1 ? fn7295 caution: these devices are sensitive to electrostatic discharge; follow proper ic handling procedures. 1-888-intersil or 321-724-7143 | intersil (and design) is a registered trademark of intersil americas inc. copyright ? intersil americas inc. 2003. all rights reserved. elantec is a registered trademark of elantec semiconductor, inc. all other trademarks mentioned are the property of their respective owners. EL7562 monolithic 2amp dc:dc step-down regulator the EL7562 is an integrated, synchronous step-d own regulator with output voltage adjustable from 1.0v to 3.8v. it is capable of delivering 2a continuous current at up to 95% efficiency. the el7 562 operates at a constant frequency pulse width modulation (pwm) mode, making external synchronization possible. patented on-chip resistorless current sensing enables current mode control, which provides cycle-by-cycle cu rrent limiting, over-current protection, and excellent step load response. the EL7562 is available in a fused-lead 16-pin qsop package. with proper external components, the whol e converter fits into a less than 0.5 in 2 area. the minimal external components and small size make this EL7562 ideal for desktop and portable applications. the EL7562 is specified for operation over the 0c to +70c temperature range. pinout EL7562 (16-pin qsop) top view features integrated synchronous mosfets and current mode controller 2a continuous output current up to 95% efficiency 3.3v or 5v nominal input voltage adjustable output from 1v to 3.8v cycle-by-cycle current limit precision reference 0.5% load and line regulation adjustable switching frequency to 1mhz oscillator synchronization possible internal soft-start over-temperature protection under-voltage lockout 16-pin qsop package applications dsp, cpu core and io supplies logic/bus supplies portable equipment dc:dc converter modules gtl + bus power supply please refer to page 4 for 3.3v input application diagram 1 2 3 4 16 15 14 13 5 6 7 12 11 10 8 9 sgnd cosc vdd pgnd pgnd vin vin en pgnd vref fb vdrv lx lx vhi pgnd r 3 r 2 l 1 2.37k ? c 3 c 4 c 1 c 2 c 5 r 1 c 6 c 7 v o (3.3v, 2a) v in (4.5v- 5.5v) 0.1f 270pf 39 ? 100f 0.1f 0.1f 1k ? 0.1f 4.7f 100f manufactured under u.s. patent no. 57,323,974 ordering information part number package tape & reel pkg. no. EL7562cu 16-pin qsop - mdp0040 data sheet june 26, 2002
2 absolute maximum ratings (t a = 25c) supply voltage between v in or v dd and gnd . . . . . . . . . . . . +6.5v v lx voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v in +0.3v input voltage . . . . . . . . . . . . . . . . . . . . . . . . gnd -0.3v, v dd +0.3v v hi voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . gnd -0.3v, v lx +6v storage temperature . . . . . . . . . . . . . . . . . . . . . . . .-65c to +150c operating ambient temperature . . . . . . . . . . . . . . . . . 0c to +70c operating junction temperature . . . . . . . . . . . . . . . . . . . . . . +135c caution: stresses above those listed in ?a bsolute maximum ratings? may cause permanent damage to the device. this is a stress o nly rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. important note: all parameters having min/max specifications are guaranteed. typical values are for information purposes only. u nless otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: t j = t c = t a dc electrical specifications v dd = v in = 5v, t a = t j = 25c, c osc = 270pf, unless otherwise specified. parameter description conditions min typ max unit v ref reference accuracy 1.24 1.26 1.28 v v reftc reference temperature coefficient 50 ppm/c v refload reference load regulation 0 < i ref < 50a -1 % v ramp oscillator ramp amplitude 1.15 v i osc_chg oscillator charge current 0.1v < v osc < 1.25v 200 a i osc_dis oscillator discharge current 0.1v < v osc < 1.25v 8 ma i vdd +v drv v dd +v drv supply current v en = 4v, f osc = 120khz 2 6.5 ma i vdd_off v dd standby current en = 0 1 1.5 ma v dd_off v dd for shutdown 2.5 2.7 v v dd_on v dd for startup 2.6 3 v t ot over-temperature threshold 135 c t hys over-temperature hysteresis 20 c i leak internal fet leakage current en = 0, l x = 5v (low fet), l x = 0v (high fet) 20 a i lmax peak current limit 3 a r dson fet on resistance wafer level test only 60 120 m ? r dsontc r dson tempco 0.2 m ? /c v fb output initial accuracy i load = 0a 0.970 0.985 1.000 v v fb_line output line regulation v in = 5v, ? v in = 10%, i load = 0a 0.5 % v fb_load output load regulation 0.1a < i load < 1a 0.5 % v fb_tc output temperature stability -40c < t a < 85c, i load = 0.5a 1 % i fb feedback input pull up current v fb = 0v 100 200 na v en_hi en input high level 3.2 4 v v en_lo en input low level 1 v i en enable pull up current v en = 0 -4 -2.5 a EL7562
3 closed-loop ac electrical specifications v s = v in = 5v, t a = t j = 25c, c osc = 270pf, unless otherwise specified. parameter description conditions min typ max unit f osc oscillator initial accuracy 493 580 667 khz t sync minimum oscillator sync width 25 ns m ss soft-start slope 0.5 v/ms t brm fet break before make delay 15 ns t leb high side fet minimum on time 150 ns d max maximum duty cycle 95 % pin descriptions pin number pin name pin function 1 sgnd control circuit negative supply 2 cosc oscillator timing capacitor; f osc can be approximated by: f osc (khz) = 0.1843/c osc , c osc in f 3 vdd control circuit positive supply 4 pgnd ground return of the regulator; connected to the source of the low-side synchronous nmos power fet 5 pgnd ground return of the regulator; connected to the source of the low-side synchronous nmos power fet 6 vin power supply input of the regulator; connect ed to the drain of the high-side nmos power fet 7 vin power supply input of the regulator; connect ed to the drain of the high-side nmos power fet 8 en chip enable, active high; a 2a internal pull- up current enables the device if the pin is left open 9 pgnd ground return of the regulator 10 vhi positive supply of the high-side driver 11 lx inductor drive pin; high current digital output whose average voltage equals the regulator output voltage 12 lx inductor drive pin; high current digital output whose average voltage equals the regulator output voltage 13 vdrv positive supply of the low-side driver and input voltage for the high-side boot strap 14 fb voltage feedback input; connected to an external resistor divider between v out and gnd; a 125na pull-up current forces v out to v s in the event that fb is floating 15 vref bandgap reference bypass capacitor; typically 0.1f to gnd 16 pgnd ground return of the regulator EL7562
4 application diagram for 3.3v input 1 2 3 4 16 15 14 13 5 6 7 12 11 10 8 9 sgnd cosc vdd pgnd pgnd vin vin en pgnd vref fb vdrv lx lx vhi pgnd r 3 l 1 c 3 c 4 c 1 c 2 c 5 c 6 c 7 v o (2.5v, 2a) v in (3v-3.6v) 0.1f 270pf 39 ? 100f 0.1f 0.1f 0.1f 4.7f 100f r 2 1.54k ? r 1 1k ? c 9 0.1f c 8 0.1f d 2 d 3 d 4 EL7562 (16-pin qsop) EL7562
5 typical performance curves efficiency vs i o v in =5v 100 95 90 85 80 75 70 65 60 0.1 1 2 load current i o (a) efficiency (%) l=coilcraft do3316p-472 v o =2.5v v o =1.8v v o =1.5v v o =1.2v v o =3.3v power loss vs i o v in =5v 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 00.511.52 load current i o (a) power loss (w) load regulation v o =3.3v 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 00.511.52 load current i o (a) output voltage (%) efficiency vs i o v o =3.3v 100 95 90 85 80 75 70 65 60 00.511.52 load current i o (a) efficiency (%) line regulation v o =3.3v 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 4.5 4.7 5.1 5.3 5.5 v in (v) v o (%) v in =4.5v v in =5v v in =5.5v v in =4.5v v in =5v v in =5.5v 4.9 i o =0.1a i o =1a i o =2a power loss vs i o v in =5v 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 00.511.52 load current i o (a) power loss (w) v o =2.5v v o =1.8v v o =1.5v v o =1.2v v o =3.3v f s =500khz v ref vs temperature 1.258 1.256 1.254 1.252 1.25 1.248 1.246 1.244 1.242 0 10 110 temperature (c) v ref (v) 20 30 40 50 60 70 80 90 100 EL7562
6 typical performance curves (continued) switching frequency vs c osc 1400 1200 1000 800 600 400 200 0 0 400 600 800 1000 c osc (pf) f s (khz) 200 oscillator frequency vs temperature 390 385 380 375 370 365 360 temperature (c) oscillator frequency (khz) 0 10 110 20 30 40 50 60 70 80 90 100 c osc =390pf input current vs temperature (enable connected to gnd) 0.96 0.94 0.92 0.88 0.86 0.84 0.82 0.8 temperature (c) input current (a) 0.9 010 110 20 30 40 50 60 70 80 90 100 v in =5.5v v in =4.5v v in =5v EL7562
7 block diagram applications information circuit description general the EL7562 is a fixed frequency, current mode controlled dc:dc converter with integrated n-channel power mosfets and a high precision reference. the device incorporates all the active circuitry required to implement a cost effective, user-programmable 2a synchronous step- down regulator suitable for use in dsp core power supplies. theory of operation the EL7562 is composed of 5 major blocks: 1. pwm controller 2. nmos power fets and drive circuitry 3. bandgap reference 4. oscillator 5. thermal shut-down pwm controller the EL7562 regulates output voltage through the use of current-mode controlled pulse width modulation. the three main elements in a pwm controller are the feedback loop and reference, a pulse width modulator whose duty cycle is controlled by the feedback error signal, and a filter which averages the logic level modulator output. in a step-down (buck) converter, the feedback loop forces the time-averaged output of the modulator to equal the desired output voltage. unlike pure voltage-mode control systems, current-mode control utilizes dual feedback loops to provide both output voltage and inductor current information to the controller. the voltage loop minimizes dc and transient errors in the output voltage by adjusting the pwm duty-cycle in response to changes in line or load conditions. since the output voltage is equal to the time-averaged of the modulator output, the relatively large lc time constant found in power supply applications generally results in low bandwidth and poor transient response. by directly monitoring changes in inductor current via a series sense resistor the controller's response time is not entirely limited by the output lc filter and can react more quickly to changes in line and load conditions. this feed-forward characteristic also simplifies ac loop compensation since it adds a zero to the overall loop response. through proper selection of the current- feedback to voltage-feedback ratio the overall loop response drivers pwm controller current sense junction temperature voltag e reference oscillator 0.1f 39 ? controller supply sgnd power power fet fet 270pf 0.1f 0.1f 4.7h v out 2370 ? 1k ? 100f vref cosc vhi vin pgnd vdd vdrv fb en 5v EL7562
8 will approach a one-pole system. the resulting system offers several advantages over traditional voltage control systems, including simpler loop compensation, pulse by pulse current limiting, rapid response to line variation and good load step response. the heart of the controller is an input direct summing comparator which sum voltage feedback, current feedback, slope compensation ramp and power tracking signals together. slope com pensation is required to prevent system instability that occurs in cu rrent-mode topologies operating at duty-cycles greater than 50% and is also used to define the open-loop gain of the overall system. the slope compensation is fixed internally and optimized for 500ma inductor ripple current. the power tracking will not contribute any input to the comparator steady-state operation. current feedback is measured by the patented sensing scheme that senses the inductor current flowing through the high-side switch whenever it is conducting. at the beginning of each oscillator period the high-side nmos switch is turned on. the comparator inputs are gated off for a minimum period of time of about 150ns (leb) af ter the high-side switch is turned on to allow the system to settle. the leading edge blanking (leb) period prevents the detection of erroneous voltages at the comparator inputs due to switching noise. if the inductor current exceeds the maximum current limit (i lmax ) a secondary over-current comparator will terminate the high-side switch on time. if i lmax has not been reached, the feedback voltage fb derived from the regulator output voltage v out is then compared to the internal feedback reference voltage. the resultant error voltage is summed with the current feedback and slope compensation ramp. the high-side switch remains on until all four comparator inputs have summed to zero, at which time the high-side switch is turned off and the low-side switch is turned on. however, the maximum on-duty ratio of the high-side switch is limited to 95%. in order to eliminate cross-conduction of the high-side and low-side switches a 15ns break-before- make delay is incorporated in the switch drive circuitry. the output enable (en) input allows the regulator output to be disabled by an external logic control signal. output voltage setting in general: however, due to the relatively low open loop gain of the system, gain errors will occur as the output voltage and loop- gain is changed. this is shown in the performance curves. a 100na pull-up current from fb to v dd forces v out to gnd in the event that fb is floating. nmos power fets and drive circuitry the EL7562 integrates low on-resistance (60m ? ) nmos fets to achieve high efficiency at 2a. in order to use an nmos switch for the high-side drive it is necessary to drive the gate voltage above the source voltage (lx). this is accomplished by bootstrapping the v hi pin above the lx voltage with an external capacitor c vhi and internal switch and diode. when the low-side switch is turned on and the lx voltage is close to gnd potential, capacitor c vhi is charged through internal switch to v drv , typically 5v. at the beginning of the next cycle the high-side switch turns on and the lx pins begin to rise from gnd to v in potential. as the lx pin rises the positive plate of capacitor c vhi follows and eventually reaches a value of v drv +v in , typically 10v, for v drv =v in =5v. this voltage is then level shifted and used to drive the gate of the high-side fet, via the v hi pin. a value of 0.1f for c vhi is recommended. reference a 1.5% temperature compensated bandgap reference is integrated in the EL7562. the external v ref capacitor acts as the dominant pole of the amplifier and can be increased in size to maximize transien t noise rejection. a value of 0.1f is recommended. oscillator the system clock is generated by an internal relaxation oscillator with a maximum duty-cycle of approximately 95%. operating frequency can be adjusted through the c osc pin or can be driven by an external source. if the oscillator is driven by an external source care must be taken in selecting the ramp amplitude. since c slope value is derived from the c osc ramp, changes to c osc ramp will change the c slope compensation ramp which determine the open-loop gain of the system. when external synchronization is required, always choose c osc such that the free-running frequency is at least 20% lower than that of sync source to accommodate component v out 0.985 1 r 2 r 1 ------ - + ?? ?? ?? = for v in = 5v v out 0.975 1 r 2 r 1 ------ - + ?? ?? ?? = for v in = 3.3v EL7562
9 all intersil u.s. products are manufactured, asse mbled and tested utilizin g iso9000 quality systems. intersil corporation?s quality certifications c an be viewed at www.intersil.com/design/quality intersil products are sold by description only. intersil corporation reserves the right to make changes in circuit design, soft ware and/or specifications at any time without notice. accordingly, the reader is cautioned to verify that data sheets are current before placing orders. information furnishe d by intersil is believed to be accurate and reliable. however, no responsibility is assumed by intersil or its subsidiaries for its use; nor for any infringements of paten ts or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of intersil or its subsidiari es. for information regarding intersil corporation and its products, see www.intersil.com and temperature variations. figure 1 shows a typical connection. thermal shut-down an internal temperature sensor continuously monitors die temperature. in the event that die temperature exceeds the thermal trip-point, t he system is in fault state and will be shut down. the upper and low trip-points are set to 135c and 115c respectively. start-up delay a capacitor can be added to the en pin to delay the converter start-up (figure 2) by utilizing the pull-up current. the delay time is approximately: layout considerations the layout is very important for the converter to function properly. power ground ( ) and signal ground ( --- ) should be separated to ensure that the high pulse current in the power ground never interferes with the sensitive signals connected to signal ground. they should only be connected at one point (normally at the negative side of either the input or output capacitor). the trace connected to pin 14 (fb) is the most sensitive trace. it needs to be as short as possible and in a ?quiet? place, preferably between pgnd or sgnd traces. in addition, the bypass capacitor connected to the v dd pin needs to be as close to the pin as possible. the heat of the chip is mainly dissipated through the pgnd pins. maximizing the copper area around these pins is preferable. in addition, a solid ground plane is always helpful for the emi performance. the demo board is a good exampl e of layout based on these principles. please refer to the EL7562 application brief for the layout. figure 1. oscillator synchronization 2 3 11 10 9 6 7 8 15 14 EL7562 1 16 external oscillator bat54s 100pf t d ms () 1200 c f () = figure 2. start-up delay time v o v in t d v out c 2 3 11 10 9 6 7 8 15 14 EL7562 1 16 EL7562
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