lt1176/lt1176-5 1 11765fb typical application features description step-down switching regulator the lt ? 1176 is a 1a monolithic bipolar switching regulator which requires only a few external parts for normal opera- tion. the power switch, all oscillator and control circuitry basic 5v positive buck converter applications n 1.2a onboard switch n 100khz switching frequency n excellent dynamic behavior n dip and surface mount packages n only 8ma quiescent current n preset 5v output available n operates up to 35v input n micropower shutdown mode n buck converter with output voltage range of 2.5v to 30v n positive-to-negative converter n negative boost converter n multiple output buck converter l , lt, ltc, ltm, linear technology, switchercad and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. and all current limit components are included on the chip. the topology is a classic positive buck configuration but several design innovations allows this device to be used as a positive-to-negative converter, a negative boost converter, and as a flyback converter. the switch output is specified to swing below ground. the lt1176 uses a true analog multiplier in the feedback loop. this makes the device respond nearly instantaneously to input voltage fluctuations and makes loop gain indepen- dent of input voltage. as a result, dynamic behavior of the regulator is significantly improved over previous designs. on-chip pulse by pulse current limiting makes the lt1176 nearly bust proof for output overloads or shorts. the input voltage range as a buck converter is 8v to 35v, but a self boot feature allows input voltages as low as 5v in the inverting and boost configurations. the lt1176 is available in a low cost 8-lead dip package with frequency preset at 100khz and current limit at 1.7a. an adjustable output is offered as well as a preset 5v ver - sion. for further design details and application help, see the lt1074/lt1076 data sheet and application note 44. 5v buck converter efficiency v c gnd lt1176-5 r3 2.7k c2 0.01f 1n5819 + c3 100f + c1 470f 25v 11765 ta01 5v, 0.8a 10v t0 35v l1* 100h *coiltronics #100-1-52 pulse engineering, inc. #pe-92102 hurricane #hl-ag210ll these are low cost powdered iron cores. optimum efficiency and smallest size is obtained by using a low loss core such as magnetics inc. kool m. see efficiency graph. v in v sw sense load current (a) 60 efficiency (%) 70 80 90 0.2 0.4 0.6 0.8 11765 ta02 1.0 0.1 0.3 0.5 0.7 0.9 l = 100h on magnetics inc. size t-50 kool m core v in = 20v v in = 10v
lt1176/lt1176-5 2 11765fb pin configuration absolute maximum ratings input voltage ............................................................. 38v switch voltage with respect to input voltage ........... 50v switch voltage with respect to ground pin (v sw negative) (note 7) ............................................ 20v feedback pin voltage ........................................ C2v, 10v shutdown pin voltage (not to exceed v in ) ............... 35v status pin voltage (current must be limited to 5ma when status pin switches on) ........................................................ 30v 1 2 3 4 8 7 6 5 top view v in i lim gnd fb/sense v sw v c status shutdown n8 package 8-lead plastic dip t jmax = 125c, ja = 90c/w 1 2 3 4 5 6 7 8 9 10 top view sw package 20-lead plastic sol 20 19 18 17 16 15 14 13 12 11 v in nc i lim gnd gnd gnd gnd nc fb/sense nc v sw nc v c gnd gnd gnd gnd status shutdown nc t jmax = 125c, ja = 50c/w order information lead free finish tape and reel part marking* package description temperature range lt1176cn8#pbf lt1176cn8 8-lead plastic dip 0c to 125c lt1176cn8-5#pbf lt1176cn8-5 8-lead plastic dip 0c to 125c lt1176csw#pbf lt1176csw#trpbf lt1176csw 20-lead plastic sol 0c to 125c lt1176csw-5#pbf lt1176csw-5#trpbf lt1176csw-5 20-lead plastic sol 0c to 125c consult ltc marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a label on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ i lim pin voltage (forced) ......................................... 5.5v maximum operating ambient temperature range lt1176c/lt1176c-5 ................................. 0c to 70c maximum operating junction temperature range lt1176c/lt1176c-5 ............................... 0c to 125c storage temperature range .................. C65c to 150c lead temperature (soldering, 10 sec) ................... 300c *these thermal resistance numbers are for typical mounting technique. lower thermal resistance can be obtained with large copper lands, thermal glues or heat sinks. (note 1)
lt1176/lt1176-5 3 11765fb electrical characteristics parameter conditions min typ max units switch on voltage (note 2) i sw = 0.2a i sw = 1a l l 1.1 1.4 v v switch off leakage v in = 25v, v sw = 0 v in = v max , v sw = 0 (note 8) 150 250 a a supply current (note 3) v fb = 2.5v, v in 35v v shdn = 0.1v (device shutdown) (note 9) l l 7.5 140.0 10 300 ma a minimum supply voltage normal mode startup mode (note 4) l l 7.3 3.5 8.0 4.8 v v switch current limit (note 5) i lim open r lim = 10k (note 6) r lim = 7k (note 6) l 1.2 1.7 1.2 0.8 2.2 a a a maximum duty cycle l 85 90 % switching frequency v fb = 0v through 2k (note 5) (lt1176) v sense = 0v (note 5) (lt1176-5) l 90 85 100 20 20 110 120 khz khz khz khz switching frequency line regulation 8v v in v max (note 8) l 0.03 0.1 %/v error amplifier voltage gain (note 10) 1v v c 4v 2000 v/v error amplifier transconductance (note 10) 3700 5000 8000 mho error amplifier source and sink current source (v fb = 2v or v sense = 4v) sink (v fb = 2.5v or v sense = 5.5v) 100.0 0.7 140 1.0 225.0 1.6 a ma feedback pin bias current (lt1176) v fb = v ref l 0.5 2 a reference voltage (lt1176) v c = 2v l 2.155 2.21 2.265 v reference voltage tolerance (lt1176) v ref (nominal) = 2.21v all conditions of input voltage, output voltage, temperature and load current l 0.5 1.0 2 3 % % sense voltage (lt1176-5) v c = 2v l 4.85 5 5.15 v sense voltage tolerance (lt1176-5) v out (nominal) = 5v all conditions of input voltage, temperature and load current l 0.5 0.1 2 3 % % sense pin divider resistance (lt1176-5) 3 5 8 k output voltage line regulation 8v v in v max (note 8) l 0.005 0.02 %/v v c voltage at 0% duty cycle overtemperature l 1.5 C4.0 v mv/c multiplier reference voltage 24 v shutdown pin current v shdn = 5v v shdn v threshold (@ 2.5v) l l 5 10 20 50 a a shutdown thresholds switch duty cycle = 0 fully shutdown l l 2.2 0.1 2.45 0.30 2.7 0.5 v v status window as a percent of output voltage 4 5 6 % status high level i status = 10a sourcing l 3.5 4.5 5.0 v the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. t j = 25c, v in 25v, unless otherwise noted.
lt1176/lt1176-5 4 11765fb application hints although the lt1176 has a peak switch rating of 1.2a and a maximum duty cycle of 85%, it must be used cautiously in applications which require high switch current and high duty cycle simultaneously, to avoid excessive chip temperature. thermal resistance is 90c/w for the 8-pin dip package and 50c/w for the 20-pin so. this limits continuous chip power dissipation to the 0.5w to 1w range. these numbers assume typical mounting techniques. extra or thick copper connected to the leads can reduce thermal resistance. bonding the package to the board or using a clip style heat sink can also help. the following formulas will give chip power dissipation and peak switch current for the standard buck converter. note that surges less than 30 seconds do not need to be considered from a thermal standpoint, but for proper regulation, they must not result in peak switch currents exceeding the 1.2a limit. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: to calculate maximum switch on voltage at current between low and high conditions, a linear interpolation may be used. note 3: a feedback pin voltage (v fb ) of 2.5v forces the v c pin to its low clamp level and the switch duty cycle to zero. this approximates the zero load condition where duty cycle approaches zero. the lt1176-5 has v sense = 5.5v. note 4: total voltage from v in pin to ground pin must be 8v after start-up for proper regulation. note 5: switch frequency is internally scaled down when the feedback pin voltage is less than 1.3v to avoid extremely short switch-on times. during testing, v fb or v sense is adjusted to give a minimum switch-on time of 1s. note 6: i lm = (r lim C 1k)/7.65k note 7: switch to input voltage limitation must also be observed. note 8: v max = 35v note 9: does not include switch leakage. note 10: error amplifier voltage gain and transconductance are specified relative to the internal feedback node. to calculate gain and transconductance from the sense pin (output) to the v c pin on the lt1176-5, multiply by 0.44. electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. t j = 25c, v in 25v, unless otherwise noted. parameter conditions min typ max units status low level i status = 1.6ma sinking l 0.25 0.4 v status delay time 9 s status minimum width 30 s power = i load (v out /v in ) + v in [7ma + 3ma (v out /v in ) + 0.012 (i load )] i peak = i load(peak) + [v out (v in C v out )]/2e 5 (v in )(l) example: v in = 15v, v out = 5v, i load = 0.5a continuous, 0.8a peak, l = 100h power (i load = 0.5a) = 0.38w i peak (i load = 0.8a) = 0.97a where component size or height is critical, we suggest using solid tantalum capacitors (singly or in parallel), but be sure to use units rated for switching applications. coiltronics is a good source for low profile surface mount inductors and avx makes high quality surface mount tantalum capacitors. for further help, use application notes 19 and 44,ltcs switchercad ? computer design program, and our knowledgeable application department.
lt1176/lt1176-5 5 11765fb 2.35v ? + power shutdown ? + 0.3v shutdown input supply current limit shutdown 6v regulator and bias i lim 6v to all circuitry 320a 10a 4.5v 10k ? + current limit comp c2 500 0.16 r r/s latch r s q ? + 100khz oscillator freq shift sync 3v p-p analog multiplier xyz z y x v in output voltage monitor status 2.21v 2.8k fb/sense 2.2k* v c 24v (equivalent) 400 switch output (v sw ) ? + a1 error amp c1 pulse width comparator *connected on 5v version only 11765 bd g1 block diagram
lt1176/lt1176-5 6 11765fb n8 package 8-lead pdip (narrow .300 inch) (reference ltc dwg # 05-08-1510) package description n8 1002 .065 (1.651) typ .045 ? .065 (1.143 ? 1.651) .130 .005 (3.302 0.127) .020 (0.508) min .018 .003 (0.457 0.076) .120 (3.048) min 1 2 3 4 8 7 6 5 .255 .015* (6.477 0.381) .400* (10.160) max .008 ? .015 (0.203 ? 0.381) .300 ? .325 (7.620 ? 8.255) .325 +.035 ?.015 +0.889 ?0.381 8.255 ( ) note: 1. dimensions are inches millimeters *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .010 inch (0.254mm) .100 (2.54) bsc
lt1176/lt1176-5 7 11765fb 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 representa - tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. revision history rev date description page number a 01/11 corrected typical application updated part markings in order information revised electrical characteristics updated package description 1 2 3 8 b 2/11 revised shutdown pin current in electrical characteristics 3
lt1176/lt1176-5 8 11765fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com linear technology corporation 1993 lt 0211 rev b ? printed in usa sw package 20-lead plastic small outline (wide .300 inch) (reference ltc dwg # 05-08-1620) s20 (wide) 0502 note 3 .496 ? .512 (12.598 ? 13.005) note 4 20 n 19 18 17 16 15 14 13 1 2 3 4 5 6 7 8 .394 ? .419 (10.007 ? 10.643) 9 10 n/2 1112 .037 ? .045 (0.940 ? 1.143) .004 ? .012 (0.102 ? 0.305) .093 ? .104 (2.362 ? 2.642) .050 (1.270) bsc .014 ? .019 (0.356 ? 0.482) typ 0 ? 8 typ note 3 .009 ? .013 (0.229 ? 0.330) .016 ? .050 (0.406 ? 1.270) .291 ? .299 (7.391 ? 7.595) note 4 45 .010 ? .029 (0.254 ? 0.737) .420 min .325 .005 recommended solder pad layout .045 .005 n 1 2 3 n/2 .050 bsc .030 .005 typ .005 (0.127) rad min inches (millimeters) note: 1. dimensions in 2. drawing not to scale 3. pin 1 ident, notch on top and cavities on the bottom of packages are the manufacturing options. the part may be supplied with or without any of the options 4. these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .006" (0.15mm) package description
|
