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max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches ????????????????????????????????????????????????????????????????? maxim integrated products 1 general description the max15118 high-efficiency, current-mode step-down regulator with integrated power switches operates from 2.7v to 5.5v and delivers up to 18a of output current in a small 2mm x 3.5mm package. the max15118 offers excellent efficiency with skip mode capability at light- load conditions, yet provides unmatched efficiency under heavy load conditions. the combination of small size and high efficiency makes this device suitable for both portable and nonportable applications. the max15118 utilizes a current-mode control archi tecture with a high-gain transconductance error ampli fier, which allows a simple compensation scheme and enables a cycle-by-cycle current limit with fast response to line and load transients. a factory-trimmed switching frequency of 1mhz (pwm operation) allows for a compact, all-ceramic capacitor design. integrated switches with low on-resistance ensure high efficiency at heavy loads while min imizing critical induc - tances. the max15118s simple layout and footprint assure first-pass success in new designs. other features of the max15118 include a capacitor- programmable soft-start to reduce inrush current, safe startup into a prebiased output, an enable input, and a power-good output for power sequencing. the regulator is available in a 28-bump (4 x 7), 2.10mm x 3.56mm wlp package, and is fully specified over the -40 n c to +85 n c extended temperature range. features s continuous 18a output current over temperature s 1% feedback accuracy over load, line, and temperature s operates from 2.7v to 5.5v supply s input undervoltage lockout s adjustable output range from 0.6v up to 0.94 x v in s programmable soft-start s factory-trimmed 1mhz switching frequency s stable with low-esr ceramic output capacitors s safe-startup into a prebiased output s external reference input s selectable skip mode option for improved efficiency at light loads s enable input/pgood output allows sequencing s remote ground sense for improved accuracy s thermal and overcurrent protection s tiny 2.10mm x 3.56mm, 28-bump wlp package applications 19-5967; rev 0; 6/11 typical operating circuits typical operating circuits continued at end of data sheet. ordering information appears at end of data sheet. notebooks servers distributed power systems ddr memory base stations for related parts and recommended products to use with this part, refer to: www.maxim-ic.com/max15118.related e v a l u a t i o n k i t a v a i l a b l e ss/refin comp fb gnd pwm mode operation lx in pgood en on off gsns skip ain bst l out c bst c out v out r1 r2 r c v in = 2.7v to 5.5v pgood c c c cc c ss c in r pull max15118 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxims website at www.maxim-ic.com.
????????????????????????????????????????????????????????????????? maxim integrated products 2 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches in, pgood to gnd ................................................ -0.3v to +6v en, comp, fb, ss/refin, gsns, skip, lx to gnd .............................................. -0.3v to (v in + 0.3v) lx to gnd (for 50ns) ........................................ -1v to (v in + 1v) lx to gnd (for 10ns) ........................................ -2v to (v in + 2v) bst to lx ................................................................. -0.3v to +6v bst to gnd ........................................................... -0.3v to +12v bst to in ................................................................. -0.3v to +6v lx continuous current (note 1) ......................................... q 20a output short-circuit duration ................................... continuous continuous power dissipation wlp (derate 81.53mw/ n c above +70 n c) ...................... 3.26w operating temperature range .......................... -40 n c to +85 n c junction temperature (note 2) ....................................... +110 n c storage temperature range ............................ -65 n c to +150 n c bump reflow temperature (note 3) ............................... +260 n c absolute maximum ratings dc electrical characteristics (v in = 5v, see the typical operating circuits , t a = -40 n c to +85 n c. typical values are at t a = +25 n c, unless otherwise noted.) (note 4) stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional opera - tion of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. note 1: lx has internal clamp diodes to gnd and in. applications that forward bias these diodes must take care not to exceed the ics package power dissipation limits. note 2: limit the junction temperature to +110 n c for continuous operation at maximum output current. note 3: the wlp package is constructed using a unique set of package techniques that impose a limit on the thermal profile. the device can be exposed to during board-level solder attach and rework. this limit permits only the use of the solder pro - files recommended in the industry-standard specification jedec 020a, paragraph 7.6, table 3 for ir/vpr and convection reflow. preheating is required. hand or wave soldering is not allowed. parameter symbol conditions min typ max units in voltage range v in 2.7 5.5 v in supply current i in v en = v in , v fb = 0.65v, no switching 4.8 7 ma in shutdown current i shdn v en = 0v 0.01 3 f a in undervoltage lockout threshold v uvlo v in rising, lx starts switching 2.6 2.68 v in undervoltage lockout threshold hysteresis v in falling, lx stops switching 200 mv erroramplifier transconductance g m 1.2 ms voltage gain a vea 90 db fb setpoint voltage v fb over line, load, and temperature 0.594 0.600 0.606 v fb input bias current i fb -500 +500 na comp to current-sense transconductance g mc 150 a/v comp clamp low voltage v fb = 0.65v, v ss/refin = 0.6v 0.97 v slope compensation ramp amplitude v slope 130 mv
????????????????????????????????????????????????????????????????? maxim integrated products 3 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches dc electrical characteristics (continued) (v in = 5v, see the typical operating circuits , t a = -40 n c to +85 n c. typical values are at t a = +25 n c, unless otherwise noted.) (note 4) parameter symbol conditions min typ max units groundsense gsns output current v ss/refin = 0.6v, v gsns = 0v 56 f a powerswitches current-limit threshold high-side switch 30 a low-side switch, sinking 30 low-side switch, sourcing 30 lx leakage current v en = 0v 3 f a bst leakage current v en = 0v 3 f a bst on-resistance r on_bst i bst = 50ma 0.63 i lx rms output current 18 a oscillator switching frequency f sw 850 1000 1150 khz maximum duty cycle d max pwm mode 94 % skip mode 85 minimum controllable on-time t on 70 ns enablefunctionality en input high threshold v ih v en rising 1.4 v en input low threshold v il v en falling 0.4 v en input leakage current -1 +1 f a skipfunctionality(note5) skip input high threshold v skip rising 1.4 v skip input low threshold v skip falling 0.4 v skip pulldown resistor 210 k i minimum lx on-current in skip mode 3.6 a zero-crossing lx threshold 0.5 a soft-startandprebiasfunctionality soft-start current i ss v ss/refin = 0.45v, sourcing 6.8 10 12.5 f a ss/refin discharge resistance r ss i ss/refin = 10ma, sinking 7 i ss/refin prebias mode stop voltage v ss/refin rising 0.58 v ss/refin external reference input range v in - 2.5 v hiccupmode number of consecutive current- limit events to hiccup mode n hic 8 events hiccup mode timeout 1024 clock cycles
????????????????????????????????????????????????????????????????? maxim integrated products 4 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches dc electrical characteristics (continued) (v in = 5v, see the typical operating circuits , t a = -40 n c to +85 n c. typical values are at t a = +25 n c, unless otherwise noted.) (note 4) note 4: all devices are 100% production tested at t a = +25 n c. limits over the operating temperature range are guaranteed by design. note 5: connect skip to en for skip mode functionality. connect skip to gnd for pwm mode functionality. typical operating characteristics (v in = 5v, v out = 1.5v, c ss = 0.1f, see the typical operating circuits , t a = +25c, unless otherwise noted.) parameter symbol conditions min typ max units power-goodoutput pgood threshold v fb falling, pgood deasserts 0.514 0.530 0.542 v pgood threshold hysteresis v fb rising 25 mv pgood output voltage low v pg_ol i pgood = 5ma, v en = 0v 18 50 mv pgood leakage current i pg_lk v pgood = 5.5v, v fb = 0.65v 1 f a thermalshutdown thermal shutdown threshold t shdn die temperature rising +150 n c thermal shutdown hysteresis 20 n c efficiency vs. output current (v in = 5v, pwm mode) max15118 toc01 output current (a) efficiency (%) 16 14 10 12 4 6 8 2 55 60 65 70 75 80 v out = 0.8v 85 90 95 100 50 0 18 v out = 1.2v v out = 1.5v v out = 1.8v v out = 2.5v v out = 3.3v efficiency vs. output current (v in = 3.3v, pwm mode) max15118 toc02 output current (a) efficiency (%) 16 14 10 12 4 6 8 2 55 60 65 70 75 80 v out = 0.8v 85 90 95 100 50 0 18 v out = 1.2v v out = 1.5v v out = 1.8v v out = 2.5v efficiency vs. output current (v in = 5v, skip mode) max15118 toc03 output current (a) efficiency (%) 16 14 10 12 4 6 8 2 55 60 65 70 75 80 v out = 0.8v 85 90 95 100 50 0 18 v out = 1.2v v out = 1.5v v out = 1.8v v out = 2.5v v out = 3.3v
????????????????????????????????????????????????????????????????? maxim integrated products 5 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches typical operating characteristics (continued) (v in = 5v, v out = 1.5v, c ss = 0.1f, see the typical operating circuits , t a = +25c, unless otherwise noted.) efficiency vs. output current (v in = 3.3v, skip mode) max15118 toc04 output current (a) efficiency (%) 16 14 10 12 4 6 8 2 55 60 65 70 75 80 v out = 0.8v 85 90 95 100 50 0 18 v out = 1.2v v out = 1.5v v out = 1.8v v out = 2.5v switching frequency vs. input voltage max15118 toc05 input voltage (v) switching frequency (khz) 5.1 4.7 4.3 3.9 3.5 3.1 950 1000 1050 1100 900 2.7 5.5 t a = +85c t a = +25c t a = -40c output voltage vs. supply voltage (pwm mode, v out = 1.5v) max15118 toc06a supply voltage (v) output voltage (v) 5.1 4.7 3.1 3.5 3.9 4.3 1.485 1.490 1.495 1.500 1.505 1.510 1.515 1.520 1.480 2.7 5.5 i load = 10a i load = 18a output voltage vs. supply voltage (skip mode, v out = 1.5v) max15118 toc06b supply voltage (v) output voltage (v) 5.1 4.7 4.3 3.9 3.5 3.1 1.48 1.49 1.50 1.51 1.52 1.53 1.47 2.7 5.5 i load = 10a i load = 2a no load output voltage error vs. supply voltage max15118 toc07 supply voltage (v) output voltage error (%) 4.85 4.20 3.55 -0.40 -0.30 -0.20 -0.10 0 0.10 0.20 0.30 0.40 0.50 normalized at v in = 3.5v -0.50 2.90 5.50 v out = 1.2v v out = 1.8v v out = 1.5v i load = 18a output voltage vs. output current (pwm mode, v out = 1.5v) max15118 toc08a output current (a) output voltage (v) 16 14 12 10 8 6 4 2 1.48 1.49 1.50 1.51 1.52 1.53 1.47 0 18 v in = 5v v in = 3.3v
????????????????????????????????????????????????????????????????? maxim integrated products 6 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches typical operating characteristics (continued) (v in = 5v, v out = 1.5v, c ss = 0.1f, see the typical operating circuits , t a = +25c, unless otherwise noted.) output voltage vs. output current (skip mode, v out = 1.5v) max15118 toc08b output current (a) output voltage (v) 16 14 12 10 8 6 4 2 1.48 1.49 1.50 1.51 1.52 1.53 1.47 0 18 v in = 5v v in = 3.3v load-transient response (v in = 5v, v out = 1.5v, i out = 0.1a to 9a) max15118 toc09 9a 0.1a v out 50mv/div ac-coupled i out 5a /div 100s/div pwm mode load-transient response (v in = 3.3v, v out = 1.5v, i load = 0.1a to 9a) max15118 toc10 9a 0.1a v out 50mv/div ac-coupled i out 5a /div 100s/div pwm mode load-transient response (v in = 5v, v out = 1.5v, i load = 0.1a to 9a) max15118 toc11 9a 0.1a v out 50mv/div ac-coupled skip mode i out 5a /div 100s/div load-transient response (v in = 3.3v, v out = 1.5v, i load = 0.1a to 9a) max15118 toc12 9a 0.1a v out 50mv/div ac-coupled skip mode i out 5a /div 100s/div load-transient response (v in = 5v, v out = 1.5v, i load = 1.8a to 16a) max15118 toc13 16a 1.8a v out 50mv/div ac-coupled pwm mode i out 5a /div 100s/div
????????????????????????????????????????????????????????????????? maxim integrated products 7 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches typical operating characteristics (continued) (v in = 5v, v out = 1.5v, c ss = 0.1f, see the typical operating circuits , t a = +25c, unless otherwise noted.) load-transient response (v in = 3.3v, v out = 1.5v, i load = 1.8a to 16a) max15118 toc14 16a 1.8a v out 50mv/div ac-coupled pwm mode i out 5a /div 100s/div switching waveforms (v in = 5v, v out = 1.5v, i load = 1.8a) max15118 toc15 i lx 10a /div v out 20mv/div ac-coupled v lx 2v/div 400ns/div switching waveforms (v in = 3.3v, v out = 1.5v, i load = 18a) max15118 toc16 i lx 10a /div v out 20mv/div ac-coupled v lx 2v/div 400ns/div switching waveforms in skip mode (v in = 3.3v, v out = 1.5v, i load = 10ma) max15118 toc17 i lx 5a /div v out 20mv/div ac-coupled v lx 2v/div 2s/div shutdown waveforms (v in = 3.3v, v out = 1.5v, i load = 9a) max15118 toc18 i lx 5a /div v enable 2v/div v out 500mv/div v pgood 2v/div 100s/div soft-start waveforms (pwm mode, i load = 10a) max15118 toc19 i lx 5a /div v enable 2v/div v out 1v/div v pgood 2v/div 1ms /div
????????????????????????????????????????????????????????????????? maxim integrated products 8 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches typical operating characteristics (continued) (v in = 5v, v out = 1.5v, c ss = 0.1f, see the typical operating circuits , t a = +25c, unless otherwise noted.) soft-start waveforms (skip mode, i load = 2a) max15118 toc20 i lx 5a /div v enable 2v/div v out 1v/div v pgood 2v/div 1ms /div quiescent current (shutdown) max15118 toc21 supply voltage (v) rms input current (a) 5.1 4.7 4.3 3.9 3.5 3.1 0.3 0.6 0.9 1.2 1.5 v en = 0v 0 2.7 5.5 hiccup mode (short on output) max15118 toc22 i in 2a /div i out 10a/div v out 500mv/div v in 200mv/div ac-coupled 1ms /div rms input current vs. supply voltage max15118 toc23 supply voltage (v) rms input current (a) 5.1 4.7 4.3 3.9 3.5 3.1 0.3 0.6 0.9 1.2 1.5 short circuit on output 0 2.7 5.5 temperature (c) fb voltage (v) 60 35 10 -15 0.590 0.595 0.600 0.605 0.610 0.615 0.585 -40 85 fb voltage vs. temperature (v out = 1.5v) max15118 toc24 no load v in = 5v, skip mode v in = 3.3v, skip mode v in = 3.3v, pwm mode v in = 5v, pwm mode soft-start waveforms with ss/ refin (no load, pwm mode) max15118 toc25 i lx 5a /div v ss /refin 500mv/div v out 1v/div v pgood 2v/div 1ms /div
????????????????????????????????????????????????????????????????? maxim integrated products 9 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches typical operating characteristics (continued) (v in = 5v, v out = 1.5v, c ss = 0.1f, see the typical operating circuits , t a = +25c, unless otherwise noted.) soft-start waveforms with ss/ refin (no load, skip mode) max15118 toc26 i lx 5a /div v ss /refin 500mv/div v out 1v/div v pgood 2v/div 1ms /div starting into a 1v prebiased output (i load = 10a) max15118 toc27 i lx 5a /div 1v v enable 2v/div v out 500mv/div v pgood 5v/div 1ms /div starting into a 1v prebiased output (no load, pwm mode) max15118 toc28 i lx 5a /div v enable 2v/div v out 500mv/div v pgood 5v/div 1ms /div 1v starting into a 1v prebiased output (no load, skip mode) max15118 toc29 i lx 5a /div v enable 2v/div v out 500mv/div v pgood 5v/div 1ms /div 1v input current vs. input voltage max15118 toc30 input voltage (v) input current (ma) 5.1 4.7 4.3 3.9 3.5 3.1 1 2 3 4 5 no load, skip mode 0 2.7 5.5
???????????????????????????????????????????????????????????????? maxim integrated products 10 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches pin description pin configuration pin name function a1 bst boost input for the high-side switch driver. connect a capacitor from bst to lx. a2, a3, a4, b2, b4, c2, c4 lx inductor connection. connect lx to the switching side of the inductor. lx is high impedance when the max15118 is in shutdown mode. a5, b5, c5, d5 in input power supply. bypass in to gnd with at least two 22 f f low-esr ceramic capacitors with suf - ficient ripple current ratings. a6 pgood power-good open-drain output. pgood asserts high when v fb is above 0.555v (typ) and deasserts when v fb falls below 0.530v (typ). a7 gsns remote ground-sense input. connect gsns to the ground terminal of the load and to the bottom of the feedback resistors. b1, b3, c1, c3, d1, d2, d3 gnd ground connection. gnd is the source terminal of the internal low-side switch. connect all gnd bumps to a component-side pcb copper ground plane at a single point near the input bypass capac - itor return terminal. b6 n.c. no connection. do not connect. b7 fb feedback input. connect fb to the center tap of an external resistor-divider from the output to the output capacitor return terminal to set the output voltage from 0.6v to 0.94 x v in . c6 skip skip mode selector input. connect skip to en for skip mode operation. connect skip to gnd or leave unconnected for continuous mode operation. do not change the state of skip when en is high. c7 ss/refin soft-start and external voltage reference input. connect a capacitor from ss/refin to gnd to set the soft-start delay. see the setting the soft-start time section for more information. to use ss/refin as an external voltage reference, apply a voltage ranging from 0v to (v in - 2.5v) to ss/refin to exter - nally control the soft-start time and feedback voltage. d4 ain filtered input voltage d6 en enable input. drive en high to enable the max15118. connect en to in for always-on operation. d7 comp error amplifier output. connect the compensation network from comp to gnd. see the compensation design guidelines section for more information. top view (bump on the bottom) a1 a2 a3 a4 a5 a6 b1 b2 b3 b4 b5 b6 c1 c2 c3 c4 c5 c6 d1 d2 d3 d4 d5 d6 wlp max15118 lx lx lx gnd lx lx lx ain bst gnd gnd gnd in in in in pgood n.c. skip en a7 b7 c7 d7 gsns fb ss/refin comp lx gnd gnd gnd +
???????????????????????????????????????????????????????????????? maxim integrated products 11 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches functional diagram skpm source sink zx in ss/refin 0.6v skpm en ain skip fb gsns 0.58v comp lx lx pgood ck bst lx in gnd ck in bias generator voltage reference en logic, in uvlo, thermal shdn skip mode logic c current-sense amplifier ss/refin buffer prebias above forced pwm start 10a error amplifier g m a v = 1 555mv, rising 530mv, falling oscillator ramp generator low-side source-sink current-limit and zero- crossing comparator pwm comparator control logic high-side current limit compensation ramp max15118
???????????????????????????????????????????????????????????????? maxim integrated products 12 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches detailed description the max15118 high-efficiency, current-mode switching regulator delivers up to 18a of output current. the regu - lator provides output voltages from 0.6v up to 0.94 x v in from 2.7v to 5.5v input supplies, making the device ideal for on-board point-of-load applications. the max15118 delivers current-mode control architec - ture using a high-gain transconductance error amplifier. the current-mode control architecture facilitates easy compensation design and ensures cycle-by-cycle cur - rent limit with fast response to line and load transients. the regulator features a 1mhz fixed switching frequen cy, allowing for all-ceramic capacitor designs and fast tran - sient responses. the high operating frequency mini mizes the size of external components. the regulator offers a selectable skip-mode functional ity to reduce current consumption and achieve a higher efficiency at light output loads. integrat ed switches ensure high efficiency at heavy loads while minimizing critical inductances. the max15118 features pwm current-mode control, allowing for an all-ceramic capacitor solution. the regu - lator offers capacitor-programmable soft-start to reduce input inrush current. the device safely starts up into a prebiased output. the max15118 includes an enable input and open-drain pgood output for sequencing with other devices. controller functionpwm logic the controller logic block is the central processor that determines the duty cycle of the high-side mosfet under different line, load, and temperature conditions. under normal operation, where the current-limit and temperature protection are not triggered, the controller logic block takes the output from the pwm comparator and generates the driver signals for both high-side and low-side mosfets. the control logic block controls the break-before-make logic and all the necessary timing. the high-side mosfet turns on at the beginning of the oscillator cycle and turns off when the comp volt age crosses the internal current-mode ramp waveform. the internal ramp is the sum of the compensation ramp and the current-mode ramp derived from the inductor current (current-sense block). the high-side mosfet also turns off if either the maximum duty cycle (94%, typ) or the cur - rent limit is reached. the low-side mosfet turns on for the remain der of the oscillation cycle. starting into a prebiased output the max15118 can soft-start into a prebiased output without discharging the output capacitor. in safe pre - biased startup, both low-side and high-side mosfets remain off to avoid discharging the prebiased output. pwm operation starts when the voltage on ss/refin crosses the voltage on fb. the max15118 can start into a prebiased voltage higher than the nominal set point without abruptly discharg - ing the output. forced pwm operation starts when the ss/refin voltage reaches 0.58v (typ), forcing the con - verter to start. the low-side current limit is increased over 350s to the maximum from the first lx pulse. when the low-side sink current-limit threshold of 30a is reached, the low-side switch turns off before the end of the clock period and the high-side switch turns on until one of the following conditions is satisfied: u high-side source current hits the reduced high-side current limit (30a, typ); in this case, the high-side switch is turned off for the remaining time of the clock period. u the clock period ends. reduced high-side current limit is activated to recirculate the current into the high-side power switch rather than into the internal high-side body diode low-side sink current limit is provided to protect the low-side switch from excessive reverse current dur ing prebiased operation. enable input and power-good (pgood) output the max15118 features independent enable control and a power-good signal that allows for flexible power sequenc - ing. drive the enable input (en) high to enable the regula - tor, or connect en to in for always-on operation. power-good (pgood) is an open-drain out put that asserts when v fb is above 555mv (typ) and deasserts low if v fb is below 530mv (typ). programmable soft-start (ss/refin) the max15118 utilizes a soft-start feature to slowly ramp up the regulated output voltage to reduce input inrush current during startup. connect a capacitor from ss/refin to gnd to set the startup time (see the setting the soft-start time section for capacitor selection details).
???????????????????????????????????????????????????????????????? maxim integrated products 13 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches error amplifier a high-gain transconductance error amplifier provides accuracy for the voltage-feedback loop regulation. connect the neces sary compensation network between comp and gnd (see the compensation design guidelines section). the error-amplifier transconduc - tance is 1.2ms (typ). comp clamp low is set to 0.97v (typ), just below the slope ramp compensation valley, helping comp to rapidly return to the correct set point during load and line transients. ground-sense amplifier the max15118 features a ground-sense amplifier to pre - vent output voltage droop under heavy load conditions. connect gsns to the negative terminal of the load output capacitor to properly kelvin-sense the output ground. route the gsns trace away from the switching nodes. pwm comparator the pwm comparator compares the comp voltage to the current-derived ramp waveform (comp voltage to lx current transconductance value is 150a/v, typ). to avoid instability due to subharmonic oscillations when the duty cycle is around 50% or higher, a slope compensation ramp is added to the current-derived ramp waveform. the compensation ramp slope is designed to ensure stable operation at any duty cycle up to 94%. overcurrent protection and hiccup mode when the converter output is shorted or the device is overloaded, each high-side mosfet current-limit event turns off the high-side mosfet and turns on the low-side mosfet. on each current-limit event (either high-side or low-side) a 3-bit counter is incremented. the counter is reset after three consecutive switching cycles that do not reach the current limit. if the current-limit condition persists, the counter fills up reaching eight events. the control logic then keeps the low-side mosfet turned on until the inductor current is fully discharged to avoid high currents circulating through the low-side body diode. the control logic turns off both high-side and low-side mosfets and waits for the hiccup period (1024 clock cycles, typ) before attempting a new soft-start sequence. the hiccup mode is also enabled during soft-start time. thermal shutdown protection the max15118 contains an internal thermal sensor that limits the total power dissipation to protect the device in the event of an extended thermal fault condition. when the die temperature exceeds +150 n c (typ), the thermal sensor shuts down the device, turning off the dc-dc converter to allow the die to cool. after the die tempera - ture falls by 20 n c (typ), the device restarts. skip mode operation the max15118 features selectable skip mode operation when skip is con nected to en. when in skip mode, the lx output becomes high impedance when the induc - tor current falls below 0.5a (typ). the inductor current does not become negative. if during a clock cycle the inductor current falls below the 0.5a threshold (during off-time), the low-side turns off. at the next clock cycle, if the output voltage is above set point, the pwm logic keeps both high-side and low-side mosfets off. if instead the output voltage is below the set point, the pwm logic drives the high-side on until a reduced cur - rent limit threshold (3.6a, typ) is reached. in this way the system can skip cycles, reducing the frequency of operation, and switches only as needed to service load at the cost of an increase in output voltage ripple (see the skip mode frequency and output ripple section). in skip mode, power dissipation is reduced and efficiency is improved at light loads because power mosfets do not switch at every clock cycle. the max15118 automatically enters continuous mode regardless of the state of skip when the load current increases beyond the skip mode current limit. do not change the state of skip when en is high.
???????????????????????????????????????????????????????????????? maxim integrated products 14 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches applications information setting the output voltage the max15118 output voltage is adjustable from 0.6v up to 94% of v in by connecting fb to the center tap of a resistor-divider between the output and gnd (see the typical operating circuits ). choose r1 and r2 values so that the dc errors due to the fb input bias current ( q 500na) do not affect the output volt age accuracy. with lower value resistors, the dc error is reduced, but the amount of power consumed in the resistor-divider increases. r2 values between 1k i and 20k i are accept - able (see table 1 for typical values). once r2 is chosen, calculate r1 using: ( ) out fb r1=r2 v /v - 1 ? ? ? ? where the feedback threshold voltage v fb = 0.6v (typ). when regulating for an output of 0.6v in skip mode, short fb to out and keep r2 connected from fb to gnd. inductor selection a high-valued inductor results in reduced inductor-ripple current, leading to a reduced output-ripple voltage. however, a high-valued inductor results in either a larger physical size or a high series resistance (dcr) and a lower saturation current rating. typically, choose an inductor value to produce a current ripple, d i l , equal to 30% of load current. choose the inductor with the follow - ing formula: out out sw load in v v l 1- f lir i v ? ? = ? ? ? ? where f sw is the fixed 1mhz switching frequen cy, and lir is the desired inductor current ratio (typically 0.3). in addition, the peak inductor current, i l_pk , must always be below the high-side current-limit and the inductor saturation current rating, i l_sat . ensure that the following relationship is satisfied: ( ) l_pk load l(p-p) l_sat out in out in l(p-p) sw 1 i i i min (24a, i ) 2 where: v v v x v i l x f = + ? < ? ? = input capacitor selection for a step-down converter, the input capacitor, c in , helps to keep the dc input voltage steady, in spite of discontinuous input ac current. use low-esr capacitors to minimize the voltage ripple due to esr. size c in using the following formula: load out in sw in_ripple in i v c f v v = ? where d v in_ripple is the maximum-allowed input-ripple voltage across the input capacitors and is recommend - ed to be less than 2% of the minimum input voltage, f sw is the switching frequency (1mhz), and i load is the output load. the impedance of the input capacitor at the switching frequency should be less than that of the input source so high-frequency switching currents do not pass through the input source, but are instead shunted through the input capacitor. ensure that the input capacitor can accommodate the input-ripple current require ment imposed by the switch - ing currents. the rms input-ripple current is given by: ( ) -1 2 out in out rms load in v v - v i i v ? ? ? ? ? ? ? ? = ? ? ? ? ? ? where i rms is the input rms ripple current. use multiple capacitors in parallel to meet the rms cur - rent rating requirement.
???????????????????????????????????????????????????????????????? maxim integrated products 15 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches output capacitor selection the key selection parameters for the output capacitor are capacitance, esr, esl, and voltage-rating requirements. these affect the overall stability, output-ripple voltage, and transient response of the dc-dc converter. the out - put ripple occurs due to variations in the charge stored in the output capacitor, the voltage drop due to the capaci - tors esr, and the voltage drop due to the capacitors esl. estimate the output-voltage ripple due to the output capacitance, esr, and esl as follows: ripple ripple(c) ripple(esr) ripple(esl) v v v v = + + where the output ripple due to output capacitance, esr, and esl is: p p ripple(c) out sw ripple(esr) p p i v 8 c f v i esr ? ? ? = = ? and v ripple(esl ) can be approximated as an inductive divider from lx to gnd: ripple (esl) lx in esl esl v v v l l = = where v lx swings from v in to gnd. the peak-to-peak inductor current ( d i p-p ) is: ( ) out in out in p p sw v v v v i l f ? ? ? ? ? ? ? ? ? = when using ceramic capacitors, which generally have low-esr, d v ripple(c) dominates. when using electro - lytic capacitors, d v ripple(esr) dominates. use ceramic capacitors for low esr and low esl at the switching fre - quency of the converter. the ripple voltage due to esl is negligible when using ceramic capacitors. as a general rule, a smaller inductor ripple-current results in less output-ripple voltage. since inductor-ripple cur - rent depends on the inductor value and input voltage, the output-ripple voltage decreases with larger inductance and increases with higher input voltages. however, the inductor-ripple current also impacts transient-response performance, especially at low v in to v out differentials. low inductor values allow the inductor current to slew faster, replenishing charge removed from the output filter capacitors by a sudden load step. load-transient response also depends on the selected output capacitance. during a load transient, the output instantly changes by esr x ?i load . before the controller can respond, the output deviates further, depending on the inductor and output capacitor values. after a short time, the controller responds by regulating the output voltage back to the predetermined value. use higher c out values for applications that require light-load operation or transition between heavy load and light load, triggering skip mode, causing output under - shooting or overshooting. when applying the load, limit the output undershooting by sizing c out according to the following formula: load out co out i c 3f v ? = ? where ?i l oad is the total load change, f co is the unity- gain bandwidth (or zero-crossing frequency), and ?v out is the desired output undershooting. when removing the load and entering skip mode, the device cannot control output overshooting, since it has no sink current capabil - ity; see the skip mode frequency and output ripple section to properly size c out under this circumstance. a worst-case analysis in sizing the minimum output capacitance takes the total energy stored in the inductor into account, as well as the allowable sag/soar (under - shoot/overshoot) voltage as follows: ( ) ( ) ( ) ( ) 2 2 out max out min out (min) 2 2 fin soar init l i i c , voltage soar (overshoot) v v v ? = + ? ( ) ( ) ( ) ( ) 2 2 out max out min out(min) 2 2 init fin sag l i i c , voltage sag (undershoot) v v v ? = ? ? where i out(max) and i out(min) are the initial and final values of the load current during the worst-case load dump, v init is the initial voltage prior to the transient, v fin is the steady-state voltage after the transient, v soar is the allowed voltage soar (overshoot) above v fin , and v sag is the allowable voltage sag below v fin . the terms (v fin + v soar ) and (v fin - v sag ) represent the maxi - mum/minimum transient output voltage reached during the transient, respectively. use these equations for initial output-capacitor selection. determine final values by testing a prototype or an evalu - ation circuit under the worst-case conditions.
???????????????????????????????????????????????????????????????? maxim integrated products 16 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches skip mode frequency and output ripple enable skip mode in battery-powered systems for high effi - ciency at light loads. in skip mode the switching frequency (f skip ), as illustrated in figure 1 , is cal culated as follows: skip on off1 off2 1 f t t t = + + where: on skip_limit in out skip_limit off1 out l t i v v l i t v = ? = and: out off2 load skip_limit skip_limit load in out out off2 load q t i i 1 1 l i i v - v v 2 t i ? = ? ? ? ? + ? ? ? ? ? ? ? ? ? = output ripple in skip mode is: ( ) skip_limit out_ripple esr_cout out in out skip_limit load l i v r c (v - v ) i - i ? ? = + ? ? ? ? figure 1. skip mode waveform i l v out i skip-limit t on i load v out_ripple t off1 t off2 = n t ck
???????????????????????????????????????????????????????????????? maxim integrated products 17 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches compensation design guidelines the max15118 uses a fixed-frequency, peak current- mode control scheme to provide easy compensation and fast transient response. the inductor peak current is monitored on a cycle-by-cycle basis and compared to the comp voltage (output of the voltage error amplifier). the regulators duty cycle is modulated based on the induc - tors peak current value. this cycle-by-cycle control of the inductor current emulates a controlled current source. as a result, the inductors pole frequency is shifted beyond the gain bandwidth of the regulator. system stability is provided with the addition of a simple series capacitor- resistor from comp to gnd. this pole-zero combination serves to tailor the desired response of the closed-loop system. the basic regulator loop consists of a power mod - ulator (composed of the regulators pulse-width modula - tor, compensation ramp, control circuitry, mosfets, and inductor), the capacitive output filter and load, an output feedback divider, and a voltage-loop error amplifier with its associated compensation circuitry. see figure 2 for a graphical representation. the power modulators transfer function with respect to v comp is: load l out load mod comp l mod r i v r g v i g = = ? ? ? ? ? ? ? ? where i l is the average inductor current, g mod is the power modulators transconductance, and r load is the equivalent load resistance value. figure 2. peak current-mode regulator transfer model l control logic v comp v out pwm comparator comp v comp r c r out g m v in power modulator output filter and load note: the g mod stage shown above models the average current of the inductor, i l , injected into the output load, i out , e.g., i l = i out . such can be used to simplify/model the modulation/control/power stage circuitry shown within the boxed area. error amplifier feedback divider compensation ramp g mc dcr i l q ls v out v out i l esr c out r load c c ref *c ff is optional, designed to extend the regulators gain bandwidth and increased phase margin for some low-duty cycle applications. fb r1 *c ff v fb r2 g mod c q hs r out = 10 avea(db)/20 g m i out
???????????????????????????????????????????????????????????????? maxim integrated products 18 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches the peak current-mode controllers modulator gain is attenuated by the equivalent divider ratio of the load resistance and the current-loop gain. g mod becomes: mod mc load s sw 1 g g r 1 k (1- d) - 0.5 f x l = + ? ? ? ? where r load = v out /i out(max) , f sw is the switching frequency, l is the output inductance, d is the duty cycle (v out /v in ), and k s is the slope compensation factor calculated as: slope sw mc s in out v f l g k 1 v - v = + where v slope = 130mv and g mc = 150a/v. the power modulators dominant pole is a function of the parallel effects of the load resistance and the current- loop gains equivalent impedance. assuming that esr of the output capacitor is much smaller than the parallel combination of the load and the current loop, f pmod can be calculated as: s pmod out load sw out [k (1- d) - 0.5] 1 f 2 c r 2 f l c = + the power modulator zero is: zmod zesr out 1 f f 2 c esr = = the total system transfer can be written as: ( ) ( ) ( ) ( ) ( ) ( ) ff ea mod filter sampling gain s g s g s g dc g s g s = where: ff ff ff avea(db)/20 c c ea avea(db)/20 c m filter load out -1 s out load sw sampling 2 2 sw c sw sc r1 1 r2 g (s) r1 r2 sc (r1||r2) 1 sc r 1 g (s) 10 10 sc 1 g g (s) r sc esr 1 k (1- d) - 0.5 1 sc 1 2 r 2 f l 1 g (s) s s f q ( f ) + = + + + = ? ? ? ? + ? ? ? ? = + ? ? + + ? ? ? ? = + c s 1 1 where q [k (1- d) - 0.5] + = the dominant poles and zeros of the transfer loop gain are: m p1 avea(db)/20 c p2 -1 s out load sw sw p3 z1 c c z2 out g f 2 c 10 1 f k (1- d) - 0.5 1 2 c r f l f f 2 1 f 2 c r 1 f 2 c esr << = ? ? + ? ? ? ? = = = the order of pole occurrence is: p1 p2 z1 co p3 z2 f f f f f f < < < < <
???????????????????????????????????????????????????????????????? maxim integrated products 19 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches figure 3 shows a graphical representation of the asymp - totic system closed-loop response, including the domi - nant pole and zero locations. the loop responses fourth asymptote (in bold, figure 3 ) is the one of interest in establishing the desired crossover frequency (and determining the compensation compo - nent values). a lower crossover frequency provides for stable closed-loop operation at the expense of a slower load and line-transient response. increasing the cross - over frequency improves the transient response at the (potential) cost of system instability. a standard rule of thumb sets the crossover frequency p 1/5 to 1/10 of the switching frequency. closing the loop: designing the compensation circuitry 1) select the desired crossover frequency. choose f co equal to 1/10th of f sw , or f co @ 100khz. 2) select r c using the transfer-loops fourth asymptote gain equal to unity (assuming f co > f p1 , f p2 , and f z1 ). r c becomes: load s sw c m mc load co out s load sw r k [(1- d) - 0.5] 1 l f r1 r2 r r2 g g r 1 2 f c esr k [(1- d) - 0.5] 1 r l f ? ? + ? ? + ? ? = ? ? ? ? ? ? + ? ? + ? ? ? ? where k s is calculated as: slope sw mc s in out v f l g k 1 v - v = + and g m = 1.2ms, g mc = 150a/v, and v slope = 130mv. figure 3. asymptotic loop response of peak current-mode regulator unity gain db 1st asymptot e r2 x (r1 + r2) -1 x 10 avea(db)/20 x g mc x r load x {1 + r load x [k s x (1 C d) C 0.5] x (l x f sw ) -1 } -1 2nd asymptote r2 x (r1 + r2) -1 x g m x (2 g c c ) -1 x g mc x r load x {1 + r load x [k s x (1 C d) C 0.5] x (l x f sw ) -1 } -1 3rd asymptote r2 x (r1 + r2) -1 x g m x (2 g c c ) -1 x g mc x r load x {1 + r load x [k s x (1 C d) C 0.5] x (l x f sw ) -1 } -1 x (2 g c ou t x {r load -1 + [k s (1 C d) C 0.5] x (l x f sw ) -1 } -1 ) -1 5th asymptote r2 x (r1 + r2) -1 x g m x r c x g mc x r load x {1 + r load x [k s x (1 C d) C 0.5] x (l x f sw ) -1 } -1 x [(2 g c ou t x {r load -1 + [k s (1 C d) C 0.5] x (l x f sw ) -1 } -1 ) -1 x (0.5 x f sw )2 x (2 g f) -2 note: r ou t = 10 avea(db)/20 x g m -1 which for esr << {r load -1 + [k s (1 C d) C 0.5] x (l x f sw ) -1 } -1 becomes f pmod = [2 g c ou t x {r load -1 + [k s (1 C d) C 0.5] x (l x f sw ) -1 } -1 ] -1 f pmod = (2 g c ou t x r load ) -1 + [k s (1 C d) C 0.5] x (2 g c ou t x l x f sw ) -1 *f pmod = [2 g c ou t x (esr + {r load -1 + [k s (1 C d) C 0.5] x (l x f sw ) -1 } -1 )] -1 6th asymptote r2 x (r1 + r2) -1 x g m x r c x g mc x r load x {1 + r load x [k s x (1 C d) C 0.5] x (l x f sw ) -1 } -1 x esr x {r load -1 + [k s (1 C d) C 0.5] x (l x f sw ) -1 } -1 x (0.5?f sw ) 2 x (2 g f) -2 4th asymptot e r2 x (r1 + r2) -1 x g m x r c x g mc x r load x {1 + r load x [k s x (1 C d) C 0.5] x (l x f sw ) -1 } -1 x (2 g c ou t x {r load -1 + [k s (1 C d) C 0.5] x (l x f sw ) -1 } -1 ) -1 1st pole [2 g c c (10 avea(db)/20 x g m -1 )] -1 2nd pole f pmod * 1st zero (2 g c c r c ) -1 frequency f co 3rd pole 0.5 x f sw 2nd zero (2 g c ou t esr ) -1
???????????????????????????????????????????????????????????????? maxim integrated products 20 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches 3) select c c . c c is determined by selecting the desired first system zero, f z1 , based on the desired phase margin. typically, setting f z1 below 1/5th of f co pro - vides sufficient phase margin. c co c 5 c 2 f r optionally, for low duty-cycle applications, the addition of a phase-leading capacitor (c ff in figure 2 ) helps miti - gate the phase lag of the damped half-frequency double pole. adding a second zero near to but below the desired crossover frequency increases both the closed-loop phase margin and the regulators unity-gain bandwidth (crossover frequency). select the capacitor as follows: ff co 1 c 2 f (r1 || r2) = using c ff , the zero-pole order is adjusted as follows: [ ] ( ) p1 p2 z1 ff 1 ff p3 z2 f f f 1/ 2 c r 1/ 2 c r1|| r2 f f < < < ? ? < < < ? ? setting the soft-start time the soft-start feature ramps up the output voltage slowly, reducing input inrush current during startup. size the c ss capacitor to achieve the desired soft-start time, t ss , using: ss ss ss fb i t c v = i ss , the soft-start current, is 10 f a (typ) and v fb is the 0.6v (typ) output feedback voltage threshold. when using large c out capacitance values, the high-side current limit can trigger during the soft-start period. to ensure the correct soft-start time, t ss , choose c ss large enough to satisfy: out ss ss out load fb v i c c (24a - i ) v >> an external tracking reference with steady-state value between 0v and (v in - 2.5v) can be applied to ss/refin. in this case, connect an rc network from the external track ing reference and ss/refin, as shown in figure 4 . the recommended value for r ss is approximately 330 i . r ss is needed to ensure that, during hiccup period, ss/refin can be pulled down internally. design examples table 1 provides values for various outputs based on the typical operating circuit. figure 4. rc network for external reference at ss/refin table 1. suggested component values (see the typical operating circuits ) note: c in , c out , and other components are the same as in the standard max15118 evaluation kit. v in (v) v out (v) l(h) lir(a/a) c15(nf) r3(k i ) c14(pf) r1(k i ) r2(k i ) 3.3 0.8 0.15 0.22 6.8 2.94 22 1.78 5.36 3.3 1.2 0.15 0.28 4.7 2.21 22 5.36 5.36 3.3 1.5 0.15 0.30 3.3 3.83 22 8.06 5.36 3.3 1.8 0.15 0.30 3.3 4.22 22 10.7 5.36 3.3 2.5 0.15 0.22 3.3 5.62 22 16.9 5.36 5 0.8 0.15 0.25 6.8 2.94 22 1.78 5.36 5 1.2 0.15 0.34 4.7 2.21 22 5.36 5.36 5 1.5 0.15 0.39 3.3 3.83 22 8.06 5.36 5 1.8 0.22 0.29 3.3 3.92 22 10.7 5.36 5 2.5 0.22 0.32 3.3 5.1 22 16.9 5.36 5 3.3 0.22 0.28 2.2 4.64 22 24.3 5.36 c ss r ss v ref_ext ss/refin max15118
???????????????????????????????????????????????????????????????? maxim integrated products 21 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches power dissipation the max15118 is available in a 28-bump wlp package and can dissipate up to 3.26w at t a = +70 n c. when the die temperature exceeds +150 n c, the thermal shut - down protection is activated (see the thermal shutdown protection section). layout procedure careful pcb layout is critical to achieve clean and stable operation. it is highly recommended to duplicate the max15118 evaluation kit (ev kit) layout for optimum perfor mance. the max15118 ev kit board has a small, quiet, ground-shape sgnd on the back side below the ic. this ground is the return for the control circuitry, especially the return of the compensation components. this sgnd is returned to the ic ground through vias close to the ground bumps of the ic. if deviation is nec - essary, follow these guidelines for good pcb layout: 1) connect a single ground plane immediately adjacent to the gnd bumps of the ic. 2) place capacitors on in and ss/refin as close as possible to the ic and the corresponding pad using direct traces. 3) keep the high-current paths as short and wide as possible. keep the path of switching current short and minimize the loop area formed by lx, the output capacitors, and the input capacitors. 4) an electrolytic capacitor is strongly recommended for damping when there is significant distance between the input power supply and the max15118. 5) connect in, lx, and gnd separately to a large cop - per area to help cool the ic to further improve effi - ciency. 6) ensure all feedback connections are short and direct. place the feedback resistors and compensa tion com - ponents as close as possible to the ic. 7) route high-speed switching nodes (such as lx and bst) away from sensitive analog areas (such as fb and comp). chip information process: bicmos ordering information + denotes a lead(pb)-free/rohs-compliant package. package information for the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. part temprange pin-package MAX15118EWI+ -40 n c to +85 n c 28 wlp package type package code outline no. land pattern no. 28 wlp (2.10mm x 3.56mm) w282b3z+1 21-0577 refer to application note 1891
???????????????????????????????????????????????????????????????? maxim integrated products 22 max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches typical operating circuits (continued) ain 2.2f r12 10i en d6 skip comp c14 22pf c15 3.3nf pgood in ss/refin in in in n.c. bst lx lx lx lx lx lx lx gnd a1 c6 a6 d4 a5 b5 c5 d5 b6 c30 10f c13 0.47f c18 4700pf c8 150f c7 150f l1 0.22h c19 10f c1 22f a4 a3 a2 b2 b4 c2 c4 b1 gnd b3 gnd c1 gnd c3 gnd d1 gnd d2 gnd d3 gsns a7 fb b7 c7 d7 s r r s s r3 3.83ki 1% r8 1i r2 5.36ki 1% r1 8.06ki 1% 470i c2 22f c3 22f v in 2.7v to 5.5v pgood c4 22f r5 100ki connect skip to en to enable skip mode connect skip to gnd for pwm mode v en < 0.4v = off 1.4v < v en < v in = on r7 4.7i c9 150f c10 150f c20 10f v out 1.5v 0 to 18a s small-signal gnd (sgnd) connect to pgnd only on component layer at via next to u1. r remote sense gnd (rgnd) connect to pgnd only at the load . power gnd (pgnd) top layer gnd flood, system gnd. c16 0.1f max15118 u1
max15118 high-efficiency, 18a, current-mode synchronous step-down regulator with integrated switches maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 23 ? 2011 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 6/11 initial release

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