1 LT1300 n up to 220ma output current at 5v from 2v supply n supply voltage as low as 1.8v n up to 88% efficiency n small inductor C10 m h n 120 m a quiescent current n shutdown to 10 m a n programmable 3.3v or 5v output n i lim pin programs peak switch current n low v cesat switch: 170mv at 1a typical n uses inexpensive surface mount inductors n 8-lead dip or soic package n palmtop computers n portable instruments n bar-code scanners n dc/dc converter module replacements n battery backup supplies n personal digital assistants n pcmcia cards the LT1300 is a micropower step-up dc/dc converter that utilizes burst mode? operation. the device can deliver 5v or 3.3v from a two-cell battery input. it features program- mable 5v or 3.3v output via a logic-controlled input, no- load quiescent current of 120 m a and a shutdown pin which reduces supply current to 10 m a. the on-chip power switch has a low 170mv saturation voltage at a switch current of 1a, a four-fold reduction over prior designs. a 155khz internal oscillator allows the use of extremely small sur- face mount inductors and capacitors. operation is guaran- teed at 1.8v input. this allows more energy to be extracted from the battery increasing operating life. the i lim pin can be used to program peak switch current with a single resistor allowing the use of less expensive and smaller inductors and capacitors in lighter load applications. the LT1300 is available in an 8-lead soic package, minimizing board space requirements. for a 5v/12v selectable out- put converter see the lt1301. for increased output cur- rent see the lt1302. descriptio n u features typical applicatio n s n u micropower high efficiency 3.3/5v step-up dc/dc converter applicatio n s u two-cell to 3.3v/5v step-up converter 5v output efficiency l1 = coilcraft do1608-103 or sumida cd54-100 c1 = avx tpsd107m010r0100 or sanyo os-con 16sa100m d1 = mbrs130lt3 or 1n5817 c1
100?
5v/3.3v
output + + l1
10? d1 c1
100? 2
aa
cell sw i lim pgnd gnd sense LT1300 select LT1300 ta1 5v/3.3v
select shdn shutdown n/c 2 67 4 5 81 3 v in
load current (ma) 10 100 500 LT1300 ta2 1 74 efficiency (%) 76 78 80 82 90 84 86 88 v in = 4.0v v in = 3.0v v in = 2.5v v in = 2.0v burst mode is a trademark of linear technology corporation.
2 LT1300 order part number absolute m axi m u m ratings w ww u package/order i n for m atio n w u u v in voltage .............................................................. 10v sw1 voltage ............................................................ 20v sense voltage .......................................................... 10v shutdown voltage................................................ 10v select voltage ....................................................... 10v i lim voltage ............................................................ 0.5v maximum power dissipation ............................. 500mw operating temperature range ..................... 0 c to 70 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c s8 part marking t jmax = 100 c, q ja = 150 c/ w 1300 LT1300cn8 LT1300cs8 consult factory for industrial grade parts. symbol parameter conditions min typ max units i q quiescent current v shdn = 0.5v, v sel = 5v, v sense = 5.5v l 120 200 m a v shdn = 1.8v l 715 m a v in input voltage range 1.8 v l 2.0 v v out output sense voltage v sel = 5v l 4.80 5.0 5.20 v v sel = 0v l 3.15 3.3 3.45 v output referred v sel = 5v (note 1) l 22 50 mv comparator hysteresis v sel = 0v (note 1) l 14 35 mv oscillator frequency current limit not asserted. see test circuit. 120 155 185 khz oscillator tc 0.2 %/ c dc maximum duty cycle 75 86 95 % t on switch on time current limit not asserted. 5.6 m s output line regulation 1.8v < v in < 6v l 0.06 0.15 %/v v cesat switch saturation voltage i sw = 700ma l 130 200 mv switch leakage current v sw = 5v, switch off l 0.1 10 m a peak switch current i lim floating (see typical application) 0.75 1.0 1.25 a (internal trip point) i lim grounded 0.4 a v shdnh shutdown pin high l 1.8 v v shdnl shutdown pin low 0.5 v v selh select pin high l 1.5 v v sell select pin low l 0.8 v i shdn shutdown pin bias current v shdn = 5v l 920 m a v shdn = 2v l 3 m a v shdn = 0v l 0.1 1 m a i sel select pin bias current 0v < v sel < 5v l 13 m a electrical characteristics t a = 25 c, v in = 2v unless otherwise noted. note 1: hysteresis specified is dc. output ripple may be higher if output capacitance is insufficient or capacitor esr is excessive. see applications section. the l denotes specifications which apply over the 0 c to 70 c temperature range. 1
2
3
4 8
7
6
5
top view gnd
sel
shdn
sense pgnd
sw
v in
i lim n8 package
8-lead plastic dip
s8 package
8-lead plastic soic
3 LT1300 typical perfor m a n ce characteristics u w no-load battery current total quiescent current in shutdown switch current (a) 0 0.1 v cesat (mv) 150 125 200 175 250 225 0.8 0.9 LT1300 g5 100 75 50 25 0 0.2 0.3 0.4 0.5 0.6 0.7 1 maximum output current vs input voltage maximum output current vs input voltage 200 m s/div 0 transient response v in = 2v, v out = 5v startup response v cesat vs i sw efficiency shutdown pin bias current v out 100mv/div ac coupled v out 1v/div v shdn 10v/div LT1300 g8 shutdown voltage (v) 0 0 shutdown current (?) 2 6 8 10 20 14 2 4 5 LT1300 g4 4 16 18 12 13 6 7 8 t a = 25? load current (ma) 1 74 efficiency (%) 76 78 80 82 10 100 1000 LT1300 g1 72 70 68 66 84 86 88 v in = 3v v in = 2v v in = 2.5v v out = 3.3v
l = 10? input voltage (v) 1.4 input current (?) 150 145 160 155 170 165 3.0 2.8 LT1300 g2 140 135 130 125 120 1.8 1.6 2.2 2.0 2.6 2.4 3.4 3.2 v out = 5v v out = 3.3v input voltage (v) 0 i shdn + i vin + i sense (?) 40 50 60 8 LT1300 g3 30 20 0 2 4 6 10 80 70 1 3 5 7 input voltage (v) 1.5 output current (ma) 500 600 700 34 LT1300 g6 400 300 2 2.5 3.5 4.5 200 100 0 v out = 5v,
i lim floating l = 22?
coilcraft
do3316-223 l = 10?
coilcraft
do1608-103 input voltage (v) 1.5 0 load current (ma) 100 300 400 500 2.5
3 3.5 900 LT1300 g7 200 2
600 700 800 l = 10? v out = 3.3v
i lim floating v out = 5v r load = 20 w LT1300 g9 500 m s/div 200ma i load
4 LT1300 pi n fu n ctio n s uuu gnd (pin 1): signal ground. sel (pin 2): output select. when tied to v in or v out converter regulates at 5v. when grounded converter regulates at 3.3v. shdn (pin 3): shutdown. pull high to effect shutdown. tie to ground for normal operation. sense (pin 4): output pin. i lim (pin 5): float for 1a switch current limit. tie to ground for approximately 400ma. a resistor between i lim and ground sets peak current to some intermediate value (see figure 5). v in (pin 6): supply pin. must be bypassed with a large value electrolytic to ground. a 0.1 m f ceramic capacitor close to the pin may be needed in some cases. sw (pin 7): switch pin. connect inductor and diode here. keep layout short and direct to minimize electronic radia- tion. pgnd (pin 8): power ground. tie to signal ground (pin 1) under the package. bypass capacitor from v in should be tied directly to the pin. figure 1. block diagra m w oscillator
155khz r2
730 w c2
sw r1
3 w q2
1x q1
160x 18mv off v in v in i lim pgnd v out enable a1
comparator + + + + 1.25v
reference
l1 d1 7 2 4 sense a2 current
comparator a3 driver bias q3 8.5k 58 shutdown 3 select 2 gnd 161k 144k 500k c1 1 LT1300 f1
5 LT1300 test circuit s
oscillator test circuit operatio n u 20 m s/div reduced by tying the i lim pin to ground, causing 15 m a to flow through r2 into q3s collector. q3s current causes a 10.4mv drop in r2 so that only an additional 7.6mv is required across r1 to turn off the switch. this corre- sponds to a 400ma switch current as shown in figure 2, trace b. the reduced peak switch current reduces i 2 r loses in q1, l1, c1 and d1. efficiency can be increased by doing this provided that the accompanying reduction in full load output current is acceptable. lower peak currents also extend alkaline battery life due to the alkaline cells high internal impedance. typical operating waveforms are shown in figure 3. operation of the LT1300 is best understood by referring to the block diagram in figure 1. when a1s negative input, related to the sense pin voltage by the appropriate resis- tor-divider ratio, is higher that the 1.25v reference voltage, a1s output is low. a2, a3 and the oscillator are turned off, drawing no current. only the reference and a1 consume current, typically 120 m a. when the voltage at a1s nega- tive input decreases below 1.25v, overcoming a1s 6mv hysteresis, a1s output goes high, enabling the oscillator, current comparator a2, and driver a3. quiescent current increases to 2ma as the device prepares for high current switching. q1 then turns on in a controlled saturation for (nominally) 5.3 m s or until current comparator a2 trips, whichever comes first. after a fixed off-time of (nominally) 1.2 m s, q1 turns on again. the LT1300s switching causes current to alternately build up in l1 and dump into capaci- tor c2 via d1, increasing the output voltage. when the output is high enough to cause a1s output to go to low, switching action ceases. c2 is left to supply current to the load until v out decreases enough to force a1s output high, and the entire cycle repeats. if switch current reaches 1a, causing a2 to trip, switch on- time is reduced and off-time increases slightly. this allows continuous mode operation during bursts. current com- parator a2 monitors the voltage across 3 w resistor r1 which is directly related to inductor l1s current. q2s collector current is set by the emitter-area ratio to 0.6% of q1s collector current. when r1s voltage drop exceeds 18mv, corresponding to 1a inductor current, a2s output goes high, truncating the on-time portion of the oscillator cycle and increasing off-time to about 2 m s as shown in figure 2, trace a. this programmed peak current can be figure 3. burst mode operation in action trace b 500ma/div i lim pin grounded LT1300 f2 figure 2. switch pin current with i lim floating or grounded trace a 500ma/div i lim pin open v out 20mv/div ac coupled v sw 5v/div i sw ia/div 20 m s/div LT1300 f2 2v 100? v in sel sense gnd pgnd shdn sw LT1300 i l 100 w 5v f out
6 LT1300 applicatio n s i n for m atio n wu u u output voltage selection the LT1300 can be selected to 3.3v or 5v under logic control or fixed at either by tying select to ground or v in respectively. it is permissible to tie select to a voltage higher than v in as long as it does not exceed 10v. efficiency in 3.3v mode will be slightly less that in 5v mode due to the fact that the diode drop is a greater percentage of 3.3v than 5v. since the bipolar switch in the LT1300 gets its base drive from v in , no reduction in switch efficiency occurs when in 3.3v mode. when v in exceeds the programmed output voltage the output will follow the input. this is characteristic of the simple step-up or boost converter topology. a circuit example that pro- vides a regulated output with an input voltage above or below the output (called a buck-boost or sepic) is shown in the typical applications section. shutdown the converter can be turned off by pulling shdn (pin 3) high. quiescent current drops to 10 m a in this condition. bias current of 3 m a to 5 m a flows into the pin (at 2.5v input). it is recommended that shdn not be left floating. tie the pin to ground if the feature is not used. i lim function the LT1300s current limit (i lim ) pin can be used for soft start. upon start-up, switching regulators require maxi- mum current from the supply. the high currents flowing can create ir drops along supply and ground lines and are especially demanding on alkaline batteries. by in- stalling an r1 and c3 as shown in figure 4, the switch current in the LT1300 is limited to 400ma until the 15 m a flowing out of the i lim pin charges up the 0.1 m f capaci- tor. input current is held to under 500ma while the output voltage ramps up to 5v as shown in figure 5. the 1meg resistor provides a discharge path for the capacitor without appreciably decreasing peak switch current. when the full capability of the LT1300 is not required, peak current can be reduced by changing the value of r3 as shown in figure 6. with r3 = 0, switch current is limited to approximately 400ma. figure 4. addition of r1 and c3 limit input current at startup 500 m s/div rep rate = 1hz LT1300 f5 v out 2vdiv i battery 500ma/div v shdn 10v/div c2
100?
c3
0.1?
r1
1m 5v/3.3v
output + + l1
10? d1 c1
100? sw i lim pgnd gnd sense LT1300 shdn select v in figure 5. startup waveforms using soft-start circuitry i load = 100ma, v out = 5v r lim ( w ) 500 switch current (ma) 700 800 1000 1100 100 10k 100k 1m LT1300 f1b 300 1k 900 600 400 1.6v v in 5v figure 6. peak switch current vs. r lim
7 LT1300 component part number vendor l ( m h) dcr ( w )i lim pin 50ma load 200ma load height (mm) phone number do1608-103 coilcraft 10 0.11 float 83 83 3.5 (708) 639C6400 do3316-223 coilcraft 22 0.050 float 85 85 5.5 do1608-223 coilcraft 22 0.31 ground 85 3.5 ctx10-1 coiltronics 10 0.038 float 85 85 4.2 (407) 241C7876 ctx20-1 coiltronics 20 0.175 ground 86 4.2 lqh3c2204k0m00 murata-frie 22 0.7 ground 81 2.0 (404) 436C1300 cd54-100m sumida 10 0.11 float 85 85 4.5 (708) 956C0666 cdrh62-220m sumida 22 0.38 ground 84 3.0 cdrh62-100m sumida 10 0.17 float 81 82 3.0 ga10-102k gowanda 10 0.038 float 85 86 6.6 through-hole (716) 532C2234 applicatio n s i n for m atio n wu u u table 1. recommended inductors inductor selection for full output power, the inductor should have a satura- tion current rating of 1.25a for worst-case current limit, although it is acceptable to bias an inductor 20% or more into saturation. smaller inductors can be used in conjunc- tion with the i lim pin. efficiency is significantly affected by inductor dcr. for best efficiency limit the dcr to 0.03 w or less. toroidal types are preferred in some cases due to their closed design and inherent emi/rfi superiority. recommended inductors are listed in table 1. capacitor selection low esr capacitors are required for both input and output of the LT1300. esr directly affects ripple voltage and efficiency. for surface mount applications avx tps series tantalum capacitors are recommended. these have been specially designed for smps and have low esr along with high surge current ratings. for through-hole application sanyo os-con capacitors offer extremely low esr in a small size. again, if peak switch current is reduced using the i lim pin, capacitor requirements can be relaxed and smaller, higher esr units can be used. low frequency output ripple can be reduced by adding multiple output capacitors. if capacitance is reduced, output ripple will increase. suggested capacitor sources are listed in table 2. table 2. recommended capacitors vendor series type phone# avx tps surface mount (803)448C9411 sanyo os-con through-hole (619) 661C6835 panasonic hfq through-hole (201) 348C5200 diode selection best performance is obtained with a schottky rectifier diode such as the 1n5817. phillips components makes this in surface mount as the prll5817. motorola makes the mbrs130lt3 which is slightly better and also in surface mount. for lower output power a 1n4148 can be used although efficiency will suffer substantially. layout considerations the LT1300 is a high speed, high current device. the input capacitor must be no more than 0.2" from v in (pin 6) and ground. connect the pgnd and gnd (pins 8 and 1) together under the package. place the inductor adjacent to sw (pin 7) and make the switch pin trace as short as possible. this keeps radiated noise to a minimum. efficiency 2.5v in , 5v out 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 LT1300 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7487 (408) 432-1900 l fax : (408) 434-0507 l telex : 499-3977 1 2 3 4 0.150 ?0. (3.810 ?3. 8 7 6 5 0.189 ?0.197*
(4.801 ?5.004) 0.228 ?0.244
(5.791 ?6.197) 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 0294 0.053 ?0.069
(1.346 ?1.752) 0.014 ?0.019
(0.355 ?0.483) 0.004 ?0.010
(0.101 ?0.254) 0.050
(1.270)
bsc *these dimensions do not include mold flash or protrusions.
mold flash or protrusions shall not exceed 0.006 inch (0.15mm). s8 package 8-lead plastic s0ic typical applicatio n s n u ? linear technology corporation 1994 lt/gp 0394 10k ? printed in usa package descriptio n u dimensions in inches (millimeters) unless otherwise noted. four-cell to 5v/3.3v up-down converter n8 package 8-lead plastic dip n8 0392 0.009 ?0.015
(0.229 ?0.381) 0.300 ?0.320
(7.620 ?8.128) 0.325 +0.025
0.015 +0.635
0.381 8.255 () 0.045 ?0.015
(1.143 ?0.381) 0.100 ?0.010
(2.540 ?0.254) 0.065
(1.651)
typ 0.045 ?0.065
(1.143 ?1.651) 0.130 ?0.005
(3.302 ?0.127) 0.020
(0.508)
min 0.018 ?0.003
(0.457 ?0.076) 0.125
(3.175)
min
12 3 4 87 6 5 0.250 ?0.010
(6.350 ?0.254)
0.400
(10.160)
max + 100? 22?
35v contrast
v out 4v to ?9v 12ma
maximum from 1.8v supply
(77% efficient)
20ma maximum from
3v supply (83% efficient) 2.2? sw pwm in
0% to 100%
cmos drive 0v to 5v 150k 12k 12k 1 10 8 2 9 3 7 4 i lim pgnd gnd sense LT1300 select LT1300 ta6 1n5819 t1 t1 = dale lpe-5047-ao45 (605) 665-9301 shdn shutdown n/c n/c v in v in
1.8v to 6v + + 1n5817 2n4403 5v, 200ma + l1*
10? *sumida cd54-100lc
coilcraft do3316-223 100? 100? 470 w 0.1? 2
aa
cell sw i lim pgnd gnd sense LT1300 select LT1300 ta5 shdn nc shutdown v in
+ step-up converter with automatic output disconnect lcd contrast supply 1n5817 5v/3.3v
220ma
80% efficient + l1*
27? *l1, l2 = gowanda ga20-272k
coilcraft do3316-273k
sumida cd73-270k
**c1, c2, c3 = sanyo os-con 16sa100m l2*
27? c1**
100? c2**
100? c3**
100? 4
aa
cell sw i lim pgnd gnd sense LT1300 select LT1300 ta3 5v/3.3v 2.5v v in 8v shdn shutdown n/c v in
+ +
|
