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power management 1 www.semtech.com sc4521 3a step-down switching regulator with programmable soft start features revision: october 5, 2007 the sc4521 is a current mode switching regulator with an integrated switch, operating at 600khz with programmable soft start and enable functions. the integrated switch allows for cost effective low power solutions (peak switch current 3 amps). high frequency operation allows for very small passive components. current mode operation allows for fast dynamic response and instantaneous duty cycle adjustment as the input varies (ideal for cpe applications where the input is a wall plug power). the low shutdown current makes it ideal for portable applications where battery life is important. the sc4521 is an 600khz switching regulator with a low pin count. the sc4521 allows customers to use large capacitive loads because its programmable soft start limits the dv/ dt of the output at start up. ? wide operating voltage range: 4.4v to 24v ? integrated 3 amp switch ? 600khz frequency of operation ? programmable soft start funchion ? current mode control ? precision enable threshold ? so-8 edp lead-free package, fully weee and rohs compliant ? xdsl modems ? cpe equipment ? dc-dc point of load applications ? portable equipment ? digtial consumer electronics c1 v out d2 r3 d1 l1 c2 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 enable c4 v in c3 r2 r1 sc4521 c6 c1 v out d2 r3 d1 l1 c2 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 enable c4 v in c3 r2 r1 sc4521 c6 typical application circuit applications description
2 ? 2007 semtech corp. www.semtech.com power management sc4521 r e t e m a r a pl o b m y ss t i m i ls t i n u e g a t l o v y l p p u s t u p n iv n i 8 2 + o t 3 . 0 -v v e v o b a n i p t s o o b w s v ( t s b v - w s )6 1v e g a t l o v n i p t s o o bv t s b 2 3 + o t 3 . 0 -v e g a t l o v n i p n ev n e 4 2 + o t 3 . 0 -v e g a t l o v n i p b fv b f 6 + o t 3 . 0 -v t n e r r u c n i p b fi b f 1a m e g a t l o v n i p s sv s s 3 +v t n e i b m a o t n o i t c n u j e c n a d e p m i l a m r e h t ) 1 ( a j 5 . 6 3w / c m u m i x a me r u t a r e p m e t n o i t c n u jt j 0 5 1c 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 5 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 d a e l 0 0 3c ) l e d o m y d o b n a m u h ( g n i t a r d s ed s e2v k r e t e m a r a pl o b m 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 i g n i t a r e p ov n i 4 2v t i m i l t n e r r u c h c t i w s m u m i x a mi w s t a % 0 5 = d , c 5 2 =5 . 35 . 5a y c n e u q e r f r o t a l l i c s of c s o 0 0 50 0 60 0 7z h k p o r d e g a t l o v n o h c t i w sv ) w s ( d i w s a 3 =0 2 2v m v n i t u o k c o l e g a t l o v r e d n u g n i s i rv o l v u t j c 5 8 o t c 0 =9 . 34 . 4v v n i s i s e r e t s y h o l v uv t s y h 0 6v m v n i t n e r r u c y l p p u si q v b f v 1 =35 . 5a m t n e r r u c y b d n a t si ) f f o ( q v n e v 0 =0 5 2a t n i o p p i r t n w o d t u h s l a m r e h t 5 5 1c s i s e r e t s y h n w o d t u h s l a m r e h t 0 1c electrical characteristics note: (1) thetaja is calculated from a package in still air, mounted to 3" x 4.5", 4 layer fr4 pcb with thermal vias under exposed pad per jesd51 standards. unless specified: v in = 12v, v comp = 0.8v, v bst = v in + 5v, en = tied to v in , sw = open. t a = t j = -40c to 125c. absolute maximum ratings exceeding the specifications below may result in permanent damage to the device, or device malfunction. operation outside of th e parameters specified in the electrical characteristics section is not implied. exposure to absolute maximum rated conditions for extended periods of time may affect device reliability.
3 ? 2007 semtech corp. www.semtech.com power management sc4521 r e t e m a r a pl o b m y ss n o i t i d n o cn i mp y tx a ms t i n u t n e r r u c t u p n i b fi b f 5 2 . 0 -1 -a e g a t l o v k c a b d e e fv b f 4 8 7 . 08 . 06 1 8 . 0v e n i l e g a t l o v k c a b d e e f n o i t a l u g e r v < v 4 . 4 n i v 4 2 < ) 1 ( 3 +v / v m v o t b f p m o c n i a g e g a t l o v ) 2 ( v 9 . 0 v p m o c v 0 . 20 5 10 5 3v / v v o t b f p m o c e c n a t c u d n o c s n a r t ) 2 ( ? i p m o c = a 0 1 0 0 50 5 80 0 3 1o h m v p m o c t n e r r u c e c r u o s n i pv b f v 6 . 0 =0 70 1 1a v p m o c t n e r r u c k n i s n i pv b f v 0 . 1 =0 7 -0 1 1 -a v p m o c t n e r r u c h c t i w s o t n i p e c n a t c u d n o c s n a r t v p m o c v 5 2 . 1 =3 . 4v / a v p m o c g n i h c t i w s m u m i x a m n i p d l o h s e r h t % 0 = e l c y c y t u d6 . 0v v p m o c d l o h s e r h t p c ov p m o c g n i s i r2v v p m o c d l o h s e r h t y r t e r p u c c i hv p m o c g n i l l a f5 2 . 0v e l c y c y t u d h c t i w s m u m i x a md x a m v p m o c i , v 2 . 1 = w s a m 0 0 4 =5 8% e v o b a e g a t l o v t s o o b m u m i n i m h c t i w s ) 2 ( 7 . 2v t n e r r u c t s o o bi w s a 1 =0 15 1a m i w s a 3 =0 35 4 e g a t l o v d l o h s e r h t t u p n i e l b a n ev h t e 1 . 17 2 . 15 . 1v t n e r r u c s a i b t u p t u o e l b a n ei l o e d l o h s e r h t w o l e b v m 0 5 = n e8a i h o e d l o h s e r h t w o l e b v m 0 5 = n e0 1a t n e r r u c g n i g r a h c t r a t s t f o s ) 3 ( i s s v s s 0 =6 1a t n e r r u c g n i g r a h c s i d t r a t s t f o si s s 2 -a m electrical characteristics (cont.) notes: (1) the required minimum input voltage for a regulated output depends on the output voltage and load condition. (2) guaranteed by design. (3) see application information. unless specified: v in = 12v, v comp = 0.8v, v bst = v in + 5v, en = tied to v in , sw = open. t a = t j = -40c to 125c.
4 ? 2007 semtech corp. www.semtech.com power management sc4521 pin configurations ordering information r e b m u n t r a p ) 2 ( ) 1 ( e g a k c a p t r t e s 1 2 5 4 c sp d e - l 8 - c i o s b v e 1 2 5 4 c sd r a o b n o i t a u l a v e notes: (1) only available in tape and reel packaging. a reel contains 2500 devices. (2) lead free product. this product is weee and rohs compliant. # n i pe m a n n i pn o i t c n u f n i p 1t s b h c t i w s s i h t r o f e g a t l o v n o n r u t m u m i n i m e h t . h c t i w s n p n l a n r e t n i e h t o t r e w o p s e d i v o r p n i p s i h t . v 7 . 2 s i 2n i g n i r u d t d / i d h g i h s e e s n i p s i h t . y r t i u c r i c r e w o p d n a l o r t n o c y b d e r i u q e r r e w o p l l a s r e v i l e d n i n i p . e l b i s s o p s a e s o l c s a n i p s i h t o t d e h c a t t a e b d l u o h s r o t i c a p a c g n i l p u o c e d a . g n i h c t i w s 3w s d e t c e n n o c e b d l u o h s e d o i d g n i l e e h w e e r f l a n r e t x e e h t . h c t i w s l a n r e t n i e h t f o r e t t i m e e h t s i w s n i p . n i p s i h t o t e l b i s s o p s a e s o l c s a 4d n g g n i l e e h w e e r f e h t d n a r o t i c a p a c g n i l p u o c e d e h t . n i p s i h t o t t c e p s e r h t i w d e r u s a e m e r a s e g a t l o v l l a . e l b i s s o p s a t r o h s s a d n g o t d e t c e n n o c e b d l u o h s e d o i d 5n e . w o l s i n e f i f f o s i t i d n a , h g i h s i n e f i n o d e h c t i w s s i r o t a l u g e r e h t . t u p n i e l b a n e p i h c e h t s i s i h t w e f a o t d e c u d e r s i t n e r r u c y l p p u s t u p n i e h t d n a , w o l s i n e n e h w e d o m y b d n a t s n i s i r o t a l u g e r e h t . s e r e p m a o r c i m 6b f. s r e l l o r t n o c t u p t u o e l b a t s u j d a r o f t u p n i k c a b d e e f 7p m o c a . r o t a r a p m o c t n e r r u c k a e p e h t f o t u p n i d n a r e i f i l p m a r o r r e l a n r e t n i e h t f o t u p t u o e h t s i s i h t . e c n a m r o f r e p d e i f i c e p s e h t e v e i h c a o t n i p s i h t o t d e t c e n n o c s i k r o w t e n n o i t a s n e p m o c 8s s . e m i t t r a t s t f o s e h t s t e s d n g o t n i p s i h t m o r f d e t c e n n o c r o t i c a p a c l a n r e t x e n a . n i p t r a t s t f o s -l a m r e h t d a p d e t c e n n o c t o n . s a i v e l p i t l u m g n i s u e n a l p d n u o r g o t t c e n n o c . s e s o p r u p g n i k n i s t a e h r o f d a p . y l l a n r e t n i pin descriptions 1 2 3 4 ss bst top view (soic-8l-edp) 5 6 7 8 comp in fb sw en gnd
5 ? 2007 semtech corp. www.semtech.com power management sc4521 block diagram typical characteristic - ocp limit fb comp r q s pwm - + power in transistor slope + + + isen 40m sw bst oscillator clk frequency slope comp ss slope ol fb en reference uvlo 1.6v internal supply ea hiccup is is gnd fb comp r q s pwm - + power in transistor slope + + + isen 40m sw bst oscillator clk frequency slope comp ss slope ol fb en reference uvlo 1.6v internal supply ea hiccup is is gnd sc4519h ocp limit vs duty cycle 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 0 20406080100 duty cycle (%) current limit (a) ilim @-40c ilim @25c ilim @125c
6 ? 2007 semtech corp. www.semtech.com power management sc4521 application information the sc4521 is a current mode buck converter regulator. the sc4521 uses two feedback loops that control the duty cycle of the internal power switch. the error amplifier functions like that of the voltage mode converter. the output of the error amplifier works as a switch current reference. this technique effectively removes one of the double poles in the voltage mode system. with this, it is much simpler to compensate a current mode converter to have better performance. soft start internally, connected to the ss pin is a 100k pull-up resistor from an internal 1.6v regulator and the collector of an npn pull-down transistor from ss to gnd. the npn transistor is ?on? when the enable pin is low or when a fault is detected (input uvlo, over-current, or over temp). when the sc4521 is disabled or when a fault is detected, the npn transistor pulls the ss pin low. the ss charging time is controlled by the internal 100k resistor and external soft-start cap. this is a closed-loop soft-start which effectively ?ramps the reference?. the ss process completes when the ss pin voltage is exceeds the internal reference voltage, 0.8v. the ss pin continues to charge up to 1.6v, well above the reference voltage to ensure it does not interfere with normal operation. the governing ss equation is: ss ss c 69000 t ? = for example, a 22nf ss cap would give a ss time of approximately 1.5ms. however, when v i is higher than about 13v, the sc4521 requires a pull-up resistor from the ss pin to v i for normal operation. the softstart time can be estimated as: )] v 8 . 0 1 ( ln [ c r t i ss ss ss ? ? ? ? = where: rss = pull-up resistance from ss pin to v i , css = capacitance from ss pin to gnd, and v i = input voltage. overcurrent protection the current sense amplifier in the sc4521 monitors the switch current during each cycle. overcurrent protection (ocp) is triggered when the current limit exceeds the upper limit of 3a, detected by a voltage on comp greater than about 2v. when an ocp fault is detected, the switch is turned off and the external comp capacitor is gradually discharged at the rate of dv/dt=3 a/ccomp . ccomp is the total capacitance value attached to comp. at the same time, the soft start cap c ss is quickly discharged. once the comp voltage has fallen below 250mv, the part enters a normal startup cycle. in the case of sustained overcurrent or dead-short, the part will continually cycle through the retry sequence as described above. enable pulling and holding the en pin below 0.4v activates the shut down mode of the sc4521 which reduces the input supply current to 250a. during the shut down mode, the switch is turned off. the sc4521 is turned on if the en pin is pulled high. oscillator its internal free running oscillator sets the pwm frequency at 600khz for the sc4521 without any external components to program the frequency. uvlo when the en pin is pulled and held above 1.8v, the voltage on pin in determines the operation of the sc4521. as vin increases during power up, the internal circuit senses vin and keeps the power transistor off until vin reaches 4.4v. load current the peak current i peak in the switch is internally limited. for a specific application, the allowed load current i omax will change if the input voltage drifts away from the original design as given for continuous current mode: s o omax f l 2 ) d 1 ( v 3 i ? ? ? ? ? = where: fs = switching frequency, vo = output voltage and d = duty ratio, v o /v i v i = input voltage.
7 ? 2007 semtech corp. www.semtech.com power management sc4521 figure 2 shows the theoretical maximum load current for the specific cases. in a real application, however, the allowed maximum load current also depends on the layout and the air cooling condition. therefore, the maximum load current may need to be degraded according to the thermal situation of the application. maximum load current vs input voltage l=10uh 2.700 2.720 2.740 2.760 2.780 2.800 2.820 2.840 2.860 2.880 2.900 4681012141618 vi (v) iomax (a) vo=2.5v vo=3.3v vo=5v figure 2. theoretical maximum load current curves inductor selection the factors for selecting the inductor include its cost, efficiency, size and emi. for a typical sc4521 application, the inductor selection is mainly based on its value, saturation current and dc resistance. increasing the inductor value will decrease the ripple level of the output voltage while the output transient response will be degraded. low value inductors offer small size and fast transient responses while they allow large ripple currents, poor efficiencies and require more output capacitance for low output ripple. the inductor should be able to handle the peak current without saturating and its copper resistance in the winding should be as low as possible to minimize its resistive power loss. a good trade-off among its size, loss and cost is to set the inductor ripple current to be within 15% to 30% of the maximum output current. the inductor value can be determined according to its operating point under its continuous mode and the switching frequency as follows: application information (cont.) omax s i o i o i f v ) v (v v l ? ? ? ? ? = where: fs = switching frequency, = ratio of the peak to peak inductor current to the output load current and v o = output voltage. the peak to peak inductor current is: omax p p i i ? = ? after the required inductor value is selected, the proper selection of the core material is based on the peak inductor current and efficiency specifications. the core must be able to handle the peak inductor current i peak without saturation and produce low core loss during the high frequency operation. 2 i i i p p omax peak ? + = the power loss for the inductor includes its core loss and copper loss. if possible, the winding resistance should be minimized to reduce inductor?s copper loss. the core must be able to handle the peak inductor current i peak without saturation and produce low core loss during the high frequency operation. the core loss can be found in the manufacturer?s datasheet. the inductor?s copper loss can be estimated as follows: winding lrms 2 copper r i p ? = where: i lrms is the rms current in the inductor. this current can be calculated as follows: 2 omax lrms 12 1 1 i i ? + ? = output capacitor selection basically there are two major factors to consider in selecting the type and quantity of the output capacitors. the first one is the required esr (equivalent series resistance) which should be low enough to reduce the output voltage deviation during load changes. the second one is the required capacitance, which should be high enough to hold up the output voltage. before the sc4521 regulates the inductor current to a new value during a
8 ? 2007 semtech corp. www.semtech.com power management sc4521 load transient, the output capacitor delivers all the additional current needed by the load. the esr and esl of the output capacitor, the loop parasitic inductance between the output capacitor and the load combined with inductor ripple current are all major contributors to the output voltage ripple. surface mount ceramic capacitors are recommended. input capacitor selection the input capacitor selection is based on its ripple current level, required capacitance and voltage rating. this capacitor must be able to provide the ripple current drawn by the converter. for the continuous conduction mode, the rms value of the input capacitor current i cin(rms) can be calculated from: i 2 o i o omax (rms) cin v ) v (v v i i ? ? ? = this current gives the capacitor?s power loss through its r cin(esr) as follows: cin(esr) (rms) cin 2 cin r i p ? = the input ripple voltage mainly depends on the input capacitor?s esr and its capacitance for a given load, input voltage and output voltage. assuming that the input current of the converter is constant, the required input capacitance for a given voltage ripple can be calculated by: ) r i v ( fs d) (1 d i c (esr) cin omax i omax in ? ? ? ? ? ? ? = where: ? v i = the given input voltage ripple. because the input capacitor is exposed to the large surge current, attention is needed for the input capacitor. if tantalum capacitors are used at the input side of the converter, one needs to ensure that the rms and surge ratings are not exceeded. for generic tantalum capacitors, it is suggested to derate their voltage ratings at a ratio of about two to protect these input capacitors. boost capacitor and its supply source selection the boost capacitor selection is based on its discharge ripple voltage, worst case conduction time and boost current. the worst case conduction time t w can be estimated as follows: max s w d f 1 t ? = where: f s = the switching frequency and dmax = maximum duty ratio, 0.85 for the sc4521. the required minimum capacitance for the boost capacitor will be: w d b boost t v i c ? = where: i b = the boost current and v d = discharge ripple voltage. with f s = 600khz, v d = 0.5v and i b = 0.045a, the required minimum capacitance for the boost capacitor is: 128nf 0.85 600k 1 0.5 0.045 d f 1 v i c max s d b boost = ? ? = ? ? = the internal driver of the switch requires a minimum 2.7v to fully turn on that switch to reduce its conduction loss. if the output voltage is less than 2.7v, the boost capacitor can be connected to either the input side or an independent supply with a decoupling capacitor. but the pin bst should not see a voltage higher than its maximum rating. freewheeling diode selection this diode conducts during the switch?s off-time. the diode should have enough current capability for full load and short circuit conditions without any thermal concerns. its maximum repetitive reverse block voltage has to be higher than the input voltage of the sc4521. a low forward conduction drop is also required to increase the overall efficiency. the freewheeling diode should be turned on and off fast with minimum reverse recovery because the sc4521 is designed for high frequency applications. ss23 schottky rectifier is recommended for certain applications. the average current of the diode, i d _ avg can be calculated by: ) d i ( i i omax avg - d ? ? = application information (cont.)
9 ? 2007 semtech corp. www.semtech.com power management sc4521 application information (cont.) thermal considerations there are three major power dissipation sources for the sc4521. the internal switch conduction loss, its switching loss due to the high frequency switching actions and the base drive boost circuit loss. these losses can be estimated as: ) (v d i 1000 10 v i 10 10.8 d r i p boost o i o 3 on 2 o total ? ? ? + ? ? ? + ? ? = ? where: i o = load current; r on = on-equivalent resistance of the switch; v boost = input voltage or output based on the boost circuit connection. the junction temperature of the sc4521 can be further determined by: total ja a j p t t ? + = ja is the thermal resistance from junction to ambient. its value is a function of the ic package, the application layout and the air cooling system. the freewheeling diode also contributes a significant portion of the total converter loss. this loss should be minimized to increase the converter efficiency by using schottky diodes with low forward drop (v f ). d) (1 i v p o f diode ? ? ? = loop compensation design the sc4521 has an internal error amplifier and requires a compensation network to connect between the comp pin and gnd pin as shown in figure 3. the compensation network includes c4, c5 and r3. r1 and r2 are used to program the output voltage according to: ) r r 1 ( 8 . 0 v 2 1 o + ? = assuming the power stage esr (equivalent series resistance) zero is an order of magnitude higher than the closed loop bandwidth, which is typically one tenth of the switching frequency, the power stage control to output transfer function with the current loop closed (ridley model) for the sc4521 will be as follows: c r 1 s 1 r 4.3 (s) g l l vd ? + ? = where: r l ? load and c ? output capacitor. the goal of the compensation design is to shape the loop to have a high dc gain, high bandwidth, enough phase margin, and high attenuation for high frequency noises. figure 3 gives a typical compensation network which offers 2 poles and 1 zero to the power stage: bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 sc4521 r2 r1 r3 c4 c d2 l1 c5 vout bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 sc4521 r2 r1 r3 c4 c d2 l1 c5 vout figure 3. compensation network provides 2 poles and 1 zero. the compensation network gives the following characteristics: 2 1 2 m p2 z 1 comp r r r g ) s (1 s s 1 (s) g + ? ? + ? + ? = where: 5 4 1 c c 1 + = 4 3 z c r 1 ? = 5 4 3 5 4 p2 c c r c c ? ? + = the loop gain will be given by: ) s (1 ) s (1 s 1 s 1 r r r c r 10 3.655 (s) g (s) g t(s) p2 p1 z 2 1 2 4 l 3 vd comp + ? + + ? + ? ? ? = ? = ? where: c r 1 l p1 ? =
10 ? 2007 semtech corp. www.semtech.com power management sc4521 the design guidelines for the sc4521 applications are as following: 1. set the loop gain crossover corner frequency c for given switching corner frequency c = 2 f c 2. place an integrator at the origin to increase dc and low frequency gains. 3. select z such that it is placed at p1 to obtain a -20db/dec rate to go across the 0db line. 4. place a high frequency compensator pole p2 ( p2 = f s ) to get the maximum attenuation of the switching ripple and high frequency noise with the adequate phase lag at c. layout guidelines: in order to achieve optimal electrical and thermal performance for high frequency converters, special attention must be paid to the pcb layouts. the goal of layout optimization is to identify the high di/dt loops and minimize them. the following guidelines should be used to ensure proper operation of the converters. 1. a ground plane is suggested to minimize switching noises and trace losses and maximize heat transferring. application information (cont.) 2. start the pcb layout by placing the power components first. arrange the power circuit to achieve a clean power flow route. put all power connections on one side of the pcb with wide copper filled areas if possible. 3. the v in bypass capacitor should be placed next to the v in and gnd pins. 4. the trace connecting the feedback resistors to the output should be short, direct and far away from any noise sources such as switching node and switching components. 5. minimize the loop including input capacitor, the sc4521 and freewheeling diode d 2 . this loop passes high di/dt current. make sure the trace width is wide enough to reduce copper losses in this loop. 6. maximize the trace width of the loop connecting the inductor, freewheeling diode d 2 and the output capacitor. 7. connect the ground of the feedback divider and the compensation components directly to the gnd pin of the sc4521 by using a separate ground trace. 8. connect pin 4 to a large copper area to remove the ic heat and increase the power capability of the sc4521. a few feedthrough holes are required to connect this large copper area to a ground plane to further improve the thermal environment of the sc4521. the traces attached to other pins should be as wide as possible for the same purpose. one integrator is added at origin to increase the dc gain. z is used to cancel the power stage pole p1 so that the loop gain has ?20db/dec rate when it reaches 0db line. p2 is placed at half switching frequency to reject high frequency switching noises. figure 4 gives the asymptotic diagrams of the power stage with current loop closed and its loop gain. c p2 z p1 loop gain t(s) power stage figure 4. asymptotic diagrams of power stage with current loop closed and its loop gain.
11 ? 2007 semtech corp. www.semtech.com power management sc4521 application information (cont.) design example 1: 5v to 1v at 2a s l a i r e t a m f o l l i b m e t iy t qe c n e r e f e re u l a vr e r u t c a f u n a m / . o n t r a p 111 cr 7 x , 5 0 8 0 , v 5 2 , f u 2 2 . 0x x k 4 2 2 y 5 0 8 0 j v : y a h s i v 21o ca z , v 0 1 , f u 0 7 4n o c i b u r 313 cf u 0 1t m 6 0 1 j o 6 1 2 3 c : k d t 414 cv 5 2 , r 7 x , 5 0 8 0 , f n 8 1y a h s i v 515 c5 0 8 0 , v 0 5 , f p 0 6 5y a h s i v 611 d3 2 3 d o s , w s 8 4 1 4 n 1 712 d2 0 a l 0 3 c e. p r o c s c i n o r t c e l e r e t n i n o h i n 811 lh u 9 . 3l 9 r 3 - p n d 5 7 8 r c r : a d i m u s 910 r5 0 8 0 , 0 0 111 r5 0 8 0 , % 1 , k 9 4 . 2e n o z t m s 1 112 r5 0 8 0 , % 1 , k 0 1 2 113 r5 0 8 0 , % 1 , k 0 2 3 1-4 r5 0 8 0 , d e s u t o n 4 11s s cf n 0 0 1 5 111 u1 2 5 4 c sh c e t m e s . e g a k c a p 5 0 8 0 h t i w n o i s i c e r p % 1 e v a h s r o t s i s e r l l a , d e i f i c e p s s s e l n u % 0 2 - / + e r a s r o t i c a p a c l l a d n a % 1 - / + e r a s r o t s i s e r c1 0.22u sc4521 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 r1 2.49k r3 20k c4 18n co 470u d2 l1 3.9uh c5 560p v i = 5v v o =1v @2a c3 10u d1 r0 0 r2 10k css 100n c1 0.22u sc4521 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 r1 2.49k r3 20k c4 18n co 470u d2 l1 3.9uh c5 560p v i = 5v v o =1v @2a c3 10u d1 r0 0 r2 10k css 100n note: the bottom pad needs a big copper area to remove the heat.
12 ? 2007 semtech corp. www.semtech.com power management sc4521 application information (cont.) design example 2: 6.2v to 1.5v at 1.5a c1 0.22u sc4521 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 r1 8.66k r3 4.87k c4 18n co 100u d2 l1 4.7uh c5 560p v i = 6.2v v o =1.5v c3 10u d1 r0 0 r2 10k css 100n note: the bottom pad needs a big copper area to remove the heat. s l a i r e t a m f o l l i b m e t iy t qe c n e r e f e re u l a vr e r u t c a f u n a m / . o n t r a p 111 cr 7 x , 5 0 8 0 , v 5 2 , f u 2 2 . 0x x k 4 2 2 y 5 0 8 0 j v : y a h s i v 21o cf u 0 0 1o y n a s 313 cf u 0 1t m 6 0 1 j o 6 1 2 3 c : k d t 414 cv 5 2 , r 7 x , 5 0 8 0 , f n 8 1y a h s i v 515 c5 0 8 0 , v 0 5 , f p 0 6 5y a h s i v 611 d3 2 3 d o s , w s 8 4 1 4 n 1 712 d3 t l 0 1 2 a r b mn o 811 lh u 7 . 47 r 4 - s a 9 1 9 : o k o t 910 r5 0 8 0 , 0y a h s i v 0 111 r5 0 8 0 , % 1 , k 6 6 . 8y a h s i v 1 112 r5 0 8 0 , % 1 , k 0 1y a h s i v 2 113 r5 0 8 0 , k 7 8 . 4y a h s i v 3 1-4 r5 0 8 0 , d e s u t o n 4 11s s cf n 0 0 1 5 111 u1 2 5 4 c sh c e t m e s . e g a k c a p 5 0 8 0 h t i w n o i s i c e r p % 1 e v a h s r o t s i s e r l l a , d e i f i c e p s s s e l n u % 0 2 - / + e r a s r o t i c a p a c l l a d n a % 1 - / + e r a s r o t s i s e r
13 ? 2007 semtech corp. www.semtech.com power management sc4521 application information (cont.) design example 3: 13v ~ 21v to 3.3v at 1a c1 0.22u sc4521 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 r1 24.9k r3 3.83k c4 18n c2 10u d2 l1 10uh c5 560p v i v o =3.3v c3 4.7u r2 8.25k d3 r0 0 css 330n rss 200k c1 0.22u sc4521 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 r1 24.9k r3 3.83k c4 18n c2 10u d2 l1 10uh c5 560p v i v o =3.3v c3 4.7u r2 8.25k d3 r0 0 css 330n rss 200k note: the bottom pad needs a big copper area to remove the heat. s l a i r e t a m f o l l i b m e t iy t qe c n e r e f e re u l a vr e r u t c a f u n a m / . o n t r a p 111 cr 7 x , 5 0 8 0 , v 5 2 , f u 2 2 . 0x x k 4 2 2 y 5 0 8 0 j v : y a h s i v 212 cf u 0 1 : n e d u y - o y i a t t - f m 6 0 1 j b 6 1 3 k d e 313 cr 5 x , v 5 2 , 6 0 2 1 , f u 7 . 4c i n o s a n a p 414 cv 5 2 , r 7 x , 5 0 8 0 , f n 8 1y a h s i v 515 c5 0 8 0 , v 0 5 , f p 0 6 5y a h s i v 612 d 4 0 s q 1 3 c e : l a n o i t a n r e t n i - n o h i n 713 d3 2 3 d o s , s w 8 4 1 4 n 1 811 lh u 0 1 : a d i m u s c n 0 0 1 - p n 8 3 d 6 h r d c 910 r5 0 8 0 , 0 0 111 r5 0 8 0 , % 1 , k 9 . 4 2e n o z t m s 1 112 r5 0 8 0 , % 1 , k 5 2 . 8e n o z t m s 2 113 r5 0 8 0 , % 1 , k 3 8 . 3e n o z t m s 3 1-s s r5 0 8 0 , k 0 0 2 4 11s s c5 0 8 0 , f n 0 3 3 5 111 u1 2 5 4 c sh c e t m e s . e g a k c a p 5 0 8 0 h t i w n o i s i c e r p % 1 e v a h s r o t s i s e r l l a , d e i f i c e p s s s e l n u % 0 2 - / + e r a s r o t i c a p a c l l a d n a % 1 - / + e r a s r o t s i s e r
14 ? 2007 semtech corp. www.semtech.com power management sc4521 c1 0.22u sc4521 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 r1 51.1k r3 4.87k c4 18n c2 10u d2 l1 10uh c5 560p v i v o =5v c3 4.7u r2 10k d3 r0 0 css 470n rss 200k c1 0.22u sc4521 bst 1 in 2 sw 3 gnd 4 en 5 fb 6 comp 7 ss 8 r1 51.1k r3 4.87k c4 18n c2 10u d2 l1 10uh c5 560p v i v o =5v c3 4.7u r2 10k d3 r0 0 css 470n rss 200k application information (cont.) design example 4: 13v ~ 21v to 5v at 1.5a note: the bottom pad needs a big copper area to remove the heat. s l a i r e t a m f o l l i b m e t iy t qe c n e r e f e re u l a vr e r u t c a f u n a m / . o n t r a p 111 cr 7 x , 5 0 8 0 , v 5 2 , f u 2 2 . 0x x k 4 2 2 y 5 0 8 0 j v : y a h s i v 212 cf u 0 1 : n e d u y - o y i a t t - f m 6 0 1 j b 6 1 3 k d e 313 cr 5 x , v 5 2 , 6 0 2 1 , f u 7 . 4c i n o s a n a p 414 cv 5 2 , r 7 x , 5 0 8 0 , f n 8 1y a h s i v 515 c5 0 8 0 , v 0 5 , f p 0 6 5y a h s i v 612 d 4 0 s q 1 3 c e : l a n o i t a n r e t n i - n o h i n 713 d3 2 3 d o s , s w 8 4 1 4 n 1 811 lh u 0 1 : a d i m u s c n 0 0 1 - p n 8 3 d 6 h r d c 910 r5 0 8 0 , 0 0 111 r5 0 8 0 , % 1 , k 1 . 1 5e n o z t m s 1 112 r5 0 8 0 , % 1 , k 0 1e n o z t m s 2 113 r5 0 8 0 , % 1 , k 7 8 . 4e n o z t m s 3 1-s s r5 0 8 0 , k 0 0 2 4 11s s c5 0 8 0 , f n 0 7 4 5 111 u1 2 5 4 c sh c e t m e s . e g a k c a p 5 0 8 0 h t i w n o i s i c e r p % 1 e v a h s r o t s i s e r l l a , d e i f i c e p s s s e l n u % 0 2 - / + e r a s r o t i c a p a c l l a d n a % 1 - / + e r a s r o t s i s e r
15 ? 2007 semtech corp. www.semtech.com power management sc4521 application information (cont.) (pcb - top) (pcb - bottom)
16 ? 2007 semtech corp. www.semtech.com power management sc4521 application information (cont.) (componet side - top) (componet side - top)
17 ? 2007 semtech corp. www.semtech.com power management sc4521 outline drawing - soic-8l edp 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 e a2 (.041) .004 .008 - .028 - - - - 0 .016 .007 .049 .000 .053 8 0 0.20 0.10 - 8 0.40 0.17 1.25 0.00 .041 .010 .069 .065 .005 1.35 (1.05) 0.72 - 1.04 0.25 - - - 1.75 1.65 0.13 0.25 - .010 .020 0.50 - c l (l1) 01 0.25 gage plane 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 exposed pad 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 f h h f h .085 .120 .095 .116 .130 .099 2.95 2.15 3.05 2.41 3.30 2.51 4. reference jedec std ms-012, variation ba.
18 ? 2007 semtech corp. www.semtech.com power management sc4521 land pattern - soic-8l-edp 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. 3. thermal vias in the land pattern of the exposed pad shall be connected to a system ground plane. failure to do so may compromise the thermal and/or functional performance of the device. e z (c) g p ? 0.36mm thermal via x y solder mask (5.20) c (.205) x y z f g p d e .024 .087 .291 .101 .118 .050 .201 .134 0.60 2.20 7.40 2.56 3.00 1.27 5.10 3.40 millimeters inches dim dimensions d f 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

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