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1 for more information www.linear.com/LT8335 typical application features description low i q boost/sepic/ inverting converter with 2a, 28v switch the lt ? 8335 is a current mode dc/dc converter capable of generating either positive or negative output voltages using a single feedback pin. it can be configured as a boost, sepic or inverting converter consuming as low as 6a of quiescent current. low ripple burst mode opera - tion maintains high efficiency down to very low output currents while keeping the output ripple below 15 mv in a typical application. the internally compensated current mode architecture results in stable operation over a wide range of input and output voltages. integrated soft-start and frequency foldback functions are included to control inductor current during start-up. the 2mhz operation combined with the small 8-lead dfn package, enables low cost, area efficient solutions. 3v to 6v input, 12v boost converter applications n 3v to 25v input voltage range n ultralow quiescent current and low ripple burst mode ? operation: i q = 6a n 2a, 28v power switch n positive or negative output voltage programming with a single feedback pin n fixed 2mhz switching frequency n programmable undervoltage lockout (uvlo) n internal compensation and soft-start n low profile (0.75mm) 8-lead (3mm 2mm) dfn package n industrial and automotive n telecom n medical diagnostic equipment n portable electronics l, lt , lt c , lt m , linear technology, the linear logo and burst mode are registered trademarks and thinsot is a trademark of linear technology corporation. all other trademarks are the property of their respective owners. efficiency and power loss lt 8335 8335f 200 300 400 500 600 0 10 20 30 40 efficiency 50 60 70 80 90 100 0 200 400 600 power loss 800 1000 efficiency (%) power loss (mw) 8335 ta01b 154k 4.7f 1f v out v in v in = 3v sw fbx gnd en/uvlo LT8335 v in 3v to 6v 12v v cc int 1m v in = 5v 1.2h 22f 4.7pf 275ma at v in = 3v 440ma at v in = 5v 520ma at v in = 6v 8335 ta01 v in = 6v load current (ma) 0 100
2 for more information www.linear.com/LT8335 absolute maximum ratings sw ............................................................................ 28 v v in , en / uvlo ............................................................ 25 v en / u vlo pin above v in pin ........................................ 6 v intv cc ( note 2) .......................................................... 4 v fbx ........................................................................... 4 v o perating junction temperature ( note 3) lt 83 35 e, lt 8335 i ............................. C 40 c to 125 c storage temperature range .................. C 65 c to 150 c (note 1) order information lead free finish tape and reel part marking package description temperature range LT8335eddb#pbf LT8335eddb#trpbf lgvm 8-lead (3mm 2mm) plastic dfn C40c to 125c LT8335iddb#pbf LT8335iddb#trpbf lgvm 8-lead (3mm 2mm) plastic dfn C40c to 125c consult ltc marketing for information on 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/. some packages are available in 500 unit reels through designated sales channels with #trmpbf suffix. top view 9 gnd ddb package 8-lead (3mm 2mm) plastic dfn 5 6 7 8 4 3 2 1fbx nc sw sw en/uvlo intv cc v in gnd ja = 80.5c/w exposed pad (pin 9) is gnd, must be soldered to pcb pin configuration http://www .linear.com/product/LT8335#orderinfo lt 8335 8335f
3 for more information www.linear.com/LT8335 electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v in = 12v, en/uvlo = 12v unless otherwise noted. parameter conditions min typ max units v in operating voltage range l 3 25 v v in quiescent current at shutdown v en/uvlo = 0.2v l 0.9 2 2 5 a a v en/uvlo = 1.5v l 2 3.6 5 9.5 a a v in quiescent current sleep mode, not switching l 5.5 8.5 10 15 a a active mode, not switching l 780 840 1100 1200 a a fbx regulation fbx regulation voltage fbx > 0v fbx < 0v l l 1.568 C0.820 1.6 C0.80 1.632 C0.780 v v fbx line regulation fbx > 0v, 3v < v in < 25v fbx < 0v, 3v < v in < 25v 0.005 0.005 0.015 0.015 %/v %/v fbx pin current fbx = 1.6v, C0.8v l C10 10 na oscillator switching frequency (f osc ) l 1.80 2.0 2.20 mhz minimum on-time 74 115 ns minimum off-time 47 65 ns switch maximum switch current limit threshold l 2.0 2.5 3.0 a switch r ds(on) i sw = 0.5a 170 m switch leakage current v sw = 28v 0.1 1 a en/uvlo logic en/uvlo pin threshold (rising) start switching l 1.620 1.68 1.745 v en/uvlo pin threshold (falling) stop switching l 1.556 1.60 1.644 v en/uvlo pin current v en/uvlo = 1.6v l C40 40 na soft-start soft-start time 1.2 ms 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: intv cc cannot be externally driven. no additional components or loading is allowed on this pin. note 3: the LT8335e is guaranteed to meet performance specifications from 0c to 125c junction temperature. specifications over the C40c to 125c operating junction temperature range are assured by design, characterization and correlation with statistical process controls. the LT8335i is guaranteed over the full C40c to 125c operating junction temperature range. high junction temperatures degrade operating lifetimes. operating lifetime is derated at junction temperatures greater than 125c. note 4: the ic includes overtemperature protection that is intended to protect the device during overload conditions. junction temperature will exceed 150c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature will reduce lifetime. lt 8335 8335f
4 for more information www.linear.com/LT8335 typical performance characteristics switching frequency vs temperature switching frequency vs v in normalized switching frequency vs fbx voltage switch current limit vs duty cycle switch minimum on-time vs temperature switch minimum off-time vs temperature fbx positive regulation voltage vs temperature fbx negative regulation voltage vs temperature en/uvlo pin thresholds vs temperature lt 8335 8335f 100 normalized switching frequency (%) 8335 g06 v in = 12v duty cycle (%) 0 20 40 60 80 100 125 2.1 2.3 2.5 2.7 2.9 switch current limit (a) 8335 g07 v in = 12v junction temperature (c) ?50 150 ?25 0 25 50 75 100 125 150 175 40 175 50 60 70 80 90 100 110 120 minimum on?time (ns) 8335 g08 1.570 v in = 12v junction temperature (c) ?50 ?25 0 25 50 75 100 125 1.580 150 175 30 35 40 45 50 55 60 minimum off?time (ns) 1.590 8335 g09 v in = 12v en/uvlo rising (turn-on) en/uvlo falling (turn-off) junction temperature (c) ?50 ?25 0 25 50 1.600 75 100 125 150 175 1.54 1.56 1.58 1.60 1.62 1.610 1.64 1.66 1.68 1.70 1.72 1.74 en/uvlo pin voltage (v) 8335 g03 1.620 v in = 12v 1.630 fbx voltage (v) 8335 g01 v in = 12v junction temperature (c) ?50 ?25 0 25 50 junction temperature (c) 75 100 125 150 175 ?0.815 ?0.810 ?0.805 ?0.800 ?0.795 ?50 ?0.790 ?0.785 fbx voltage (v) 8335 g02 v in = 12v junction temperature (c) ?50 ?25 0 25 ?25 50 75 100 125 150 175 1.90 1.92 1.94 1.96 0 1.98 2.00 2.02 2.04 2.06 2.08 2.10 switching frequency (mhz) 8335 g04 v in (v) 25 0 5 10 15 20 25 1.85 1.90 1.95 2.00 50 2.05 2.10 2.15 switching frequency (mhz) 8335 g05 v in = 12v fbx voltage (v) ?0.8 ?0.4 0.0 75 0.4 0.8 1.2 1.6 0 25 50 75 100 125
5 for more information www.linear.com/LT8335 typical performance characteristics switching waveforms (in ccm) switching waveforms (in dcm/light burst mode) switching waveforms (in deep burst mode) v out transient response: load current transients from 200ma to 440ma to 200ma v in pin current (sleep mode, not switching) vs temperature v in pin current (active mode, not switching) vs temperature burst frequency vs load current v out transient response: load current transients from 40ma to 440ma to 40ma lt 8335 8335f 100 125 150 175 0 1.25 2.50 3.75 5.00 6.25 v in = 12v 7.50 8.75 10.00 v in pin current (a) 8335 g10 v in = 12v junction temperature (c) ?50 ?25 0 junction temperature (c) 25 50 75 100 125 150 175 600 650 700 ?50 750 800 850 900 950 1000 v in pin current (a) 8335 g11 front page application v in = 5v, v out = 12v ?25 load current (ma) 0 50 100 150 200 0 0.5 1.0 1.5 0 2.0 2.5 switching frequency (mhz) 8335 g12 v in = 5v, v out = 12v, i load = 440ma 1s/div front page application v sw 5v/div i l 500ma/div 25 8335 g13 v in = 5v, v out = 12v, i load = 100ma 1s/div front page application v sw 5v/div 8335 g14 i l 500ma/div v in = 5v, v out = 12v, i load = 10ma 1s/div 50 front page application v sw 5a/div 8335 g15 i l 500ma/div front page application: v in = 5v, v out = 12v 100s/div v out 200mv/div i load 75 200ma/div 8335 g16 front page application: v in = 5v, v out = 12v 100s/div v out 200mv/div i load 200ma/div 8335 g17
6 for more information www.linear.com/LT8335 pin functions en/uvlo: shutdown and undervoltage detect pin . the LT8335 is shut down when this pin is low and active when this pin is high. below an accurate 1.6v threshold the part enters undervoltage lockout and stops switching . this allows an undervoltage lockout (uvlo) threshold to be programmed for system input voltage by resistively dividing down system input voltage to the en/uvlo pin. an 80 mv pin hysteresis ensures part switching resumes when the pin exceeds 1.68v. en/uvlo pin voltage below 0.2v reduces v in current below 1a. if shutdown and uvlo features are not required, the pin can be tied directly to system input. fbx: voltage regulation feedback pin for positive or negative outputs. connect this pin to a resistor divider between the output and gnd. fbx reduces the switching frequency during start-up and fault conditions when fbx is close to gnd. gnd: ground connection for the LT8335. the dfn package has an exposed pad (pin 9) on the bottom of the package. this exposed pad must be soldered to a ground plane. pin 5 should also be connected to a ground plane. the ground plane should be connected to large copper layers to spread heat dissipated by the LT8335. intv cc : regulated 3v supply for internal loads. the intv cc pin must be bypassed with a minimum 1 f low esr ceramic capacitor to ground. no additional components or loading is allowed on this pin. nc: no internal connection. tie directly to local ground. sw: the output of internal power switch. minimize the metal trace area connected to this pin to reduce emi. v in : input supply. this pin must be locally bypassed. be sure to place the positive terminal of the input capacitor as close as possible to the v in pin , and the negative terminal as close as possible to the gnd pin. lt 8335 8335f
7 for more information www.linear.com/LT8335 block diagram gnd 8335 bd + ? + ? error amp select frequency foldback intv cc uvlo oscillator 2mhz switch logic burst detect a5 a2 a1 error amp error amp slope vc slope soft-start 1.6v fbx v out r2 r1 ?0.8v uvlo ? + ? + a3 + ? a4 driver m1 i limit r sense pwm comparator intv cc t j > 170c + ? a6 1.68v(+) 1.6v(?) en/uvlo internal reference uvlo v in c in sw r4 opt r3 opt v in c out c vcc d l v out uvlo 3v regulator m2 lt 8335 8335f
8 for more information www.linear.com/LT8335 operation the LT8335 uses a fixed frequency, current mode control scheme to provide excellent line and load regulation. op - eration can be best understood by referring to the block diagram . an internal 2mhz oscillator turns on the internal power switch at the beginning of each clock cycle. current in the inductor then increases until the current comparator trips and turns off the power switch . the peak inductor current at which the switch turns off is controlled by the voltage on the internal vc node . the error amplifier servos the vc node by comparing the voltage on the fbx pin with an internal reference voltage (1.60v or C0.80v, depending on the chosen topology ). when the load current increases it causes a reduction in the fbx pin voltage relative to the internal reference. this causes the error amplifier to increase the vc voltage until the new load current is satis - fied. in this manner, the error amplifier sets the correct peak switch current level to keep the output in regulation . the LT8335 is capable of generating either a positive or negative output voltage with a single fbx pin. it can be configured as a boost or sepic converter to generate a positive output voltage, or as an inverting converter to generate a negative output voltage. when configured as a boost converter, as shown in the block diagram, the fbx pin is pulled up to the internal bias voltage of 1.60v by a voltage divider (r1 and r2) connected from v out to gnd. amplifier a2 becomes inactive and amplifier a1 performs (inverting) amplification from fbx to vc. when the LT8335 is in an inverting configuration, the fbx pin is pulled down to C0.80v by a voltage divider from v out to gnd. amplifier a1 becomes inactive and amplifier a2 performs (non-inverting) amplification from fbx to vc. if the en/uvlo pin voltage is below 1.6v, the LT8335 enters undervoltage lockout (uvlo), and stops switching. when the en/uvlo pin voltage is above 1.68v (typical), the LT8335 resumes switching. if the en/uvlo pin volt - age is below 0.2v, the LT8335 only draws 1a from v in . to optimize efficiency at light loads , the LT8335 operates in burst mode operation in light load situations . between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 6a. achieving ultralow quiescent current to enhance efficiency at light loads the LT8335 uses a low ripple burst mode architecture . this keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and output ripple. in burst mode operation the LT8335 delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor. while in sleep mode the LT8335 consumes only 6a. as the output load decreases, the frequency of single cur - rent pulses decreases (see figure 1) and the percentage of time the LT8335 is in sleep mode increases, resulting in much higher light load efficiency than for typical con - verters. to optimize the quiescent current performance at light loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. in addition, all possible leakage currents from figure 1. burst frequency vs load current applications information the output should also be minimized as they all add to the equivalent output load. the largest contributor to leakage current can be due to the reverse biased leakage of the schottky diode (see diode selection in the applications information section). lt 8335 8335f 0 0.5 1.0 1.5 2.0 2.5 switching frequency (mhz) 8335 f01 front page application v in = 5v, v out = 12v load current (ma) 0 50 100 150 200
9 for more information www.linear.com/LT8335 applications information while in burst mode operation , the current limit of the switch is approximately 500ma, resulting in the output voltage ripple shown in figure 2. increasing the output capacitance will decrease the output ripple proportionally . as the output load ramps upward from zero the switch - ing frequency will increase but only up to the fixed 2mhz defined by the internal oscillator as shown in figure 1. the output load at which the LT8335 reaches the fixed 2mhz frequency varies based on input voltage, output voltage, and inductor choice. figure 2. burst mode operation programming input turn-on and turn-off thresholds with en/uvlo pin the en/uvlo pin voltage controls whether the LT8335 is enabled or is in a shutdown state. a 1.6v reference and a comparator a6 with built-in hysteresis ( typical 80mv ) allow the user to accurately program the system input voltage at which the ic turns on and off (see the block diagram). the typical input falling and rising threshold voltages can be calculated by the following equations: v in (falling,uvlo(?)) = 1.60 r3 + r4 r4 v in (falling,uvlo(?)) = 1.68 r3 + r4 r4 v in current is reduced below 1a when the en/uvlo pin voltage is less than 0.2v. the en/uvlo pin can be con - nected directly to the input supply v in for always-enabled operation. a logic input can also control the en/uvlo pin. when operating in burst mode operation for light load currents, the current through the r3 and r4 network can easily be greater than the supply current consumed by the LT8335. therefore, r3 and r4 should be large enough to minimize their effect on efficiency at light loads. intv cc regulator a low dropout (ldo) linear regulator, supplied from v in , produces a 3 v supply at the intv cc pin. a minimum 1f low esr ceramic capacitor must be used to bypass the intv cc pin to ground to supply the high transient currents required by the internal power mosfet gate driver. no additional components or loading is allowed on this pin. the intv cc rising threshold (to allow soft start and switching) is typically 2.6v. the intv cc falling threshold (to stop switching and reset soft start) is typically 2.5v. duty cycle consideration the LT8335 minimum on-time, minimum off-time and switching frequency (f osc ) define the allowable minimum and maximum duty cycles of the converter (see minimum on-time, minimum off-time , and switching frequency in the electrical characteristics table). minimum allowable duty cycle = minimum on-time (max) ? f osc(max) maximum allowable duty cycle = 1 C minimum off-time (max) ? f osc(max) the required switch duty cycle range for a boost converter operating in continuous conduction mode (ccm) can be calculated as: d min = 1? v in(max) v out + v d d max = 1? v in(min) v out + v d where v d is the diode forward voltage drop. if the above duty cycle calculations for a given application violate the minimum and/or maximum allowed duty cycles for the LT8335, operation in discontinuous conduction mode (dcm) might provide a solution. for the same v in and v out levels, operation in dcm does not demand as low a duty cycle as in ccm. dcm also allows higher duty cycle operation than ccm. the additional advantage of dcm is lt 8335 8335f 5s/div v out 10mv/div i l 500ma/div 8335 f02
10 for more information www.linear.com/LT8335 applications information the removal of the limitations to inductor value and duty cycle required to avoid sub-harmonic oscillations and the right half plane zero (rhpz). while dcm provides these benefits, the trade-off is higher inductor peak current, lower available output power and reduced efficiency. setting the output voltage the output voltage is programmed with a resistor divider from the output to the fbx pin. choose the resistor values for a positive output voltage according to: r1 = r2 v out 1.60v ? 1 ? ? ? ? ? ? choose the resistor values for a negative output voltage according to: r1 = r2 ? v out ? 0.80v ? 1 ? ? ? ? ? ? the locations of r1 and r2 are shown in the block dia - gram. 1% resistors are recommended to maintain output voltage accuracy. higher-value fbx divider resistors result in the lowest input quiescent current and highest light-load efficiency. fbx divider resistors r1 and r2 are usually in the range from 25k to 1m. most applications use a phase-lead capacitor from v out to fbx in combination with high-value fbx divider resistors (see compensation in the applications information section). soft-start the LT8335 contains several features to limit peak switch currents and output voltage (v out ) overshoot during start-up or recovery from a fault condition . the primary purpose of these features is to prevent damage to external components or the load. high peak switch currents during start-up may occur in switching regulators. since v out is far from its final value, the feedback loop is saturated and the regulator tries to charge the output capacitor as quickly as possible, resulting in large peak currents. a large surge current may cause inductor saturation or power switch failure. figure 3. soft-start waveforms the LT8335 addresses this mechanism with an internal soft-start function. as shown in the block diagram, the soft-start function controls the ramp of the power switch current by controlling the ramp of vc through m2. this allows the output capacitor to be charged gradually toward its final value while limiting the start-up peak currents. figure 3 shows the output voltage and supply current for the first page t ypical application. it can be seen that both the output voltage and supply current come up gradually. intv cc undervoltage (intv cc < 2.5v) and/or thermal lockout (t j > 170c) will immediately prevent switching, will reset the internal soft-start function and will pull down vc. once all faults are removed, the LT8335 will soft-start vc and hence inductor peak current. frequency foldback during start-up or fault conditions in which v out is very low, extremely small duty cycles may be required to maintain control of inductor peak current. the minimum on-time limitation of the power switch might prevent these low duty cycles from being achievable. in this scenario inductor current rise will exceed inductor current fall during each cycle, causing inductor current to walk up beyond the switch current limit. the LT8335 provides protection from this by folding back switching frequency whenever fbx pin is close to gnd ( low v out levels ). this frequency foldback provides a larger switch-off time, allowing inductor current to fall enough each cycle (see normalized switch - ing frequency vs fbx voltage in the typical performance characteristics section). lt 8335 8335f 500s/div v out 5v/div i l 500ma/div 8335 f03
11 for more information www.linear.com/LT8335 applications information thermal lockout if the LT8335 die temperature reaches 170c (typical), the part will stop switching and go into thermal lockout. when the die temperature has dropped by 5c (nominal), the part will resume switching with a soft-started inductor peak current. switching frequency and inductor selection the LT8335 switches at 2mhz, allowing small value in - ductors to be used . 0.68 h to 10h will usually suffice. choose an inductor that can handle at least 3a without saturating, and ensure that the inductor has a low dcr ( copper-wire resistance) to minimize i 2 r power losses. note that in some applications, the current handling re - quirements of the inductor can be lower, such as in the sepic topology where each inductor only carries one-half of the total switch current . for better efficiency, use similar valued inductors with a larger volume. many different sizes and shapes are available from various manufacturers. choose a core material that has low losses at 2mhz, such as a ferrite core . the final value chosen for the inductor should not allow peak inductor currents to exceed 2a in steady state at maximum load. it is also recommended to choose inductor values for an inductor ripple current to be 600ma or more. due to tolerances, be sure to account for minimum possible inductance value , switching frequency and converter efficiency. table 1. inductor manufacturers sumida (847) 956-0666 www.sumida.com tdk (847) 803-6100 www.tdk.com murata (714) 852-2001 www.murata.com coilcraft (847) 639-6400 www.coilcraft.com wrth (605) 886-4385 www.we-online.com input capacitor bypass the input of the LT8335 circuit with a ceramic ca - pacitor of x7r or x5r type placed as close as possible to the v in and gnd pins. y5 v types have poor performance over temperature and applied voltage, and should not be used. a 4.7f to 10f ceramic capacitor is adequate to bypass the LT8335 and will easily handle the ripple cur - rent. if the input power source has high impedance, or there is significant inductance due to long wires or cables , additional bulk capacitance may be necessar y. this can be provided with a low performance electrolytic capacitor . a precaution regarding the ceramic input capacitor con - cerns the maximum input voltage rating of the LT8335. a ceramic input capacitor combined with trace or cable inductance forms a high quality ( under damped) tank cir - cuit. if the LT8335 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8335s voltage rating. this situation is easily avoided (see application note 88). output capacitor and output ripple low esr (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. multilayer ceramic capacitors are an excellent choice, as they are small and have extremely low esr. use x5r or x7r types. this choice will provide low output ripple and good transient response. a 4.7f to 22f output capaci - tor is sufficient for most applications, but systems with ver y low output currents may need only a 1f or 2.2f output capacitor. a poscap capacitor is also a potential choice for its low voltage coefficient and high capacitance density. solid tantalum or os-con capacitors can be used, but they will occupy more board area than a ceramic and will have a higher esr. always use a capacitor with a sufficient voltage rating. compensation the LT8335 is internally compensated . the decision to use either low esr (ceramic) capacitors or the higher esr ( tantalum or os-con) capacitors, for the output capacitor, can affect the stability of the overall system. the esr of any capacitor, along with the capacitance itself, contributes a zero to the system. for the tantalum and os-con capacitors, this zero is located at a lower frequency due to the higher value of the esr, while the zero of a ceramic capacitor is at a much higher frequency and can generally be ignored. a phase lead zero can be intentionally introduced by placing a capacitor in parallel with the resistor between v out and fbx. by choosing the appropriate values for the resistor and lt 8335 8335f
12 for more information www.linear.com/LT8335 capacitor, the zero frequency can be designed to improve the phase margin of the overall converter . the typical target value for the zero frequency is between 30khz to 60khz. a practical approach to compensation is to start with one of the circuits in this data sheet that is similar to your ap - plication. optimize performance by adjusting the output capacitor and / or the feed forward capacitor (connected across the feedback resistor from output to fbx pin). ceramic capacitors ceramic capacitors are small , robust and have very low esr. however, ceramic capacitors can cause problems when used with the LT8335 due to their piezoelectric nature. when in burst mode operation, the LT8335s switching frequency depends on the load current, and at very light loads the LT8335 can excite the ceramic capacitor at audio frequencies, generating audible noise. since the LT8335 operates at a lower current limit during burst mode op - eration, the noise is typically very quiet to a casual ear. if this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. low noise ceramic capacitors are also available. figure 4. suggested boost converter layout table 2. ceramic capacitor manufacturers taiyo yuden (408) 573-4150 www.t-yuden.com avx (803) 448-9411 www.avxcorp.com murata (714) 852-2001 www.murata.com diode selection a schottky diode is recommended for use with the LT8335. low leakage schottky diodes are necessary when low quiescent current is desired at low loads . the diode leakage appears as an equivalent load at the output and should be minimized. choose schottky diodes with sufficient reverse voltage ratings for the target applications. table 3. recommended schottky diodes part number average forward current (ma) reverse voltage (v) reverse current (a) manufacturer pmeg3010bep 1000 30 50 nxp dfls140 1000 40 20 diodes inc rb060mm-30 2000 30 50 rohm layout hints the high speed operation of the LT8335 demands careful attention to board layout. careless layout will result in per - formance degradation. figure 4 shows the recommended component placement. note the vias under the exposed pad. these should connect to a local ground plane for better thermal performance. applications information 8335 f04 r2 r4 r1 gnd c3 l1 d1 v out v out c4 fb v in 1 2 3 4 8 7 6 5 c1 c2 r3 (v in ) lt 8335 8335f
13 for more information www.linear.com/LT8335 applications information thermal considerations care should be taken in the layout of the pcb to ensure good heat sinking of the LT8335. the exposed pad (pin ?9) must be soldered to a ground plane. pin 5 should also be connected to a ground plane. the ground plane should be connected to large copper layers to spread heat dissipated by the LT8335 and to further reduce the thermal resis - tance ( ja ) values listed in the pin configuration section. power dissipation within the LT8335 (p diss_LT8335 ) can be estimated by subtracting the inductor and schottky diode power losses from the total power losses calculated in an efficiency measurement. the junction temperature of LT8335 can then be estimated by, t j (LT8335) = t a + ja ? p diss additional topologies : sepic and inverting in addition to the boost topology, the LT8335 can be configured in a sepic or inverting topology . sepic and inverting converters are analyzed below. sepic converter applications the LT8335 can be configured as a sepic (single-ended primary inductance converter ), as shown in figure 5. this topology allows for the input to be higher , equal, or lower than the desired output voltage . the conversion ratio as a function of duty cycle is: v out + v d v in = d 1 ? d in continuous conduction mode (ccm). in a sepic converter , no dc path exists between the input and output . this is an advantage over the boost converter for applications requiring the output to be disconnected from the input source when the cir cuit is in shutdown. sepic converter: switch duty cycle and frequency for a sepic converter operating in ccm, the duty cycle of the main switch can be calculated based on the output voltage (v out ), the input voltage (v in ) and the diode forward voltage (v d ). the maximum duty cycle (d max ) occurs when the converter operates at the minimum input voltage: d max = v out + v d v in(min) + v out + v d conversely, the minimum duty cycle (d min ) occurs when the converter operates at the maximum input voltage: d min = v out + v d v in(max) + v out + v d be sure to check that d max and d min obey: d max < 1-minimum off-time (max) ? f osc(max) and d min > minimum on-time (max) ? f osc(max) where minimum off-time , minimum on-time and f osc are specified in the electrical characteristics table. sepic converter: the maximum output current capability and inductor selection as shown in figure 5, the sepic converter contains two inductors: l 1 and l2. l 1 and l2 can be independent, but can also be wound on the same core , since identical voltages are applied to l1 and l2 throughout the switching cycle. figure 5. LT8335 configured in a sepic topology lt 8335 8335f LT8335 v in v cc int d1 c in c out c dc 8335 f05 l1 l2 v out v in sw fbx gnd en/uvlo
14 for more information www.linear.com/LT8335 for the sepic topology, the current through l1 is the converter input current. based on the fact that, ideally, the output power is equal to the input power, the maximum average inductor currents of l1 and l2 are: i l1(max)(ave) = i in(max)(ave) = i o(max) d max 1 ? d max i l2(max)(ave) = i o(max) in a sepic converter, the switch current is equal to i l1 + i l2 when the power switch is on, therefore, the maximum average switch current is defined as: i sw(max)(ave) = i l1(max)(ave) + i l2(max)(ave) = i o(max) 1 1 ? d max and the peak switch current is: i sw(peak) = 1 + 2 ? ? ? ? ? ? i o(max) 1 1 ? d max the constant r in the preceding equations represents the percentage peak-to-peak ripple current in the switch , relative to i sw(max)( ave ) , as shown in figure 6. then, the switch ripple current ?i sw can be calculated by: ? i sw = r ? i sw(max)( ave ) it is recommended to have a ?i sw of 600ma or more. the inductor ripple currents ?i l1 and ?i l2 are identical: ? i l1 = ?i l2 = 0.5 ? ?i sw the inductor ripple current has a direct effect on the choice of the inductor value. choosing smaller values of ?i l requires large inductances and reduces the current loop gain (the converter will approach voltage mode). accepting larger values of ?i l allows the use of low in - ductances, but results in higher input current ripple and greater core losses . it is recommended that r falls in the range of 0.2 to 0.6. due to the current limit of its internal power switch, the LT8335 should be used in a sepic converter whose maximum output current (i o(max) ) is less than the output current capability by a sufficient margin (10% or higher is recommended): i o(max) < (1 C d max ) ? (2a C 0.5 ? 6i sw ) ? (0.9) given an operating input voltage range, and having cho - sen ripple current in the inductor, the inductor value (l1 and l 2 are independent) of the sepic converter can be determined using the following equation: l1 = l2 = v in(min) 0.5 i sw f osc d max for most sepic applications, the equal inductor values will fall in the range of 1h to 47h. by making l 1 = l 2, and winding them on the same core, the value of inductance in the preceding equation is replaced by 2l, due to mutual inductance: l = v in(min) i sw f osc d max this maintains the same ripple current and energy storage in the inductors. the peak inductor currents are: i l1(peak) = i l1(max) + 0.5 ? 6i l1 i l2(peak) = i l2(max) + 0.5 ? 6i l2 the maximum rms inductor currents are approximately equal to the maximum average inductor currents. based on the preceding equations, the user should choose the inductors having sufficient saturation and rms cur - rent ratings. applications information f t s c sepic c 8335 f06 i sw = ? i sw(max)(ave) i sw t dt s i sw(max)(ave) t s lt 8335 8335f
15 for more information www.linear.com/LT8335 sepic converter: output diode selection to maximize efficiency , a fast switching diode with a low forward drop and low reverse leakage is desirable . the average forward current in normal operation is equal to the output current. it is recommended that the peak repetitive reverse voltage rating v rrm is higher than v out + v in(max) by a safety margin (a 4v safety margin is usually sufficient). the power dissipated by the diode is: p d = i o(max) ? v d where v d is diode s forward voltage drop, and the diode junction temperature is: t j = t a + p d ? r ja the r ja used in this equation normally includes the r jc for the device, plus the thermal resistance from the board, to the ambient temperature in the enclosure. t j must not exceed the diode maximum junction temperature rating. sepic converter: output and input capacitor selection the selections of the output and input capacitors of the sepic converter are similar to those of the boost converter . sepic converter: selecting the dc coupling capacitor the dc voltage rating of the dc coupling capacitor (c dc , as shown in figure 5) should be larger than the maximum input voltage: v cdc > v in(max) c dc has nearly a rectangular current waveform. during the switch off-time, the current through c dc is i in , while approximately Ci o flows during the on-time. the rms rating of the coupling capacitor is determined by the fol- lowing equation: i rms(cdc) > i o(max) v out + v d v in(min) a low esr and esl, x5r or x7r ceramic capacitor works well for c dc . inverting converter applications the LT8335 can be configured as a dual-inductor inverting topology, as shown in figure 7. the v out to v in ratio is: v out ? v d v in = ? d 1 ? d in continuous conduction mode (ccm). applications information inverting converter: switch duty cycle and frequency for an inverting converter operating in ccm, the duty cycle of the main switch can be calculated based on the negative output voltage (v out ) and the input voltage (v in ). the maximum duty cycle (d max ) occurs when the converter has the minimum input voltage: d max = v out ? v d v out ? v d ? v in(min) conversely, the minimum duty cycle (d min ) occurs when the converter operates at the maximum input voltage : d min = v out ? v d v out ? v d ? v in(max) figure 7. a simplified inverting converter c dc v in c in l1 d1 c out v out 8335 f07 + gnd LT8335 sw l2 + ? + ? + lt 8335 8335f
16 for more information www.linear.com/LT8335 be sure to check that d max and d min obey : d max < 1-minimum off-time (max) ? f osc(max) and d min > minimum on-time (max) ? f osc(max) where minimum off-time , minimum on-time and f osc are specified in the electrical characteristics table. inverting converter: inductor, output diode and input capacitor selections the selections of the inductor, output diode and input capacitor of an inverting converter are similar to those of the sepic converter. please refer to the corresponding sepic converter sections. inverting converter: output capacitor selection the inverting converter requires much smaller output capacitors than those of the boost, flyback and sepic converters for similar output ripples . this is due to the fact that, in the inverting converter, the inductor l2 is in series with the output, and the ripple current flowing through the output capacitors are continuous. the output ripple voltage is produced by the ripple current of l2 flowing through the esr and bulk capacitance of the output capacitor: v out(p?p) = i l2 esr cout + 1 8 f c out ? ? ? ? ? ? after specifying the maximum output ripple, the user can select the output capacitors according to the preceding equation. the esr can be minimized by using high quality x 5r or x7r dielectric ceramic capacitors. in many applications, ceramic capacitors are sufficient to limit the output volt - age ripple. the rms ripple current rating of the output capacitor needs to be greater than: i rms(cout) > 0.3 ? ?i l2 inverting converter: selecting the dc coupling capacitor the dc voltage rating of the dc coupling capacitor (c dc , as shown in figure 7) should be larger than the maximum input voltage minus the output voltage (negative voltage): v cdc > v in(max) C v out c dc has nearly a rectangular current waveform. during the switch off-time, the current through c dc is i in , while approximately Ci o flows during the on-time. the rms rating of the coupling capacitor is determined by the fol- lowing equation: i rms(cdc) > i o(max) d max 1 ? d max a low esr and esl, x5r or x7r ceramic capacitor works well for c dc . applications information lt 8335 8335f
17 for more information www.linear.com/LT8335 typical applications 3v to 6v input, 12v boost converter efficiency 8v to 16v input, 24v boost converter efficiency 3v to 6v input, 24v boost converter efficiency lt 8335 8335f v in 300 400 500 600 700 800 50 60 70 80 sw 90 100 efficiency (%) 8335 ta03a 4.7f 71.5k 8335 ta04 4.7f 1f 4.7pf fbx v out 60ma at v in = 3v v in sw fbx gnd en/uvlo LT8335 3v to 6v 0.47h gnd v in 24v 70ma at v in = 5v 80ma at v in = 6v v cc int 1m c1 c2 c3 en/uvlo r1 r2 l1 d1 d1: nxp pmeg3010bep l1: wurth elektronik we-lhmi 744373240047 c3: murata grm32er71h475k c4 v in = 3v v in = 5v LT8335 v in = 6v load current (ma) 0 20 40 60 80 50 60 70 3v to 6v 80 90 efficiency (%) 8335 ta04a 1.2h v in 12v 22f 440ma at v in = 5v v cc int 1m c1 c2 c3 c4 r1 r2 154k l1 d1 520ma at v in = 6v d1: rohm rb060mm-30 l1: cooper sd25-1r2 c3: murata grm32er71e226k v in = 3v v in = 5v v in = 6v load current (ma) 8335 ta02 0 100 200 300 400 500 600 50 60 70 4.7f 80 90 100 efficiency (%) 8335 ta02a 10f 71.5k 8335 ta03 4.7f 1f 1f 4.7pf 287k v out 400ma at v in = 8v v in sw fbx gnd en/uvlo LT8335 4.7pf 8v to 16v 3.3h v in 24v 600ma at v in = 12v 800ma at v in = 16v v cc int 1m c1 v out c2 c3 c4 r1 r2 l1 d1 d1: rohm rb060mm-30 l1: wurth elektronik we-lqs 74404063033 c3: murata grm32er71h106k 275ma at v in = 3v 1m r3 r4 v in = 8v v in = 12v v in = 16v load current (ma) 0 100 200
18 for more information www.linear.com/LT8335 typical applications 5v to 12v input, C12v inverting converter 4v to 16v input, C5v inverting converter 4v to 16v input, 5v sepic converter efficiency efficiency efficiency + lt 8335 8335f v out 1m r4 806k v in = 4v v in = 12v v in = 16v load current (ma) 0 150 300 v in 450 600 750 900 30 40 50 60 70 80 sw 90 efficiency (%) 8335 ta06a 22f 232k 8335 ta07 4.7f 1f 5.6pf c5 fbx 1f l1 l2 1m 806k v out v in sw fbx gnd gnd en/uvlo LT8335 4v to 16v 1.8h v in 5v v cc int 499k d1 en/uvlo c1 c2 c3 d1: rohm rb060mm-30 l1, l2: wurth elektronik inddd 744877001 r1 r2 c4 1.8h r3 LT8335 r4 500ma at v in = 4v 550ma at v in = 5v 650ma at v in = 12v 700ma at v in = 16v c3: murata grm31cr71a226k c5: murata grm31mr71e105k v in = 4v v in = 5v v in = 12v 5v to 12v v in = 16v load current (ma) 0 150 300 450 600 750 50 60 3.3uh 70 80 90 efficiency (%) 8335 ta07b v in 22f ?12v v cc int 1m d1 c1 c2 c3 d1: nxp pmeg3010bep l1, l2: wurth elektronik we-lqs 74404054033 71.5k r1 r2 c4 3.3h 350ma at v in = 5v 450ma at v in = 12v c3: murata grm32er71e226k c5: murata grm31cr71h105k l1 l2 4.7f r3 1m r4 665k v in = 5v v in = 12v load current (ma) 0 100 200 1f 300 400 500 50 60 70 80 90 efficiency (%) 8335 ta05a 10pf 47f 191k 4.7f 1f 10pf 8335 ta06 c5 1f v out v in 8335 ta05 sw fbx gnd en/uvlo LT8335 4v to 16v 2.2h 2.2h v in ?5v c5 v cc int 1m d1 c1 c2 c3 d1: rohm rb060mm-30 l1, l2: cooper drq73-2r2 r1 1f r2 c4 550ma at v in = 4v 820ma at v in = 12v 850ma at v in = 16v c3: panasonic 6tpc47m c5: murata grm31cr71h105k l1 l2 r3
19 for more information www.linear.com/LT8335 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 please refer to http://www .linear.com/product/LT8335#packaging for the most recent package drawings. 2.00 0.10 (2 sides) note: 1. drawing conforms to version (wecd-1) in jedec package outline m0-229 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package 0.40 0.10 bottom view?exposed pad 0.56 0.05 (2 sides) 0.75 0.05 r = 0.115 typ r = 0.05 typ 2.15 0.05 (2 sides) 3.00 0.10 (2 sides) 1 4 8 5 pin 1 bar top mark (see note 6) 0.200 ref 0 ? 0.05 (ddb8) dfn 0905 rev b 0.25 0.05 0.50 bsc pin 1 r = 0.20 or 0.25 45 chamfer 0.25 0.05 2.20 0.05 (2 sides) recommended solder pad pitch and dimensions 0.61 0.05 (2 sides) 1.15 0.05 0.70 0.05 2.55 0.05 package outline 0.50 bsc ddb package 8-lead plastic dfn (3mm 2mm) (reference ltc dwg # 05-08-1702 rev b) lt 8335 8335f
20 for more information www.linear.com/LT8335 ? linear technology corporation 2016 lt 0616 ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/LT8335 related parts typical application 4v to 16v input, 5v converter part number description comments lt1930/lt1930a 1a (i sw ), 1.2mhz/2.2mhz high efficiency step-up dc/dc converter v in = 2.6v to 16v, v out(max) = 34v, i q = 4.2ma/5.5ma, i sd < 1a, thinsot package lt 1935 2a (i sw ), 40v, 1.2mhz high efficiency step-up dc/dc converter v in = 2.3v to 16v, v out(max) = 38v, i q = 3ma, i sd < 1a, thinsot package lt 3467 1.1a (i sw ), 1.3mhz high efficiency step-up dc/dc converter v in = 2.4v to 16v, v out(max) = 40v, i q = 1.2ma, i sd < 1a, thinsot, 2mm 3mm dfn packages lt 3580 2a (i sw ), 42v, 2.5mhz, high efficiency step-up dc/dc converter v in = 2.5v to 32v, v out(max) = 42v, i q = 1ma, i sd = <1a, 3mm 3mm dfn-8, msop-8e lt 8330 1a (i sw ), 60v, 2.0mhz high efficiency boost/sepic/ inverting dc/dc converter v in = 3v to 40v, v out(max) = 60v, i q = 6a (burst mode operation), i sd =< 1a, thinsot, 2mm 3mm dfn packages lt8331 0.5a (i sw ), 140v, 500khz high efficiency boost/flyback/ sepic/inverting dc/dc converter v in = 4.5v to 100v, v out(max) = 135v, i q = 6a (burst mode operation), i sd =< 1a, msop-16(12)e lt8494 70v, 2a boost/sepic 1.5mhz high efficiency step-up dc/dc converter v in = 1v to 60v (2.5v to 32v start-up), v out(max) = 70v, i q = 3a (burst mode operation), i sd = <1a, 20-lead tssop lt8570/lt8570-1 65v, 500ma/250ma boost/inverting dc/dc converter v in(min) = 2.55v, v in(max) = 40v, v out(max) = 60v, i q = 1.2ma, i sd = <1ma, 3mm 3mm dfn-8, msop-8e lt8580 1a (i sw ), 65v 1.5mhz, high efficiency step-up dc/dc converter v in : 2.55v to 40v, v out(max) = 65v, i q = 1.2ma, i sd = <1a, 3mm 3mm dfn-8, msop-8e efficiency lt 8335 8335f 806k c6 1f 22f 5.6pf ?v out v in sw fbx gnd 22f en/uvlo LT8335 4v to 16v 1.2h 1.2h v in ?5v v cc int 499k 232k d1 c1 c2 c3 d1, d2 : rohm rb060mm-30 l1a, l1b, l1c : wurth elektronik transformer 750316134 r1 r2 r3 r4 8335 ta08 c4 +v out +5v d2 l1a l1b l1c 1.2h load 250ma at v in = 4v 4.7f 300ma at v in = 12v 300ma at v in = 16v c3, c4 : murata grm31cr71h105k c7 +v out v in = 4v v in = 12v v in = 16v load current (ma) 0 1f 50 100 150 200 250 300 30 40 50 60 c5 70 80 90 efficiency (%) 8335 ta08a 1f 1m

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