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1 lt1306 typical applicatio n u applicatio s u descriptio u features synchronous, fixed frequency step-up dc/dc converter output disconnected from input during shutdown output voltage remains regulatedwhen v in > v out controlled input current during start-up 300khz current mode pwm operation can be externally synchronized internal 2a switches operates with v in as low as 1.8v automatic burst mode operation at light loads quiescent current: 160 m a shutdown current: 9 m a typ the lt 1306 is a fully integrated, fixed frequency syn- chronous boost converter capable of generating 5v at 1afrom a li-ion cell. the device contains both the main power switch and synchronous rectifier on chip and automatically disconnects the output from the input in shutdown, eliminating the need for external load discon- nect circuitry. additionally, the output remains regulated when v in exceeds v out , allowing difficult step-up/step- down converter functions to be easily realized using asingle inductor. the internal 300khz oscillator of the lt1306 can be easily synchronized to an external clock from 425khz to 500khz. this allows switching harmonics to be tightly controlled and eliminates any beat frequencies that may result from a multifrequency system. the lt1306 automatically shifts into power saving burst mode tm operation at light loads. at heavy loads the lt1306 operates in fixed frequencycurrent mode. no-load quiescent current is 160 m a and reduces to 9 m a in shutdown mode. the lt1306 is available in an so-8 package. , ltc and lt are registered trademarks of linear technology corporation. burst mode is a trademark of linear technology corporation. satellite phones portable instruments personal digital assistants palmtop computers load current (ma) 1 60 efficiency (%) 80 85 90 10 100 1000 1306 ta01 7570 65 v in = 4.2v v in = 3.6v v in = 2.6v v o = 5v l1 = 10 h (figure 1) sw l1 10 m h d1 c1 1 m f v in cap lt1306 r3 118k r2249k r1768k c z 68nf c in2 0.1 m f c in1 22 m f 1-cell li-ion c p 68pf c o2 1 f c o1 220 m f c in1 : avx tajc226m010 c o1 : avx tpse227m010r0100 c in1 , c o2 : ceramic c1: avx taja105k020d1: mmbd914lt1 l1: ctx10-2 1306 f01 5v1a out s/s fb v c gnd + + + efficiency figure 1. single li-ion cell to 5v converter downloaded from: http:///
2 lt1306 parameter conditions min typ max units reference voltage measured at the fb pin 1.22 1.24 1.26 v reference line regulation 1.8v v in 7v 0.002 0.1 %/v fb input bias current v fb = v ref 10 25 na error amplifier transconductance d i = 0.2 m a 80 150 220 mw ? error amplifier output source current v fb = 1v, v c = 0.8v 5 7.5 11 m a error amplifier output sink current v fb = 1.5v, v c = 0.8v 5 7.5 11 m a error amplifier output clamp voltage v fb = 1v 1.18 1.28 1.38 v v in undervoltage lockout threshold 1.55 1.8 v idle mode output leakage current v fb = 1.5v, v out = 5.5v, v sw = 1.7v 61 5 m a output source current in shutdown v out = 0v, v in = v sw = 7v, v cap = 7.2v, v s/s = 0v ? m a switching frequency 1.8v v in 7v, 0 c t a 85 c 260 310 415 khz 1.8v v in 7v, t a = 40 c 225 305 390 khz maximum duty cycle v fb = 1v, 0 c t a 85 c8 0 9 0 % v fb = 1v, t a = 40 c6 5 8 0 % switch current limit duty cycle = 0.1 (note 3) 2.3 a duty cycle = 0.8 (note 3) 2.0 a burst mode operation switch current limit 250 ma switch v cesat i sw = 2a 0.45 0.575 v rectifier v cesat i sw = 2a 0.49 0.675 v stepdown mode rectifier voltage v out = 0v, i sw = 1a 0.3 + v in 0.7 + v in v v out = 2.2v, i sw = 1a 1.3 1.8 v switch and rectifier leakage current v out = 0v, v in = v sw = 7v, v cap = 7.2v, v s/s = 0v 0.1 20 m a absolute m axi m u m ratings w ww u package/order i n for m atio n w u u order part number (note 1)v in voltage ............................................................. 10v s/s voltage ............................................................... 7v fb voltage .............................................................. 10v v out voltage .......................................................... 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 consult factory for industrial and military grade parts. s8 part marking lt1306es8 1306 t jmax = 125 c, q ja = 90 c/ w 12 3 4 87 6 5 top view s8 package 8-lead plastic so v c fb v out gnd s/sv in capsw electrical characteristics the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 2.5v, v s/s = v in , v c open unless otherwise noted. downloaded from: http:///
3 lt1306 parameter conditions min typ max units s/s pin current v s/s = v in 6 m a v s/s = 0v 3 m a shutdown pin input high voltage 1.2 v shutdown pin input low voltage 0.45 v shutdown delay 12 20 50 m s synchronization frequency range 425 500 khz operating supply current 4.5 8 ma quiescent supply current v s/s = v in , v fb = 1.5v 160 250 m a shutdown supply current v s/s = 0v 9 16 m a cap pin leakage current v in = v cap = 7v, v s/s = 2.5v, i sw = 0 10 m a output boost-to-stepdown threshold v in v output stepdown-to-boost threshold v in ?0.1 v the denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v in = 2.5v, v s/s = v in , v c open unless otherwise noted. electrical characteristics note 1: absolute maximum ratings are those values beyond which the life to the device may be impaired.note 2: the lt1306e is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the 40 c to 85 c operating temperature range are assured by design, characterization and correlationwith statistical process controls. note 3: switch current limit guaranteed by design/correlation to static tests. typical perfor m a n ce characteristics uw v in (v) 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 i loadmax (a) 1.0 1.5 1306 ?g01 0.5 0 v o = 5v l = 10 m h t j = 125 c t a = 25 c t a = 50 c v o = 3.3v temperature ( c) ?0 reference voltage (v) 80 1306 ?g02 04 0 1.2391.238 1.237 1.236 1.235 1.234 1.233 1.232 1.231 20 20 60 100 v s/s (v) 54 3 2 1 0 ?? ? ? ? i s/s ( m a) 1306 ?g03 05 4 3 2 1 t a = ?0 c t a = 85 c t a = 25 c maximum load current vsinput voltage reference voltage vstemperature s/s pin current vs s/s pin voltage downloaded from: http:///
4 lt1306 typical perfor m a n ce characteristics uw s/s pin current vs temperature shutdown supply current vsinput voltage idle-mode supply current vstemperature oscillator frequency lineregulation frequency vs temperature maximum duty ratio v in (v) 0 frequency (khz) 9 87 6 1306 ?g07 24 320315 310 305 300 135 1 0 temperature ( c) ?0 frequency (khz) 315310 305 300 295 290 285 280 275 270 265 0 40 60 1306 ?g08 ?0 20 80 100 temperature ( c) ?0 9590 85 80 75 70 65 60 20 60 1306 ?g09 ?0 0 40 80 100 duty ratio (%) v in = 2.5v current limit vs duty cycle switch saturation voltagevs current maximum allowable rise time ofsynchronizing pulse synchronizing pulse amplitude (v) 1 maximum rise time (ns) 600500 400 300 200 100 0 1.5 2.0 2.5 3.0 1306 ?g10 3.5 duty cycle (%) 0 2.0 current limit (a) 2.2 2.6 2.8 3.0 20 40 50 90 1306 ?g11 2.4 10 30 60 70 80 t a = 25 c switch current (a) 0 0.70.6 0.5 0.4 0.3 0.2 0.1 0 1.5 1306 ?g12 0.5 1.0 2.0 2.5 switch voltage (v) t a = ?0 c t a = 85 c t a = 25 c input voltage (v) supply current ( m a) 4035 30 25 20 15 10 5 1306 ?g04 0 2 4681 01 2 t a = 85 c t a = 25 c t a = ?0 c temperature ( c) ?0 idle-mode supply current ( m a) 80 1306 ?g06 04 0 155150 145 140 135 20 20 60 100 temperature ( c) s/s current ( m a) 5.02.5 0 ?.5 1306 ?g05 ?0 ?0 02040 80 60 100 v s/s = 2.5v v s/s = 0v downloaded from: http:///
5 lt1306 typical perfor m a n ce characteristics uw rectifier current (a) 0 0.70.6 0.5 0.4 0.3 0.2 0.1 0 1.5 1306 ?g13 0.5 1.0 2.0 2.5 rectifier voltage (v) t a = ?0 c t a = 25 c t a = 85 c rectifier current (a) 0 1.901.85 1.80 1.75 1.70 1.65 1.60 1.55 1.5 1306 ?g14 0.5 1.0 2.0 rectifier voltage (v) v in = 6v v out = 5v t a = 25 c rectifier saturation voltagevs current stepdown-mode rectifier voltagevs current continuous-conduction modeswitching waveforms in boost operation v o 0.1v/div ac v sw 5v/div i l 0.5a/div v in = 4.2v v o = 5v 2 m s/div 1ms/div 2 m s/div 1ms/div v in = 2.5v v o 5v/div v sw 5v/div i l 2a/div v s/s 5v/div start-up to shutdown transientresponse* continuous-conduction modeswitching waveforms in stepdown mode v in = 6v v o = 5v v o 50mv/div ac v sw 5v/div i l 0.5v/div transient response of theconverter in figure 1 with a 50ma to 800ma load step v in = 3.6v v o = 5v load current 0.5a/div dc inductor current 1a/div output 0.1v/div ac *notice that the input start-up current is well controlled and the output voltage falls to zero in shutdown. downloaded from: http:///
6 lt1306 pi n fu n ctio n s uuu v c (pin 1): compensation pin for error amplifier. v c is the output of the transconductance error amplifier. loopfrequency compensation is done by connecting an rc network from the v c pin to ground. fb (pin 2): inverting input of the error amplifier. connect the resistor divider tap here. set output voltage accordingto v out = 1.24v (1 + r1/r2). v out (pin 3): output of the switching regulator and emit- ter of the synchronous rectifier. connect appropriateoutput capacitor from here to ground. v out must be kept below 5.5v. gnd (pin 4): ground. connect to local ground plane. sw (pin 5): switch pin. the collectors of the grounded power switch and the synchronous rectifier. keep the swtrace as short as possible to minimize emi. cap (pin 6): power supply to the synchronous rectifier driver. the bootstrap capacitor and the blocking diodeare tied to this pin. the cap voltage switches between a low level of v in ?v d to a high level determined by the v sw high level.v in (pin 7): supply or battery input pin. must be closely bypassed to ground plane.s/s (pin 8): shutdown and synchronization pin. shut- down is active low with a typical threshold of 0.9v. fornormal operation, the s/s pin is tied to v in . to externally synchronize the switching regulator, drive the s/s pinwith a pulse train. block diagra w figure 2. lt1306 block diagram + a1 g m + + + v c v b + + + 2 1 v in a4 7 fb 8 s/s 4 gnd pwm control 1306 f02 5 1.24v 1.65v uvlo s ramp compensation ref/bias shutdown delay shdn sync 300khz osc clk idle sw x5 x4 6 cap s q r q1 q2 i rect > 0 i rect r s a2 sense amp dcm control 3 out rectifier + v ce2 x1 x2 x4 x3 a5 a3 downloaded from: http:///
7 lt1306 operatio u the lt1306 is a fixed frequency current mode pwmregulator with integrated power transistor q1 and syn- chronous rectifier q2. in the block diagram, figure 2, the pwm control circuitis enclosed within the dashed line. it consists of the current sense amplifier (a2), the oscillator, the compen- sating ramp generator, the pwm comparator (a4), the logic (x1 and x2), the power transistor driver (x4) and the main power switch (q1). notice that the clock (clk) ?lanks?q1 conduction. the internal oscillator frequency is 300khz. the pulse width of the clock determines the maximum on duty ratio of q1. in the lt1306 this is set to 88%. q1 turns on at the trailing edge of the clock pulse. to prevent subharmonic oscillation above 50% duty ratio, a com- pensating ramp (generated from the oscillator sawtooth) is added to the sensed q1 current. q1 is turned off when this sum exceeds the error amplifier a1 output, v c . q1? absolute current limit is reached when v c ? upward excursion is clamped internally at 1.28v. the error amplifier output, v c , determines the peak switch current required to regulate the output voltage. v c is a measure of the output power. at heavy loads, the averageand the peak inductor currents are both high. v c moves to the upper end of its operating range and the lt1306 oper-ates in continuous conduction mode (ccm). as load decreases, the average inductor current de-creases. in ccm, the peak-to-peak inductor current ripple to the first order depends only on the inductance, the input and the output voltages. when the average inductor current falls below 1/2 of the peak-to-peak inductor current ripple, the converter enters discontinuous con- duction mode (dcm). the switching frequency remains constant except that the inductor current always returns to zero within each switching cycle. in both ccm and dcm, the output voltage is regulated with negative feedback. a1 amplifies the error voltage between the internally generated 1.24v reference and the attenuated output voltage. the rc network from the v c pin to ground provides the loop compensation. further reduction in the load moves v c towards the lower end of its operating range. both the peak inductor current and switch q1? on-time decrease. hysteretic comparatora3 determines if v c is too low for the lt1306 to operate efficiently. as v c falls below the trip voltage v b , the output of a3 goes high. all circuits except the error amplifier, comparators a3 and a5, and the rectifier driver control x5, are turned off. after the remaining energy stored in the inductor is delivered to the output through the synchro- nous rectifier q2, the lt1306 stops switching. in this idle state, the lt1306 draws only 160 m a from the input. with switching stopped and the load being powered by theoutput filter capacitor, the output voltage decreases. v c then starts to increase. q1 does not start to switch until v c rises above the upper trip point of a3. the lt1306 againdelivers power to the output as a current mode pwm converter except that the switch current limit is only about 250ma due to the low value of v c . if the load is still light, the output voltage will rise and v c will fall, causing the converter to idle again. power delivery therefore occurs inbursts. the on-off cycle frequency, or burst frequency, depends on the operating conditions, the inductance and the output filter capacitance. the output voltage ripple in burst mode operation is usually higher than either ccm or dcm operation. burst mode operation increases light load efficiency because it delivers more energy to the output during each clock cycle than is possible with dcm operation? extremely low peak switch current. this al- lows fewer switching cycles per unit time to maintain a given output. chip supply current therefore becomes a small fraction of the total input current. the synchronous rectifier is represented as npn transis- tor, q2, in the block diagram (figure 2). a rectifier drive circuit, x5, supplies variable base drive to q2 and controls the voltage across the rectifier. the supply voltage, v cap , for the driver is generated locally with the bootstrap cir-cuit, d1 and c1 (figure 1). when q1 is on, the bootstrap capacitor c1 is charged from the input to the voltage v in ?v d1(on) ?v cesat1 . the charging current flows from the input through d1, c1 and q1 to ground. after q1 isswitched off, the node sw goes above v o by the rectifier drop v cesat2 . d1 becomes back-biased and the cap volt- age is pushed up to v o + v cesat2 + v in ?v d1(on) ?v cesat1 . c1 supplies the base drive to q2. the consumed charge isreplenished during the q1 on interval. downloaded from: http:///
8 lt1306 operatio u in boost operation, x5 drives the rectifier q2 into satura-tion. the voltage across the rectifier is v cesat . as the inductor current decreases, q2? base drive also de-creases. x5 ceases supplying base current to q2 when the inductor current falls to zero. if v in > v o , q2 will no longer be driven into saturation. instead the voltage across q2 is allowed to increase so thatthe inductor voltage reverses polarity as q1 switches. since the inductor voltage is bipolar, volt-second balance can be maintained regardless of the input voltage. the lt1306 is therefore capable of operating as a step-down regulator with the basic boost topology. input start-up current is also well controlled since the inductor current cannot increase during q1? off-time with negative inductor voltage. the rectifier voltage drop depends on both the input and the output voltages. efficiency in the step-down mode is less than that of a linear regulator. for sustained step- down operation, the maximum output current will be limited by the package thermal characteristics. mode 1306 f04 v o + 0.1v v o v in boost stepdown figure 4. dc transfer characteristics of the mode controlcomparator plotted with v in as an independent variable. v o is considered fixed. mode 0 1306 f03 v in ?0.1v v in v o boost stepdown figure 3. dc transfer characteristics of the mode controlcomparator plotted with v o as an independent variable. v in is considered fixed. a hysteretic comparator in driver x5 controls the modeof operation. dc transfer characteristics of the compara- tor are shown in figure 3 and figure 4. a logic low at the s/s pin (pin 8) initiates shutdown. first, all circuit blocks in the lt1306 are switched off. the synchronous rectifier q2 and its driver are kept on to allow stored inductive energy to flow to the output. as v o drops below v in , the voltage across the rectifier q2 increases so that the inductor voltage reverses. inductorcurrent continues to fall to zero. driver x5 then turns off and the rectifier, q2, becomes an open circuit. the lt1306 dissipates only 9 m a in shutdown. the lt1306 is guaranteed to start with a minimum v in of 1.8v. comparator a5 senses the input voltage and gen-erates an undervoltage lockout (uvlo) signal if v in falls below this minimum. in uvlo, v c is pulled low and q1 stops switching. the lt1306 draws 160 m a from the input. downloaded from: http:///
9 lt1306 output voltage settingthe output voltage of the lt1306 is set with a resistive divider, r1 and r2 (figure 1 and figure 5), from the output to ground. the divider tap is tied to the fb pin. current through r2 should be significantly higher than the fb pin input bias current ( 25na). with r2 = 249k, the input bias current of the error amplifier is 0.5% of the current in r1. v o r1 r1r2 v o = 1.24v 1 + ?1 fb pin r2 1306 f05 () v o 1.24 r1 = r2 () figure 5. feedback resistive divider synchronization and shutdownthe s/s pin (pin 8) can be used to synchronize the oscillator or disconnect the load from the input. the s/s pin is tied to the input (v in > 1.8v) for normal operation. the oscillator in the lt1306 can be externally synchro-nized by driving the s/s pin with a pulse train (see the graph ?aximum allowable rise time of synchronizing pulse? in the typical performance characteristics). the synchronization is positive edge triggered. the recom- mended frequency of the external clock ranges from 425khz to 500khz. if synchronization results in switching jitter, reducing the rising edge dv/dt of the external clock pulse usually cures the problem. shutdown will be activated if the s/s pin voltage staysbelow the shutdown threshold (0.45v) for more than 50 m s. this shutdown delay is reset whenever the s/s pin goes above the shutdown threshold. inductorthe value of the energy storage inductor l1 (figure 1) is usually selected so that the peak-to-peak ripple current is less than 40% of the average inductor current. for 1- or 2-cell alkaline or single li-ion to 5v applications, 10 m h to 20 m h is recommended for the lt1306 running at 300khz. a 5 m h to 10 m h inductor can be used if the lt1306 is externally synchronized at 500khz. the inductor should be able to handle the full load peakinductor current without saturation. the peak inductor current can be as high as 2a. this places a lower limit on the core size of the inductor. powder iron cores have unacceptable core losses and are not suitable for high efficiency applications. most ferrite core materials have manageable core losses and are recommended. inductor dc winding resistance (dcr) also needs to be considered for efficiency. usually there are trade-offs between core loss, dcr, saturation current, cost and size. for emi sensitive applications, one may want to use magnetically shielded or toroidal inductors to contain field radiation. table 1 lists a number of inductors suitable for lt1306 applications. table 1. inductors suitable for use with the lt1306 part value max dcr core height vendor no. ( m h) ( w ) type (mm) bh electronics 511-0033 5.0 0.023 toroid 4.8 coilcraft do3308-103 10 0.09 open 3.0 do3316-472 4.7 0.018 open 5.2 do3316-103 10 0.029 open 5.2 do3316-153 15 0.046 open 5.2 coiltronics ctx5-2 5 0.021 toroid 6.0 ctx10-2 10 0.032 toroid 6.0 murata lqn6c4r7 4.7 0.034 open 5.0 sumida cdrh73-100 10 0.072 magnetic 3.4 shielding cd43-4r7 4.7 0.109 open 3.2 capacitorsthe output filter capacitor is usually chosen based on its equivalent series resistance (esr) and the acceptable change in output voltage as a result of load transients. the output voltage ripple at the switching frequency can be estimated by considering the peak inductor current and the capacitor esr. ii iv v peak in oo in ?? () ( ) output ripple @ (esr)(i peak ) = esr i v v oo in () ( ) () applicatio n s i n for m atio n wu u u downloaded from: http:///
10 lt1306 since a boost converter produces high output currentripple, one also needs to consider the maximum ripple current rating of the output capacitor. capacitor reliability will be affected if the ripple current exceeds the maximum allowable ratings. this maximum rating is usually specified as the rms ripple current. in the lt1306 the rms output capacitor ripple current is: i vv v o oi n in C for 2-cell to 5v applications, 220 m f low esr solid tanta- lum capacitors (avx tps series or sprague 593d series)work well. to reduce output voltage ripple due to heavy load transients or burst mode operation, higher capaci- tance may be used. for through-hole applications, sanyo os-con capacitors are also good choices. in a boost regulator, the input capacitor ripple current is much lower. maximum ripple current rating and input voltage ripples are not usually of concern. a 22 m f tantalum capacitor soldered near the input pin is generally anadequate bypass. bootstrap supply diode d1 and capacitor c1 generate a pulsating supply voltage, v cap , which is higher than the output. the rectifier drive circuit runs off this supply. during rectifier on-time,the rectifier base current drains c1. q2 base current and the maximum allowable v cap ripple voltage determine the size of c1. a 1 m f capacitor is sufficient to keep v cap ripple below 0.3v. for a 2-cell input (v in > 1.8v) over an extended temperature range, a bat54 schottky diode may be usedfor d1. the use of a schottky diode increases the bootstrap voltage and the operating headroom for the rectifier driver, x5. diodes like a 1n4148 or 1n914 work well for 2-cell inputs over the 0 c to 70 c commercial temperature range.the charge drawn from c1 during the rectifier on-time has to be replenished during the switch on-interval. as duty cycle decreases, the amplitude of the c1 charging current can increase dramatically especially when delivering high power to the load. this charging current flows through the switch and can cause the current limit comparator to triperratically. for boost applications where v in is a few tenths of a volt below v o , a 1 m f or 2.2 m f tantalum capacitor (such as avx taj series) can be used for c1. the esr of thetantalum capacitor limits the charging current. a low value resistor (2 w to 5 w ) can also be added in series with c1 for further limiting the charging current although this tends tolower the converter efficiency slightly. frequency compensation current mode switching regulators have two feedbackloops. the inner current feedback loop controls the inductor current in response to the outer loop. the outer or overall feedback loop tightly regulates the output voltage. the high frequency gain asymptote of the inner current loop rolls off at 20db/decade and crosses the unity gain axis at a frequency w c between 1/6 to 2/3 of the switching frequency. the current loop is stable and iswideband compared to the overall voltage feedback loop. the low frequency current loop gain is not high (usually between unity and 10) but it increases the low frequency impedance of the inductor as seen by the output filter capacitor. (in a boost regulator, the inductor is con- nected to the output during the switch off-time.) current mode control introduces an effective series resistance (>> dcr) to the inductor that damps the lc tank re- sponse. the complex high-q poles of the lc filter are now separated, resulting in a dominant pole determined by the filter capacitance and the load resistance and a second high frequency pole. for a boost regulator the control to output transfer func-tion can be shown to have a dominant pole at the load corner frequency w p l o r c = ? ? ?? () 1 2 and a moving right-half plane (rhp) zero with a minimumvalue of w z l max rd l = () 1 2 C applicatio n s i n for m atio n wu u u downloaded from: http:///
11 lt1306 where r maximum load output voltage maximum dc load current d maximum converter duty cycle l max == = = + + vv v o in min o C . () 05 01 there is also a second pole at the current loop crossoverfrequency w c (figure 6). w z is much lower in frequency than w c . the loop is compensated by adjusting the midband gain with resistor r3 (figure 7) so that the overall loop gaincrosses 0db before the minimum frequency rhp zero (i.e., corresponding to the highest duty ratio). the value of r3 can be estimated with the fromula: r vdc r l o max o l 3 390 1 = (C ) due to the low transconductance of the error amplifier, thegain setting resistor r3 is ac-coupled with capacitor c z . this prevents r3 from inducing an offset to the input of theerror amplifier. it also creates a pole at dc and a low frequency zero. the amplitude response of the error amplifier with the compensation network shown is: ? ? ? ? ? v v g r rr sr c sc sr c cc c o m z zp zp = + ? ? ?? + () + () [] >> 2 12 13 13 applicatio n s i n for m atio n wu u u the low frequency zero 1/r3c z of the compensation network is placed at w p /2. c r z p = 2 3 w the capacitor c p ensures adequate gain margin beyond the rhp zero. the high frequency pole 1/r3c p of the amplifier frequency response is placed beyond w z . c r p z = 1 33 w higher output filter capacitance rolls off the gain responsefrom a lower corner frequency so higher midband gain is required in the compensation network to make the overall loop gain cross 0db just below w z . layout considerationto minimize emi and high frequency resonances, it is essential to keep the sw and the cap trace leads as short as possible. the input and the output bypass capacitors c in and c out should be placed close to the ic package and soldered to the ground plane. a ground plane under theswitching regulator is highly recommended. figure 8 shows a suggested component placement and pc board layout. downloaded from: http:///
12 lt1306 0 1306 f06 amount of midband gain needed gain (db) 1 (r3)(c z ) 1 (g m )(r3)(r2) r1 + r2 midband gain = v o v c v c v o w w z w c current loopcrossover frequency overall loop gainafter compenstion amplitude responseof the error amplifier amplitude response of control-to-output transfer function before compensation r l (1 ?d max ) 2 l rhp zero = r l 2 () (c o ) w p frequency ? 13 w z loop gain crossover figure 6. gain asymptotes of the control-to-output ? ? v v o c ? ? ?? and error amplifier ? ? v v c o ? ? ?? transfer function figure 7. current mode boost converter overall-loop compensation applicatio n s i n for m atio n wu u u + g m v c v in l v o 1.24v lt1306 1306 f07 pwm control logic q1 r1 fb r2 r l i o r3 c z c p c o gnd q2 rectifier sw downloaded from: http:///
13 lt1306 ground plane s/s v c r2 r1 v out v in c o1 1306 f08 gnd l1 vias + r3 + + c o2 c in2 c1 d1 c in1 c p c z 12 3 4 87 6 5 lt1306 applicatio n s i n for m atio n wu u u figure 8. recommended component placement for lt1306.notice that the input and the output capacitors are grounded at the same point. a ground plane under the dc/dc converter is highly recommended. use multiple vias to tie pin 4 copper to the ground plane downloaded from: http:///
14 lt1306 sw l1 4.7 m h 2v/500khz d1 c1 1 m f v in cap lt1306 r3 95k r2249k r1412k c z 5.6nf c in1 0.1 m f ceramic c in2 22 m f 2v to 3v c p 39pf c o 220 m f c in1 : avx tajc226m010 c o1 : avx tpse227m010r0100 c1: avx taja105k020d1: cmdsh-3 l1: lqn6c4r7 1306 f09 3.3v1a out s/s fb v c gnd + + + load current (ma) 1 60 efficiency (%) 80 85 90 10 100 1000 2000 1306 f09a 7570 65 v in = 3v v in = 2.5v v in = 1.8v v o = 3.3v l1 = 4.7 h 2-cell nimh to 3.3v output efficiency typical applicatio s u downloaded from: http:///
15 lt1306 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. package descriptio n u dimensions in inches (millimeters) unless otherwise noted. 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:///
16 lt1306 ? linear technology corporation 1999 1306f lt/tp 0400 4k ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear-tech.com part number description comments lt1302 high output current micropower dc/dc converter 5v/600ma from 2v, 2a internal switch, 200 m a i q lt1304 2-cell micropower dc/dc converter 5v/200ma, low-battery detector active in shutdown lt1307/lt1307b single cell, micropower, 600khz pwm dc/dc converters 3.3v at 75ma from one cell, msop package lt1308a/lt1308b high output current micropower dc/dc converter 5v at 1a from single li-ion cell lt1316 burst mode operation dc/dc with programmable current limit 1.5v minimum, precise control of peak current limit lt1317/lt1317b micropower, 600khz pwm dc/dc converters 100 m a i q , operate with v in as low as 1.5v lt1610 single-cell micropower dc/dc converter 3v at 30ma from 1v, 1.7mhz fixed frequency lt1613 1.4mhz switching regulator in 5-lead sot-23 5v at 200ma from 4.4v input, tiny sot-23 package lt1615 micropower step-up dc/dc in 5-lead sot-23 20 m a i q , 36v/350ma internal switch, v in as low as 1.2v ltc1624 high efficiency n-channel switching regulator controller v out = 1.19v to 30v in stepdown; v in = 3.5v to 36v so-8 package lt1949 600khz, 1a switch pwm dc/dc converter 1.1a, 0.5 w /30v internal switch, v in as low as 1.5v related parts sw l1 10 m h d1 c1 1 m f v in cap lt1306 r3 75k r2249k r1768k c z 15nf c in2 0.1 m f ceramic c in1 22 m f 3.6v to 6.5v c p 22pf c o2 1 m f ceramic c in1 : avx tajc226m010 c o1 : avx tpse227m010r0100 c1: avx taja105k020d1: mmbd914lt1 l1: ctx10-3 1306 f09 5v1a out s/s fb v c gnd + + c o1 220 m f + load current (ma) 1 60 efficiency (%) 80 85 90 10 100 1000 2000 1306 f10a 7570 65 v in = 4.8v v in = 3.6v v in = 6v v o = 5v l1 = 10 h typical applicatio s u 4-cell nimh to 5v output efficiency transient response with step input (4v to 6v) 0.5ms/div v in 5v/div v sw 5v/div v o 0.1v/div ac i l 500ma/div downloaded from: http:///

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