for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. general description the max1896 step-up dc-dc converter incorporates high-performance current-mode, fixed-frequency, pulse-width modulation (pwm) circuitry and an internal 0.7 ? n-channel mosfet to provide a highly efficient regulator with fast response. high switching frequency (1.4mhz) allows fast loop response and easy filtering with small components. the max1896 can produce an output voltage as high as 13v from an input as low as 2.6v. soft-start is program- mable with an external capacitor, which sets the input current ramp rate. in shutdown mode, current con- sumption is reduced to 0.01?. the max1896 is available in a space-saving 6-pin sot23 package. the ultra-small package and high switching frequency allow cost and space-efficient implementations. applications notebook computers lcd displays pcmcia cards portable applications hand-held devices features ? >90% efficiency ? adjustable output up to 13v ? guaranteed 12v/120ma output from 5v input ? 2.6v to 5.5v input range ? lt1613 pin compatible ? 0.01? shutdown current ? programmable soft-start ? space-saving 6-pin sot23 package max1896 1.4mhz sot23 current-mode step-up dc-dc converter ________________________________________________________________ maxim integrated products 1 gnd shdn fb 16 in 5 ss lx max1896 sot23 top view 2 34 pin configuration on off max1896 input 2.6v to 5.5v output up to 13v up to 600ma r1 r2 in lx fb shdn ss gnd t ypical operating circuit part temp range pin-package MAX1896EUT-T -40 c to +85 c6 sot23-6 19-2221; rev 1; 3/04 ordering information
max1896 1.4mhz sot23 current-mode step-up dc-dc converter 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = v shdn = 3v, fb = gnd, ss = open, t a = 0? to +85? , unless otherwise noted.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. lx to gnd ..............................................................-0.3v to +14v in, shdn , fb to gnd...............................................-0.3v to +6v ss to gnd ...................................................-0.3v to (v in + 0.3v) rms lx pin current ..............................................................0.6a continuous power dissipation (t a = +70?) (note 1) 6-pin sot23 (derate 9.1mw/? above +70?)...........727mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units input supply range v in 2.6 5.5 v output voltage adjust range v out circuit of figure 1 13 v v in undervoltage lockout uvlo v in rising, 50mv hysteresis 2.25 2.4 2.55 v v fb = 1.3v, not switching 0.2 0.4 quiescent current i in v fb = 1.0v, switching 1 5 ma v shdn = 0, t a = +25 c 0.01 0.5 shutdown supply current v shdn = 0 0.01 10 ? error amplifier feedback regulation set point v fb 1.2 1.24 1.25 v fb input bias current i fb v fb = 1.24v 21 80 na line regulation 2.6v < v in < 5.5v 0.05 0.20 %/v oscillator frequency f osc 1000 1400 1800 khz maximum duty cycle dc 82 86 % power switch current limit (note 2) i lim v fb = 1v, duty cycle = 50% 0.55 0.8 a on-resistance r on 0.7 1 ? v lx = 12v, t a = +25 c 0.1 1 leakage current i lxoff v lx = 12v 10 ? soft-start reset switch resistance 100 ? charge current v ss = 1.2v 1.5 4 7.0 ? control input input low voltage v il v shdn, v in = 2.6v to 5.5v 0.3 v input high voltage v ih v shdn, v in = 2.6v to 5.5v 1.0 v v shdn = 3v 25 50 shdn input current i shdn v shdn = 0 0.01 0.1 ? note 1: thermal properties are specified with product mounted on pc board with one square-inch of copper area and still air.
max1896 1.4mhz sot23 current-mode step-up dc-dc converter _______________________________________________________________________________________ 3 electrical characteristics (v in = v shdn = 3v, fb = gnd, ss = open, t a = -40? to +85? , unless otherwise noted.) (note 3) note 2: current limit varies with duty cycle due to slope compensation. see the output current capability section. note 3: specifications to -40? are guaranteed by design and not production tested. parameter symbol conditions min typ max units input supply range v in 2.6 5.5 v output voltage adjust range v out circuit of figure 1 13 v v in undervoltage lockout uvlo v in rising, 50mv hysteresis. 2.25 2.55 v v fb = 1.3v, not switching 0.4 quiescent current i in v fb = 1.0v, switching 5 ma shutdown supply current v shdn = 0 10 a error amplifier feedback regulation set point v fb 1.2 1.25 v fb input bias current i fb v fb = 1.24v 80 na line regulation 2.6v < v in < 5.5v 0.20 %/v oscillator frequency f osc 1000 1800 khz maximum duty cycle dc 82 % power switch current limit (note 2) i lim v fb = 1v, duty cycle = 50% 0.55 a on-resistance r on 1 ? leakage current i lxoff v lx = 12v 10 ? soft-start reset switch resistance 100 ? charge current v ss = 1.2v 1.25 7.50 ? control input input low voltage v il v shdn = v in = 2.6v to 5.5v 0.3 v input high voltage v ih v shdn = v in = 2.6v to 5.5v 1.0 v v shdn = 3v 50 shdn input current i shdn v shdn = 0 0.1 ?
max1896 1.4mhz sot23 current-mode step-up dc-dc converter 4 _______________________________________________________________________________________ t ypical operating characteristics (circuit of figure 1, v in = 3.3v, t a = +25?, unless otherwise noted.) 100 50 11 0 100 1000 efficiency vs. output current 60 max1896 toc01 output current (ma) efficiency (%) 70 80 90 v in = 3.3v, v out = 5v, circuit of figure 1 100 50 11 0 100 1000 efficiency vs. output current 60 max1896 toc02 output current (ma) efficiency (%) 70 80 90 v in = 3.3v, v out = 13v, circuit of figure 3 100 50 11 0 100 1000 efficiency vs. output current 60 max1896 toc03 output current (ma) efficiency (%) 70 80 90 v in = 5v, v out = 13v, circuit of figure 3 2.0 1.5 1.0 0.5 0 2.5 4.0 3.0 3.5 4.5 5.0 5.5 no load supply current vs. input voltage max1896 toc04 input voltage (v) no load supply current (ma) v out = 13v, circuit of figure 3 12.90 12.95 13.00 13.05 13.10 output voltage vs. output current max1896 toc05 output current (ma) output voltage (v) 0 100 50 150 200 circuit of figure 3 t a = -40 c t a = +85 c t a = +25 c load current 100ma/div output voltage ac-coupled 200mv/div inductor current 500ma/div 200s/div c ff = 100pf, c out = 0.1f ceramic + 10f ceramic load transient (v out = 13v) max1896 toc06 load current 200ma/div output voltage ac-coupled 200mv/div inductor current 500ma/div 400s/div c out = 0.1f ceramic + 22f tantalum load transient (v out = 5v) max1896 toc07 shdn 5v/div output voltage 5v/div inductor current 500ma/div 100 s/div v in = 3.3v, c out = 0.1 f ceramic + 3.3 f tantalum circuit of figure 3 startup waveform without soft-start max1896 toc08 shdn 5v/div output voltage 5v/div i out = 10ma inductor current 500ma/div 2ms/div v in = 3.3v, c ss = 33nf, c out = 3.3f tantalum + 0.1f ceramic circuit of figure 3 startup waveform with soft-start max1896 toc09
max1896 1.4mhz sot23 current-mode step-up dc-dc converter _______________________________________________________________________________________ 5 pin description t ypical operating characteristics (continued) (circuit of figure 1, v in = 3.3v, t a = +25?, unless otherwise noted.) shdn 5v/div output voltage 5v/div i out = 100ma inductor current 500ma/div 2ms/div v in = 3.3v, c ss = 33nf, c out = 3.3f tantalum + 0.1f ceramic circuit of figure 3 startup waveform with soft-start max1896 toc10 lx voltage 5v/div output voltage ac-coupled 200mv/div inductor current 500ma/div 400ns/div v in = 5v, c out = 0.1f ceramic + 2.2f ceramic switching waveform max1896 toc11 i out = 150ma 600 500 v out = 5v v out = 12v 300 400 100 200 0 2.5 4.0 3.0 3.5 4.5 5.0 5.5 maximum output current vs. input voltage max1896 toc12 input voltage (v) maximum output current (ma) maximum output current defined at 90% of no load output voltage pin name function 1lx power switching connection. connect lx to the inductor and output rectifier. connect components as close to lx as possible. 2 gnd ground 3fb feedback input. connect a resistive voltage-divider from the output to fb to set the output voltage. see the setting the output voltage section. 4 shdn shutdown input. drive shdn low to turn off the converter. to automatically start the converter, connect shdn to in. drive shdn with a slew rate of 0.1v/? or greater. do not leave shdn unconnected. shdn draws up to 50?. 5ss soft-start input. connect a soft-start capacitor from ss to gnd to soft-start the converter. leave ss open to disable the soft-start function. see the soft-start section. 6in internal bias voltage input. connect in to the input voltage source. bypass in to gnd with a 1? or greater capacitor as close to in as possible.
max1896 1.4mhz sot23 current-mode step-up dc-dc converter 6 _______________________________________________________________________________________ detailed description the max1896 is a highly efficient power supply that employs a current-mode, fixed-frequency pulse-width modulation (pwm) architecture for fast-transient response and low-noise operation. the functional diagram is shown in figure 2. as the load varies, the error amplifier sets the inductor peak current necessary to supply the load and regulate the output voltage. to maintain stability at high duty cycle, a slope-compensation signal is internally summed with the current-sense signal. at light loads, this architecture allows the max1896 to skip cycles to prevent overcharging the output voltage. in this region of operation, the inductor ramps up to a peak value of about 100ma, discharges to the output and waits until another pulse is needed again. output-current capability the output-current capability of the max1896 is a func- tion of current limit, input voltage, and inductor value. because of the slope compensation used to stabilize the feedback loop, the duty cycle affects the current limit. the output-current capability is governed by the following equation: where: i lim = current limit specified at 50% (see electrical characteristics ) v diode = catch diode forward drop at i lim , (v) f osc = oscillator frequency, (hz) l = inductor value, (h) = conversion efficiency, 0.85 nominal v in = input voltage, (v) v out = output voltage, (v) soft-start the max1896 can be programmed for soft-start upon power-up with an external capacitor. when the max1896 is turned on, the soft-start capacitor (c ss ) is charged at a constant current of 4?, ramping up to 0.5v. during this time, the ss voltage directly controls the peak-inductor current, allowing 0a at v ss = 0.5v to the full current limit at v ss = 1.5v. the maximum load current is available after the soft-start cycle is complet- ed. when the max1896 is turned off, the soft-start capacitor is internally discharged to ground. shutdown the max1896 shuts down to reduce the supply current to 0.01? when shdn is low. in this mode, the internal reference, error amplifier, comparators, biasing circuit, and n-channel mosfet are turned off. the step-up converter? output is still connected to in via the exter- nal inductor and output rectifier. applications information the max1896 operates well with a variety of external components. the components in figure 1 are suitable for most applications. see the following sections to opti- mize external components for a particular application. inductor selection inductor selection depends on input voltage, output volt- age, maximum current, size, and availability of inductor values. other factors can include efficiency and ripple voltage. inductors are specified by their inductance (l), peak current (i pk ), and resistance (r l ). the following step-up circuit equations are useful in choosing the inductor values based on the application. they allow the trading of peak current and inductor value while consid- ering component availability and cost. the equation used here assumes a constant lir, which is the ratio of the inductor peak-to-peak ac current to average dc inductor current. a good compromise between the size of the inductor versus loss and output ripple is to choose an lir of 0.3 to 0.5. the peak induc- tor current is then given by: where: i out(max) = maximum output current, (a) v in(min) = minimum input voltage, (v) i ixv xv x lir pk out max out in min () () = ? ? ? ? ? ? + ? ? ? ? ? ? 1 2 duty duty cycle vvv vixrv out in diode out lim on diode == + + ? ? i i duty x v f xx v v out max lim xx duty in osc x l in out () ( . . )) ( . = ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? 145 09 05
the inductance (h) value is then given by: diode selection the output diode should be rated to handle the output voltage and the peak switch current. make sure the diode? peak current rating is at least i pk and that its breakdown voltage exceeds v out. schottky diodes are recommended. if a junction rectifier is used, it must be an ultra-fast type (t rr < 50ns) to prevent excessive loss in the rectifier. input and output capacitor selection the max1896 operates with both tantalum and ceramic output capacitors. when using tantalum capacitors, the zero caused by the esr of the tantalum is used to ensure stability. when using ceramic capacitors, the zero due to the esr will be at too high a frequency to be useful in stabilizing the control loop. when using ceramic capacitors, use a feedforward capacitor to increase the phase margin, improving the control-loop stability. figure 3 shows the circuit with ceramic capac- itors and the feedforward capacitor, c ff . use the fol- lowing equation to determine the value of the feedforward capacitor: where: r1 = see figure 3, ( ? ) c out = total output capacitance including any bypass capacitor on the output bus, (farads). see figure 3. v out = output voltage, (v) v in = input voltage, (v). setting the output voltage the max1896 operates with an adjustable output from v in to 13v. connect a resistive voltage-divider from the output to fb (see typical operating circuit ). choose a value for r2 between 10k ? and 50k ? . calculate r1 using the equation: where v fb , the step-up regulator feedback set point, is 1.24v. connect the resistive-divider as close to the ic as possible. soft-start capacitor the soft-start capacitor should be large enough that the current limit does not reach final value before the output has reached regulation. calculate c ss to be: where: k 2 = 21 x 10 -6 , (s) v out = maximum output voltage, (v) i inrush = peak inrush current allowed, (a) i out = maximum output current during power-up stage, (a) v in = minimum input voltage, (v) the soft-start duration (t ss ) is the time it takes the cur- rent limit to reach its final value. the soft-start duration can be calculated by the equation: t ss = k 3 ? c ss where: k 3 = 6.67 ? 10 5 ? ckxcx vvxv vxi i xv ss out out in out in inrush out out > ? ? ? ? ? ? ? ? ? ? 2 2 rrx v v out fb 12 1 = ? ? ? ? ? ? ? kx with units of xf a 1714 10 4 05 . . = ? ? ? ? ? ? ? ? c k r x cxv v ff out out in . = ? ? ? ? ? ? ? ? 1 1 2 05 l vxxvv vx lir x i x f in min out in min out out max osc [ ( )] () () () = ? 2 2 max1896 1.4mhz sot23 current-mode step-up dc-dc converter _______________________________________________________________________________________ 7
max1896 application circuits 1-cell to 3.3v sepic power supply figure 4 shows the max1896 in a single-ended primary inductance converter (sepic) topology. this topology is useful when the input voltage can be either higher or lower than the output voltage, such as when converting a single lithium-ion (li+) cell to a 3.3v output. l1 and l2 are two windings on a single inductor or two sepa- rate inductors. the coupling capacitor between these two windings must be a low-esr type to achieve maxi- mum efficiency, and must also be able to handle high ripple currents. ceramic capacitors are best for this application. layout procedure good pc board layout and routing are required in high- frequency switching power supplies to achieve good regulation, and stability. it is strongly recommended that the evaluation kit pc board layouts be followed as closely as possible. refer to the max1896 ev kit for a good layout. place power components as close togeth- er as possible, keeping their traces short, direct, and wide. avoid interconnecting the ground pins of the power components using vias through an internal ground plane. instead, keep the power components close together and route them in a star ground configu- ration using component side copper, then connect the star ground to internal ground using multiple vias. 1.4mhz sot23 current-mode step-up dc-dc converter 8 _______________________________________________________________________________________ figure 1. typical application circuit lx in v in 2.6v to 4.5v gnd v out 5v shdn fb max1896 on/off ss c ss 33nf c in c1 10 f 10v c2 0.1 f l 10 h sumida cd43-100 0.1 f c out 22 f 16v r1 36k ? r2 12k ? nihon ec10qso2l chip information transistor count: 970
max1896 1.4mhz sot23 current-mode step-up dc-dc converter _______________________________________________________________________________________ 9 figure 2. functional diagram gnd lx in fb 4a n error comparator transconductance error amplifier enable comparator ss clock enable bias shdn max1896 current sense control and driver logic soft- start slope compen- sation oscillator 1.24v figure 3. max1896 with ceramic output capacitor and feed- forward capacitor lx in v in 2.6v to 5.5v c ss 33nf c out 10 f ceramic 10 f ceramic 0.1 f ceramic d1 nihon ec10qso2l c ff 100pf l 10 h cd43-100 r2 12k ? v out 13v r1 115k ? r3 10k ? gnd shdn fb max1896 ss on/off figure 4. max1896 in an sepic configuration lx in v in 2.6v to 5.5v gnd v out shdn on/off fb max1896 ss r2 r1 c out l1 c1 l2 c2
package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) max1896 1.4mhz sot23 current-mode step-up dc-dc converter maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. 6lsot.eps f 1 1 21-0058 package outline, sot-23, 6l
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