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ltc3261 1 3261f typical application features description high voltage, low quiescent current inverting charge pump the ltc ? 3261 is a high voltage inverting charge pump that operates over a wide 4.5v to 32v input range and is capable of delivering up to 100ma of output current. the charge pump employs either low quiescent current burst mode operation or low noise constant frequency mode. in burst mode operation the charge pump v out regulates to C0.94 ? v in and the ltc3261 draws only 60a of quiescent current. in constant frequency mode the charge pump produces an output equal to Cv in and operates at a fixed 500khz or to a programmed frequency between 50khz to 500khz using an external resistor. the ltc3261 is available in a thermally enhanced 12-pin msop package. applications n 4.5v to 32v v in range n inverting charge pump generates Cv in n 60a quiescent current in burst mode ? operation n charge pump output current up to 100ma n 50khz to 500khz programmable oscillator frequency n short-circuit/thermal protection n low profile thermally enhanced 12-pin msop package n bipolar/inverting supplies n industrial/instrumentation bias generators n portable medical equipment n portable instruments l , lt, ltc, ltm, burst mode, linear technology and the linear logo are registered trademarks and thinsot is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. 15v to C15v inverter 10f 10f C15v 3261 ta01 v out 15v ltc3261 gnd v in mode c C rt en c + 1f v out ripple 100s/div v out 10mv/div ac-coupled v out = C14.8v v out = C14.1v mode = l mode = h v out 200mv/div ac-coupled 3261 ta01a v in = 15v f osc = 500khz i out = 5ma
ltc3261 2 3261f absolute maximum ratings v in , en, mode.. ......................................... C0.3v to 36v v out ........................................................... C36v to 0.3v rt ................................................................ C0.3v to 6v v out short-circuit duration ............................. indefinite operating junction temperature range (note 2) .................................................. C40c to 125c storage temperature range ................. C65c to 150c lead temperature (soldering, 10 sec) ................... 300c (notes 1, 3) 1 2 3 4 5 6 nc rt nc v out c C nc 12 11 10 9 8 7 nc mode en v in c + nc top view mse package 12-lead plastic msop 13 gnd t jmax = 150c, ja = 40c/w exposed pad (pin 13) is gnd, must be soldered to pcb pin configuration order information lead free finish tape and reel part marking* package description temperature range ltc3261emse#pbf ltc3261emse#trpbf 3261 12-lead plastic msop C40c to 125c ltc3261imse#pbf ltc3261imse#trpbf 3261 12-lead plastic msop C40c to 125c consult ltc marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a la bel on the shipping container. consult ltc marketing for information on non-standard lead based finish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ltc3261 3 3261f electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c (note 2). v in = en = 12v, mode = 0v, rt = 200k. symbol parameter conditions min typ max units charge pump v in input voltage range l 4.5 32 v v uvlo v in undervoltage lockout threshold v in rising v in falling l l 3.4 3.8 3.6 4v v i vin v in quiescent current shutdown, = en = 0v mode = v in , i vout = 0ma mode = 0v, i vout = 0ma 2 60 3.5 5 120 5.5 a a ma v rt rt regulation voltage 1.200 v v out v out regulation voltage mode = 12v mode = 0v C0.94 ? v in Cv in v v f osc oscillator frequency rt = gnd 450 500 550 khz r out charge pump output impedance mode = 0v, rt = gnd 32 i short_ckt max i vout short-circuit current v out = gnd, rt = gnd l 100 160 250 ma v mode(h) mode threshold rising l 1.1 2 v v mode(l) mode threshold falling l 0.4 1.0 v i mode mode pin internal pull-down current v in = mode = 32v 0.7 a v en(h) en threshold rising l 1.1 2 v v en(l) en threshold falling l 0.4 1.0 v i en en pin internal pull-down current v in = en = 32v 0.7 a note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the ltc3261 is tested under pulsed load conditions such that t j t a . the ltc3261e is guaranteed to meet specifications from 0c to 85c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the ltc3261i is guaranteed over the C40c to 125c operating junction temperature range. high junction temperatures degrade operating lifetimes; operating lifetime is derated for junction temperatures greater than 125c. note that the maximum ambient temperature consistent with these specifications is determined by specific operating conditions in conjunction with board layout, the rated package thermal impedance and other environmental factors. the junction temperature (t j , in c) is calculated from the ambient temperature (t a , in c) and power dissipation (p d , in watts) according to the formula: t j = t a + (p d ? ja ), where ja = 40c/w is the package thermal impedance. note 3: this ic includes overtemperature protection that is intended to protect the device during momentary overload conditions. junction temperatures will exceed 150c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature may result in device degradation or failure.
ltc3261 4 3261f typical performance characteristics oscillator frequency vs supply voltage effective open-loop resistance vs temperature quiescent current vs supply voltage (constant frequency mode) quiescent current vs temperature (constant frequency mode) oscillator frequency vs rt v out short-circuit current vs supply voltage v out short circuit current vs temperature shutdown current vs temperature quiescent current vs temperature (burst mode operation) (t a = 25c, c fly = 1f, c in = c out = 10f unless otherwise noted) supply voltage (v) 0 0 500 600 400 300 200 100 20 25 30 10 15 535 3261 g01 rt = gnd rt = 200k oscillator frequency (khz) rt (k) 1 0 500 600 400 300 200 100 100 1000 10 10000 3261 g02 oscillator frequency (khz) temperature (c) C50 0 25 20 15 10 5 50 25 100 75 0 C25 150 125 3261 g03 shutdown current (a) v in = 5v v in = 12v v in = 32v temperature (c) C50 0 140 100 120 60 80 40 20 50 25 100 75 0 C25 150 125 3261 g04 quiescent current (a) rt = gnd v in = 32v v in = 12v v in = 5v supply voltage (v) 0 0 14 10 12 6 8 4 2 15 10 25 20 535 30 3261 g05 quiescent current (ma) f osc = 50khz f osc = 200khz f osc = 500khz temperature (c) C50 0 9 7 8 5 6 4 3 2 1 50 25 0 100 75 C25 150 125 3261 g06 quiescent current (ma) f osc = 50khz f osc = 200khz f osc = 500khz v in = 12v temperature (c) C50 20 60 50 55 40 45 35 30 25 50 25 0 100 75 C25 150 125 3261 g07 effective open loop resistance () v in = 12v v in = 25v v in = 32v f osc = 500khz supply voltage (v) 0 0 250 150 200 50 100 15 10 525 20 35 30 3261 g08 v out short circuit current (ma) f osc = 500khz f osc = 200khz temperature (c) C50 100 200 180 160 140 120 C25 0 25 50 125 75 100 3261 g8b v out short circuit current (ma) v in = 12v rt = gnd
ltc3261 5 3261f typical performance characteristics voltage loss (v in C |v out |) vs output current (constant frequency mode) (t a = 25c, c fly = 1f, c in = c out = 10f unless otherwise noted) effective open-loop resistance vs supply voltage average input current vs output current v out load transient burst mode operation (mode = h) v out ripple v out transient (mode = low to high) output current (ma) 0.1 0.0 3.0 2.0 2.5 1.0 0.5 1.5 1 100 10 3261 g09 voltage loss (v) f osc = 500khz f osc = 200khz f osc = 50khz v in = 12v supply voltage (v) 0 0 90 70 80 50 40 30 20 10 60 5 101520 35 25 30 3261 g10 effective open loop resistance () f osc = 200khz f osc = 500khz v out 500mv/div ac-coupled 2ms/div 3261 g11 v in = 12v f osc = 500khz C5ma i out C50ma v out 500mv/div ac-coupled 2ms/div 3261 g12 v in = 12v f osc = 500khz i out = C5ma mode output current (ma) 0.1 0.1 100 10 1 1 100 10 3261 g13 average input current (ma) mode = l mode = h v in = 12v f osc = 500khz 100s/div v out 10mv/div ac-coupled v out 200mv/div ac-coupled 3261 g14 v in = 15v f osc = 500khz i out = 5ma mode = l mode = h
ltc3261 6 3261f block diagram charge pump and input logic 50khz to 500khz osc v in v out s1 s4 s3 2 13 gnd 3261 bd 5 c + c C 8 9 4 10 en mode rt 11 s2 pin functions nc (pins 1, 3, 6, 7,12): no connect pins. these pins are not connected to the ltc3261 die. these pins should be left floating or connected to ground. pins 6 and 7 can also be shorted to adjacent pins. rt (pin 2): input connection for programming the switch- ing frequency. the rt pin servos to a fixed 1.2v when the en pin is driven to a logic high. a resistor from rt to gnd sets the charge pump switching frequency. if the rt pin is tied to gnd, the switching frequency defaults to a fixed 500khz. v out (pin 4): charge pump output voltage. in constant frequency mode (mode = low) this pin is driven to Cv in . in burst mode operation, (mode = high) this pin voltage is regulated to C0.94 ? v in using an internal burst comparator with hysteretic control. c C (pin 5): flying capacitor negative connection. c + (pin 8): flying capacitor positive connection. v in (pin 9): input voltage for the charge pump. v in should be bypassed with a low impedance ceramic capacitor. en (pin 10): logic input. a logic high on the en pin enables the inverting charge pump. mode (pin 12): logic input. the mode pin deter- mines the charge pump operating mode. a logic high on the mode pin forces the charge pump into burst mode operation regulating v out to approximately C0.94 ? v in with hysteretic control. a logic low on the mode pin forces the charge pump to operate as an open- loop inverter with a constant switching frequency. the switching frequency in both modes is determined by an external resistor from the rt pin to gnd. in burst mode, this represents the frequency of the burst cycles before the part enters the low quiescent current sleep state. gnd (exposed pad pin 13): ground. the exposed pack- age pad is ground and must be soldered to the pc board ground plane for proper functionality and for rated thermal performance.
ltc3261 7 3261f operation (refer to the block diagram) the ltc3261 is a high voltage inverting charge pump. it supports a wide input power supply range from 4.5v to 32v. shutdown mode in shutdown mode, all circuitry except the internal bias is turned off. the ltc3261 is in shutdown when a logic low is applied to the enable input (en). the ltc3261 only draws 2a (typical) from the v in supply in shutdown. constant frequency operation the ltc3261 provides low noise constant frequency opera- tion when a logic low is applied to the mode pin. the charge pump and oscillator circuit are enabled using the en pin. at the beginning of a clock cycle, switches s1 and s2 are closed. the external flying capacitor across the c + and c C pins is charged to the v in supply. in the second phase of the clock cycle, switches s1 and s2 are opened, while switches s3 and s4 are closed. in this configuration the c + side of the flying capacitor is grounded and charge is delivered through the c C pin to v out . in steady state the v out pin regulates at Cv in less any voltage drop due to the load current on v out . the charge transfer frequency can be adjusted between 50khz and 500khz using an external resistor on the rt pin. at slower frequencies the effective open-loop output resistance (r ol ) of the charge pump is larger and it is able to provide smaller average output current. figure 1 can be used to determine a suitable value of rt to achieve a required oscillator frequency. if the rt pin is grounded, the part operates at a constant frequency of 500khz. burst mode operation the ltc3261 provides low power burst mode operation when a logic high is applied to the mode pin. in burst mode operation, the charge pump charges the v out pin to C0.94 ? v in (typical). the part then shuts down the internal oscillator to reduce switching losses and goes into a low current state. this state is referred to as the sleep state in which the ic consumes only about 60a. when the output voltage droops enough to overcome the burst comparator hysteresis, the part wakes up and commences charge pump cycles until output voltage exceeds C0.94 ? v in (typical). this mode provides lower operating current at the cost of higher output ripple and is ideal for light load operation. the frequency of charging cycles is set by the external resistor on the rt pin. the charge pump has a lower r ol at higher frequencies. for burst mode operation it is recommended that the rt pin be tied to gnd. this minimizes the charge pump r ol , quickly charges the output up to the burst threshold and optimizes the duration of the low current sleep state. figure 1. oscillator frequency vs rt soft-start the ltc3261 has built in soft-start circuitry to prevent excessive current flow during start-up. the soft-start is achieved by internal circuitry that slowly ramps the amount of current available at the output storage capacitor. the soft-start circuitry is reset in the event of a commanded shutdown or thermal shutdown. short-circuit/thermal protection the ltc3261 has built-in short-circuit current limit as well as overtemperature protection. during a short-circuit condition, the part automatically limits its output current to approximately 160ma. if the junction temperature ex- ceeds approximately 175c the thermal shutdown circuitry disables current delivery to the output. once the junction temperature drops back to approximately 165c current delivery to the output is resumed. when thermal protection is active the junction temperature is beyond the specified operating range. thermal protection is intended for mo- mentary overload conditions outside normal operation. continuous operation above the specified maximum op- erating junction temperature may impair device reliability. rt (k) 1 0 500 600 400 300 200 100 100 1000 10 10000 3261 f01 oscillator frequency (khz)
ltc3261 8 3261f applications information effective open-loop output resistance the effective open-loop output resistance (r ol ) of a charge pump is a very important parameter which determines the strength of the charge pump. the value of this parameter depends on many factors such as the oscillator frequency (f osc ), value of the flying capacitor (c fly ), the nonoverlap time, the internal switch resistances (r s ) and the esr of the external capacitors. typical r ol values as a function of temperature are shown in figure 2 figure 2. typical r ol vs temperature v ripple(p-p) i out c out ? 1 f osc Ct on ? ? ? ? ? ? where f osc is the oscillator frequency t on is the on-time of the oscillator (1s) typical and c out is the value of the output capacitor. just as the value of c out controls the amount of output ripple, the value of c in controls the amount of ripple present at the input (v in ) pin. the amount of bypass capacitance required at the input depends on the source impedance driving v in . for best results it is recommended that v in be bypassed with at least 2f of low esr capacitance. a high esr capacitor such as tantalum or aluminum will have higher input noise than a low esr ceramic capacitor. therefore, a ceramic capacitor is recommended as the main bypass capacitance with a tantalum or aluminum capacitor used in parallel if desired. flying capacitor selection the flying capacitor controls the strength of the charge pump. a 1f or greater ceramic capacitor is suggested for the flying capacitor for applications requiring the full rated output current of the charge pump. for very light load applications, the flying capacitor may be reduced to save space or cost. for example, a 0.2f capacitor might be sufficient for load currents up to 20ma. a smaller flying capacitor leads to a larger effective open- loop resistance (r ol ) and thus limits the maximum load current that can be delivered by the charge pump. ceramic capacitors ceramic capacitors of different materials lose their capaci- tance with higher temperature and voltage at different rates. for example, a capacitor made of x5r or x7r material will retain most of its capacitance from C40c to 85c whereas a z5u or y5v style capacitor will lose considerable capacitance over that range. z5u and y5v capacitors may also have a poor voltage coefficient causing them to lose 60% or more of their capacitance when the rated voltage is applied. therefore when comparing different capacitors, it is often more ap- propriate to compare the amount of achievable capacitance for a given case size rather than discussing the specified capacitance value. the capacitor manufactures data sheet input/output capacitor selection the style and value of capacitors used with the ltc3261 determine several important parameters such as regulator control loop stability, output ripple, charge pump strength and minimum turn-on time. to reduce noise and ripple, it is recommended that low esr ceramic capacitors be used for the charge pump output. the charge pump output capacitor should retain at least 2f of capacitance over operating temperature and bias voltage. tantalum and aluminum capacitors can be used in parallel with a ceramic capacitor to increase the total capacitance but should not be used alone because of their high esr. in constant frequency mode, the value of c out directly controls the amount of output ripple for a given load current. increasing the size of c out will reduce the output ripple at the expense of higher minimum turn-on time. the peak-to-peak output ripple at the v out pin is approximately given by the expression: temperature (c) C50 20 60 50 55 40 45 35 30 25 50 25 0 100 75 C25 150 125 3261 f02 effective open loop resistance () v in = 12v v in = 25v v in = 32v f osc = 500khz
ltc3261 9 3261f applications information should be consulted to ensure the desired capacitance at all temperatures and voltages. table 1 is a list of ceramic capacitor manufacturers and their websites. table 1 avx www.avxcorp.com kemet www.kemet.com murata www.murata.com taiyo yuden www.t-yuden.com vishay www.vishay.com tdk www.component.tdk.com layout considerations due to high switching frequency and high transient currents produced by ltc3261, careful board layout is necessary for optimum performance. a true ground plane and short connections to all the external capacitors will improve performance and ensure proper regulation under all condi- tions. figure 3 shows an example layout for the ltc3261. the flying capacitor nodes c + and c C switch large currents at a high frequency. these nodes should not be routed close to sensitive pins such as the rt pin . thermal management at high input voltages and maximum output current, there can be substantial power dissipation in the ltc3261. if the junction temperature increases above approximately 175c, the thermal shutdown circuitry will automatically deactivate the output. to reduce the maximum junction temperature, a good thermal connection to the pc board ground plane is recommended. connecting the exposed pad of the package to a ground plane under the device on two layers of the pc board can reduce the thermal resistance of the package and pc board considerably. derating power at high temperatures to prevent an overtemperature condition in high power applications, figure 4 should be used to determine the maximum combination of ambient temperature and power dissipation. the power dissipated in the ltc3261 should always fall under the line shown for a given ambient temperature. the power dissipated in the ltc3261 is: p d = (v in C |v out |) ? (i out ) where i out denotes output current at the v out pin. the derating curve in figure 4 assumes a maximum thermal resistance, ja , of 40c/w for the package. this can be achieved from a printed circuit board layout with a solid ground plane and a good connection to the exposed pad of the ltc3261 package. it is recommended that the ltc3261 be operated in the region corresponding to t j 150c for continuous opera- tion as shown in figure 4. short-term operation may be acceptable for 150c < t j < 175c but long-term operation in this region should be avoided as it may reduce the life of the part or cause degraded performance. for t j > 175c the part will be in thermal shutdown. figure 3. recommended layout figure 4. maximum power dissipation vs ambient temperature ambient temperature (c) C50 0 6 4 5 2 3 1 75 50 25 0 125 100 C25 175 150 3261 f04 maximum power dissipation (w) ja = 40c/w thermal shutdown recommended operation t j = 150c t j = 175c gnd gnd 3261 f03 c fly r t v in v out en mode
ltc3261 10 3261f typical applications 3261 ta06 4.5v to 32v note: i 2vin t* C2vin t* out < = 100ma ~ 2v in ~ C2v in Cv in c1 4.7f 50v c2 1f 50v c3 1f 50v c4 1f 50v c7 4.7f 50v d3 1n4148 c6 4.7f 100v mode rt c v in c C v out en gnd ltc3261 c5 4.7f 100v d1 1n4148 d2 1n4148 d4 1n4148 3261 ta07 4.5v to 32v c1 4.7f 50v c2 1f 50v c3 1f 50v d3 mbr0540 d2 mbr0540 d1 mbr0540 mode rt c + v in c C v out v out en gnd ltc3261 c4 4.7f 50v v out C v in Cv f C|i out | t r ol 2 Cv f ? ? ? ? ? ? high input divide by 2 voltage divider inverting charge pump with bipolar doubler high voltage to inverted low voltage charge pump c3 4.7f 25v c2 1f 50v 9v to 32v v in /2 c1 4.7f 50v v in v out mode rt en c + gnd 3261 ta04 c C ltc3261 note: minimum load of 120a is required to assure start-up
ltc3261 11 3261f information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description msop (mse12) 0911 rev f 0.53 0.152 (.021 .006) seating plane 0.18 (.007) 1.10 (.043) max 0.22 C?0.38 (.009 C .015) typ 0.86 (.034) ref 0.650 (.0256) bsc 12 12 11 10 9 8 7 7 detail b 1 6 note: 1. dimensions in millimeter/(inch) 2. drawing not to scale 3. dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.152mm (.006") per side 4. dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.152mm (.006") per side 5. lead coplanarity (bottom of leads after forming) shall be 0.102mm (.004") max 6. exposed pad dimension does include mold flash. mold flash on e-pad shall not exceed 0.254mm (.010") per side. 0.254 (.010) 0 C 6 typ detail a detail a gauge plane recommended solder pad layout bottom view of exposed pad option 2.845 0.102 (.112 .004) 2.845 0.102 (.112 .004) 4.039 0.102 (.159 .004) (note 3) 1.651 0.102 (.065 .004) 1.651 0.102 (.065 .004) 0.1016 0.0508 (.004 .002) 123456 3.00 0.102 (.118 .004) (note 4) 0.406 0.076 (.016 .003) ref 4.90 0.152 (.193 .006) detail b corner tail is part of the leadframe feature. for reference only no measurement purpose 0.12 ref 0.35 ref 5.23 (.206) min 3.20 C 3.45 (.126 C .136) 0.889 0.127 (.035 .005) 0.42 0.038 (.0165 .0015) typ 0.65 (.0256) bsc mse package 12-lead plastic msop, exposed die pad (reference ltc dwg # 05-08-1666 rev f) please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
ltc3261 12 3261f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2012 lt 0412 ? printed in usa related parts typical application 24v to C24v inverter c3 10f c1 10f C24v 3261 ta03 v out 9 85 10 11 13 2 4 24v ltc3261 gnd v in mode c C rt en c + c2 1f part number description comments ltc1144 switched-capacitor wide input range voltage converter with shutdown wide input voltage range: 2v to 18v, i sd < 8a, so8 package ltc1514/ltc1515 step-up/step-down switched-capacitor dc/dc converters v in : 2v to 10v, v out : 3.3v to 5v, i q = 60a, so8 package lt ? 1611 150ma output, 1.4mhz micropower inverting switching regulator v in : 0.9v to 10v, v out = 34v, thinsot? package lt1614 250ma output, 600khz micropower inverting switching regulator v in : 0.9v to 6v, v out = 30v, i q = 1ma, ms8, so8 packages LTC1911 250ma, 1.5mhz inductorless step-down dc/dc converter v in : 2.7v to 5.5v, v out = 1.5v/1.8v, i q = 180a, ms8 package ltc3250/ltc3250-1.2/ ltc3250-1.5 inductorless step-down dc/dc converters v in : 3.1v to 5.5v, v out = 1.2v, 1.5v, i q = 35a, thinsot package ltc3251 500ma spread spectrum inductorless step-down dc/dc converter v in : 2.7v to 5.5v, v out : 0.9v to 1.6v, 1.2v, 1.5v, i q = 9a, ms10e package ltc3252 dual 250ma, spread spectrum inductorless step-down dc/dc converter v in : 2.7v to 5.5v, v out : 0.9v to 1.6v, i q = 50a, dfn12 package lt1054/lt1054l switched-capacitor voltage converters with regulator v in : 3.5v to 15v/7v, i out = 100ma/125ma, n8, s08, so16 packages

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