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general description the max1765 is a high-efficiency, low-noise, step-up dc-dc converter intended for use in battery-powered wireless applications. this device operates at a high 1mhz fixed frequency while maintaining an exception- ally low quiescent supply current (200?). its small external components and tiny package make this device an excellent choice for small hand-held applica- tions that require the longest possible battery life. the max1765 uses a synchronous-rectified pulse- width-modulation (pwm) boost topology to generate 2.5v to 5.5v outputs from a wide range of input sources, such as one to three alkaline or nicd/nimh cells or a single lithium-ion (li+) cell. maxim's propri- etary architecture significantly improves efficiency at low load currents while automatically transitioning to fixed-frequency pwm operation at medium to high load currents to maintain excellent full-load efficiency. forced-pwm mode is available for applications that require constant-frequency operation at all load cur- rents, and the max1765 may also be synchronized to an external clock to protect sensitive frequency bands in communications equipment. the max1765? low-dropout (ldo) linear regulator and dc-dc converter have separate shutdown control. the linear regulator's 250m pass device maintains excel- lent dropout voltage at currents up to 500ma. the max1765 also features analog soft-start and current- limit functions to permit optimization of efficiency, exter- nal component size, and output voltage ripple. the max1765 comes in a 16-pin qsop package and a thermally enhanced 16-pin tssop-ep. ____________________________features high-efficiency step-up converter up to 93% efficiency adjustable output from +2.5v to +5.5v up to 800ma output pwm synchronous-rectified topology 1mhz operating frequency (or sync) ldo linear regulator 500ma ldo linear regulator 2.85v linear regulator output or adjustable (1.25v to 5v) low 125mv dropout at 500ma +0.7v to +5.5v input range 0.1a logic-controlled shutdown adjustable inductor current limit and soft-start thermal shutdown 1.5w, 16-pin tssop-ep package available max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator ________________________________________________________________ maxim integrated products 1 19-1805; rev 1; 4/11 for price, delivery, and to place orders, please contact maxim distribution at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 fbl onl track inl pout lx pgnd outl top view max1765 qsop/tssop-ep onb iset ref out gnd fb ona clk/sel pin configuration wireless handsets pcs phones palmtop computers personal communicators hand -held instruments portable audio players applications fbl ref ilim onl ona (0.7v to 5.5v) 3.3h outl = 2.85v (adj 1.25v to 5v) out = 3.3v out outl pout fb gnd pgnd track lx clk/sel onb inl max1765 typical operating circuit ordering information * ep = exposed pad. + denotes a lead(pb)-free/rohs-compliant package. part temp range pin-package MAX1765EEE+ -40 c to +85 c 16 qsop max1765eue+ -40 c to +85 c 16 tssop-ep*
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v out = v pout = v inl = v ona = v onl = 3.6v, clk/sel = fbl = onb = track = pgnd = gnd, iset = ref (bypassed with 0.22?), lx = open, outl = open (bypassed with 4.7?), t a = 0? to +85?, unless otherwise noted. typical values are at t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. ona, onb , onl, track, out, inl to gnd..............-0.3v, +6v pgnd to gnd.....................................................................?.3v lx to gnd ...............................................-0.3v to (pout + 0.3v) outl to gnd ..............................................-0.3v to (inl + 0.3v) clk/sel, ref, fb, fbl, iset, pout to gnd...................................................-0.3v to (out + 0.3v) outl short circuit .....................................................continuous continuous power dissipation (t a = +70?) 16-pin qsop (derate 8.3mw/? above +70?)...........667mw 16-pin tssop-ep (derate 19mw/? above +70?) ....1500mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? soldering temperature (reflow) .......................................+260? parameter symbol conditions min typ max units dc-dc converter input voltage range (note 1) 0.7 5.5 v inl voltage range (note 1) 2.3 5.5 v minimum startup voltage i load < 1ma, t a = +25 c, figure 2 0.9 1.1 v temperature coefficient of startup voltage i load < 1ma -2 m v / c fb regulation voltage v fb clk/sel = out, 0 < i lx < 0.55a 1.215 1.250 1.275 v fb input leakage current v fb = 1.35v 0.01 100 na output voltage adjust range 2.5 5.5 v load regulation clk/sel = out, 0 < i load < 800ma -1 % out voltage in track mode v outl > 2.0v, inl = pout v outl + 0.4 v outl + 0.5 v outl + 0.6 v frequency in startup mode f lx v out = 1.5v 125 1000 khz startup to normal mode transition voltage rising edge only (note 2) 2.00 2.15 2.30 v iset input leakage current v iset = 1.25v 0.01 50 na supply current in normal mode (note 3) clk/sel = onl = gnd, no load 100 200 a v fb = 1.5v 130 200 a supply current in low-noise pwm mode (note 3) c lk/s e l = ou t, no l oad fb = gn d ( lx sw i tchi ng ) 2.5 ma supply current in shutdown ona = onl = gnd, onb = out 1 10 a
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator _______________________________________________________________________________________ 3 electrical characteristics (continued) (v out = v pout = v inl = v ona = v onl = 3.6v, clk/sel = fbl = onb = track = pgnd = gnd, iset = ref (bypassed with 0.22?), lx = open, outl = open (bypassed with 4.7?), t a = 0? to +85?, unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units dc-dc switches pout leakage current v lx = 0v, v out = 5.5v 0.1 10 ? lx leakage current v lx = v out = v onb = 5.5v, ona = gnd 0.1 10 ? n-channel 0.17 0.28 switch on-resistance p-channel 0.22 0.5 n - c hannel c ur r ent li m i t ( n ote 4) i lim v iset = 1.25v, clk/sel = gnd or out 1000 1250 1600 ma p-channel turn-off current clk/sel = gnd 10 50 120 ma reference reference output voltage v ref i ref = 0a 1.230 1.250 1.270 v reference load regulation -1? < i ref < 50? 5 15 mv reference supply regulation 2.5v < v out < 5.5v 0.2 5 mv linear regulator inl voltage range (note 1) 2.3 5.5 v inl startup voltage v inl v out = 2v, rising edge only 2.15 2.30 2.45 v output voltage in internal feedback mode fbl = gnd, i outl = 10ma 2.80 2.85 2.90 v fbl dual-mode threshold 150 250 350 mv fbl regulation voltage v fbl fbl = outl, i outl = 10ma, i ref = 0a 1.230 1.250 1.270 v fbl input leakage current v fbl = 1.5v 0.01 50 na outl adjust range 1.25 5 v short-circuit current limit v fbl = 1v 550 1300 ma dropout resistance v fbl = 1v, i outl = 500ma 0.25 0.5 load regulation 1ma < i outl < 500ma, fbl = gnd 0.5 1 % line regulation 2.5v < (v out = v inl = v pout ) < 5.5v, fbl = outl -0.5 0.5 % inl supply current in shutdown outl = ona = onl = gnd 0.1 10 ? inl no-load supply current i outl = 0a, v inl = 5.5v 90 250 ? ac power-supply rejection f = 10khz 65 db thermal shutdown hysteresis approximately 10? 160 ?
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 4 _______________________________________________________________________________________ electrical characteristics (continued) (v out = v pout = v inl = v ona = v onl = 3.6v, clk/sel = fbl = onb = track = pgnd = gnd, iset = ref (bypassed with 0.22?), lx = open, outl = open (bypassed with 4.7?), t a = 0c to +85c, unless otherwise noted. typical values are at t a =+25 c.) parameter symbol conditions min typ max units control inputs 1.1v < v out < 1.8v 0.2 o n a, o nb , o n l ( n ote 5) 1.8v < v out < 5.5v 0.4 clk/sel 1.2v < v out < 5.5v 0.2 v out input low level track 1.2v < v inl < 5.5v 0.2 v inl v 1.1v < v out < 1.8v v out - 0.2 o n a, o nb , o n l ( n ote 5) 1.8v < v out < 5.5v 1.6 clk/sel 1.2v < v out < 5.5v 0.8 v out input high level track 1.2v < v inl < 5.5v 0.8 v inl v input leakage current (clk/sel, ona, onb , onl, track) 0.01 1 a internal oscillator frequency clk/sel = out 0.8 1 1.2 mhz external oscillator synchronization range 0.5 1.2 mhz oscillator maximum duty cycle 80 86 90 % minimum clk/sel pulse 200 ns m axi m um c lk/s e l ri se/fal l ti m e 100 ns
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator _______________________________________________________________________________________ 5 electrical characteristics (v out = v pout = v inl = v ona = v onl = 3.6v, clk/sel = fbl = onb = track = pgnd = gnd, iset = ref (bypassed with 0.22?), lx = open, outl = open (bypassed with 4.7?), t a = -40? to +85?, unless otherwise noted.) (note 6) parameter symbol conditions min typ max units dc-dc converter fb regulation voltage v fb clk/sel = out, 0 < i lx < 0.55a 1.210 1.280 v out voltage in track mode v outl > 2.0v, inl = pout v outl + 0.4 v outl + 0.6 v startup to normal mode transition voltage rising edge only (note 2) 2.00 2.30 v supply current in normal mode (note 3) clk/sel = onl = gnd, no load 200 ? supply current in low-noise pwm mode (note 3 c lk/s e l = ou t, v fb = 1.5v , no l oad 200 ? supply current in shutdown ona = onl = gnd, onb = out 10 ? dc-dc switches pout leakage current v lx = 0v, v out = 5.5v 10 ? lx leakage current v lx = v out = v onb = 5.5v, ona = gnd 10 ? n-channel 0.28 switch on-resistance p-channel 0.50 n - c hannel c ur r ent li m i t ( n ote 4) i lim v iset = 1.25v, clk/sel = gnd or out 1000 1600 ma p-channel turn-off current clk/sel = gnd 5 120 ma reference reference output voltage i ref = 0a 1.225 1.275 v linear regulator output voltage in internal feedback mode fbl = gnd, i outl = 10ma 2.79 2.90 v fbl input threshold 150 350 mv fbl regulation voltage fbl = outl, i outl = 10ma, i ref = 0a 1.225 1.275 v ldo startup voltage v out = 2v, rising edge only 2.15 2.45 v dropout resistance v fbl = 1v, i outl = 500ma 0.5 inl supply current in shutdown outl = ona = onl = gnd 10 ? inl no-load supply current i outl = 0a, v inl = 5.5v 250 ?
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 6 _______________________________________________________________________________________ electrical characteristics (continued) (v out = v pout = v inl = v ona = v onl = 3.6v, clk/sel = fbl = onb = track = pgnd = gnd, iset = ref (bypassed with 0.22?), lx = open, outl = open (bypassed with 4.7?), t a = -40c to +85c, unless otherwise noted.) (note 6) parameter symbol conditions min typ max units control inputs 1.1v < v out < 1.8v 0.2 o n a, o nb , o n l ( n ote 5) 1.8v < v out < 5.5v 0.4 clk/sel 1.2v < v out < 5.5v 0.2 v out input low level track 1.2v < v inl < 5.5v 0.2 v inl v 1.1v < v out < 1.8v v out - 0.2 o n a, o nb , o n l ( n ote 5) 1.8v < v out < 5.5v 1.6 clk/sel 1.2v < v out < 5.5v 0.8 v out input high level track 1.2v < v inl < 5.5v 0.8 v inl v input leakage current (clk/sel, ona, onb , onl, track) 1 a internal oscillator frequency clk/sel = out 0.8 1.2 mhz oscillator maximum duty cycle 79 90 % note 1: operating voltage. since the regulator is bootstrapped to the output, once started it will operate down to 0.7v input. note 2: the device is in startup mode when v out is below this value (see low-voltage startup oscillator section). do not apply full load current. note 3: supply current into the out and pout pins. this current correlates directly to the actual battery-supply current, but is reduced in value according to the step-up ratio and efficiency. note 4: minimum recommended iset voltage in normal mode is 0.625v. note 5: ona, onb, onl have hysteresis of approximately 0.15 v out . note 6: specifications to -40? are guaranteed by design and not production tested.
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator _______________________________________________________________________________________ 7 typical operating characteristics (t a = +25?, unless otherwise noted.) 0 0.001 1 0.1 0.01 track mode efficiency vs. load current (v outl = +5v) 30 10 70 50 90 40 20 80 60 max1765 toc05 load current (a) efficiency (%) v in = +1.2v v in = +1.2v v in = +3.6v normal mode v in = +2.4v v in = +3.6v v in = +2.4v pwm mode 0 0.05 0.10 0.15 0.20 0.25 0.30 0 200100 300 400 500 600 700 800 linear regulator dropout voltage vs. load current max1765 toc07 load current (ma) dropout voltage (v) v outl = +2.5v v outl = +2.85v v outl = +5v 0 1 1000 100 10 startup input voltage vs. output current 2.5 1.0 0.5 2.0 1.5 max1765 toc08 output current (ma) startup input voltage (v) t a = +25c t a = -40c t a = +85c 0 4 2 10 8 6 16 14 12 18 0 1.0 1.5 0.5 2.0 2.5 3.0 3.5 no-load supply current vs. input voltage max1765 toc09 input voltage (v) supply current (ma) fpwm mode normal mode 90 0 0.001 1 0.1 0.01 efficiency vs. load current (v out = +3.3v) 30 10 70 50 100 40 20 80 60 max1765 toc01 load current (a) efficiency (%) v in = +2.4v normal mode v in = +1.2v v in = +2.4v v in = +1.2v pwm mode 90 0 0.001 1 0.1 0.01 efficiency vs. load current (v out = +5v) 30 10 70 50 100 40 20 80 60 max1765 toc02 load current (a) efficiency (%) pwm mode v in = +3.6v v in = +2.4v v in = +1.2v v in = +3.6v normal mode v in = +2.4v v in = +1.2v 90 0 0.001 1 0.1 0.01 track mode efficiency vs. load current (v outl = +2.85v) 30 10 70 50 100 40 20 80 60 max1765 toc03 load current (a) efficiency (%) normal mode v in = +1.2v v in = +2.4v v in = +1.2v v in = +2.4v pwm mode 0 0.001 1 0.1 0.01 track mode efficiency vs. load current (v outl = +3.3v) 30 10 70 50 90 40 20 80 60 max1765 toc04 load current (a) efficiency (%) v in = +1.2v v in = +1.2v v in = +2.4v v in = +3.6v v in = +2.4v normal mode normal mode/ pwm mode pwm mode 0 600 400 200 800 1000 1200 02.0 1.5 0.5 1.0 2.5 3.0 3.5 4.0 4.5 5.0 maximum output current vs. input voltage max1765 toc06 input voltage (v) output current (ma) v out = +5v, i set = ref v out = +3.3v, i set = ref v out = +3.3v, i set = 0.5 ref v out = +5v, i set = 0.5 ref
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 8 _______________________________________________________________________________________ load transient response max1765 toc14 a: i out , 500ma/div b: v out ,100mv/div a b 50s/div v in = +2.4v, v out = +3.3v, i out = 0 to 500ma typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) 0 -10 -20 -30 -40 -50 -60 -70 -80 0.1 10 100 1 1000 ldo psrr vs. frequency (100hz to 1mhz) max1765 toc10 frequency (khz) ldo psrr (db) 16 0.1 1 10 boost followed by ldo output noise spectrum 0 max1765 toc11 frequency (mhz) noise (mv rms ) 4 2 8 10 6 12 14 v in = +2.4v v out = +3.3v line transient response (dc-dc) max1765 toc12 100s/div a: v in , 500mv/div b: v out , 1mv/div, ac-coupled a b v out = +3.3v, i = 0ma v in = +1.4v to +2.4v line transient response (linear) max1765 toc13 a: v in , 2v/div b: v out , 5mv/div, ac-coupled a b i = 0ma, v in = +3v to +5v, v out = +3.3v turn-on waveforms no soft-start components max1765 toc15a a: 0na, 5v/div b: v out , 2v/div c: input current, 1a/div a b c soft-start waveforms (r ss = 500k, c ss = 0.1f) max1765 toc15b a: 0na, 5v/div b: input current, 100ma/div c: v out , 1v/div a b c 2.5ms/div heavy-load switching waveforms (i out = 650ma, v in = +2.4v, v out = 3.3v) max1765 toc16 a: lx, 5v/div b: inductor current, 200ma/div c: output ripple, 50mv/div, ac-coupled a b c 500ns/div
max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator _______________________________________________________________________________________ 9 pin name function 1 fbl low-dropout linear regulator dual-mode feedback input. connect fbl to ground for 2.85v nominal output voltage. connect fbl to a resistor-divider from outl to ground for an adjustable output voltage. fbl regulates to 1.25v. 2 iset set n-channel current limit. for maximum current limit, connect iset to ref. to reduce current limit, use a resistor-divider from ref to gnd. if soft-start is desired, a capacitor can be added from iset to gnd. when ona = lo and onb = hi or v ref < 80% of nominal value, an on-chip 100k switchable resistor discharges iset to gnd. 3 ref 1.25v reference output. connect a 0.22? bypass capacitor to gnd; 50? of external load current is allowed. the reference is enabled if ona = hi, onb = lo, or onl = hi. 4 gnd ground. connect to pgnd with short trace. 5fb boost converter feedback input. connect a resistor-divider between out and gnd to set the output voltage in the range of 2.5v to 5v. in track mode, fb is disabled after outl is in regulation. 6 out boost converter ic power is derived from out. connect out to pout through a 4.7 resistor and bypass to gnd with a 0.68? capacitor. 7 ona on input. when high, the dc-dc is operational (table 2). 8 clk/sel clock input for the dc-dc converter. also serves to program operating mode of switch as follows: clk/sel = low: normal mode. operates at a fixed frequency, automatically switching to low-power (skip) mode when the load is minimized. clk/sel = hi: forced pwm mode. operates in low-noise, constant-frequency mode at all loads. clk/sel = clocked: synchronized forced pwm mode. the internal oscillator is synchronized to an external clock in the 500khz to 1200khz frequency range. pin description 0 0.4 0.2 0.8 0.6 1.2 1.0 1.4 0 0.4 0.6 0.2 0.8 1.0 1.2 1.4 switch current limit vs. v iset max1765 toc19 v iset (v) switch current limit (a) v out = +3.3 typical operating characteristics (continued) (t a = +25?, unless otherwise noted.) light-load switching waveforms (v in = +2.4v, v out = +3.3v, i out = 10ma) max1765 toc17 a: lx node, 5v/div b: inductor current, 200ma/div, ac-coupled c: output ripple, 20mv/div, ac-coupled a b c 500ns/div 450 0.1 1 10 linear-regulator output noise 50 0 max1765 toc18 frequency (mhz) noise (mv rms ) 150 250 350 i ldo = 200ma v ldo = 2.85v
max1765 detailed description the max1765 is a highly efficient, low-noise power supply for portable rf hand-held instruments. this boost power supply combines an ldo linear regulator, a low-noise, high-power, step-up switching regulator, an n-channel power mosfet, a p-channel synchro- nous rectifier, shutdown control, and a precision volt- age reference in a single 16-pin qsop or a thermally enhanced tssop-ep (figure 1). the switching dc-dc converter boosts a 1-cell to 3-cell nimh/nicd or a single li+ battery input to an adjustable output voltage between 2.5v and 5.5v. the max1765 guarantees startup with voltages as low as 1.1v and will remain operational down to 0.7v (figure 2). the internal ldo regulator provides linear postregulation for noise- sensitive circuitry, or it can be used as a separate volt- age output adjustable from 1.25v up to pout. the max1765 is optimized for use in cellular phones and other applications requiring low noise during full-power operation, as well as low quiescent current for maximum battery life during standby and shutdown. the device automatically transitions to a low-quiescent-current pulse-skipping control scheme during light loads that reduces the quiescent power consumption to 360?. the supply current of the device can be further reduced to 1? when the device is shut down. figure 2 shows a typical application of the max1765 in normal mode. the switching regulator supports two low-noise modes: fixed-frequency pwm for low noise in all load condi tions, and synchronization of the internal oscillator to an external clock driving the clk input. in track mode, the dc and linear regulator work together to maintain excellent psrr without excessive efficiency loss. additional max1765 features include synchronous rec- tification for high efficiency and increased battery life, dual boost shutdown controls for ? or a pushbutton momentary switch, and a separate shutdown control for the linear regulator. step-up converter during dc-dc converter operation, the internal n-chan- nel mosfet turns on for the first part of each cycle, allowing current to ramp up in the inductor and store energy in a magnetic field. during the second part of each cycle, the mosfet turns off and inductor current flows through the synchronous rectifier to the output filter capacitor and the load. as the energy stored in the inductor is depleted, the current ramps down and the synchronous rectifier turns off. the clk/sel pin deter- mines whether a pulse-skipping or pwm control method is used at light loads (table 1). normal operation pulling clk/sel low selects the max1765? normal operating mode. in this mode, the device operates in pwm when driving medium to heavy loads and auto- matically switches to skip mode if the load requires less power. skip mode allows higher efficiency than pwm under light-load conditions. 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 10 ______________________________________________________________________________________ pin name function 9 onb on input. when low, the dc-dc is operational (table 2). 10 pgnd power ground 11 lx inductor connection to the drain of p-channel synchronous rectifier and n-channel switch. 12 pout boost converter power output. pout is the source of the p-channel synchronous-rectifier mosfet switch. connect pout to inl. bypass pout to pgnd with a 100? capacitor. 13 inl linear regulator power input. source of pfet pass device connected between inl and outl. connect inl to pout. 14 outl linear regulator output. outl can source up to 500ma. bypass outl to gnd with a 4.7? capacitor. 15 track track-mode control input for dc-dc converter. in track mode, the boost converter output is sensed at out and set to 0.5v above outl to improve efficiency. set track to out for track mode and to gnd for normal operation (table 2). 16 onl linear regulator on input. enables the linear regulator output when track = low. ona and onb determine the linear regulator? output state when track = high. ep exposed pad (tssop only). internally connected to gnd and pgnd. connect to a large ground plane. pin description (continued)
light-load operation in normal mode at light loads, the max1765 operates by turning on the dc-dc converter? n-channel field-effect transistor (fet) when v fb < v ref , synchronized with the rising edge of the oscillator. the n-channel fet will remain on, ramping up the inductor current past the minimum inductor current, until the internal error amplifier and current mode circuitry determine that the needs of the system have been met or the device hits the iset cur- rent limit. the n-channel is then turned off and the p- channel is turned on until current decays to the p-channel turn-off current level. the n-channel will remain off until v fb is again less than v ref , and a rising edge of the oscillator occurs. max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator ______________________________________________________________________________________ 11 2.15v on outl pout lx pgnd ref shutdown logic thermal sensor max1765 error amp startup oscillator en q p p n mosfet driver with current limiting en 1mhz oscillator en d osc mode skip/pwm q q ifb pwm controller rdy 1.250v reference ic pwr iref ics fbl out v out onl inl onb gnd ona v out - 300mv iset onl ref clk/sel fb track track iset figure 1. functional diagram table 1. selecting the operating mode clk/sel mode features 0 normal operation high-efficiency pulse skipping at light loads, pwm at medium and heavy loads 1 forced pwm low noise, fixed frequency at all loads e xter nal c l ock 500kh z to 1.2m h z synchronized pwm low noise, fixed frequency at all loads
max1765 pwm operation in normal mode the max1765 transitions to fixed-frequency pwm oper- ation under medium and heavy loads. the n-channel fet is engaged when v fb < v ref and is kept on to ramp up the current in the inductor until one of the fol- lowing conditions occurs: the system needs are met, the next falling edge of the internal oscillator is achieved, or the maximum inductor current (iset) is reached. the n-channel is turned off, activating the p- channel synchronous rectifier that remains on until the inductor current gets to the p-channel turn-off current level, or v fb < v ref and there is a rising oscillator clock edge. the 1mhz fixed-frequency operation pro- duces an easily filtered fixed-noise spectrum. forced pwm operation when clk/sel is high, the max1765 operates in a low- noise pwm-only mode. the n-channel fet is turned on when v fb < v ref and is kept on to ramp up the induc- tor current until one of the following conditions occurs: the system needs are met, the next falling edge of the internal oscillator is achieved, or the iset is reached. the n-channel is then turned off, activating the p-chan- nel synchronous rectifier that remains on until the next rising edge of the oscillator, where the n-channel is again turned on under most conditions. the p-channel zero detect circuitry is deactivated in forced pwm mode. this means an n- or p-channel fet is on all the time for most load conditions. at light loads, the p-channel will remain on so the device can pass current back to the input from the out- put. the p-channel will only pass current for two cycles before it is disabled. then, the device remains inactive until v fb < v ref . during forced pwm operation, the max1765 switches at a constant frequency (1mhz) and modulates the mosfet switch pulse width to control the power trans- ferred per cycle in order to regulate the output voltage for most output currents. switching harmonics generat- ed by fixed-frequency operation are consistent and easily filtered. (see the boost followed by ldo output noise spectrum plot in the typical operating characteristics. ) synchronized pwm operation the max1765 can be synchronized in pwm mode to an external frequency of 500khz to 1.2mhz by applying an external clock signal to clk/sel. this allows inter- ference to be minimized in wireless applications. the synchronous rectifier is active during synchronized pwm operation. synchronous rectifier the max1765 features an internal 250m , p-channel synchronous rectifier to enhance efficiency. synchronous rectification provides a 5% efficiency improvement over similar nonsynchronous boost regulators. in pwm mode, the synchronous rectifier is turned on during the second portion of each switching cycle. at light loads (in normal mode), an internal comparator turns on the synchronous rectifier when the voltage at lx exceeds the boost regu- lator output, and turns it off when the inductor current drops below 50ma. low-voltage startup oscillator the max1765 uses a low-voltage startup oscillator for a 1.1v guaranteed minimum input startup input voltage. a schottky diode placed across lx and pout reduces the startup voltage to 0.9v. at startup, the low-voltage oscillator switches the n-channel mosfet until the out- put voltage reaches 2.15v. above this level, the normal boost-converter feedback and control circuitry takes over. once the device is in regulation, it can operate down to 0.7v input since internal power for the ic is bootstrapped from the out pin. do not apply full load until the output exceeds 2.3v. 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 12 ______________________________________________________________________________________ figure 2. typical application circuit clk/sel pgnd gnd onl track onb 4.7f fbl outl 33f 3.3h ref ilim 4.7 lx pout out fb logic inputs 0.22f 100f 0.68f 0.7v to 3.2v max1765 ona v in v outl = 2.85v 100k 165k v out 3.3v inl
linear regulator the max1765 contains an ldo with a fixed 2.85v (or adjustable) output. the max1765 linear regulator fea- tures a 250m , p-channel mosfet pass transistor. this provides several advantages, including longer bat- tery life, over similar designs using a pnp pass transis- tor. the p-channel mosfet requires no base-drive current. this reduces quiescent current considerably, since pnp-based regulators tend to waste base-drive current in dropout when the pass transistor saturates. connect the input of the linear regulator (inl) to pout. the linear regulator can be used to postfilter the switch- ing regulator or regulate a separate supply voltage. this regulated output is intended to power noise-sensi- tive analog circuitry, such as low-noise amplifiers and if stages in cellular phones and other instruments, and can deliver up to 500ma. use a 4.7? capacitor with less than a 1 equivalent series resistance (esr) on the output to provide stability. the linear regulator has an internal 1.3a (max) current limit and thermal-over- load protection circuitry to protect this output. configurations there are several useful circuit configurations that can be implemented with the max1765. the track input divides the circuit configurations into two types, one where the dc-dc converter tracks to the ldo output, and the other where the boost and the ldo regulate independently. track mode asserting the track input places the max1765 into track mode, where the dc-dc switching regulator? feedback pin (fb) is ignored, and the boost output (pout) ?racks?to 500mv above the linear regulator output. the primary use of the max1765 in track mode is as a simple or very-low-noise step-up/down power supply (see figures 3 and 4; also see the maximum output current vs. input voltage plot in the typical operating characteristics. ) this circuit operates as a linear regulator when the input supply (a battery) is greater than v ldo. when the battery discharges below v ldo, the dc-dc converter turns on, boosting pout to a constant 500mv above the linear regulator output. this configuration also allows for true shutdown (see true shutdown ). dual-supply mode when the track input is low, the max1765 operates two independent power supplies, a dc-dc converter, and a linear regulator. one such application of this con- figuration is shown in figure 4. in this mode, the device generates two boosted voltages from a single battery supply. the dc-dc converter could be used to supply the power amplifier (pa) of a cell phone, while the linear regulator powers the baseband functions within the phone. asserting track switches the device into track mode when the high-voltage supply for the pa is no longer needed, thus improving efficiency in standby- receive mode. when the pa again needs 5v, deassert the track input. shutdown the max1765 has a shutdown mode that reduces qui- escent current to 1?. during shutdown, the reference, ldo, dc-dc converter, and all feedback and control circuitry are off. table 2 shows the max1765 shutdown truth table. if ona, onb, and onl are all deasserted, the device is shut down. true shutdown when a typical boost converter is placed into shut- down, current can flow through the body diode of the synchronous rectifier to the load. the max1765 can be configured to allow true shutdown as shown in figure 5. the shutdown function is active low and is connected to both ona and onl. when asserted, both the dc-dc converter and the ldo are shut down simultaneously. max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator ______________________________________________________________________________________ 13 figure 3. simple step-up/step-down converter pgnd gnd max1765 fb v out = 2.5v - 5.0v at 500ma 4.7f 33f lx out pout track inl outl ilim ref onl clk/sel onb ona shdn input 0.7v to 5.5v * * * optional components fbl 0.22f *
max1765 the ldo acts like a switch in this situation and discon- nects the input from the load. connect fbl to a resis- tor-divider from v ref to gnd (r3 and r4 in figure 5) so that v fbl = 0.5v (above the dual mode threshold) when outl is regulated, to ensure that the linear regu- lator is saturated. another method to configure the max1765 for true shutdown is shown in figure 6. this shutdown function is active high and connects to the gate of a low-impedance pfet and onb. the pfet acts like a switch in this situation and disconnects the input from the load. reference the max1765 has an internal 1.25v, 1% reference. connect a 0.22? ceramic bypass capacitor to gnd within 0.2in (5mm) of the ref pin. ref can source up to 50? of external load current. typically connect iset to ref to give the max1765 full inductor current limit. design procedure setting dc-dc converter voltage set the output voltage between +2.5v and +5.5v by connecting a resistor voltage-divider from out to fb to gnd (figure 7). connect the resistor voltage-divider as close to the ic as possible, within 0.2in (5mm) of fb. choose r2 of 40k or less, then calculate r1 using: where v fb , the boost-regulator feedback set point, is +1.25v. for output voltages above 4v, connect a schottky diode between lx and pout to prevent voltage transi- tion from exceeding the lx voltage rating. setting the linear regulator voltage the ldo regulation voltage can also be set similarly to the dc-dc converter. connecting fbl to gnd sets the ldo output to 2.85v. to set other output voltages between 1.25v and pout, connect a resistor-divider from outl to fbl to gnd (figure 7). connect the resistor voltage-divider as close to the ic as possible, within 0.2in (5mm) of fbl. the maximum input bias cur- rent for the fbl input is 50na. choose r4 of 40k or less, then calculate r3 using: where v fbl , the linear regulator feedback set point, is +1.25v. setting the switch current limit and soft-start the iset pin adjusts the inductor current limit and implements soft-start. with iset connected to ref, the inductor current limits at 1.25a. with iset connected to a resistive divider set from ref to gnd, the current limit is reduced according to: i = lim 125 2 12 .a r rr ss ss ss + ? ? ? ? ? ? rr v v outl fbl 34 = ? ? ? ? ? ? - 1 rr v v out fb 12 = ? ? ? ? ? ? - 1 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 14 ______________________________________________________________________________________ table 2. operating mode truth table operating mode track ona onb onl linear regulator dc-dc converter ref shutdown x l h l off off off hhx x track hxlx on on on lhxh independent regulation lxlh on on on lhx l dc-dc only lxll off on on ldo only x l h h on off on dual mode is a trademark of maxim integrated products
implement soft-start by placing a resistor from iset to ref and a capacitor from iset to gnd (figure 8). in shutdown, iset is discharged to gnd through an on-chip 100k resistor. at power-up, iset is 0v and the current limit is zero. as the capacitor voltage rises, the current limit increases and the output voltage rises. the soft-start time constant is: placing a capacitor across the lower resistor of the cur- rent-limiting resistive divider provides both features simultaneously (figure 9). package selection the max1765 is available in two packages, a 16-pin qsop and a thermally enhanced tssop-ep. the qsop is the less expensive of the two packages, and requires a less complex layout design. this layout allows the designer to route underneath the device. the power dissipation for the qsop is 0.7w. the tssop-ep comes with an exposed metal pad that is connected to the substrate of the ic. this increases the power dissipation up to 1.5w for the tssop-ep. to achieve maximum power capability, the exposed pad of the tssop-ep should be reflowed to a pad with low thermal resistance. for convenience, this pad can be connected to agnd or pgnd. inductor selection the max1765? high switching frequency allows the use of a small surface-mount inductor. for most appli- cations, a 3.3? inductor works well. the inductor t = rise rc ss ss max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator figure 4. dual-output power supply max1765 input 0.7v to 5.5v gnd clk/sel fbl pgnd outl pout lx out ref ilim 4.7 0.68f 150k v ldo = 2.85v fb 33f x 2 3.3h track onl onb ona off on on off track track = low, v out = 5.0v track = high, v out = 3.35v 0.22f 50k 4.7f inl figure 5. ldo enable allows true boost shutdown lx pout inl outl output input max1765 onl ona shdn on off fbl r3 r4 figure 6. pfet allows true boost shutdown lx pout fb out output input max1765 shdn onb off on ______________________________________________________________________________________ 15
max1765 should have a saturation current rating exceeding the n-channel switch current limit; however, it is accept- able to bias the inductor current into saturation by as much as 20% if a slight reduction in efficiency is acceptable. lower current-rated inductors may be used if iset is employed to reduce the peak inductor current (see setting the switch current limit and soft- start ). for high efficiency, choose an inductor with a high-frequency core material to reduce core losses. to minimize radiated noise, use a toroid or shielded induc- tor. see table 3 for suggested components and table 4 for a list of component suppliers. output diode to assist startup with input voltages below 1.1v or when v out is set for >4v, use a schottky diode?uch as a 1n5817, mbr0520l or equivalent?etween lx and pout (figure 2). the schottky diode carries cur- rent after the synchronous rectifier turns off. thus, its current rating only needs to be 500ma. connect the diode as close to the ic as possible. do not use ordi- nary rectifier diodes; their slow switching speeds and long reverse-recovery times render them unacceptable. for input voltages over 1.8v, the schottky diode may improve light-load efficiency. input and output filter capacitors choose input and output filter capacitors that will ser- vice the input and output peak currents with accept- able voltage ripple. choose input capacitors with working voltage ratings over the maximum input volt- age and output capacitors with working voltage ratings higher than the output. a 100?, 100m , low equiva- lent-series-resistance (esr) tantalum output capacitor is recommended for most applications. at the output of the linear regulator (outl), use a 4.7? ceramic capacitor for stability at loads up to 500ma. the input filter capacitor reduces peak currents drawn from the input source and also reduces input switching noise. the input voltage source impedance determines the required size of the input capacitor. when operat- ing directly from one or two nimh cells placed close to the max1765, use a single 33? low-esr input filter capacitor. the sanyo poscap, panasonic sp/cb, and kemet t510 are good low-esr capacitors. low-esr tantalum capacitors offer a good trade-off between price and performance. do not exceed the ripple current ratings of tantalum capacitors. avoid aluminum electrolytic capacitors; their high esr typically results in higher output ripple voltage. bypass capacitors bypass ref to gnd with 0.22?. also, bypass out to gnd with a 0.68? ceramic capacitor, and connect out to pout with a 4.7 resistor. each of these com- ponents should be placed as close to its respective ic pins as possible, within 0.2in (5mm). layout considerations high switching frequencies and large peak currents make pc board layout a critical part of design. poor design will cause excessive emi and ground bounce, both of which can cause instability or regulation errors by corrupting the voltage and current feedback signals. power components?uch as the inductor, converter ic, filter capacitors, and output diode?hould be placed as close together as possible, and their traces should be kept short, direct, and wide. connect the inductor from the battery to the lx pins as close to the ic as possible. keep the voltage feedback network very close to the ic, within 0.2in (5mm) of the fb pins. keep noisy traces, such as those from the lx pin, away from the voltage feedback networks and guarded from them using grounded copper. refer to the max1765 ev kit for a full pc board example. 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 16 ______________________________________________________________________________________ figure 7. feedback connections max1765 inl outl pout out fbl fb gnd pgnd r3 r4 r2 r1 step-up output linear- regula tor output
applications information use in a typical wireless phone application the max1765 is ideal for use in digital cordless and pcs phones. the pa is connected directly to the step- up converter output for maximum voltage swing and power efficiency (figure 10). the internal linear regula- tor is used for postregulation to generate low-noise power for dsp, control, and rf circuitry. the following equations may be used to estimate the typical available output current under conditions other than those listed here: where i lim is the peak inductor current limit, f sw is the operating frequency (typically 1.2mhz), l is the induc- tance of the chosen inductor, l resr is the resistance of the chosen inductor, r nch and r pch are the resis- tances of the internal n-channel and p-channel, respectively. ii i id i f d l vi r l d vvi rl virr out max lim ripple ripple sw in lim nch esr out in lim nch esr out lim pch nch , =? ? ? ? ? ? ? ? () =? + () [] = ?+ + () +? () 2 1 max1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator ______________________________________________________________________________________ 17 figure 9. soft-start, maximum current limit c ss r ss i lim = 1.25a t ss = r ss c ss 500k < r ss < 1m max1765 ref iset 0.22f figure 8. soft-start, reduced current limit c ss max1765 ref iset 0.22f r ss1 r ss2 i lim = 1.25a t ss = (r ss1 || r ss2 ) c ss ( ) r ss2 r ss1 + r ss2 table 3. component selection guide production 3.3 h inductors capacitors schottky diodes surface mount coilcraft ds3316p coilcraft lpt3305 avx tps series kemet t510 series sanyo poscap series motorola mbr0520l nihon ep10qy03 table 4. component suppliers supplier country phone avx usa 843-448-9411 coilcraft usa 847-639-6400 kemet usa 810-287-2536 usa 408-629-4789 motorola japan 81-45-474-7030 usa 847-956-0666 sumida japan 81-3-3607-3302 note: please indicate that you are using the max1765 when contacting these component suppliers.
max1765 table 5 lists the typical available output current when oper- ating with one or more nicd/nimh cells or one li+ cell. adding a manual power reset a momentary pushbutton switch can be used to turn the max1765 on and off (figure 11). ona is pulled low and onb is pulled high to turn the device off. when the momentary switch is pressed, onb is pulled low and the regulator turns on. the switch must be pressed long enough for the microcontroller (?) to exit reset and drive ona high. a small capacitor is added to help debounce the switch. the ? issues a logic high to ona, which holds the device on, regardless of the switch state. to turn the regulator off, press the switch again, allowing the ? to read the switch status and pull ona low. when the switch is released, onb is pulled high. 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator 18 ______________________________________________________________________________________ table 5. typical available output current number of cells input voltage (v) output voltage (v) output current (ma) 1 nicd/nimh 1.2 3.3 330 2.4 3.3 730 2 nicd/nimh 2.4 5.0 460 3 nicd/nimh or 1 li+ 3.6 5.0 720 pa rf lx pout gnd outl control inputs c i/o max1765 inl c v dd i/o ona onb pout i/o 0.1f on/off 270k 270k max1765 figure 10. typical phone application figure 11. momentary pushbutton on/off switch package information for the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages . note that a ?? ?? or ??in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. package type package code outline no. land pattern no. 16 qsop e16+1 21-0055 90-0167 16 qsop-ep u16e+3 21-0108 90-0120
800ma, low-noise, step-up dc-dc converter with 500ma linear regulator maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 _____________________ 19 2011 maxim integrated products maxim is a registered trademark of maxim integrated products. max1765 revision history revision number revision date description pages changed 0 12/00 initial release 1 4/11 added lead-free designation, updated tocs 1 and 2, and updated pin description section 1, 7, 10

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