note : all information contained in this data sheet has been carefully checked and is believed to be accurate as of the date of publi cation; however, this data sheet cannot be a ?controlled document?. current revisions, if any, to these specifications are maintained at the factory and are available upon your request. we recommend checking the revision level befor e finalization of your design documentation. ? 2001 elantec semiconductor, inc. e l 7 5 1 2 c - p r e l i m i n a r y general description the el7512c is a high frequency, high efficiency step-up dc:dc regulator operated at fixed frequency pwm mode. with an integrated 1a mosfet, it can deliver up to 600ma output current at up to 90% efficiency. the adjustable switching frequency is up to 1.2mhz, mak- ing it ideal for dsl applications. when shut down, it draws <3a of current. this feature, along with the minimum starting voltage of 2v, makes it suitable for portable equipment powered by one lithium ion or 3 to 4 nimh cells. the el7512c is available in a 10-pin msop package, with maximum height of 1.1mm. with proper external components, the whole con- verter takes less than 0.25in 2 pcb space. this device is specified for operation over the full -40c to +85c temperature range. typical application diagram 1 2 3 4 10 9 8 7 5 6 el7512c pgnd sgnd rt en lbi lx vdd fb ss lbo 47f 80.6k w 10k w 4.7nf 10h 100k 20nf 10f v in (2v- 9v) v out (12v up to 400ma) features ? 90% efficiency ? up to 600ma i out ? 5v < v out < 18v ? v in > 2v ? up to 1.2mhz adjustable frequency ? < 3a shutdown current ? adjustable soft-start ? low battery detection ? internal thermal protection ? 1.1mm max height 10-pin msop package applications ? 3v to 5v, 12v, and 18v converters ? 5v to 12v and 16v converters ? tft-lcd ? dsl ? portable equipment ? desktop equipment ordering information part no package tape & reel outline # EL7512CY 10-pin msop mdp0043 el7512c - preliminary high frequency pwm step-up regulator o c t o b e r 2 , 2 0 0 1
2 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y absolute maximum ratings (t a = 25c) values beyond absolute maximum ratings can cause the device to be pre- maturely damaged. absolute maximum ratings are stress ratings only and functional device operation is not implied v in , lbi, v dd +18v lx voltage 20v storage temperature -65c to +150c operating temperature -40c to +85c lead temperature 300c important note: all parameters having min/max specifications are guaranteed. typ values are for information purposes only. unless otherwise note d, all tests are at the specified temperature and are pulsed tests, therefore: t j = t c = t a electrical characteristics v in = 5v, v out = 12v, i out = 0ma, f osc = 600khz , t a = 25 c unless otherwise specified. parameter description condition min typ max unit iq1 quiescent current - shut-down v shdn = 0v 3 a iq2 quiensent current v shdn = 2v, frequency = 600khz 2.5 4 ma vfb feedback voltage 1.31 1.35 1.39 v ib feedback input bias current 0.10 a v in input voltage range 2 v d max maximum duty cycle 84 90 % i lim current limit - max average input current 1000 1250 1500 ma i shdn shut-down input bias current 1 a v lbi lbi threshold voltage 190 220 250 mv v ol-lbo lbo output low ilbo = 1ma 0.1 0.2 v i leak-lbo lbo output leakage current vlbi = 250mv, vlbo = 5v 0.02 1 a r ds-on switch on resistance at 12v output 300 m w i leak-switch switch leakage current 1 a d v out / d v in line regulation 3v < v in < 6v, v out = 12v, no load 0.15 %/v d v out / d i out load regulation i out < 250a 0.5 1 % f osc-range frequency range 1200 khz f osc1 switching frequency r osc = 100k w 530 670 800 khz vhi- shdn shdn input high threshold 1.6 v vlo -shdn shdn input low threshold 0.5 v pin descriptions pin number pin name pin function 1 pgnd power ground; connected to the source of internal n-channel power mosfet 2 sgnd signal ground; ground reference for all the control circuitry; needs to have only a single connection to pgnd 3 rt timing resister to adjust the oscillation frequency of the converter 4 en chip enable; connects to logic hi (>1.6v) for chip to function 5 lbi low battery input; connects to a sensing voltage, or left open if function is not used 6 lbo low battery detection output; connected to the open drain of a mosfet; able to sink 1ma current 7 ss soft-start; connects to a capacitor to control the start of the converter 8 fb voltage feedback input; needs to connect to resistor divider to decide v o 9 vdd control circuit positive supply 10 lx inductor drive pin; connected to the drain of internal n-channel power mosfet
3 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y block diagram - + start-up oscillator thermal shut-down - + i lout pwm logic rt en lbo lbi fb vdd lx sgnd pgnd ss max_duty vref vramp 210mv 80.6k w 10k w v out 15f v in 0.3 w 80m w 7.2k 12a pwm comparato reference generator 100k w 20nf 10f 47f 4.7nf
4 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y typical performance curves f s vs v dd 1400 1200 800 400 200 0 5 7 13 19 v dd (v) f s ( k h z ) f s vs temperature 760 740 700 680 660 640 f s ( k h z ) -50 0 50 150 t j (c) 1000 600 9 15 11 17 r t =51.1k w r t =71.5k w r t =100k w r t =200k w 720 100 r t =100k w v dd =15v v dd =5v v dd =10v efficiency v in =3.3v, v o =5v efficiency v in =3.3v, v o =12v efficiency v in =5v, v o =12v internal v ref vs t j 100 80 60 40 20 0 e f f i c i e n c y ( % ) 10 110 210 510 i o (ma) 100 80 60 40 20 0 e f f i c i e n c y ( % ) 1.4 1.25 1.15 1.05 1 v r e f ( v ) 100 80 60 40 20 0 e f f i c i e n c y ( % ) 10 60 110 210 i o (ma) 10 60 160 360 i o (ma) -50 0 50 150 t j (c) 310 410 f s =670khz 160 f s =670khz 110 210 260 310 f s =670khz v dd =12v 100 1.35 1.3 1.2 1.1
5 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y typical performance curves steady state operation (inductor continuous conduction) v in =5v, v o =12v, i o =300ma power-up v in =5v, v o =12v, i o =300ma steady state operation (inductor discontinuous conduction) v in =5v, v o =12v, i o =25ma load transient response v in =5v, v o =12v, i o =50ma-300ma d v i v lx d v o i l v in v o i l d v i v lx d v o i l i o d v o
6 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y applications information the el7512c is a step-up regulator, operated at fixed frequency pulse-width-modulation (pwm) control. the input voltage is 2v-12v and output voltage is 5v-16v. the switching frequency (up to 1.2mhz) is decided by the resistor connected to rt pin. start-up after vdd reaches a threshold of about than 2v, the power mosfet is controlled by the start-up oscillator, which generates fixed duty-ratio of 0.5-0.7 at a fre- quency of several hundred kilohertz. this will boost the output voltage. when vdd reaches about 3.7v, the pwm comparator takes over the control. the duty ratio will be decided by the multiple-input direct summing comparator, max_duty signal (about 90% duty-ratio), and the cur- rent limit comparator, whichever is the smallest. the soft-start is provided by the current limit compari- tor. as the internal 12a current source changes the external css, the peak mosfet current is limited by the voltage on the capacitor. this in turn controls the ris- ing rate of output voltage. the regulator goes through the start-up sequence as well after the en signal is pulled to hi. steady-state operation when the output reaches the preset voltage, the regulator operates at steady state. depending on the input/output condition and component, the inductor operates at either continuous-conduction mode or discontinuous-conduc- tion mode. in the continuous-conduction mode, the inductor current is a triangular waveform and lx voltage a pulse wave- form. in the discontinuous-conduction mode, the inductor current is complete dry out before the mosfet is turned on again. the input voltage source, the induc- tor, and the mosfet and output diode parasitic capacitors forms a resonant circuit. oscillation will occur in this period. this oscillation is normal and will not affect the regulation. at very low load, the mosfet will skip pulse some- times. this is normal. current limit the mosfet current limit is nominal 1.2a and guaran- teed 1a. this restricts the maximum output current iomax based on the following formula: where: d i l is the inductor peak-to-peak current ripple and is decided by: d is the mosfet turn-on radio and is decided by: f s is the switching frequency. the following table gives typical values: component considerations it is recommended that c in is larger than 10f. theoret- ically, the input capacitor has ripple current of d il. due to high-frequency noise in the circuit, the input current ripple may exceed the theoretical value. larger capacitor will reduce the ripple further. maximum output current v in (v) v o (v) l (h) f s (khz) i omax (ma) 2 5 10 600 360 2 9 10 600 190 2 12 10 600 140 3 5 10 600 540 3 9 10 600 270 3 12 10 600 200 4.5 9 10 600 400 4.5 12 10 600 280 4.5 15 10 600 220 9 12 10 600 600 9 15 10 600 420 i omax 1 d i l 2 --------- v in v o ---------- ? = d i l v in l ---------- d f s ------ = d v o v in ? v o ------------------------- =
7 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y the inductor has peak and average current decided by: the inductor should be chosen to be able to handle this current. furthermore, due to the fixed internal compen- sation, it is recommended that maximum inductance of 10h and 15h to be used in the 5v and 12v or higher output voltage, respectively. the output diode has average current of i o , and peak current the same as the inductor's peak current. schottky diode is recommended and it should be able to handle those currents. output voltage ripple is the product of peak inductor current times the esr of output capacitor. low esr capacitor is to be used to reduce the output ripple. the minimum out capacitance of 330f, 47f, and 33f is recommended for 5v, 12v, and 16v for 600khz switch- ing frequency, respectively. for 1mhz switching frequency, 220f, 33f, and 22f capacitor can be used for the output voltages. in addition to the voltage rating, the output capacitor should also be able to handle the rms current is given by: layout considerations the layout is very important for the converter to func- tion 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. the trace connected to pin 8 (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 vdd 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 example of layout based on these principles. please refer to the el7512c applica- tion brief for the layout. i lpk i lavg d i l 2 --------- + = i lavg i o 1d ? ------------- = i corms 1 ( d ) d d i l 2 i lavg 2 -------------------- + ? ? ? 1 12 ------ ? ? ? i lavg =
8 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y package outline drawing note: the package drawing shown here may not be the most recent revision. to verify the latest version, please refer to the elantec website at: http://www.elantec.com/pages/package_outline.html
9 el7512c - preliminary high frequency pwm step-up regulator e l 7 5 1 2 c - p r e l i m i n a r y general disclaimer specifications contained in this data sheet are in effect as of the publication date shown. elantec, inc. reserves the right to make changes in the cir- cuitry or specifications contained herein at any time without notice. elantec, inc. assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. warning - life support policy elantec, inc. products are not authorized for and should not be used within life support systems without the specific written consent of elantec, inc. life support systems are equipment intended to sup- port or sustain life and whose failure to perform when properly used in accordance with instructions provided can be reasonably expected to result in significant personal injury or death. users con- templating application of elantec, inc. products in life support systems are requested to contact elantec, inc. factory headquarters to establish suitable terms & conditions for these applications. elan- tec, inc.?s warranty is limited to replacement of defective components and does not cover injury to persons or property or other consequential damages. elantec semiconductor, inc. 675 trade zone blvd. milpitas, ca 95035 telephone: (408) 945-1323 (888) elantec fax: (408) 945-9305 european office: 44-118-977-6020 o c t o b e r 2 , 2 0 0 1 printed in u.s.a. japan technical center: 81-45-682-5820
|
