View SC1408IMSTRT_6715468.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

power management 1 www.semtech.com sc1408 low voltage, boost dc-dc controller features applications revision: november 23, 2005 typical application circuit description the sc1408 is a low voltage boost controller that operates from a 1.8v to 16.5v input range. the sc1408 was designed for two cell alkaline or single cell lithium ion battery applications. with the proper external components it can be used as a boost converter or a buck/boost converter. a shutdown pin allows the user to turn the controller off, reducing supply current to less than 2a typical. output voltage can be preset to 5v or is adjustable from 3v to 16.5v with a resistor divider. the controller changes frequency in light load conditions to improve efficiency. ? 1.8v to 16.5v input range ? preset (5v) or adjustable output ? ground referenced current limit ? on chip precision reference ? up to 300khz switching frequency ? 10a max shutdown current ? industrial temperature range ? so-8 and msop-8 packages. lead free packages available are fully weee and rohs compliant ? pda power supplies ? battery powered applications ? positive lcd bias generator ? portable communications (cellular phones) ? peripheral card supplies ? industrial power supplies vin (1.8v to 16.5v) vout (3v to 16.5v) u1 sc1408 8 1 2 3 4 5 6 7 isense gate bst fb shdn ref agnd gnd l1 r2 q1 d1 + c1 r4 r3 + c2 c3
2 ? 2005 semtech corp. www.semtech.com power management sc1408 electrical characteristics absolute maximum ratings r e t e m a r a pl o b m y sm u m i x a ms t i n u e g a t l o v t u p n id n g o t t s b8 1 o t 3 . 0 -v d n u o r g r e w o p o t d n u o r g l a n g i s l l a m sd n g a o t d n g+1 . 0v d n g o t e t a g 5 r o 3 . 0 + t s b v o t 3 . 0 -v d n g o t e s n e s i , f e r , n d h s , b f 5 r o 3 . 0 + t s b v f o . n i m o t 3 . 0 -v e r u t a r e p m e t g n i t a r e p ot a 5 8 + o t 0 4 -c e g n a r e r u t a r e p m e t n o i t c n u jt j 0 5 1 + o t 0 4 -c e g n a r e r u t a r e p m e t e g a r o t st g t s 0 6 1 + o t 5 6 -c . c e s 0 1 ) g n i r e d l o s ( e r u t a r e p m e t d a e lt l 0 0 3 +c t n e i b m a o t n o i t c n u j , e c n a t s i s e r l a m r e h t 8 - o s 8 - p o s m a j 8 2 1 6 1 2 w / c e s a c o t n o i t c n u j , e c n a t s i s e r l a m r e h t 8 - o s 8 - p o s m c j 0 5 0 7 w / c unless specified: v out = 5v; i load = 0ma; t a = +25c r e t e m a r a pm y ss n o i t i d n o cn i mp y tx a ms t i n u e g a t l o v t u p n iv n i t a 5 2 = o c8 . 15 . 6 1v t a 0 4 - = o 5 8 + o t c o c8 . 15 . 6 1v t n e r r u c y l p p u sv t u o n d h s , v 5 . 6 1 = 3 ? 2005 semtech corp. www.semtech.com power management sc1408 r e t e m a r a pm y ss n o i t i d n o cn i mp y tx a ms t i n u e g a t l o v t n i o p p i r t b fv b f t a 5 2 = o c t a 0 4 - = o 5 8 + o t c o c6 7 1 . 1 0 0 2 . 1 4 2 2 . 1 v t n e r r u c t u p n i b fi m f t a 5 2 = o c t a 0 4 - = o 5 8 + o t c o c 4 - 0 4 a n e g a t l o v h g i h t u p n i n d h sv n i v t u o v 5 . 6 1 o t v 7 . 2 =6 . 1v e g a t l o v w o l t u p n i n d h sv l i v t u o v 5 . 6 1 o t v 7 . 2 =4 . 0v t n e r r u c t u p n i n d h sv t u o v 5 r o v 0 = n d h s , v 5 . 6 1 =1 a l e v e l p i r t t i m i l t n e r r u cv s c v t u o v 5 . 6 1 o t v 3 =t a 5 2 = o c t a 0 4 - = o 5 8 + o t c o c 5 8 0 8 0 0 15 1 1 0 2 1 v m t n e r r u c t u p n i e s n e s i 1 0 . 01 a e m i t e s i r e t a gv t u o d n g o t e t a g m o r f f n i , v 5 =0 5s n e m i t l l a f e t a gv t u o d n g o t e t a g m o r f f n i , v 5 =0 5 e c n a t s i s e r n o e t a gw o l r o h g i h = e t a g5 10 3 ? electrical characteristics (cont.) unless specified: v out = 5v; i load = 0ma; t a = +25c note: (1) this device is esd sensitive. use of standard esd handling precautions is required.
4 ? 2005 semtech corp. www.semtech.com power management sc1408 block diagram vdd trig q trig q r s q + - + - + - fb 50mv + - isense 0.1v bst 2.5v gate shdn agnd ref gnd 1.20v reference low voltage oscillator min off time one shot 2.3us max on time one shot 16us bias current sense amp error comp mode detect start up comp pin configuration ordering information pin descriptions r e b m u n t r a pe g a k c a p ) 1 ( t ( e g n a r p m e t a ) r t . s i 8 0 4 1 c s 8 - o s c 5 8 + o t 0 4 - t r t s i 8 0 4 1 c s ) 2 ( r t . s m i 8 0 4 1 c s 8 - p o s m ) 3 ( t r t s m i 8 0 4 1 c s ) 2 ( notes: (1) only available in tape and reel packaging. a reel contains 2500 devices. (2) lead free product. this product is fully weee and rohs compliant. (3) contact factory for msop availability # n i pe m a n n i pn o i t c n u f n i p 1e t a g. t u p t u o e v i r d e t a g 2t s b. e g a t l o v y l p p u s 3b fk c a b d e e f e g a t l o v 4n d h s. r e t r e v n o c e h t n w o d s t u h s h g i h c i g o l 5f e r. n i p t u p t u o e c n e r e f e r 6d n g a. d n u o r g l a t i g i d d n a g o l a n a l a n g i s l l a m s 7d n g. d n u o r g r e w o p 8e s n e s i. n i p e s n e s t n e r r u c 1 2 3 4 isense gate top view (so-8/msop-8) 5 6 7 8 gnd bst agnd fb ref shdn
5 ? 2005 semtech corp. www.semtech.com power management sc1408 applications information theory of operation the sc1408 is a modified hysteretic boost converter controller. the power switch is turned on when the output voltage falls slightly below it?s setpoint. it remains on for approximately 16s, or until the inductor current reaches limit, whichever occurs first. the power switch is then turned off for 2.3 s, or until the output voltage once again falls below setpoint, whichever occurs last. the sc1408 is normally powered from the output voltage. internal circuitry, such as the bandgap, comparators and one shots, will not function properly until the bst pin volt- age reaches 2.5v. to ensure start-up at low input volt- ages, the normal control circuitry is disabled and a spe- cial, low voltage start up oscillator generates an approxi- mate square wave at the gate pin, initiating boost action. when the output voltage reaches 2.5v, the normal control circuitry is enabled and the start up oscillator shuts down. to conserve power, a shdn pin is provided which, when pulled high, shuts down most internal circuitry. the out- put voltage will then be 1 diode drop below the input. component selection boost converter r sense the value of the sense resistor is the primary determin- ing factor for maximum output current. the sc1408 has a fixed current limit voltage threshold, which is devel- oped by the peak inductor current flowing through r sense . r sense may be determined either from the maximum out- put current curves or from the equation below: ()( ) dcr inductor and r fet, across voltage v drop voltage forward diode output v : where v v v v v v v v l 2 t v v v v v v 1 r v i sense fet f fet f o in f o fet in off fet f o in f o sense cs ) max ( o = = ? ? ? ? ? ? ? ? ? + ? + ? ? ? ? ? ? ? ? ? ? ? + ? + ? = in the equation above, the use of 2.3 s for t off may lead to slightly optimistic current values for low v o /v in ratios. the theoretical curves use the actual value of t off , v f =0.5v, v fet =0.3v and v cs =0.08v and are generated for l=22h. output voltage output voltage can be set to 5v by connecting the fb pin to gnd, or to any voltage in the 3.0v to 16.5v range using external divider resistors. the bottom resistor in the divider chain (r4 in the typical application circuits) should be 300k ? or less and the top resistor (r3 in the application circuits) can be calculated from ? ? ? ? ? ? ? ? ? = 1 v v 4 r 3 r ref o inductor the sc1408 will work with a wide range of inductor val- ues. a good choice for most applications is 22 h. smaller inductor values result in higher peak currents and in- crease output ripple, while larger values will result in slower loop response. transistor selection normally the power switch will be an n-channel mosfet, although in certain circumstances an npn bipolar may be substituted. the choice of fet can be critical, especially in battery pow- ered applications where the converter must be able to use all of the available energy in the battery. this requires that the converter be capable of starting up from very low in- put voltages. for example a two cell alkaline system?s ter- minal voltage will drop to 1.8v as it approaches full dis- charge. for these demanding applications, a fet with low v gs(th) is required. a good rule of thumb is that v gs(th) should be at least 0.5v less than the minimum input voltage. diode for most applications, a schottky diode should be used as the output rectifier. it will be subjected to reverse volt- ages of at least v o , and average current will be some- what less than the inductor peak current. industry stan- dard 1n5817 series or an equivalent surface mount part would be suitable. output capacitors output capacitors should be low esr to minimize ripple voltage and maximize efficiency. low esr tantalum or oscon capacitors should be used. ripple voltage will be approximately: input capacitors input capacitors on a boost converter are less critical than the output capacitors, since there are no fast current pulses drawn from the input supply. a 100 f tantalum will be adequate for most applications.
6 ? 2005 semtech corp. www.semtech.com power management sc1408 component selection sepic converter r sense again, with the sepic topology, the value of the sense resistor is the primary determining factor for maximum output current. the simplest approach to select r sense is to add vin to vo and use this value as the output voltage in the output current curves or in the equation for boost converter. output voltage output voltage setting works exactly the same in sepic topology as in boost, including the ability to set to 5v by connecting the fb pin to gnd. care must be taken to ensure that the ic supply (pin2; bst) does not exceed its 16.5v rating. in the circuit of fig.2: this requires maxi- mum output voltage to be limited to 16.5v-vin. higher output voltages are possible with different ic supply strat- egies. inductor the sepic topology requires a coupled inductor. again a good choice for most applications is 22h. smaller induc- tor values result in higher peak currents and increase out- put ripple, while larger values will result in slower loop re- sponse. transistor selection the choice of fet can be critical, especially in battery pow- ered applications where the converter must be able to use all of the available energy in the battery. this requires that the converter be capable of starting up from very low input voltages. for example a two cell alkaline system?s applications information (cont.) terminal voltage will drop to 1.8v as it approaches full discharge. for these demanding applications, a fet with low v gs(th) is required. a good rule of thumb is that v gs(th) should be at least 0.5v less than the minimum input volt- age. diode for most applications, a schottky diode should be used as the output rectifier. it will be subjected to reverse volt- ages of at least v o +v in and average current will be some- what less than the inductor peak current. industry stan- dard 1n5817 series or an equivalent surface mount part would be suitable. output capacitors output capacitors should be low esr to minimize ripple voltage and maximize efficiency. low esr tantalums, oscons or the newer polymer capacitors should be used. input capacitors input capacitors on a sepic converter are less critical than the output capacitors, since there are no fast cur- rent pulses drawn from the input supply. a 100 f tanta- lum will be adequate for most applications. series capacitors the series capacitor(s) must be capable of handling an rms current given by:- in o o rms v 5 . 0 v i i + =
7 ? 2005 semtech corp. www.semtech.com power management sc1408 typical characteristics figs.5 - 8: maximum output current vs. input voltage and sense resistor value. (boost mode) figs.9-11:efficiency in the boost application circuit of fig.1 vo=5v 60% 70% 80% 90% 100% 1 10 100 1000 io (ma) efficiency (%) vin=5.0v vin=4.0v vin=3.3v vin=3.0v vo=12v 60% 70% 80% 90% 100% 1 10 100 1000 io (ma) efficiency (%) vin=5.0v vin=3.0v vin=1.8v vo=15v 60% 70% 80% 90% 100% 1 10 100 1000 io (ma) efficiency (%) vin=12v vin=9.0v vin=5.0v vin=3.0v vin=1.8v vo=3.3v 100mohm 50mohm 35mohm 25mohm 20mohm 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 2.0 2.2 2.4 2.6 2.8 3.0 3.2 vin (v) io (a) l=22uh vo=5v 100mohm 50mohm 35mohm 25mohm 20mohm 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 vin (v) io (a) l=22uh vo=12v 100mohm 50mohm 35mohm 25mohm 20mohm 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 2.0 4.0 6.0 8.0 10.0 12.0 vin (v) io (a) l=22uh vo=15v 100mohm 50mohm 35mohm 25mohm 20mohm 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 vin (v) io (a) l=22uh
8 ? 2005 semtech corp. www.semtech.com power management sc1408 typical characteristics load transient; vin=2v, vo=5v, io=0 to 500ma ch1 = output voltage ch2 = load current (0.5a/div) load transient; vin=3v, vo=5v, io=0 to 500ma ch1 = output voltage ch2 = load current (0.5a/div) output ripple voltage; vin=3v, vo=5v, io=470ma ch1 = output ripple ch2 = voltage at gate pin output ripple voltage; vin=3v, vo=5v, io=810ma ch1 = output ripple ch2 = voltage at gate pin
9 ? 2005 semtech corp. www.semtech.com power management sc1408 typical application circuit (cont.) fig.1: typical application - boost configuration d1 b130t l1 22uh c9 see text u1 sc1408cs 8 1 2 3 4 5 6 7 isense gate bst fb en ref agnd gnd + c3 100uf + c8 100uf r3 see table vin to 16.5v out r2 0.1ohm q1 irlr024n r4 10.0k c5 0.1uf + c2 100uf 1.8v-16.5v in coilcraft do3316p-223 fig.2: typical application - buck/boost (sepic) configuration d1 b130t r2 0.1ohm r3 see table + c8 100uf d2 1n4148 q1 irll3303 l1a 22uh 1 2 r4 10.0k c9 see text 0v to (16.5v-vin) out l1b 22uh 4 3 c5 0.1uf 1.8v to 5v in u1 sc1408cs 8 1 2 3 4 5 6 7 isense gate bst fb en ref agnd gnd c4 0.1uf + c2 100uf + c3 100uf l1a/l1b is coupled inductor pulse pe-53718 or equivalent + c1 100uf
10 ? 2005 semtech corp. www.semtech.com power management sc1408 typical application circuit (cont.) fig.3: achieving output voltages greater than 16.5v + c8 100uf u1 sc1408cs 8 1 2 3 4 5 6 7 isense gate bst fb en ref agnd gnd c5 0.1uf c4 0.1uf + c3 100uf r2 0.05ohm 3.3v in d1 b130t l1 22uh q1 irl3103s r3 200k d4 1n4148 r4 10.0k d3 12v r6 470 + c2 100uf 25v out fig.4: implementing shutdown with input/output isolation + c3 100uf + c8 100uf d1 b130t short = run open = shutdown c5 0.1uf r3 90k + c2 100uf 12v out c4 0.1uf r4 10.0k r5 5.1k l1 22uh r2 0.05ohm u1 sc1408cs 8 1 2 3 4 5 6 7 isense gate bst fb en ref agnd gnd q1 irll3303 q2 si2301ds j1 1 2 3.3v in
11 ? 2005 semtech corp. www.semtech.com power management sc1408 outline drawing - so-8 minimum land pattern - so-8 see detail detail a a .050 bsc .236 bsc 8 .010 .150 .189 .154 .193 .012 - 8 0.25 1.27 bsc 6.00 bsc 3.90 4.90 - .157 .197 3.80 4.80 .020 0.31 4.00 5.00 0.51 bxn 2x n/2 tips seating aaa c e/2 2x 12 n a d a1 e1 bbb c a-b d ccc c e/2 a2 (.041) .004 .008 - .028 - - - - 0 .016 .007 .049 .004 .053 8 0 0.20 0.10 - 8 0.40 0.17 1.25 0.10 .041 .010 .069 .065 .010 1.35 (1.04) 0.72 - 1.04 0.25 - - - 1.75 1.65 0.25 0.25 - .010 .020 0.50 - c l (l1) 01 0.25 gage plane h h 3. dimensions "e1" and "d" do not include mold flash, protrusions or gate burrs. -b- controlling dimensions are in millimeters (angles in degrees). datums and to be determined at datum plane notes: 1. 2. -a- -h- side view a b c d e h plane reference jedec std ms-012, variation aa. 4. l1 n 01 bbb aaa ccc a b a2 a1 d e e1 l h e c dim min millimeters nom dimensions inches min max max nom e (.205) (5.20) z g y p (c) 3.00 .118 1.27 .050 0.60 .024 2.20 .087 7.40 .291 x inches dimensions z p y x dim c g millimeters this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. reference ipc-sm-782a, rlp no. 300a. 2.
12 ? 2005 semtech corp. www.semtech.com power management sc1408 outline drawing - msop-8 land pattern - msop-8 0 .010 .004 - .016 .003 .024 (.037) - .000 .030 - - - - 0.25 0.10 8 0 - 8 0.60 (.95) .032 .009 0.40 0.08 .043 .006 .037 0.75 0.00 - 0.80 0.23 - 0.95 1.10 0.15 - - - 3. dimensions "e1" and "d" do not include mold flash, protrusions or gate burrs. -b- controlling dimensions are in millimeters (angles in degrees). datums and to be determined at datum plane notes: 1. 2. -a- -h- side view a b c e h e/2 d plane detail .193 bsc .026 bsc aaa c seating ccc c 2x n/2 tips indicator e/2 pin 1 2x 8 bbb c a-b d see detail a1 a a2 bxn d 0.25 a plane gage .005 e1 12 n .114 .114 .118 .118 .009 - 8 01 c (l1) l a 0.13 3.00 3.00 4.90 bsc 0.65 bsc .122 .122 2.90 2.90 .015 0.22 3.10 3.10 0.38 - reference jedec std mo-187, variation aa. 4. dim ccc a1 e bbb aaa 01 l1 n l d e1 e a2 b c a millimeters nom dimensions inches min nom max min max e this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. p x (c) y z g .224 .063 .016 .026 (.161) .098 (4.10) 5.70 1.60 0.40 0.65 2.50 millimeters dimensions dim inches x z y c p g h c n a r b n a w i a t 0 8 3 3 - 8 4 7 2 - 2 - 6 8 8 : l e t fx a0 9 3 3 - 8 4 7 2 - 2 - 6 8 8 : h b m g d n a l r e z t i w s h c e t m e s h c n a r b n a p a j 0 5 9 0 - 8 0 4 6 - 3 - 1 8 : l e t 1 5 9 0 - 8 0 4 6 - 3 - 1 8 : x a f h c n a r b a e r o k tl e7 7 3 4 - 7 2 5 - 2 - 2 8 : f6 7 3 4 - 7 2 5 - 2 - 2 8 : x a ) . k . u ( d e t i m i l h c e t m e s 0 0 6 - 7 2 5 - 4 9 7 1 - 4 4 : l e t 1 0 6 - 7 2 5 - 4 9 7 1 - 4 4 : x a f e c i f f o i a h g n a h s t0 3 8 0 - 1 9 3 6 - 1 2 - 6 8 : l e 1 3 8 0 - 1 9 3 6 - 1 2 - 6 8 : x a f l r a s e c n a r f h c e t m e s 0 0 - 2 2 - 8 2 - 9 6 1 ) 0 ( - 3 3 : l e t 8 9 - 2 1 - 8 2 - 9 6 1 ) 0 ( - 3 3 : x a f f o y r a i d i s b u s d e n w o - y l l o h w a s i g a l a n o i t a n r e t n i h c e t m e s . a . s . u e h t n i s r e t r a u q d a e h s t i s a h h c i h w , n o i t a r o p r o c h c e t m e s h b m g y n a m r e g h c e t m e s 3 2 1 - 0 4 1 - 1 6 1 8 ) 0 ( - 9 4 : l e t 4 2 1 - 0 4 1 - 1 6 1 8 ) 0 ( - 9 4 : x a f contact information for semtech international ag

▲Up To Search▲

Price & Availability of SC1408IMSTRT

	To Download SC1408IMSTRT Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .