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1 www.semtech.com SC192 synchronous buck converter with integrated power devices power management revision 8, march 26, 2007 description features typical application circuit applications the SC192 is a synchronous step-down converter with integrated power devices designed for battery operated systems. the internal power switches reduce system size and cost. in addition, an efficiency of 95% can be achieved for significant line and load ranges. the SC192 is designed for single-cell li-ion battery applications, but also performs well in fixed 3.3v or 5v input circuits. the SC192 has a flexible clocking scheme. it can be synchronized to an external oscillator, fixed to the inter- nal oscillator, or allowed to modulate the frequency dur- ing light loads (psave) for maximum battery life, by the method called pulse frequency modulation (pfm). shut- down places the switches in a high impedance state and turns off all control circuitry to achieve a typical quies- cent current of 0.1 a. line and load regulation is to +/-0.5% of the output volt- age. the internal mosfet switches provide >1a peak current to provide a dc output of at least 700ma. grounding the ilim pin reduces the current limit by half. the SC192 can achieve 100% duty cycle for excellent low dropout performance and comes in a tiny mlpd-10, 3 x 3 package having a maximum height of 1mm. ? 2.7v to 7v input range ? output adjustable from 0.75v to vin ? fixed frequency or psave for maximum efficiency over wide load current range ? 700ma guaranteed output current ? no schottky diode required ? 35 a quiescent current ? 100% duty cycle in dropout ? 95% efficiency ? fast transient response ? over temperature protection ? space-saving micro lead-frame package mlpd-10 3x3 ? cell phones ? cordless phones ? notebook and subnotebook computers ? pdas and mobile communicators ? 1 li-ion or 3 nimh/nicd powered devices vin en ilim bp gnd comp sync/pwm pgnd adj lx SC192 vin = 2.7v to 7v c1 c3 l1 c5 r1 r2 c6 r8 c4 vout = 0.75v to vin 1 8 6 2 34 7 10 5 9
2 ? 2007 semtech corp. www.semtech.com SC192 preliminary power management electrical characteristics absolute maximum ratings unless otherwise noted: vin = 3.6v, sync/pwm = vin, ilim = vin, en = vin, t a =-40 to 85c. typical values are at t a = +25c. 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 n a r e g a t l o v t u p n iv n i 7 . 25 . 5v e g a t l o v n o i t a l u g e r j d av j d a 1 3 7 . 05 7 . 09 6 7 . 0v t n e r r u c t u p n i j d ai j d a v 5 7 . 0 = j d a0 5 -00 5a n e g n a r t s u j d a e g a t l o v t u p t u ov t u o v j d a v n i v n o i t a l u g e r e n i lg e r e n i l 5 . 0 -5 . 0 +% n o i t a l u g e r d a o l ) 1 ( g e r d a o l = t n e r r u c r o t c u d n i k a e p a m 0 0 7 o t 0 06 . 0% e c n a t s i s e r n o l e n n a h c - pr p s d i x l a m 0 0 2 =3 . 0 e c n a t s i s e r n o l e n n a h c - nr n s d i x l a m 0 0 2 =4 . 0 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. * tied to pcb with 1 square inch, 2 ounce copper. note: this device is esd sensitive. use of esd handling precautions is required. r e t e m a r a pl o b m y sm u m i x a ms t i n u t u p n i n i vv n i 7 o t 3 . 0 -v t u p n i m w p / c n y sv c n y s 7 o t 3 . 0 -v t u p n i n ev n e 7 o t 3 . 0 -v d n g o t d n g pv n d g p 3 . 0 o t 3 . 0 -v e g a t l o v x lv x l 1 + n i v o t 1 -v e g a t l o v m i l iv m i l i 3 . 0 + n i v o t 3 . 0 -v e g a t l o v j d av j d a 3 . 0 + n i v o t 3 . 0 -v e g a t l o v p m o cv p m o c 3 . 0 + n i v o t 3 . 0 -v e g a t l o v p bv p b 3 . 0 + n i v o t 3 . 0 - n i vv 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 a j 7 5 * w / c d n g o t t i u c r i c t r o h s t u p t u ot c s s u o u n i t n o cs t n e r r u c x li x l 6 . 1 +a e r u t a r e p m e t w o l f e r r i k a e p s 0 3 - s 0 1 ) g n i r e d l o s ( r t l m i 2 9 1 c s s 0 4 - s 0 2 ) g n i r e d l o s ( t r t l m i 2 9 1 c s t d a e l 0 4 2 0 6 2 c e r u t a r e p m e t e g a r o t st s 0 6 1 + o t 5 6 - c -0.3 to 7.5 -0.3 to 7.5 -0.3 to 7.5 7
3 ? 2007 semtech corp. www.semtech.com SC192 power management electrical characteristics cont. unless otherwise noted: vin = 3.6v, sync/pwm = vin, ilim = vin, en = vin, t a =-40 to 85c. typical values are at t a = +25c. 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 i m i l t n e r r u c l e n n a h c - p i ) p ( m i l d n g = m i l i0 2 40 0 60 8 7a m v = m i l i n i 0 4 80 0 2 10 6 5 1a m t i m i l t n e r r u c l e n n a h c - n i ) n ( m i l e d o m e v a s p , d n g = m w p / c n y s5 45 0 15 6 1a m 0 2 3 -0 2 4 -0 2 5 -a m t n e r r u c t n e c s e i u qi q e d o m e v a s p , d n g = m w p / c n y s5 30 5a t n e r r u c n w o d t u h si d s t , n e p o = x l , 0 = n e a 5 2 = c1a s o m p t n e r r u c e g a k a e l x li p x l v 0 = n e , v 0 = x l , v 5 . 5 = n i v1a s o m n t n e r r u c e g a k a e l x li n x l v 0 = n e , v 5 . 5 = x l , v 5 . 5 = n i v0 2 -a y c n e u q e r f r o t a l l i c s of c s o 0 5 60 5 70 3 8z h k e g n a r y c n e u q e r f c n y sf c n y s 0 0 50 0 0 1z h k e g n a r e l c y c y t u dd e d o m e v a s p , d n g = m w p / c n y s0 20 0 1% d l o h s e r h t o l v uv l v u 5 3 . 25 . 25 6 . 2v s i s e r e t s y h o l v uv s y h l v u 0 5v m n w o d t u h s l a m r e h t 0 6 1 c h g i h t u p n i c i g o lv h i m i l i , m w p / c n y s , n e2v w o l t u p n i c i g o lv l i m i l i , m w p / c n y s , n e8 . 0v h g i h t n e r r u c t u p n i c i g o li h i m i l i , m w p / c n y s , n e2 -2a w o l t n e r r u c t u p n i c i g o li l i m i l i , m w p / c n y s , n e2 -2a notes: (1) load regulation limits are specified from 0 to 700ma. this specification is calculated based on parameters measured individ ually and is not a tested parameter. see the load regulation limit graph on page 13 for more detailed view of performance.
4 ? 2007 semtech corp. www.semtech.com SC192 preliminary power management pin descriptions pin configuration ordering information # n i pe m a n n i pn o i t c n u f n i p 1n i v . s e h c t i w s t e f s o m l a n r e t n i e h t o t y l t c e r i d s e o g t u p n i s i h t ; e g a t l o v y l p p u s r e w o p t u p n i 2p b a s e d i v o r p r o t s i s e r l a n r e t n i n a h t i w d e n i b m o c r o t i c a p a c l a n r e t x e n a ; n i p r o t i c a p a c s s a p y b o t p b m o r f r o t i c a p a c f u 1 . 0 a t c e n n o c . y r t i u c r i c l o r t n o c l a n r e t n i e h t r o f e g a t l o v y l p p u s d e r e t l i f . d n u o r g 3d n g. d n u o r g g o l a n a 4p m o c. r e i f i l p m a r o r r e e h t r o f n i p n o i t a s n e p m o c 5j d a . e g a t l o v t u p t u o e h t t e s o t r e d i v i d r o t s i s e r a o t t c e n n o c ; n i p t s u j d a t u p t u o 6m i l i r o f n i v o t m i l i t c e n n o c ; t n e r r u c a 6 . 0 r o f d n g o t m i l i t c e n n o c . t u p n i t c e l e s t i m i l t n e r r u c l a t i g i d . t i m i l t n e r r u c a 2 . 1 7m w p / c n y s e v a s r e w o p e l b a n e o t d n g , e d o m m w p d e c r o f r o f n i v o t e i t . t u p n i n o i t a z i n o r h c n y s r o t a l l i c s o . n o i t a z i n o r h c n y s y c n e u q e r f r o f l a n g i s k c o l c l a n r e t x e n a r o , e d o m 8n e s e c u d e r d n a e c i v e d e h t s e l b a s i d w o l a 2 9 1 c s e h t s e l b a n e t u p n i h g i h a ; t u p n i l a t i g i d e l b a n e . e c n a d e p m i h g i h s e m o c e b x l , n w o d t u h s n i . a u 1 . 0 o t t n e r r u c t n e c s e i u q 9x l. s t e f g n i h c t i w s e h t o t n o i t c e n n o c r o t c u d n i 0 1d n g p. d n u o r g r e w o p td a p l a m r e h t 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 e c i v e d ) 1 ( e g a k c a p r t l m i 2 9 1 c s 3 x 3 0 1 - d p l m t r t l m i 2 9 1 c s ) 2 ( b v e 2 9 1 c sd r a o b n o i t a u l a v e note: (1) only available in tape and reel packaging. a reel contains 3000 devices. (2) lead free product. this product is fully weee and rohs compliant. mlpd-10: 3x3 10 lead top view ilim adj lx en 10 9 pgnd sync/pwm 8 7 6 5 1 2 3 4 vin bp gnd comp t
5 ? 2007 semtech corp. www.semtech.com SC192 power management block diagram pw m comp - + error amp - + 750mv control logic nlimit comp - + osc a n d s l o p e generation plimit amp - + current amp - + v v g nd en adj comp sync/ pw m ilim bp vin lx pg nd
6 ? 2007 semtech corp. www.semtech.com SC192 preliminary power management description description the SC192 step-down, pulse-width-modulated (pwm), dc-dc converter has an adjustable output range from 0.75v to the input voltage. the device has an internal synchronous rectifier and does not require a schottky diode on the lx pin. at moderate to heavy loads, the converter operates in the pwm mode with a fixed frequency of 750khz. at light loads the converter enters the power save mode by modulating the frequency, pulse-frequency-modulation (pfm) which achieves high efficiency under light load conditions. normal mode this is a standard fixed frequency current mode topol- ogy. the current feedback is through the pmos current path and is amplified and summed with the internal slope compensation network and dc offset. the voltage feed- back loop is through the resistor divider attached to the adj pin. the transconductance error amplifier output is the compensation (comp) pin with the usual external compensation network attached. the pwm comp pin closes the loop by comparing the summed current feed- back and the comp signal to determine the length of the on time. the period is set by the on-board oscillator or external clock attached to the sync pin. power save mode if sync/pwm is dc low, power save mode is used at light loads to improve efficiency. when the output cur- rent reaches a low enough level, the part goes into a voltage hysteresis mode of operation. the current level for this is set to be the current reversal protection on the nmos device. the output voltage is then allowed to decay to a lower threshold with the part in a reduced quiescent current (psave) state. after this lower thresh- old is reached the part is reawoken to normal operation, but with a current offset on the comp pin to drive the output voltage regulation point to be above an upper threshold point. however the offset is removed once the upper threshold is reached. if the load current is now sufficiently large the part will return to normal regulation, if not another psave cycle will start. frequency foldback when the adj pin is low the output switching frequency is folded back in several discrete steps to protect against a short to gnd on the output and improve inrush cur- rent control during start-up. forced pwm if sync/pwm is dc high, the forced pwm mode is en- abled. this ensures that the switching frequency of the converter is maintained over the full range of output loads. this means that the current reversal threshold of the nmos is changed to a negative value and the 100% duty cycle and power save modes are also disabled. 100% duty-cycle operation normally the control loop constrains the duty cycle of the converter with minimum on and off times, but if the output voltage droops to the lower power-save thresh- old and the on time is not terminated by the pwm com- parator or pmos current limit, then the next pmos on time is allowed to extend until either the pwm compara- tor or pmos current limit trips. this is then followed by a minimum off time. this maximum on time/minimum off time is allowed to continue until the upper power-save threshold is reached. this allows the part to go into a dropout mode of operation if the input supply collapses down to the output voltage. if this happens, the output voltage is equal to the input voltage minus the voltage drop across the p-channel mosfet. soft start the soft start mode is enabled after every shutdown cycle to limit inrush current from the battery. in conjunction with the frequency foldback this controls the maximum current during start-up. the pmos current limit is stepped from 25%, to 50%, to 75%, and then 100% by an inter- nal 2ms timer. as soon as the part reaches regulation, soft start mode is disabled.
7 ? 2007 semtech corp. www.semtech.com SC192 power management evaluation board schematic tp1 vin tp4 lx 1.8v r5 100k r4 100k tp6 sy nc r8 28k r2 309k c5 47pf sy nc tp7 en r1 442k tp5 vout r3 100k l1 10uh vin tp2 gnd c6 22uf tp8 ilim en u1 SC192 1 2 3 4 5 6 7 8 9 10 vin bp gnd comp adj ilim sy nc en lx pgnd c1 10uf c3 0.1uf c4 470pf tp3 comp gnd sw1 dip 1 2 3 6 5 4 r6 1k vin c2 0.1uf r7 1k
8 ? 2007 semtech corp. www.semtech.com SC192 preliminary power management evaluation board gerber plots top copper bottom copper top silkscreen bottom silkscreen
9 ? 2007 semtech corp. www.semtech.com SC192 power management applications information selecting components when selecting components for the an SC192 application the main factors are typically performance, size and cost. for higher performance the designer will select higher values of input and output capacitors to reduce ripple current and voltage. however, for an application that can tolerate higher ripple, less expensive and smaller compo- nents can be utilized. the schematics below show two possibilities. the first shows the use of 10 f capacitors on the input and output with l1 = 10 h, while the second shows the use of smaller less expensive 4.7 f capacitors and l1 = 4.7 h. the only circuit consideration for choosing one over the other is the compensation components c4 & r8. when these components are in place the values of r2 can be chosen for a given output voltage. the values that should be used are indicated in table 1 below. using a different value for r1 is not advised since this will change the loop characteristics and may cause the supply to become unstable. any output voltage is achievable using r1 of 442k and then selecting r2 to achieve the desired output voltage. the equation for vout is: 0.75 1 r2 r1 vout ? ? ? ? ? ? ? + = because the SC192 has external compensation the use of small inexpensive ceramic capacitors can be used for the output capacitor allowing the designer greater flexibility. r2 l1 10uh r8 12k r1 442k c3 0.1uf c5 47pf c1 4.7uf c4 470pf vin SC192 1 2 3 4 5 6 7 8 9 10 vin bp gnd comp adj ilim sy nc en lx pgnd vout c4 470pf vout r8 6.19k r2 c6 4.7uf c1 10uf r1 442k c6 10uf c3 0.1uf l1 4.7uh vin c5 47pf SC192 1 2 3 4 5 6 7 8 9 10 vin bp gnd comp adj ilim sy nc en lx pgnd
10 ? 2007 semtech corp. www.semtech.com SC192 preliminary power management applications information cont. the plots below were taken at vin = 3.6v, vout = 1.8v, with the compensation components listed in table 1. the upper plot is lx, the middle plot is output voltage, the lower plot is the current transient of 0.1a to 0.6a psave, cout = 20uf, lout = 10uh pwm, cout = 20uf, lout = 10uh psave, cout = 10uf, lout = 10uh pwm, cout = 10uf, lout = 10uh table 1 t u o vt u o v t u o v t u o vt u o v2 r2 r 2 r 2 r2 r f u 0 1 = t u o c = 6 cf u 0 1 = t u o c = 6 c f u 0 1 = t u o c = 6 c f u 0 1 = t u o c = 6 cf u 0 1 = t u o c = 6 c h u 0 1 = 1 lh u 0 1 = 1 l h u 0 1 = 1 l h u 0 1 = 1 lh u 0 1 = 1 l f u 2 2 = t u o c = 6 cf u 2 2 = t u o c = 6 c f u 2 2 = t u o c = 6 c f u 2 2 = t u o c = 6 cf u 2 2 = t u o c = 6 c h u 0 1 = 1 lh u 0 1 = 1 l h u 0 1 = 1 l h u 0 1 = 1 lh u 0 1 = 1 l f u 7 . 4 = t u o c = 6 cf u 7 . 4 = t u o c = 6 c f u 7 . 4 = t u o c = 6 c f u 7 . 4 = t u o c = 6 cf u 7 . 4 = t u o c = 6 c h u 7 . 4 = 1 lh u 7 . 4 = 1 l h u 7 . 4 = 1 l h u 7 . 4 = 1 lh u 7 . 4 = 1 l v 3 . 3k 0 3 1 f p 0 7 4 = 4 c k 2 1 = 8 r f p 0 7 4 = 4 c k 8 2 = 8 r f p 0 7 4 = 4 c k 9 1 . 6 = 8 r v 5 . 2k 7 8 1 v 8 . 1k 9 0 3 v 5 . 1k 2 4 4 v 0 . 1m 0 3 . 1
11 ? 2007 semtech corp. www.semtech.com SC192 power management inductor selection the inductor values listed in table 1 will work for nearly all combinations of output current and output voltages. after selecting 4.7uh or 10uh for the inductor value two additional inductor parameters should be considered. the current rating of the inductor and the dc resistance. the dc resistance has a great impact on efficiency due to copper losses. however, small inductors tend to have higher dc resistance. therefore a compromise between size and efficiency will need to be made. the inductor current must be chosen to prevent the in- ductor from saturation. the most conservative approach would be to select an inductor with a saturation current slightly above the maximum current capability of the SC192 which is 1.56a peak current for ilim = vin or 780ma for ilim = gnd. a more accurate design of the inductor would be to rate the inductor for the maximum output current plus the inductor ripple current that can be calculated as follows: 2 i i i l ) o(max l(max) + = out in out l v f l v v - 1 i ? ? ? ? ? ? ? ? ? ? ? ? ? ? = f = switching frequency l = inductor value i l = peak-to-peak inductor ripple current i l = maximum inductor current v out = output voltage v in = input voltage c out = output capacitance i out = output current i out(max) = maximum dc output current output capacitor selection because the SC192 has external compensation avail- able, low esr ceramic capacitors can be used. this elimi- nates the need for bulky tantalum capacitors. values for the output capacitors in table 1 will work for nearly all combinations of output current and output voltages. the equation for determining the size of the output capaci- tor in terms of minimizing the ripple voltage is given as follows: ? ? ? ? ? ? + ? ? ? = esr f c 8 1 i v out l o input capacitor selection the input ripple current can be reduced with properly selecting the input capacitor. again, values for the input capacitors in table 1 will work for nearly all combina- tions of input current and output voltages. the input ca- pacitor should be rated for the maximum input ripple current calculated as: psave, cout = 4.7uf, lout = 4.7uh pwm, cout = 4.7uf, lout = 4.7uh applications information cont.
12 ? 2007 semtech corp. www.semtech.com SC192 preliminary power management in out out in out rms v i v - v v i ? ? = the worst case rms ripple current occurs at a duty cycle of 0.5 and its value at that point is 2 i out . ceramic capacitors are recommended for input capaci- tors because of their low esr and high ripple current capabilities. in addition, it is advised that the input ca- pacitor be placed as close to the input pin of the ic as possible. layout considerations pcb layout is of utmost importance because the switch- ing frequency is 750khz with peak currents over 1a. a careful layout will avoid potential stability and emi prob- lems. traces should be as wide and as short as possible. keep the input capacitor as close to the package as pos- sible. this will help minimize large loop areas. keep the power ground and analog ground separated and tie the two together at one common point. notice the top cop- per gerber plot (see page 8), pin 3 and pin 10 are tied together under the package. be aware of the high cur- rent paths and avoid tying signal grounds to the high power grounds where the signal paths might experience large fluctuations in voltages as high currents pass though copper traces. applications information cont. efficiency at vin = 3.6v 80 85 90 95 100 1 1030507090200400600 load current (ma) efficiency (%) vo = 2.5v vo = 1.8v line regulation at iout = 300ma 0.00 0.02 0.04 0.06 0.08 0.10 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 input voltage (volts) line regulation (% ) vo = 1.8v load regulation at vin = 3.6v 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 1 20 40 60 80 100 200 300 400 500 600 ouput current (ma) load regulation (%) vo = 1.8v vo = 2.5v efficiency at vin = 5v 60 65 70 75 80 85 90 95 100 1 10 30 50 70 90 200 400 600 load current (ma) efficiency (%) vo = 3.3v
13 ? 2007 semtech corp. www.semtech.com SC192 power management SC192 load regulation limits 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 00.20.40.60.811.2 peak inductor current (amps) load regulation (%) load reg max load reg typ load reg min shutdown current vs temperature 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -40 0 25 85 125 temperature ( o c) shutdown current (a) vin = 3.6v oscillator frequency vs temperature over v in 710 715 720 725 730 735 740 745 750 755 760 -60 -40 -20 0 20 40 60 80 100 120 140 temp ( o c) fosc (khz) vin = 2.7 v vin = 3.6v vin = 5.5v oscillator frequency vs v in over temperature 710 715 720 725 730 735 740 745 750 755 760 22.533.544.555.56 v in (volts) fosc (khz) temp = -40c temp = 0c temp = 25c temp = 85c temp = 125c line regulation at i out = 300ma 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 input voltage (volts) line regulation (%) vo = 2.5v
14 ? 2007 semtech corp. www.semtech.com SC192 preliminary power management outline drawing - mlpd-10, 3 x 3 min aaa bbb b e l n d c e a1 a2 a dim millimeters nom dimensions max nom inches min max .114 .118 .122 2.90 3.00 3.10 - - - - (laser mark) indicator pin 1 1 n 2 notes: controlling dimensions are in millimeters (angles in degrees). coplanarity applies to the exposed pad as well as terminals. 2. 1. .003 .007 .042 10 .009 .048 - .000 .031 (.008) 0.08 0.23 10 .011 .052 0.18 1.06 .039 - .002 - 0.00 0.80 1.31 0.30 1.21 - 0.05 1.00 (0.20) .004 0.10 0.50 bsc .020 bsc 0.30 .012 .020 .016 0.40 0.50 a aaa c a2 seating plane a1 a bxn bbb c a b b e c c d lxn e e .074 .079 .083 1.87 2.02 2.12 192 yyww yy = two-digit year of manufacture ww = two-digit week of manufacture top marking marking information
15 ? 2007 semtech corp. www.semtech.com SC192 power management land pattern - mlpd-10, 3 x 3 .087 .055 2.20 1.40 .150 .020 .012 .037 3.80 0.30 0.95 0.50 (.112) .075 1.90 (2.85) k h x this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. inches dimensions g k h x y p z c dim millimeters y z g (c) p visit us at: www .semtech.com semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 contact information

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