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a s7 6 2 0 5 00 m a h y st e r e ti c hi g h vo l ta g e s t ep - d o w n co n ve r t e r w i t h d u a l p o w e r m o n i to r www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 1 16 d at ash ee t 1 general description the as7620 is an easytouse, highefficiency, high voltage, hysteretic stepdown dcdc converter, operating in asynchronous mode. its lowpower architecture extends holdup ti me in battery backed and critical applications where maximum upt ime over a wide input supply voltage range is needed, while still p roviding for high efficiencies of up to 90% during peak current deman ds. although the as7620 is optimized for 24v applicatio ns found in industrial and medical systems, its ability to supp ort 100% duty cycle makes the as7620 ideal for applications deman ding maximum uptime and soft power fail behavior. in combinatio n with low idle current of only 30a, ondemand switching reduces o perating current at low load currents. by selecting an appropriate inductor value, operati ng current can be lowered and switching frequencies tuned to certain load conditions. a pinstrapped current limit input minimizes induct or peak current and thus inductor size and cost for any given appli cation. the device further includes output shortcircuit pr otection and thermal shutdown. in shutdown mode, only 1a (typ) of current is consumed. figure 1. as7620 block diagram 2 key features low quiescent current for efficient partial load op eration wide supply voltage range, 3.6v to 32v 100% duty cycle extends operating range pinprogrammable cyclebycycle current limit integrated pmos eliminates bootstrap capacitor resistorprogrammable early power fail warning inpu t powergood flag thermal shutdown fixed 3.3v and adjustable output (1.2v to v in ) small 4x4mm 12lead mlpq enhanced power package specified from 40oc to +125oc junction and 85oc ma ximum ambient temperatures 3 applications the as7620 is suitable for industrial 24vdc applica tions like plcs, robotics; home security and building control applic ations; solid state utility meters; signage and led column power; and sensor interfaces. + - + - + - lx ilim pg pf vin shdn fb vepf ldo temp level shifter softstart i sense v ref hysteretic controller as7620
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 2 16 as7620 datasheet p i n a s s i g n m e n t s 4 pin assignments figure 2. pin assignments (top view) 4.1 pin descriptions table 1. pin descriptions pin number pin name description 1 v in high voltage power supply input 2 gnd must be connected to gnd 3 lx power output to inductor 4 gnd must be connected to gnd 5 fb feedback input 6 ilim current limit input 7 shdn shutdown input, active low 8 gnd must be connected to gnd 9 gnd must be connected to gnd 10 pf early power fail output, open drain, active low 11 vepf comparator voltage input for early power fail warni ng 12 pg power good, open drain, active high output, monitor s feedback voltage pad pgnd exposed pad. connect to gnd plane to help thermal d issipation 1 2 3 4 5 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/dcdc_stepdown/as7620 revision 1.17 3 16 as7620 datasheet a b s o l u t e m a x i m u m r a t i n g s 5 absolute maximum ratings stresses beyond those listed in table 2 may cause permanent damage to the device. these ar e stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in electrical characteristics on page 4 is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. table 2. absolute maximum ratings parameter min max units comments electrical parameters 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 input current (latchup immunity) 30 +30 ma norm: jedec 78 1 1. voltage on pin 7 (shdn) limited to +5.5v electrostatic discharge electrostatic discharge hbm +/ 1 kv norm: mil 883 e m ethod 3015 temperature ranges and storage conditions package power dissipation 1 w q ja = 32oc/w for a 4layer board, 4 vias, t amb = +70oc storage temperature 55 150 oc junction temperature 150 oc package body temperature 260 oc the reflow peak soldering temperature (body temperature) specified is in accordance with ipc/ jedec jstd020moisture/reflow sensitivity classification for nonhermetic solid state surface mount devices. the lead finish for pbfree leaded packages is matt e tin (100% sn). humidity noncondensing 5 85 % moisture sensitive level 3 represents a max. floor li fe time of 168h
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 4 16 as7620 datasheet e l e c t r i c a l c h a r a c t e r i s t i c s 6 electrical characteristics v out =3.3v, l x =10h, c x =100f, typical values at v in = +24v and t amb = +25oc (unless otherwise specified). all limits ar e guaranteed. the parameters with min and max values are guaranteed w ith production tests or sqc (statistical quality co ntrol) methods. table 3. electrical characteristics symbol parameter conditions min typ max units t amb operating temperature range 40 85 oc t j operating junction temperature 40 125 oc v in input voltage range 3.6 24 32 v v cc vepf, ilim 0.3 3.6 v v st startup voltage 3.3 v v out output voltage as7620a 1.19 v in v as7620b initial, at 25oc amb. 3.267 3.300 3.333 v over line, load and temperature 3.218 3.383 v fb feedback voltage as7620a initial, at 25oc amb. 1.178 1.190 1.202 v over line and temperature 1.166 1.214 v as7620b 3.218 3.300 3.383 v hys controller hysteresis as7620a at fb node 8 15 30 mv as7620b 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 w 0.1 % / v load regulation 10% to 90% load change 0.9 % i fb input bias current as7620a fb pin 200 na as7620b 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, ple ase refer to performance graphs. 192 240 288 ma ilim=v out 2 2. v out from 1.5v to 3.6v 576 720 864 ilim=open 800 1000 1200 pchannel on resistance 0.4 0.8 w maximum duty cycle at v in =3.6v 100 % t on minimum ontime current limit is not attained to turn off the switch before the minimum ontime expired 8 10 12 s t off minimum offtime 0.22 0.42 0.62 s i q quiescent current nonswitching 30 45 a i out =500a 37 a i shdn shutdown current t amb = +25oc 1 5 a v lo shutdown threshold shdn 1 v i ibn logic input bias current shdn 1 a t shdn shutdown temperature 160 oc t shdn hysteresis 10 oc
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 5 16 as7620 datasheet ty p i c a l o p e r a t i n g c h a r a c t e r i s t i c s 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 0 100 200 300 400 500 600 700 800 900 1000 -40 -20 0 20 40 60 80 100 120 temp (c) rdson (mohm) . 30 40 50 60 70 80 90 100 1 10 100 1000 iout (ma) 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 -20 0 20 40 6 0 80 100 1 2 0 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
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 6 16 as7620 datasheet ty p i c a l o p e r a t i n g c h a r a c t e r i s t i c s figure 7. current limit threshold vs. v in figure 8. average switching frequency vs. v in figure 9. average switching frequency vs. i out (ilim=open) figure 10. shutdown current vs. temper ature figure 11. line regulation @ i out =10ma figure 12. line regulation @ i out =500ma 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 5 10 15 20 25 30 vin (v) cl (ma) ilim gnd ilim v out ilim floating 100 1000 10000 100000 1000000 5 7 9 11 13 15 1719 21 23 25 27 29 31 vin (v) fsw (hz) i out =500a i out =5ma i out =50ma i out =500ma 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 (%)
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 7 16 as7620 datasheet ty p i c a l o p e r a t i n g c h a r a c t e r i s t i c s figure 13. load regulation figure 14. line regulation v out =5v @ 10ma 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 specifi ed in figure 17 , unless otherwise specified. -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 % v out v in v out v in
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 8 16 as7620 datasheet d e t a i l e d d e s c r i p t i o n 8 detailed description figure 17. system diagram of as7620a with early p ower fail warning 8.1 shut down the device can be shut down by providing a voltage lower than 1v at the shdn pin (7). in this condition, the consumption is onl y 1a (typ). the as7620 is providing an internally regulated pullup circuit. no external pullup resistor shall be use d, which could otherwise damage the shutdown input. connect the shdn input directly to an open drain port only. 8.2 soft start the device implements a soft start by limiting the inrush current into the output choke. initially, th e 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 tur ned on again when the current approaches 0a. in this time frame, the fb v oltage (v fb ) will be lower than the reference and so the duty cycle will be driven by the current limit only. 8.3 regulation both as7620a and as7620b are based on a hystereti c control method. moreover, the switch current is m onitored to make the converter always work in discontinuous current mode (dcm). th e advantages of this 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 pr actice, considering the most common application con ditions (l=10h 100h; c=10f 100f) and setting the cl threshold according to the load, the on time is normally ter minated 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/dcdc_stepdown/as7620 revision 1.17 9 16 as7620 datasheet d e t a i l e d d e s c r i p t i o n 8.4 v out selection the as7620b features a 3.3v fixed output voltage. the as7620a provides an adjustable output from 1.2 v (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 acco rding to the following formula: (eq 1) where: rh is the high side resistor 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 w in order to limit the current consumption. 8.5 current limit the current is sensed during the on time of the int ernal pmos. three different current limit threshold s 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 current limit. i f the current reaches the threshold during the on t ime, 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. 8.6 switching frequency the switching frequency (f sw ) changes according to the application conditions a nd, in particular, to the output current in order t o optimize the efficiency in any load condition. anyway, it is alw ays possible to estimate the f sw during the design process. as described in the reg ulation (refer to page 8) C the converter always works in dcm and, normally, the peak current into the inductor is th e cl threshold (ilim). the average of the inductor current must be equal to the output curren t. the following formula provides the relationship 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=10h, ilim=1a) v out v ref 1 rh rl ------- + ? ? ? ? = 1 tsw ---------- 12 --- ilim 2 l v in v in v out C ( ) v out -------------------------------------------------- fsw 2 i out v in v out C ( ) 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.com/dcdc_stepdown/as7620 revision 1.17 10 16 as7620 datasheet d e t a i l e d d e s c r i p t i o n 8.7 power fail / power good as7620ab 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 about early input po wer fail (active low) and output within regulation. figure 19 illustrates the typical connection 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 thr eshold 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 contribut ion from v dd is added at the vpf pin, realizing in fact a hyste resis to eliminate pf oscillation due to power supply noise. figure 19. opendrain output stage for comparator table 5 provides the resistors values covering all the sta ndard input bus. the resistors values are 1% commer cial values. it is mandatory to use the correct resistors values to guarantee the respe ct 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 l eft floating. terminology: vrst: reset voltage for the epf. it is 90% of the i nput bus voltage. vtrip: trip voltage for the epf. it is 80% of the i nput bus voltage. 8.8 thermal protection the internal junction temperature is continuously m onitored. if it reaches 150oc (min), the pmos is tu rned off. the device can switch again if the temperature is decreased by at least 10oc. if the o vertemperature persists, the device will be shut d own again resulting in a hiccup mode for the output power. table 5. epf network selection with different inpu t bus v in (v) vrst (v) vtrip (v) r3 (k w ) r4 (k w ) r5 (k w ) r6 (k w ) 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 3.632v vdd 1.23.6 power fail r on r6 r3 r4 v ref r5 inv +
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 11 16 as7620 datasheet a p p l i c a t i o n i n f o r m a t i o n 9 application information 9.1 input capacitors an input capacitor is required to sustain the peak current requested by the turning on of the internal pmos. when used, the capacitor helps to reduce the noise and saves the input 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 voltage range , the worst case of irms=1/2*i out must be considered. suggested capacitors are low e sr oscon, polymer, aluminum or mlccs. tantalum types a re not recommended for their weakness in withstandi ng big inrush currents. 9.2 output inductor the inductor together with the output capacitor rep resents the output filter. using the as7620, the in ductor is charged and completely discharged at every switching cycle being that the converter i s 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 cu rrent (ilim) and the rms current 9.3 output capacitor the output capacitor together with the inductor rep resents the output filter. the bigger the capacitan ce is, the lower will be the output ripple. usually, low esr mlccs are preferred as they are in expensive and small in size. any value from 10f is suitable, considering the load transient specifications of the application as well. 9.4 free wheeling diode the inductor current is forced through the diode du ring the offtimes. the average current flowing thr ough it is the reverse voltage must be higher than the input v oltage and safely it is common to consider 30% more . normally, a schottky diode is preferred because of its low forward voltage. 9.5 stability even though the hysteretic voltage mode is intrinsi cally stable, an excessive noise at the fb could ca use instability. for this reason care must be taken drawing the layout, reducing the noise and sh ielding the fb path from it. the main noise generat or is the switching node, which is commutated from gnd to v in by the internal pmos and the free wheeling diode a nd 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 be tween the lx pin and the external components (inductor and diode). it is preferable to draw the fb path as far as possible 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. 9.6 100% duty cycle operation thanks to the pmos structure of the internal switch , the device can actually work at 100% duty cycle. this feature is very helpful during the load transient, because the maximum power can be transfe rred 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 win dows threshold. moreover, in this condition, the s afety is always guaranteed by the current limit. irms i out v out v in v out C ( ) v in -------------------------------------------------- = irms i out 2 il 2 d 3 ----------- + = 12 --- fsw ilim 2 l v out ------------------------
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 12 16 as7620 datasheet a p p l i c a t i o n i n f o r m a t i o n 9.7 demo board a demonstration board is available to test the devi ce functionalities and performance in a standard ap plication. for further information, please refer to the as7620eb datasheet. figure 20. demo board photograph
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 13 16 as7620 datasheet p a c k a g e d r a w i n g s a n d m a r k i n g s 10 package drawings and markings figure 21. 12pin mlpq 4x4mm marking table 6. packaging code yywwxzz yy ww x zz last two digits of the current year manufacturing week plant identifier free choice / traceability code
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 14 16 as7620 datasheet p a c k a g e d r a w i n g s a n d m a r k i n g s figure 22. 12pin mlpq 4x4mm package
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 15 16 as7620 datasheet o r d e r i n g i n f o r m a t i o n 11 ordering information the devices are available as the standard products shown in table 7 . * available on request note: all products are rohs compliant. buy our products or get free samples online at icdi rect: http://www.austriamicrosystems.com/icdirect technical support is found at http://www.austriamicrosystems.com/technicalsuppor t for further information and requests, please contac t us mailto:sales@austriamicrosystems.com or find your local distributor at http://www.austriamicrosystems.com/distributor design the as7620 online at http://www.austriamicrosystems.com/analogbench analog bench is a powerful design and simulation support tool th at operates in online and offline mode to evaluat e performance and generate applicationspecific billofmaterials for austriamicrosystems' power management devices. table 7. ordering information ordering code marking output description delivery form package as7620bqft as7620 or as7620a adjustable 500ma hysteretic high voltage stepdown converter with dual power monitor tape and reel 12pin mlpq 4x4mm as7620bbqft* as7620b 3.3v 500ma hysteretic high voltage stepdown converter with dual power monitor without output delay tape and reel 12pin mlpq 4x4mm
www.austriamicrosystems.com/dcdc_stepdown/as7620 revision 1.17 16 16 as7620 datasheet copyrights copyright ? 19972011, austriamicrosystems ag, tobe lbaderstrasse 30, 8141 unterpremstaetten, austriae urope. trademarks registered ?. all rights reserved. the material herein may not be reproduced, adapted, merged, translated, stored, o r used without the prior written consent of the copyright owner. all products and companies mentioned are trademarks or registered trademarks of their respective compa nies. disclaimer devices sold by austriamicrosystems ag are covered by the warranty and patent indemnification provisio ns 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 freedom of the described devices from patent in fringement. austriamicrosystems ag reserves the rig ht to change specifications and prices at any time and without notice. therefore, prior to de signing this product into a system, it is necessary to check with austriamicrosystems ag for current information. this product is intended for u se in normal commercial applications. applications requiring extended temperature range, unusual environmental requirements, or high reliabi lity applications, such as military, medical lifes upport or lifesustaining equipment are specifically not recommended without additional pro cessing by austriamicrosystems ag for each applicat ion. for shipments of less than 100 parts the manufacturing flow might show deviations from the standard production flow, such as test flo w or test location. the information furnished here by austriamicrosyste ms ag is believed to be correct and accurate. howev er, austriamicrosystems ag shall not be liable to recipient or any third party for any d amages, including but not limited to personal injur y, property damage, loss of profits, loss of use, interruption of business or indirect, special, inci dental or consequential damages, of any kind, in co nnection with or arising out of the furnishing, performance or use of the technical data herein. no obligation or liability to recipient or any third party shall arise or flow out of austriamicrosystems ag rendering of technical or oth er services. contact information headquarters austriamicrosystems ag tobelbaderstrasse 30 a8141 unterpremstaetten, austria tel: +43 (0) 3136 500 0 fax: +43 (0) 3136 525 01 for sales offices, distributors and representatives , please visit: http://www.austriamicrosystems.com/contact

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