloaded from: http:///
11 lt1612 sn1612 1612fs dimension in inches (millimeters) unless otherwise noted. package descriptio n u 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. s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 0.016 ?0.050 (0.406 ?1.270) 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) so8 1298 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) typ 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** downloaded from: http:///
12 lt1612 sn1612 1612fs lt/tp 1100 4k ? printed in usa ? linear technology corporation 1999 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear-tech.com related parts part number description comments ltc 1474 low i q step-down switching regulator 10 m a i q , v in from 3v to 18v, msop package up to 300ma lt1616 600ma, 1.4mhz step-down regulator in sot-23 v in from 3.6v to 25v, sot-23 package ltc1701 sot-23 step-down switching regulator 500ma in sot-23 package, 1mhz switching frequency ltc1707 monolithic synchronous step-down switching regulator 500ma, v in from 2.65v to 8.5v ltc1772 constant frequency step-down controller in sot-23 high current, high efficiency: up to 94% ltc1877/ltc1878 high efficiency, monolithic synchronous step-down regulator 10 m a i q , 2.65 v in 10v, msop package up to 600ma ltc3404 1.4mhz high efficiency monolithic synchronous step-down reg 10 m a i q , high efficiency: up to 95%, msop package v in 5v c3 0.1 f r333.2k r2 232k 1% r1 1m 1% l1 10 h c4680pf c1 10 f c222 f c1: taiyo-yuden lmk325bj106mnc2: taiyo-yuden lmk325bj226mn l1: sumida cd43-100 1612 ta01a v out 3.3v500ma 20pf v in sw fb boost mode shdn v c gnd lt1612 load current (ma) 1 efficiency (%) 8580 75 70 65 60 55 50 10 100 1000 1612 ta01b v in = 5v v out = 3.3v efficiency 5v to 3.3v converter u typical applicatio downloaded from: http:///

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