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as7620 500ma hysteretic high voltage step-down converter with dual power monitor www.austriamicrosystems.com revision 1.13 1 - 16 datasheet 1 general description the as7620 is an easy-to-use, high-efficiency, high- voltage, hysteretic step -down dc-dc converter, operating in asynchronous mode. its low-power architecture extends hold-up time in battery-backed and critical applications where maximum up-time over a wide input supply voltage range is needed, while still providing for high efficiencies of up to 90% during peak current demands. although the as7620 is optimized for 24v applications found in industrial and medical systems, its ability to support 100% duty cycle makes the as7620 ideal for applications demanding maximum up-time and soft power fail behavior. in combination with low idle current of only 30a, on-demand s witching reduces operating current at low load currents. by selecting an appropriate inductor value, operating current can be lowered and switching frequencies tuned to certain load conditions. a pin-strapped current limit input minimizes inductor peak current and thus inductor size and cost for any given application. the device further includes output short-circuit protection and thermal shutdown. in shutdown mode, only 1a (typ) of current is consumed. figure 1. block diagram 2 key features low quiescent current for efficient partial load operation wide supply voltage range, 3.6v to 32v 100% duty cycle extends operating range pin-programmable cycle-by-cycle current limit integrated pmos eliminates bootstrap capacitor resistor-programmable ea rly power fail warning input power-good flag thermal shutdown fixed 3.3v and adjustable output (1.2v to v in ) small 4x4mm 12-lead mlpq enhanced power package specified from -40oc to +125oc junction and 85oc maximum ambient temperatures 3 applications the as7620 is suitable for industrial 24vdc applications like plcs, robotics; home security and building control applications; solid-state utility meters; signage and led column power; and sensor interfaces. + - + - + - lx ilim pg pf vin shdn fb vepf ldo tem p level shifter soft-start i sense v ref hysteretic controller as7620
www.austriamicrosystems.com revision 1.13 2 - 16 as7620 datasheet - pin assignments 4 pin assignments figure 2. pin assignments (top view) pin descriptions table 1. pin descriptions pin name pin number description v in 1 high voltage power supply input gnd 2 must be connected to gnd lx 3 power output to inductor gnd 4 must be connected to gnd fb 5 feedback input ilim 6 current limit input shdn 7 shutdown input, active low gnd 8 must be connected to gnd gnd 9 must be connected to gnd pf 10 early power fail output, open drain, active low vepf 11 comparator voltage input for early power fail warning pg 12 power good, open drain, active high output, monitors feedback voltage pgnd pad exposed pad. connect to gnd plane to help thermal dissipation 1 2 3 45 6 7 8 9 10 11 12 v in gnd lx gnd fb ilim pg vepf pf gnd gnd shdn as7620 pgnd
www.austriamicrosystems.com revision 1.13 3 - 16 as7620 datasheet - absolute maximum ratings 5 absolute maximum ratings stresses beyond those listed in table 2 may cause permanent damage to the device. these are stress ratings only, and functional operation of the de vice at these or any other cond itions beyond those indicated in electrical characteristics on page 4 is not implied. exposure to absolute maxi mum rating conditions for extended periods may affect device reliability. table 2. absolute maximum ratings parameter min max units comments v in -0.3 40 v lx -0.3 v in +0.3 v fb, shdn -0.3 v in +0.3 or 5.5 v whichever is lower all other pins except lx, fb and shdn -0.3 3.6 v latch-up -30 +30 ma norm: jedec 78 1 1. voltage on pin 7 (shdn) limited to +5.5v package power dissipation 1 w ja = 32oc/w for a 4-layer board, 4 vias, t amb = +70oc operating temperature range -40 +125 oc junction temperature electrostatic discharge -1000 +1000 v no rm: hbm mil-std. 883e 3015.7 methods humidity (non-condensing) 5 90 %r.h. storage temperature -55 125 oc junction temperature 150 oc package body temperature 260 oc norm: ipc/jedec j-std-020d. the reflow peak soldering temperature (body temperature) specified is in accordance with ipc/jedec j-std-020d ?moisture/reflow sensitivity classification for non-hermetic solid state surface mount devices?.
www.austriamicrosystems.com revision 1.13 4 - 16 as7620 datasheet - electrical characteristics 6 electrical characteristics t j = -40 to +125oc, v out =3.3v, l x =10h, c x =100f (unless otherwise specified). typ. values at v in = +24v and t amb = +25oc. table 3. electrical characteristics symbol parameter conditions min typ max units v in input voltage range 3.6 24 32 v v cc vepf, ilim -0.3 3.6 v v st start-up voltage 3.3 v v out output voltage as7620-a 1.19 v in v as7620-b initial, at 25oc amb. 3.267 3.300 3.333 v over line, load and temperature 3.218 3.383 v fb feedback voltage as7620-a initial, at 25oc amb. 1.178 1.190 1.202 v over line and temperature 1.166 1.214 v as7620-b 3.218 3.300 3.383 v hys controller hysteresis as7620-a at fb node 81530 mv as7620-b 22 42 82 v epf early power fail threshold at v epf 1.19 v v pg power good threshold of v fb at fb pin 91 93 95 % line regulation v in =8v to 24v, r l =200 0.1 % / v load regulation 10% to 90% load change 0.9 % i fb input bias current as7620-a fb pin 200 na as7620-b 3 5 a i out output current i lim /2 ma i lim switch current limit ilim=0v 1 1. lx=100h, c x =10f, initial accuracy only. for temperature variation, please refer to performance graphs. 192 240 288 ma ilim=v out 2 2. vout from 1.5v to 3.6v 576 720 864 ilim=open 800 1000 1200 p-channel on resistance 0.4 0.8 maximum duty cycle at v in =3.6v 100 % t on minimum on-time current limit is not attained to turn off the switch be fore the minimum on-time expired 81012s t off minimum off-time 0.22 0.42 0.62 s i q quiescent current non-switching 30 45 a i out =500a 37 a i shdn shutdown current 15a v lo shutdown threshold shdn 1 v i ibn logic input bias current shdn 1 a t shdn shutdown temperature 150 175 oc t shdn hysteresis 10 oc t j operating temperature junction -40 125 oc t amb ambient -40 85 oc
www.austriamicrosystems.com revision 1.13 5 - 16 as7620 datasheet - typical operating characteristics 7 typical operating characteristics figure 3. efficiency vs output current, v out =4.5v figure 4. pmos rdson vs. temperature figure 5. gnd current vs. i out @ t amb figure 6. gnd current vs. temperature @ i out =0a figure 7. current limit threshold vs v in figure 8. average switching frequency vs v in 0 100 200 300 400 500 600 700 800 900 1000 -40 -20 0 20 40 60 80 100 120 tem p (c) rdson (mohm) . 30 40 50 60 70 80 90 100 1 10 100 1000 iout (m a) efficiency (%) vin=32v vin=12v vin=24v vin=5v 28.0 30.0 32.0 34.0 36.0 38.0 40.0 42.0 -40 - 2 0 0 20 40 6 0 80 10 0 1 20 temp (c) ignd (ua) 1 10 100 1000 10000 1.0 10.0 100.0 1000.0 iout (ma) ignd (ua) vin=32v vin=24v vin=12v vin=5v vin=32v vin=24v vin=5v vin=12v 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 5 1015202530 vi n (v) cl (ma) ilim gnd ilim vout ilim floating 100 1000 10000 100000 1000000 5 7 9 11 13 15 1719 21 23 25 27 29 31 vi n (v) fsw (hz) iout=500a iout =5ma iout=50ma iout=500ma
www.austriamicrosystems.com revision 1.13 6 - 16 as7620 datasheet - typical operating characteristics figure 9. average switching frequency vs i out (ilim=open) figure 10. shutdow n current vs. temperature figure 11. line regulation @ i out =10ma figure 12. line regulation @ i out =500ma figure 13. load regulation figure 14. line regulation v out =5v @ 10ma 0 30000 60000 90000 120000 150000 180000 210000 240000 270000 300000 330000 0 100 200 300 400 500 iout (ma) fsw (hz) vin=5v vin=12v vin=24v vin=32v 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 -40 -20 0 20 40 60 80 100 120 temp (c) ishdn (ua ) vin=5v vin=12v vin=24v vin=32v -10% 10% -0.800% -0.600% -0.400% -0.200% 0.000% 0.200% 0.400% 0.600% 0.800% vout variation (%) vin variation (%) -10% 10% -0.400% -0.300% -0.200% -0.100% 0.000% 0.100% 0.200% 0.300% 0.400% vout variation (%) vin variation (%) -1.000% -0.800% -0.600% -0.400% -0.200% 0.000% 0.200% 0.400% 0.600% 0.800% 1.000% 0.1 1 10 100 1000 iout (ma) vout variation % vout vin
www.austriamicrosystems.com revision 1.13 7 - 16 as7620 datasheet - typical operating characteristics figure 15. line regulation v out =5v @ 10ma figure 16. load regulation v out =5v 10ma 500ma note: all measurements taken at v in =24v, v out =3.3v, and t amb =25oc using the typical application circuit specified in figure 17 , unless otherwise specified. vout vin
www.austriamicrosystems.com revision 1.13 8 - 16 as7620 datasheet - detailed description 8 detailed description figure 17. system diagram of as7620-a with early power fail warning shut down the device can be shut down by providin g a voltage lower than 1v at the shdn pin (7). in this condition, the consumption is only 1a (typ.). the as7620 is providing an internally regulated pull-up circuit. no external pull-up resistor shall be used, which could otherwis e damage the shutdown input. connect the shdn input directly to an open drain port only. soft start the device implements a soft start by limiting the inrush curr ent into the output choke. initially, the internal pmos is turned on until the current reaches the programmed current limit (see current limit on page 9) and then is immediately turned off. it will be turned on again when the current approaches 0a. in this time frame, the fb voltage (v fb ) will be lower than the refe rence and so the duty cycle will be driven by the cu rrent limit only. regulation both as7620-a and as7620-b are based on a hysteretic control method. moreover, the switch current is monitored to make the converter always work in discontinuous current mo de (dcm). the advantages of th is type of control system can be summarized as following: high efficiency even at light load intrinsically stable simplicity readiness during the load transient the internal pmos is switched on when the v fb is lower than v ref -v hyst /2 and the current is 0a (dcm). the on time will be terminated if the v fb is over v ref +v hyst /2 or if the current limit (cl) is triggered. in practice, considering the most common application conditions (l=10h 100h; c=1 0f - 100f) and setting the cl threshold according to the load, the on time is norma lly terminated by the cl intervention and the output voltage ripple will stay within 1.25% of the output voltage (typ.) or v hyst * v out / v ref . table 4. as7620 output voltage options as7620 AS7620A-BQFT as7620b-bqft v out adj. 3.3v 2.2f 100f d 1 10h v out 3.6v to 32v v in l x fb i lim c out pf r 7 r 6 r 5 r 3 r 4 c in pg as7620-a v epf v hys j 1 v in shdn j 2 r 1 r 3 3.3v c 1
www.austriamicrosystems.com revision 1.13 9 - 16 as7620 datasheet - detailed description v out selection the as7620-b features a 3.3v fixed ou tput voltage. the as7620-a provides an adjustable output from 1.2v (v ref ) up to virtually v in (see 100% duty cycle operation on page 11) . to select the desired v out , the related resistor divider has to be tuned according to the following formula: (eq 1) where: rh is the high side resist or of the output divider rl is the resistor of the output divider note: it is suggested to select resistors in the range of hundreds of k in order to limit the current consumption. current limit the current is sensed during the on time of the internal pmos. three different current li mit thresholds can be selected by the ilim pin: 1. 240ma (typ.) ilim shorted to gnd 2. 720ma (typ.) ilim shorted to v out (from 1.5v to 3.6v) 3. 1000ma (typ.) ilim floating this threshold is intended as peak curr ent limit. if the current r eaches the threshold during the on time, the pmos is turned off and it will be turned on again only when the current approaches 0a and the feedback voltage is equal or lower than v ref . the maximum output current is ilim/2. switching frequency the switching frequency (f sw ) changes according to the application conditions and, in particular, to the output current in order to optimize the efficiency in any load conditi on. anyway, it is always possible to estimate the f sw during the design process. as described in the regulation (refer to page 8) ? the converter always works in dcm and, normally, the peak current into the inductor is the cl threshold (ilim). the average of the inductor current must be equal to the output current. the following formula provides the relati onship between inductor current and output current: i out = (eq 2) consequently, the f sw can be expressed as following: (eq 3) figure 18. chart illustrating the fsw vs. i out in a standard application (v in =24v, v out =3.3v, l=10 h, ilim=1a) v out v ref 1 rh rl ------ - + ?? ?? ? = 1 tsw --------- - 1 2 -- - ilim 2 l ? v in ? v in v out ? () v out ? -------------------------------------------------- ? ? fsw 2 i out ? v in v out ? () v out ? ? ilim 2 l ? v in ? ---------------------------------------------------------------------------- = fsw vs. iout 0 50 100 150 200 250 300 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 iout (a) fsw (khz)
www.austriamicrosystems.co m revision 1.13 10 - 16 as7620 datasheet - detailed description power fail / power good as7620a-b monitors input and output voltage by vepf (pin 11) and v fb (pin 5) respectively. two dedicated flags pf (pin 10) and pg (pin 12) are provided outside to inform abo ut early input power fail (a ctive low) and output within regulation. figure 19 illustrates the typical connecti on for vepf. during start up, pf is initially low. by selecting r3, r4, r5 and r6, it is possible to set the desired input voltage threshold above which the input power is considered stable. once v in (vddh in figure 19 ) reaches vinth, pf is released and so an additional voltage contribution from v dd is added at the vpf pin, realizing in fact a hysteresis to eliminate pf oscillation due to power supply noise. figure 19. open-drain output stage for comparator ta b l e 5 provides the resistors values covering all the standar d input bus. the resistors values are 1% commercial values. it is mandatory to use the correct resistors values to guarantee the respect of maximum absolute voltages at epf and pf pin. vdd has been considered 3.3v. otherwise epf pin should be shorted to gnd and pf left floating. terminology: vrst: reset voltage for the epf. it is 90% of the input bus voltage. vtrip: trip voltage for the epf. it is 80% of the input bus voltage. thermal protection the internal junction temperature is continuously monitored. if it reaches 150oc (min), the pmos is turned off. the device can switch again if the temperatur e is decreased by at least 10oc. if t he over-temperature persists, the device will be shut down again resulting in a hiccup mode for the output power. table 5. epf network select ion with different input bus v in (v) vrst (v) vtrip (v) r3 (k ) r4 (k ) r5 (k ) r6 (k ) 5 4.5 4 365 143 1740 1370 6 5.4 4.8 464 143 1870 1430 9 8.1 7.2 768 140 2050 1580 12 10.8 9.6 1070 140 2100 1650 15 13.5 12 1370 140 2150 1690 20 18 16 1870 140 2210 1740 24 21.6 19.2 2260 140 2260 1740 28 25.3 22.5 2670 140 2260 1740 vddh 3.6?32v vdd 1.2?3.6 power fail r on r6 r3 r4 v ref r5 inv - +
www.austriamicrosystems.co m revision 1.13 11 - 16 as7620 datasheet - application information 9 application information input capacitors an input capacitor is required to sustain the peak curren t requested by the turning on of the internal pmos. when used, the capacitor helps to reduce the noise and saves the in put battery life. the input capacitor has to withstand the input rms current, which can be calculated by the following formula: (eq 4) while designing for wide input/output volt age range, the worst case of irms=1/2*i out must be considered. suggested capacitors are low esr oscon, polymer, aluminum or mlccs. tantalum types are not recommended for their weakness in withstanding big inrush currents. output inductor the inductor together with the output capacitor represents the output filter. using the as76 20, the inductor is charged and completely discharged at every swit ching cycle being that the converter is forced to work in dcm. values from 10h to 100h are suitable to work with as7620 and its selection should consider the following statements: bigger inductor implies lower f sw bigger inductor implies lower bandwidth the inductor must be rated to withstand the peak current (ilim) and the rms current output capacitor the output capacitor together with the inductor represents t he output filter. the bigger the capacitance is, the lower will be the output ripple. usually, low esr mlccs are preferred as they are inexpensive and small in size. any value from 10f is suitable, considering the load transi ent specifications of the application as well. free wheeling diode the inductor current is forced through the diode during t he off-times. the average current flowing through it is the reverse voltage must be higher than the input voltage and safely it is common to consider 30% more. normally, a schottky diode is preferred because of its low forward voltage. stability even though the hysteretic voltage mode is intrinsically stable, an excessive noise at the fb could cause instability. for this reason care must be taken drawing the layout, reduci ng the noise and shielding the fb path from it. the main noise generator is the s witching node, which is commutated from gnd to v in by the internal pmos and the free wheeling diode and through which a pulse current flows. it is wise to add a mlcc capacitor as close as possible to the v in pin of the device and provide a wide/short path between the lx pin and the external components (inductor and diode). it is preferable to draw the fb path as far as possi ble from the lx node and, pe rhaps, shielding it with a gnd track. another recommendation is to use low esl output capacitors, thus avoiding electrolytic parts. a big esl adds a square wave contribution on the fb that can make the device work improperly. 100% duty cycle operation thanks to the pmos structure of the inte rnal switch, the device can actually wo rk at 100% duty cycle. this feature is very helpful during the load transient, because the maximum power can be transferred to the output in order to recover as fastest. the device will try to work at 100% duty whenever the fb voltage is lower than the upper window?s threshold. moreover, in this condition, the safety is always guaranteed by the current limit. irms i out v out v in v out ? () ? v in -------------------------------------------------- ? = irms i out 2 il 2 3 ----------- + = 1 2 -- - fsw ilim 2 l ? v out ------------------------ ? ?
www.austriamicrosystems.co m revision 1.13 12 - 16 as7620 datasheet - application information demo board a demonstration board is available to test the device fu nctionalities and performance in a standard application. for further information, please refer to the as7620eb datasheet. figure 20. demo board photograph
www.austriamicrosystems.co m revision 1.13 13 - 16 as7620 datasheet - package drawings and markings 10 package drawings and markings the device is available in a 12-lead mlpq package. figure 21. 4x4mm mlpq package drawings
www.austriamicrosystems.co m revision 1.13 14 - 16 as7620 datasheet - package drawings and markings table 6. 4x4mm mlpq package dimensions
www.austriamicrosystems.co m revision 1.13 15 - 16 as7620 datasheet - ordering information 11 ordering information the devices are available as the standard products shown in table 7 . *) on request note: all products are rohs compliant and pb-free. buy our products or get free samples online at icdirect: http://www.austriamicr osystems.com/icdirect for further information and requests, please contact us mailto:sales@austriamicrosystems.com or find your local distributor at http://www.a ustriamicrosystems.com/distributor table 7. ordering information ordering code marking description delivery form package AS7620A-BQFT as7620 or as7620a 500ma hysteretic buck converter, adjustable output tape and reel 12-lead mlpq, 4x4mm as7620b-bqft* as7620b 500ma hysteretic buck converter, 3.3v output tape and reel 12-lead mlpq, 4x4mm
www.austriamicrosystems.co m revision 1.13 16 - 16 as7620 datasheet copyrights copyright ? 1997-200 9, austriamicrosystems ag, tobelbaderstrasse 30, 8141 unterpremstaet ten, austria-europe. trademarks registered ?. all rights reserved. the mate rial herein may not be reproduced, adapted, merged, translated, stored, or used wit hout the prior written consent of the copyright owner. all products and companies mentioned are trademarks or registered trademarks of their respective companies. disclaimer devices sold by austriamicrosystems ag are covered by t he warranty and patent indemni fication provisions appearing in its term of sale. austriamicrosystems ag makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freed om of the described devices from patent infringement. austriamicrosystems ag reserves the right to change spec ifications and prices at an y time and without notice. therefore, prior to designing this pro duct into a system, it is necessary to check with austriam icrosystems ag for current information. this product is intended for use in normal commercial applications. applications requiring extended temperature range, unus ual environmental requirements, or high reliability applications, such as military, medical life-support or life-sustaining equipment are specifically not recommended without additional processing by austriamicrosystems ag for each application. for shipments of less than 100 parts the m anufacturing flow might show deviations from the standard production flow, such as test flow or test location. the information furnished here by austriamicrosystems ag is believed to be correct and accurate. however, austriamicrosystems ag shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. no obligation or liability to reci pient or any third party shall arise or flow out of austriamicrosystems ag rendering of technical or other services. contact information headquarters austriamicrosystems ag tobelbaderstrasse 30 a-8141 unterpremstaetten, austria tel: +43 (0) 3136 500 0 fax: +43 (0) 3136 525 01 for sales offices, distributors a nd representatives, please visit: http://www.austriamicrosystems.com/contact

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