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_______________________________________________________________ maxim integrated products 1 for pricing, delivery, and ordering information, pl ease contact maxim direct at 1-888-62-62, or visit maxims esite at maxim-iccom internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds eneral description the max17115 includes a high-performance step-up regulator, a high-accuracy, high-voltage, low-dropout linear regulator (, a high-performance uffer ampi- fier, and a logic-controlled high-voltage switch loc the - converter is a high-freuency (1m current-mode step-up regulator with a uilt-in power mt t provides fast-transient response to pulsed loads while producing efficiencies over the uilt-in power mt allows output voltages as high as 1 from inputs from 5 to 55 a programmale soft- start function controls startup inrush currents the operational amplifier, typically used to drive the acplane (m, features high-output short-circuit current (ma, fast slew rate (5 f s, and wide and- width (m ts rail-to-rail input and output maimie application fleiility the high-voltage is adustale and has a high accuracy of q 5 t is typically used to drive a gamma reference divider string the high-voltage switch control loc modulates the shape of the gate-on supply and provides an adustale delay for power-up seuencing the high-voltage stress ( function is used to tem- porarily increase the source-driver supply voltage of the panel for aging tests the digital input controls an open-drain internal switch, which is typically used to change the feedac divider of the step-up regulator the max17115 is availale in a lead-free, -pin, thin pacage the pacage is a 5mm 5mm suare with a maimum thicness of mm for thin panel design pplications monitors ts features s 2.5v to 5.5v input supply range s pin-programmable 640kh1.2h siting reueny s urrent-oe step-p onerter at-ranient repone to pule oa hig-uray utput voltage 0. uilt-in 20v 4.6 0.1 i n-annel poer s yle-by-yle urrent imit hig iieny s programmable sot-start s hig-perormane perational mpliier 200m utput sort-iruit urrent 45v sle rate 20h - anit rail-to-rail input an utput s hig-voltage hig 0.5 uray 40m uarantee utput urrent s ogi-ontrolle hig-voltage sit it utable elay s hig-voltage stre oe s uilt-in seuening s ermal-erloa protetion s ate rier or input-sie rue suton? sit s ogi-eel suton input s imer-elaye ault suton or oot- regulator utput true shutdown is a trademark of maxim integrated pr oducts, inc. 19-47 e 1 41 in configuration rdering inforation enotes a eadp-freeos-comiant ackage. vi i vi max17115 thin qfn 5mm x 5mm top view 2930 28 27 1211 13 vref_o vop opo opi opgnd 14 vref_fb rhvspgnd pgnd fblx lx 1 2 n.c. 4 5 6 7 23 24 22 20 19 18 vdp vgh gnden fre hvs_en vref_i n.c. 3 21 31 10 vgh vdet 32 9 drn xo ss 26 15 in gnd 25 16 in vfl gte 8 17 cop pr p r pi-p max17115t - n to 5 n t downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 2 ______________________________________________________________________________________ stresses eond those isted under soute maximu m atings ma cause ermanent damage to the deice . these are stress ratings on, and functiona oeration of the deice at these or an other condi tions eond those indicated in the oerationa sec tions of the secifications is not imied. xosur e to asoute maximum rating conditions for extended eriods ma affect deice reiaiit. , , to a - to 75 t, xa, , , , to a - to 75 m, , m, at, to a - to ( , to a - to to a - to ( x to - to , to a - to to a - to m, to a - to ( m to - to , to - to ( maimum ontinuous utput urrent q 75ma x, m urrent ating (per pin 1a ontinuous ower issipation (t a 7 n -in t (derate 5m n aove 7 n 75m perating temperature ange - n to 5 n unction temperature 15 n torage temperature ange -5 n to 1 n ead temperature (soldering, 1s n oldering temperature (reflow n ri hrrisis ( 5, ircuit of igure 1, 1, , 0 to 5 , unless otherwise noted typical values are at t a 5 s i ris prr iis i p is spp nput-upply ange (ote 1 5 ndervoltage ocout rising, hysteresis m 5 uiescent urrent 1, x not switching 5 1 ma 1, switching 5 5 thermal hutdown temperature rising 1 ysteresis 15 hih-v nput oltage ange 1 1 ndervoltage ocout rising 5 5 nput-ias urrent o load 1 5 a ropout oltage - ma 5 5 egulation oltage 1ma ma 1 1 1 1 1, ma, - m maimumutput urrent ma sp-p rr utput-oltage ange 1 egulation oltage o load 1 1 15 ault trip evel alling edge 1 ault elay 5 55 ms oad egulation 1ma a 5a -1 ine egulation 5 to 5 15 nput-ias urrent 1 t a 5 1 5 na transconductance m 5a 1 5 5 x urrent imit 1, duty cycle 75 5 a downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds _______________________________________________________________________________________ ri hrrisis ontinue ( 5, ircuit of igure 1, 1, , 0 to 5 , unless otherwise noted typical values are at t a 5 prr iis i p is x n-esistance 5 1 w 1 x ias urrent x , t a 5 1 5 a urrent-ense transresistance 5 15 5 a sirreuency 5 7 5 1 1 1 ulldown urrent 5 a maimum uty ycle or 5 minimum n-time 1 ns s-sr eset esistance , 1ma 1 i harge urrent 1 a one threshold voltage rising 1 time n on pin ms psiiv -rivr ii r sihs m apacitor harge urrent m startup, m 5 a m turn-n threshold m rising 11 1 17 m ulldown esistance m 1ma 1 i nput ow oltage 5 to 7 nput igh oltage 5 < 5 1 5 < nput eaage urrent or 5, t a 5 -1 1 a -to- ropagation elay rising and falling ns nput-oltage ange 5 nput urrent m 15, 5 5 a m 15, 5 a -to-m esistance m 15, 5, 1ma 15 i m-to- esistance m 15, , 1ma i ip sris sih rivrat utput in urrent at 5 1 1 a at 1 ma at one oltage threshold at falling 5 at utput oltage ow at 1ma 1 5 at utput oltage igh at -1ma, - 5 - pri piir upply ange 1 vervoltage threshold rising 1 1 upply urrent o load 5 ma downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 4 ______________________________________________________________________________________ ri hrrisis ontinue ( 5, ircuit of igure 1, 1, , 0 to 5 , unless otherwise noted typical values are at t a 5 ri hrrisis ( 5, ircuit of igure 1, 1, , -40 to 5 , unless otherwise noted (ote prr iis i p is spp nput upply ange (ote 1 5 ndervoltage ocout rising, hysteresis m 5 uiescent urrent 1, x not switching 1 ma 1, switching 5 prr iis i p is nput ffset oltage -1 1 m nput-ias urrent , , t a 5 -5 5 na nput ommon-modeoltage ange utput oltage igh 5ma, - 1 - m utput oltage ow -5ma, 1 m lew ate to of , a 1p, a 1 w 5 s -d andwidth a 1p, a 1 w m hort-ircuit urrent ourcing, - , - 1 ma ining, , 1 ower-upply eection atio ,1 p p 1 d i t threshold t falling, 5 1 1 1 t ysteresis 5 m t nput-ias urrent t or 5, t a 5 -1 1 a xa utput oltage t , xa 1ma 1 hih-v srss nput ow oltage nput igh oltage 1 ulldown esistance i utput oltage (ote 1 eaage urrent , , t a 5 a n-esistance 5, 1ma w r ips nput ow oltage , 5 to nput igh oltage , 5 to 5 to 5 1 ysteresis , 15 nput-ias urrent t a 5 -1 1 a downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds _______________________________________________________________________________________ 5 ri hrrisis ontinue ( 5, ircuit of igure 1, 1, , -40 to 5 , unless otherwise noted (ote prr iis i p is hih-v nput-oltage ange 1 1 ndervoltage ocout rising 5 nput-ias urrent o load 5 a ropout oltage ma, - 5 egulation oltage 1ma ma 1 15 1 1, ma, - m maimum utput urrent ma sp-p rr utput-oltage ange 1 egulation oltage o load 1 15 ine egulation 5 to 15 transconductance m 5a 55 sih x urrent imit 1, duty cycle 75 5 a x n-esistance 5 w urrent-ense transresistance 5 a sirreuency 5 7 5 1 1 ulldown urrent 5 a maimum uty ycle or 5 s-sr eset esistance , 1ma w harge urrent 1 a psiiv -rivr ii r sihs m apacitor harge urrent m startup, m a m turn-n threshold m rising 11 17 m ulldown esistance m 1ma w nput ow oltage 5 to 7 nput igh oltage 5 < < 5 1 5 < < nput-oltage ange 5 nput urrent m 15, 5 a m 15, a 5 -to-m esistance m 15, 5, 1ma 15 w m-to- esistance m 15, , 1ma w downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 6 ______________________________________________________________________________________ ri hrrisis ontinue ( 5, ircuit of igure 1, 1, , -40 to 5 , unless otherwise noted (ote ote 1 or 55 , use for no longer than 1 of lifetime or continuous operation, input voltage should not eceed 55 ote 2 pecifications to t a - n are guaranteed y design, not production tested prr iis i p is ip sris sih rivr at utput in urrent at 5 1 a at 1 ma at one oltage threshold at falling 5 at utput oltage ow at 1ma 5 at utput oltage igh at -1ma, - 5 pri piir upply ange 1 vervoltage threshold rising 1 1 upply urrent o load 5 ma nput ffset oltage -1 1 m nput ommon-mode oltage ange utput oltage igh 5ma, - 1 m utput oltage ow -5ma, 1 m hort-ircuit urrent ourcing, - , - 1 ma ining, , 1 ower-upply eection atio , 1 p p 1 d i t threshold t falling, 5 1 1 xa utput oltage t , xa 1ma hih-v srss nput ow oltage nput igh oltage 1 ulldown esistance i utput oltage (ote 1 n-esistance 5, 1ma w r ips nput ow oltage , 5 to nput igh oltage , 5 to 5 to 5 1 downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds _______________________________________________________________________________________ tpical perating characteristics (ircuit of igure 1, 5, ma 1, t a 5 n , unless otherwise noted step-up regulator efficiency vs. load current load current (ma) efficiency (%) 100 1000 5550 45 75 70 6560 90 85 80 40 10 max17115 toc01 u 50 u power-up sequence max17115 toc02 a0v 0v c 0v d 0v 0v e f 0v b 10ms/div r load = 47 i a: v s 5v/div b: v lx 10v/div c: v ma 10v/div d: v vrefo 10v/div e: v vdm 2v/div f: v vm 20v/div in supply quiescent current vs. in voltage in voltage (v) current (ma) 3.5 4.0 4.5 5.0 5.5 3.0 1 2 30 2.5 maxx17115 toc03 switcing nonswitcing step-up regulator output load regulation vs. load current load current (ma) load regulation error (%) 100 1000 -0.6 -0.8 -0.2-0.4 0 0.4 0.2 -1.0 10 maxx17115 to04 u 5 reference voltage output load regulation vs. load current load current (ma) load regulation error (%) 40 60 80 20 -0.40 -0.60 0 0.40 0.20 -0.20 -0.80 0 maxx17115 to05 reference voltage output line regulation (%) v vref_i voltage (v) line regulation error (%) 17 18 19 20 16 0 0.05 -0.05 0.10 -0.10 15 maxx17115 to06 downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds ______________________________________________________________________________________ tpical perating characteristics continued (ircuit of igure 1, 5, ma 1, t a 5 n , unless otherwise noted step-up regulator load-transient response 100s/div load current500ma/div v main (ac-coupled)200mv/div 2a/div0a inductorcurrent 50ma 0v max17115 0 power-up sequence 10ms/div a b 0v 0v 0v 0v a: v sup , 5v/div d: v vref_o , 10v/div b: v lx , 10v/div e: v vdpm , 2v/div c: v main , 10v/div f: v vm , 20v/div 0v 0v e c f d max1115 10 r load i operational amplifier frequency response frequency (hz) gain (db) 1000 10,000 100,000 -6 -8 0 -2-4 42 -10 100 maxx17115 t11 n a 100f a operational amplifier large-signal step response 100ns/div v opi 2v/div v opo 2v/div 2v 2v max17115 toc12 v vop = 10v step-up regulator soft-start (heavy load) 2ms/div r load = 47 i v sup 2v/divv gate 2v/div v main 10v/div 1a/div0a inductorcurrent 0v 0v 0v max17115 07 step-up regulator pulsed load-transient response 10s/div load current1a/div v main (ac-coupled)200mv/div 1a/div0a inductorcurrent 50ma 0v max17115 0 downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds _______________________________________________________________________________________ tpical perating characteristics continued (ircuit of igure 1, 5, ma 1, t a 5 n , unless otherwise noted operational amplifier load-transient response 400ns/div v opo (ac-coupled)1v/div i opo 100ma/div 0v 0ma max17115 toc15 operational amplifier small-signal step response 40ns/div 100mv/div(ac-coupled) v opi v opo 100mv/div(ac-coupled) 0v 0v max17115 toc1 operational amplifier rail-to-rail input/output 4s/div v opi 5v/div v opo 5v/div 0v 0v max17115 toc14 v vop = 10v downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 10 _____________________________________________________________________________________ in description pi i 1 igh-oltage egulator eedac nput onnect to the center of a resistive voltage- divider etween and a to set the output voltage lace the resistive voltage-divid- er within 5mm of igh-oltage egulator utput ypass to a with a minimum f capacitor within 5mm of the pin igh-oltage egulator upply nput ypass to a with a minimum 1 f capacitor within 5mm of the pin perational amplifier upply nput typically connected to the output of the step-up regulator ypass to with a minimum 1 f capacitor within 5mm of the pin 5 perational amplifier utput is high impedance in shutdown perational amplifier oninverting nput 7 perational amplifier round igh-oltage witch ontrol nput hen is high, the high-voltage switch etween and m is on and the high-voltage switch etween m and is off hen is low, the switch etween and m is off and the switch etween m and is on is inhi- ited y the and when the voltage on m is less than 1 xa eset and xa unction utput 1 t oltage-etection nput onnect t to the center of a resistive voltage-divider etween and a to set the threshold voltage for the xa function 11 igh-oltage tress ontrol nput hen is high, the internal switch etween and a is on hen is low, is high impedance 1 reuency-elect nput onnect to a to select the step-up regulators operating freuency onnect to to select the step-up regulators 1m operating freuency this input has f a pulldown current 1 hutdown ontrol nput onnect to a to disale the oost operation onnect to to enale the oost operation 1, a analog round 15, 1 ower-upply nput supplies the internal reference and other internal circuitry onnect to the input supply voltage and ypass to a with a minimum 1 f ceramic capacitor (in 15 sup- plies current to internal analog circuits sing an filter on pin 15 improves noise performance of the minimum resistor should e used on pin 1 due to high current through pin 1 17 at ternal p-hannel mt ate-rive utput f used, connect at to the gate of an eternal p-channel mt etween the input supply and the step-up converters inductor (see igure 1 f not used, leave at unconnected 1, 1 x tep-p egulator witching ode rain of the internal n-channel mt etween x and onnect the inductor and catch diode here and minimie trace area for lowest m , 1 ower round ource of the internal n-channel mt etween x and , o onnection ot internally connected pen-rain utput of the nternal n-hannel mt to a onnect to through a resistor to adust the step-up converters output to a higher voltage f unused, leave uncon- nected hen is low, is high impedance hen is logic-high, con- nects to a tep-p egulator eedac nput onnect to the center of a resistive voltage-divider etween the step-up regulator output and a to set the regulators output voltage lace the resistive voltage-divider within 5mm of downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds ______________________________________________________________________________________ 11 in description continued pi i 5 m ompensation in for rror amplifier onnect a series from m to a typical values are 75 i and 5p 7 oft-tart ontrol in onnect a capacitor ( to this pin eave unconnected if a slow soft- start is not desired the soft-start capacitor is charged y a f a current source the full current limit is reached after around t f sn the soft-start capacitor is discharged to a when is low n s rise, the soft-start capacitor is uicly charged t o , after which, soft-start egins m igh-oltage witch elay nput onnect a capacitor from m to a to set the high-voltage switch startup delay igh-oltage witch upply nput ource of the internal high-voltage p-channel mt etween and m ypass to with a minimum of 1 f capacitor within 5mm of 1 m igh-oltage witch utput m is the common unction of the internal high-voltage mts m is typically used to power the gate-driver s positive supply input igh-oltage witch nput rain of the internal high-voltage mt switch etween and m posed ad onnect to a downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 12 _____________________________________________________________________________________ igure 1. tica erating ircuit v gon 30v/20ma c310 f 25v 33nf 1 f 1 f 2.2 f c410 f 25v q1 v goff -6.8v/20ma c1 10 f 6.3v r1137k r3 150k r211.5k r510k r610k 150k 100k 110k 100k c210f 6.3v c5 1 f 0.1 f 1k 33nf 20k 6.8v 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f l1 3 h v sup 4.5v to 5.5v v in v in v main 16v/500ma gat f l pgn agn ss rhvs vop opgn opo opi vrfi vrfo vrff vt in comp n fr hvsn v gon vgh vghm rn vfl v in from tcon to gat rivr vpm ao to vcomacplan v gamma 15v/20ma v main v main v sup p 30 2 3 1 r4 5.6 r4 4.5k opn 560f max17115 downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds ______________________________________________________________________________________ 1 tpical perating circuit the max17115 typical operating circuit (igure 1 is a complete power-supply system for tt displays the circuit generates a 15ma source-driver sup- ply and ma and -ma gate-driver sup- plies the input-voltage range for the is from 5 to the listed load currents in igure 1 are availale from a 5 to 55 supply tale 1 lists some rec- ommended components, and tale lists the contact information of component suppliers detailed description the max17115 contains a high-voltage step-up regula- tor, a high-accuracy linear regulator, a high-performance amplifier, a high-voltage switch control loc for gate- driver supply modulation, and a logic-controlled open- drain mt switch to a for high-voltage stress aging tests igure shows the max17115 functional diagram step-p regulator the main step-up regulator employs a current-mode, fied-freuency (1m-selectale m archi- tecture to maimie loop andwidth and provides fast- transient response to pulsed loads typical of tt- panel source drivers igh switching freuency opera- tion allows the use of low-profile inductors and ceramic capacitors to minimie the thicness of panel designs a current-control eternal capacitor-controlled programmale soft-start minimies inrush currents the output voltage can e set from to 1 with an eter- nal resistive voltage-divider the regulator controls the output voltage and the power delivered to the output y modulating the duty cycle ( of the internal power mt in each switching cycle the duty cycle of the mt is approimated y ma ma - able 1. omponent it able 2. omponent supplier rr sii sripi 1, 1 f , x5 ceramic capacitors (5 t 1x51 , 1 f , 5 x5 ceramic capacitors (1 t 1x511m 1 a, chotty diode (m-flat toshia m rr sii sripi , ma, 1 dual diodes (t airchild mm1 1 f , a inductor umida - 1 -7 ia, p-channel mt, -m i ishay owera sppir ph si airchild emiconductor 7--1 7--5 wwwfairchildsemicom umida orp -- --1 wwwsumidacom t orp 7-55-7 7-55-7 wwwcomponenttdcom toshia america lectronic omponents, nc -55- -5- wwwtoshiacomtaec ishay -5- -5- wwwvishaycom downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 14 _____________________________________________________________________________________ igure . m1711 unctiona iagram v gon v goff v in v main gate fb lx pgnd agnd ss rhvs vop opo opgnd opi vref_i vref_o vref_fb vdet in step-up controller in en comp freq hvs_en vgh vghm drn vflk vdpm xao oscillator linear regulator switch control ref soft-start ep max17115 downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds ______________________________________________________________________________________ 15 igure . ste- eguator unctiona iagram igure shows the functional diagram of the step-up regulator an error amplifier compares the signal at to 1 and changes the m output the voltage at m sets the pea inductor current as the load var- ies, the error amplifier sources or sins current to the m output accordingly to produce the inductor pea current necessary to service the load to maintain stail- ity at high duty cycles, a slope-compensation signal is summed with the current-sense signal n the rising edge of the internal cloc, the controller sets a flip-flop, turning on the n-channel mt and apply- ing the input voltage across the inductor the current through the inductor ramps up linearly, storing energy in its magnetic field nce the sum of the current-feedac signal and the slope compensation eceeds the m voltage, the controller resets the flip-flop and turns off the mt ince the inductor current is continuous, a transverse potential develops across the inductor that turns on the oost diode (1 the voltage across the inductor then ecomes the difference etween the out- put voltage and the input voltage this discharge condi- tion forces the current through the inductor to ramp ac down, transferring the energy stored in the magnetic field to the output capacitor and the load the mt remains off for the rest of the cloc cycle perational plifier the max17115 has one operational amplifier the uffer amplifier is typically used to drive the acplane voltage (m in tt s t features high output cur- rent, 5 f s slew rate, and md andwidth the rail-to-rail input and output capaility maimies system fleiility in ss 1.24v 1.00v fb comp oscillator current sense logic and driver ilim comparator error amp pwm comparator fault comparator to fault logic freq lx pgnd soft-start clock slope comp c downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 16 _____________________________________________________________________________________ ort-ircuit urrent imit the operational amplifier limits short-circuit current to approimately q ma if the output is directly shorted to or to f the short-circuit condition persists, the unction temperature of the rises until it reaches the thermal-shutdown threshold (1 n typ and acti- vates the thermal-fault protection, shutting off all the s outputs the restarts automatically when the device cools down y approimately 15 n driving a pure apacitive oad n general, the acplane (m consists of a dis- triuted series capacitance and resistance, a load that can e easily driven y the uffer owever, if the uffer is used in an application with a pure capacitive load, steps must e taen to ensure stale operation as the uffer amplifiers capacitive load increases, the amplifiers andwidth decreases and gain peaing increases a 5 i to 5 i small resistor placed etween and the capacitive load reduces peaing, ut also reduces the gain an alternative method of reducing peaing is to place a series networ (snuer in par- allel with the capacitive load the networ does not continuously load the output or reduce the gain typical values of the resistor are etween 1 i and i , and the typical value of the capacitor is 1n nderoltage locout vl the circuit compares the input voltage at with the threshold (5 typ to ensure the input voltage is high enough for reliale operation the wide m (typ hysteresis prevents supply transients from causing a restart the startup procedure egins when the input voltage eceeds the rising threshold and goes aove threshold uring normal operation, if the input voltage falls elow the falling threshold, the controller turns off the main step-up regulator, turns off the linear regulator, pulls at high to turn off the eternal p-channel mt, disales the uffer, plac- ing its output into a high-impedance state, and disales the switch control loc, placing m into a high- impedance state high-ccurac high-voltage ld regulator the features high output accuracy ( q 5 and low-dropout ( voltage (5 typ and can supply at least ma the is typically used to drive a gamma uffer reference resistor string and its output voltage is adustale through a resistor-divider ower-p seuence and soft-start nce eceeds its (5 typ and is aove its logic-high threshold, the startup procedure egins at is initially high and pulled low to turn on the eter- nal p-channel mt if no output fault is detected after at reaches its at-done threshold, the main step-up regulators soft-start egins ith the main step- up regulators soft-start, the voltage on and rises nce or eceeds the , the relative uffer amplifier and are enaled igure shows the power-up seuence the employs a current-ased, eternal-capacitor adustale soft-start for the step-up regulator to control inrush current and voltage overshoot and to ensure a well-defined startup ehavior the voltage level on the pin directly controls an internal current limit the cur- rent limit reaches its full current limit at approimately t f sn the step-up regulator output voltage usually reaches regulation efore reaches its fully charged state a capacitor ( m from m to a determines the switch-control-loc startup delay after the s oft-start routine is complete, a 5 f a current source starts charging m nce the capacitor voltage eceeds 1 (typ, the switch-control loc is enaled as shown in ig ure after the switch-control loc is enaled, m can e connected to or through the internal hig h- voltage p-channel switches, depending upon the stat e of efore startup ( is low or when is less than its , oth m switches are turned off and m is internally connected to a to discharge m elect m to set the delay time using the following euation m 5 a atm 1 f switch-control bloc the switch-control loc is not activated until all four of the following conditions are satisfied u the input voltage eceeds its u the soft-start routine of the oost regulator is complete u o fault condition is detected u m eceeds its turn-on threshold m egins charging when reaches the internal threshold nce activated, if is high, the 5 i (typ internal p-channel switch etween and m turns on and the i (typ p-channel switch etween m downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds ______________________________________________________________________________________ 1 igure 4. power- seuence in uvlo v th > 2.1v 0.4v ss done v in time v en time v gate time v ss time v main v gon time v goff v vref_o time v vghm v vdpm time 5.4v 1.24v startup procedure begins soft-start begins vghm depends on vflk soft-start ends vghm is floating downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 1 _____________________________________________________________________________________ and turns off f is low, the 5 i (typ internal p-channel switch etween and m turns off and the i (typ p-channel switch etween m and turns on efore activation, neither switch is turned on and m is in a high-impedance state fault rotection uring steady-state operation, if the output of the main regulator does not eceed its respective fault-detection threshold, the max17115 activates an internal fault timer f the continuous fault eceeds the fault-timer duration (55ms typ, the max17115 sets the fault latch to shut down all the outputs and turn off the eternal p-channel mt (at is pulled high nce the fault condition is removed, cycle the input voltage to clear the fault latch and reactivate the device the max17115 also provides for the output of the step-up regulator y monitoring the voltage on the pin uring normal operation, if is higher than the overvoltage threshold ( typ, the step-up con- verter stops switching to prevent ecessive voltage from damaging the max17115 nce drops elow the threshold voltage, the step-up regulator resumes switch- ing and regulates the needed output voltage theral-erload rotection thermal-overload protection prevents ecessive power dissipation from overheating the max17115 hen the unction temperature eceeds t 1 n (typ, a ther- mal sensor immediately activates the fault protection to shut down all outputs and turns off the eternal p-chan- nel mt (at is pulled high, allowing the device to cool down nce the device cools down y approi- mately 15 n , the max17115 starts up automatically the thermal-overload protection protects the controller in the event of fault conditions or continuous operation, do not eceed the asolute maimum unction temperature rating of t 15 n high-voltage stress hvs ode the mode is used to increase the supply voltage of tt for aging tests the max17115 provides an internal open-drain switch to a that is typically used to change the feedac divider impedance of the step- up regulator ( onnect an appropriate resistor from to to implement this feature a control input ( determines when the switch is turned on hen is high, the internal switch is turned on and the output voltage is adusted accord- ing to the resistor connected to the feedac input onversely, when is low, the switch is turned off and the output remains in its original voltage setting function xa is an open-drain output that connects to a w hen- ever is elow its threshold (5 typ or t is elow its detection threshold (1 typ n the m eantime, m is tied to xa is guaranteed to remain lo w until falls elow the xa level (17 ma design rocedure step-p regulator inductor election the minimum inductance value, pea current rating, and series resistance are factors to consider when select- ing the inductor these factors influence the converters efficiency, maimum output load capaility, transient- response time, and output-voltage ripple ie and cost are also important factors to consider the maimum output current, input voltage, output volt- age, and switching freuency determine the inductor value ery high inductance values minimie the current ripple and therefore reduce the pea current, which decreases core losses in the inductor and conduction losses in the entire power path owever, large induc- tor values also reuire more energy storage and more turns of wire, which increase sie and can increase con- duction losses in the inductor ow-inductance values decrease the sie, ut increase the current ripple and pea current inding the est inductor involves choos- ing the est compromise etween circuit efficiency, inductor sie, and cost the euations used here include a constant, , which is the ratio of the inductor pea-to-pea ripple current to the average inductor current at the full-load cur- rent the est trade-off etween inductor sie and circuit efficiency for step-up regulators generally has an etween and owever, depending on the a characteristics of the inductor core material and ratio of inductor resistance to other power-path resistances, the est can shift up or down f the inductor resis- tance is relatively high, more ripple can e accepted to reduce the numer of turns reuired and increase the wire diameter f the inductor resistance is relatively low, increasing inductance to lower the pea current can decrease losses throughout the power path f etremely thin high-resistance inductors are used, as is common for panel applications, the est can increase to etween 5 and 1 downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds ______________________________________________________________________________________ 1 nce a physical inductor is chosen, higher and lower values of the inductor should e evaluated for efficiency improvements in typical operating regions n igure 1, the s gate-on and gate-off supply voltages are generated from two unregulated charge pumps driven y the step-up regulators x node the additional load on x must therefore e considered in the inductance and current calculations the effective maimum output current, ma( ecomes the sum of the maimum load current of the step-up regulators output plus the contriutions from the positive and nega- tive charge pumps ma( ma(max e ( e 1 where ma(max is the maimum step-up output cur- rent, e is the numer of negative charge-pump stag- es, e is the numer of positive charge-pump stages, is the negative charge-pump output current, and is the positive charge-pump output current, assum- ing the initial pump source for is ma sing the typical operating circuit of igure 1, calculate the approimate inductor value using the typical input voltage ( , the maimum output current ( ma( , the epected efficiency ( e t taen from an appropriate curve in the tica erating haracteristics section, and an estimate of ased on the aove discussion ma t ma ma( - ( ( ( f hoose an availale inductor value from an appropriate inductor family alculate the maimum input current at the minimum input voltage ( (m using con- servation of energy and the epected efficiency at that operating point ( e m taen from the appropriate curve in the tica erating haracteristics ma( ma (,max (m m alculate the ripple current at that operating point and the pea current reuired for the inductor (m ma ma (m ( - f a (,max the inductors saturation current rating and the max17115s x current limit ( m should eceed a , and the inductors current rating should eceed (,max or good efficiency, choose an inductor with less than 1 i series resistance onsidering igure 1, the maimum load current ( ma(max is 5ma, with a 1 output and a typical input voltage of 5 the effective full-load step-up cur- rent is ma( 5ma 1 o ma (11 o ma 5ma onsidering the typical operating circuit, the switching freuency is set to 1m, the maimum load current ( ma(max is 5ma with a 1 output and a typical input voltage of 5 hoosing an of 5 and estimat- ing efficiency at this operating point 5 1 - 5 ( ( ( 1 5a 1m 5 f sing the circuits minimum input voltage (5 and esti- mating efficiency of at that operating point (,max 5a 1 a 5 = the ripple current and the pea current are 5 (1-5 a 1 1m f a a a 5a + = utput-apacitor election the total output voltage ripple has two components the capacitive ripple caused y the charging and discharg- ing of the output capacitance, and the ohmic ripple due to the capacitors and ( ( ( ( a (t ma ma t ma f ? + = ? ? ? ? ? ? where a is the pea inductor current (see the inductor seection section or ceramic capacitors, downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 20 _____________________________________________________________________________________ the output-voltage ripple is typically dominated y ( the voltage rating and temperature charac- teristics of the output capacitor must also e considered input-apacitor election the input capacitor ( reduces the current peas drawn from the input supply and reduces noise inection into the two 1 f ceramic capacitors are used in the typical operating circuit (igure 1 ecause of the high source impedance seen in typical la setups actual applications usually have much lower source impe- dance since the step-up regulator often runs directly from the output of another regulated supply typically, can e reduced elow the values used in the typi- cal operating circuit nsure a low-noise supply at y using adeuate alternatively, greater voltage varia- tion can e tolerated on if is decoupled from using an lowpass filter (see and 5 in igure 1 ectifier diode the max17115s high switching freuency demands a high-speed rectifier chotty diodes are recommended for most applications ecause of their fast recovery time and low forward voltage n general, a a chotty diode complements the internal mt well tep-p egulator utput-oltage election the output voltage of the main step-up regulator is set y connecting a resistive voltage-divider from the output ( ma to a with the center tap connected to (see igure 1 elect in the 1 i to 5 i range alculate 1 with the following euation ma 1 ( -1 where , the step-up regulators feedac set point, is 1 lace 1 and close to the ig-oltage tress mode utput-oltage etting ee igure 1 for the typical operating circuit is con- nected to to change the output voltage whenever is high the reuired value for can e calcu- lated with the following euation ma 1 1 (1 ? + oop ompensation hoose m to set the high-freuency integrator gain for fast-transient response hoose m to set the integrator ero to maintain loop staility or low- output capacitors, use the following euations to otain stale performance and good transient response t t m ma(max t t m ma(max m 5 1 to further optimie transient response, vary m in steps and m in 5 steps while oserving transient-response waveforms high-voltage ld linear regulator utput-oltage election the output voltage of the high-accuracy is set y connecting a resistive voltage-divider from the output ( to a with the center tap connected to (see igure 1 elect in the 1 i to 5 i range alculate 5 with the following euation 5 ( -1 where , the s feedac set point, is 1 lace 5 and close to the input and utput apacitor election to ensure staility of the , use a minimum of 1 f on the regulators input ( and a minimum of f on the regulators output ( lace the capaci- tors near the pins and connect their ground connections directly together pplications inforation ower dissipation an s maimum power dissipation depends on the thermal resistance from the die to the amient environ- ment and the amient temperature the thermal resis- tance depends on the pacage, copper area, other thermal mass, and airflow more copper, cool- er amient air, and more airflow increase the possile dissipation, while less copper or warmer air decreases the s dissipation capaility the maor components of power dissipation include the power dissipated in the step-up regulator and the power dissipated y the uffer amplifier and high-voltage downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds ______________________________________________________________________________________ 21 tep-p egulator the largest portions of power dissipation in the step- up regulator are the internal mt, the inductor, and the output diode f the step-up regulator has efficiency, approimately to 5 of the power is lost in the internal mt, approimately to in the inductor, and approimately 1 in the output diode the remaining 1 to is distriuted among the input and output capacitors and the traces f the input power is approimately 5, the power loss in the internal mt is approimately 15m to 5m the follow- ing formula can e used to estimate the power loss in the internal power mt (ecluding switching losses x (,max = where is the on-resistance for the internal power mt perational mplifiers the power dissipated in the uffer amplifier depends on the output current, the output voltage, and the supply voltage ( ) - where is the output current sourced y the amplifier, and is the output current that the amplifier sins ig-oltage d egulator the power dissipation of the high-voltage depen ds on load current and the voltage drop etween and t can e estimated y the following formul a a where a is the output current from the and is the voltage drop etween and cb laout and rounding areful layout is important for proper operation se the following guidelines for good layout u minimie the area of high-current loops y placing the inductor, the output diode, and the output capa ci- tors near the input capacitors and near the x and pins the high-current input loop goes from th e positive terminal of the input capacitor to the ind uc- tor, to the s x pin, out of , and to the in put capacitors negative terminal the high-current out put loop is from the positive terminal of the input cap aci- tor to the inductor, to the output diode (1, and to the positive terminal of the output capacitors, reconne ct- ing etween the output capacitor and input capacitor ground terminals onnect these loop components with short, wide connections avoid using vias in the high-current paths f vias are unavoidale, use many vias in parallel to reduce resistance and inductance reate a power-ground island ( consisting of the input and output capacitor grounds, pin, and any charge-pump components onnect all these together with short, wide traces or a small ground plane maimiing the width of the power ground traces improves efficiency and reduces out- put voltage ripple and noise spies reate an analog ground plane (a consisting of the a pin, all the feedac-divider ground connections, the opera- tional amplifier divider ground connection, the m, m and capacitor ground connections, and the devices eposed acside pad onnect the a and islands y connecting the pin directly to the eposed acside pad mae no other connections etween these separate ground planes u lace all feedac voltage-divider resistors within 5mm of their respective feedac pins the dividers center trace should e ept short lacing the resis- tors far away causes their traces to ecome antennas that can pic up switching noise tae care to avoid running any feedac trace near x or the switching nodes in the charge pumps, or provide a ground shield u lace the pin ypass capacitors as close as pos- sile to the device the ground connection of the ypass capacitor should e connected directly to the a pin with a wide trace u minimie the length and maimie the width of the traces etween the output capacitors and the load for est transient response u minimie the sie of the x node while eeping it wide and short eep the x node away from feedac nodes ( and analog ground se traces to shield necessary efer to the max17115 evaluation it for an eample of proper layout downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds 22 _____________________________________________________________________________________ chip inforation im acage inforation or the latest pacage outline information and land patterns, go to .maim-i.ompakage ote that a , , or - in the pacage code indicates o status only acage drawings may show a different suffi character, ut the drawing pertains to the pacage regardless of o status p p p . t t-55 21-0140 downloaded from: http:///
internal-switch boost regulator and high-voltage, low-dropout linear regulator for tft lcds maxim cannot assume resonsiiit for use of an circuitr other than circuitr entire emodied in a maxim roduct. o circuit atent icenses are imied. maxim reseres the right to change the circuitr and secifications without notice at an time. ai integrated roducts, san ariel drie, sunnale, c -- 2 ? 1 maim ntegrated roducts maim is a registered trademar of maim ntegrated roducts, nc reision histor rvisi r rvisi sripi ps h 7 nitial release 1 1 added reflow temperature and removed a line in the fault-protection description , , , 1, downloaded from: http:///

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