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1 www.semtech.com sc1548 linear fet controller power management revision: november 10, 2004 typical application circuit the sc1548 is a power supply controller designed to provide a simple single regulated power supply with over current protection. it is part of semtech?s smartldo? family of products. the sc1548 can provide a 1.818v power supply for the i/o plane or 1.515v for gtl+ / agp from either 3.3v or 2.5v. an adjustable option allows generation and control of any voltage from 1.263v up to 5v. sc1548 features include tight output voltage regulation, an enable control and over current protection. over current protection is provided by feedback to the sense pin. if the output drops below 50% of the nominal output voltage (typical) for greater than 4ms (typical), the output will be shut down. the sc1548 is available in a tiny 5-pin sot-23 surface mount package. ? motherboards ? graphics cards ? microcontrollers ? simple power supplies ? 2.5% output accuracy over line, load and temperature ? 1.515v, 1.818v and adjustable output voltage options available ? enable control ? over current protection ? 5-pin sot-23 package 1.818v out 3.3v in 12v in enable q1 irl530n c4 0.1uf + c1 100uf + c2 100uf + c3 22uf u1 sc1548csk-1.8 1 2 3 4 5 sns gnd drv in en adjustable output voltage version 2.5v out 3.3v in 12v in enable q1 irl530n c4 0.1uf + c1 100uf + c2 100uf + c3 22uf r1 97.6 r2 100 u1 sc1548csk 1 2 3 4 5 adj gnd drv in en fixed output voltage versions description features applications
2 ? 2004 semtech corp. www.semtech.com sc1548 power management r e t e m a r a p l o b m y sm u m i x a ms t i n u e g a t l o v y l p p u s t u p n i v n i 5 1 + o t 5 . 0 -v s n i p t u p n i v j d a v , n e v , s n s 7 + o t 5 . 0 -v e s a c 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 c j 1 8w / c 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 6 5 2w / c e g n a r e r u t a r e p m e t t n e i b m a g n i t a r e p o t a 0 7 + o t 0c e g n a r e r u t a r e p m e t n o i t c n u j g n i t a r e p o t j 5 2 1 + o t 0c e g n a r e r u t a r e p m e t e g a r o t s t 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 l t d a e l 0 0 3c r e t e m a r a pl o b m y ss n o i t i d n o c t s e tn i mp y tx a ms t i n u n i e g a t l o v y l p p u sv n i 8 2 . 1 1 0 0 . 2 1 2 7 . 2 1 v t n e r r u c t n e c s e i u qi q 0 . 15 . 1a m 0 . 2 t u o k c o l e g a t l o v r e d n u d l o h s e r h t t r a t so l v u789v n e t n e r r u c n i p e l b a n ei n e v n e v 0 =0 0 10 5 1a e g a t l o v d l o h s e r h tv ) n e ( h t v n e g n i s i r8 . 13 . 2v s i s e r e t s y hv t s y h 0 0 2v m e m i t y a l e d e l b a n e ) 3 ( ) 2 ( t ) n o ( d v n e m o r f d e r u s a e m , h g i h o t w o l = v n e v = ) n e ( h t v % 0 1 o t v r d 0 0 5s n e m i t y a l e d e l b a s i d ) 3 ( ) 2 ( t ) f f o ( d v n e m o r f d e r u s a e m , w o l o t h g i h = v n e v = ) n e ( h t v % 0 9 o t v r d 0 5 1s n ) s t r a p e g a t l o v t u p t u o d e x i f ( s n s t n e r r u c n i p e s n e si s n s g n i k n i s 5 7 0 0 1 5 2 1 a ) s t r a p e g a t l o v t u p t u o e l b a t s u j d a ( j d a t n e r r u c n i p t s u j d ai j d a g n i c r u o s5 2 . 0a e g a t l o v e c n e r e f e r ) 2 ( v j d a v 0 . 3 v r w p ) 4 ( a m 1 , v 6 . 3 i t u o a 1% 5 . 1 -3 6 2 . 1% 5 . 1 +v % 5 . 2 -% 5 . 2 + absolute maximum ratings electrical characteristics (1) unless specified: t a = 25c, v in = 12v, v pwr = 3.3v, i out = 0a. values in bold apply over full operating temperature range. 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 ? 2004 semtech corp. www.semtech.com sc1548 power management notes: (1) this device is esd sensitive. use of standard esd handling precautions is required. (2) see application circuit on page 1. (3) see timing diagram on page 4. (4) connected to fet drain. r e t e m a r a pl o b m y ss n o i t i d n o c t s e tn i mp y tx a ms t i n u ) s t r a p e g a t l o v t u p t u o d e x i f ( n o i t a l u g e r e g a t l o v t u p t u o e g a t l o v t u p t u o ) 2 ( v t u o v 0 . 3 v r w p ) 4 ( a m 1 , v 6 . 3 i t u o a 1% 5 . 1 -v t u o % 5 . 1 +v % 5 . 2 -% 5 . 2 + v r d t n e r r u c t u p t u oi v r d v v r d v , v 4 = s n s v 2 . 1 = 5 0 1a m e g a t l o v t u p t u ov v r d i , n o l l u f v r d a m 0 = 0 . 9 5 . 0 1v e m i t e s i r ) 3 ( ) 2 ( t r v n e m o r f d e r u s a e m , h g i h o t w o l = v n e v = ) n e ( h t v % 0 9 o t v r d 0 . 1s m e m i t l l a f ) 3 ( ) 2 ( t f v n e m o r f d e r u s a e m , w o l o t h g i h = v n e v = ) n e ( h t v % 0 1 o t v r d 0 5 5s n o i t c e t o r p t n e r r u c r e v o d l o h s e r h t p i r tv ) c o ( h t 0 3 0 5 0 7 v % t u o t r o h s t u p t u o p u - r e w o p y t i n u m m i t i u c r i c 15 0 6s m h c t i l g t i u c r i c t r o h s t u p t u o y t i n u m m i 5 . 040 3s m n o i t c e s l o r t n o c h t d i w d n a bv v r d c , % 5 = d h t , v 9 = l f p 0 0 6 =5z h m unless specified: t a = 25c, v in = 12v, v pwr = 3.3v, i out = 0a. values in bold apply over full operating temperature range. electrical characteristics (cont.) (1)
4 ? 2004 semtech corp. www.semtech.com sc1548 power management timing diagram
5 ? 2004 semtech corp. www.semtech.com sc1548 power management pin descriptions top view sot-23-5l notes: (1) where -x.x denotes voltage options. available voltages are: 1.515v (-1.5) and 1.818v (-1.8). leave blank for adjustable version. (2) only available in tape and reel packaging. a reel contains 3000 units. (3) lead free product. this product is fully weee and rohs compliant. r e b m u n t r a p ) 2 ( ) 1 ( e g a k c a p r t x . x - k s c 8 4 5 1 c s 5 - 3 2 - t o s t r t k s c 8 4 5 1 c s ) 3 ( pin configuration ordering information block diagram n i pe m a n n i pn o i t c n u f n i p 1s n s j d a e h t f o e c r u o s e h t o t e s n e s e t o m e r a s a e s u . s n o i t p o e g a t l o v t u p t u o d e x i f r o f t u p n i e s n e s r o t a l u g e r . t e f s o m l e n n a h c - n o t r e f e r ( s w o l l o f s a e g a t l o v t u p t u o t e s . n o i s r e v e g a t l o v t u p t u o e l b a t s u j d a r o f t u p n i e s n e s r o t a l u g e r : ) 1 e g a p n o t i u c r i c n o i t a c i l p p a 2d n g. d n u o r g 3v r d t u p t u o e h t n i a t n i a m o t t e f s o m l e n n a h c - n n a f o e t a g e h t s e v i r d . r o t a l u g e r f o t u p t u o . d e r i s e d e g a t l o v 4n i. y l p p u s v 2 1 + 5n e s i n e n e h w f f o s n r u t r o t a l u g e r f o t u p t u o . p u l l u p l a n r e t n i h t i w l o r t n o c e l b a n e h g i h e v i t c a . w o l n e k a t ? ? ? ? ? ? + ? = 2 r 1 r 1 263 . 1 vo
6 ? 2004 semtech corp. www.semtech.com sc1548 power management 0 25 50 75 100 125 150 0 25 50 75 100 125 t j (c) i en (a) v in = 12v v en = 0v 0 100 200 300 400 500 600 700 800 900 1000 0 25 50 75 100 125 t j (c) t d(on) (ns) v in = 12v enable pin current vs. junction temperature enable delay time vs. junction temperature quiescent current vs. junction temperature start threshold vs. junction temperature enable threshold voltage vs. junction temperature enable hysteresis vs. junction temperature typical characteristics (1) 0 100 200 300 400 500 600 700 800 900 1000 0 25 50 75 100 125 t j (c) i q (a) v in = 12v, v en = 3.3v 6.0 6.5 7.0 7.5 8.0 8.5 9.0 0 25 50 75 100 125 t j (c) uvlo (v) 1.80 1.85 1.90 1.95 2.00 2.05 2.10 2.15 2.20 2.25 2.30 0 25 50 75 100 125 t j (c) v th(en) (v) v in = 12v v en rising 0 50 100 150 200 250 300 350 400 450 500 0 25 50 75 100 125 t j (c) v hyst (mv) v in = 12v v en falling
7 ? 2004 semtech corp. www.semtech.com sc1548 power management typical characteristics (cont.) (1) 0 25 50 75 100 125 150 175 200 0 25 50 75 100 125 t j (c) t d(off) (ns) v in = 12v 75 80 85 90 95 100 105 110 115 120 125 0 25 50 75 100 125 t j (c) i sns (a) v in = 12v v en = 3.3v v sns = v o(nom) 9.00 9.50 10.00 10.50 11.00 11.50 12.00 0 25 50 75 100 125 t j (c) v drv (v) v in = 12v v sns = 0v i drv = 0ma 1.790 1.795 1.800 1.805 1.810 1.815 1.820 1.825 1.830 1.835 1.840 1.845 0 25 50 75 100 125 t j (c) v o (v) v in = 12v v en = 3.3v 3.0v v pwr 3.6v 1ma i o 1a disable delay time vs. junction temperature sense pin current vs. junction temperature drive output voltage vs. junction temperature output voltage (sc1548csk-1.8) vs. junction temperature ocp trip threshold (sc1548csk-1.8) vs. junction temperature power-up output short circuit immunity vs. junction temperature 0 0.2 0.4 0.6 0.8 1 1.2 0 25 50 75 100 125 t j (c) v th(oc) (v) v in = 12v v en = 3.3v 0 1 2 3 4 5 6 7 8 9 10 0 25 50 75 100 125 t j (c) power-up short circuit immunity (ms) v in = 12v v en switched from 0v to 3.3v r out = 0 ? two representative parts shown
8 ? 2004 semtech corp. www.semtech.com sc1548 power management output short circuit glitch immunity vs. junction temperature drive pin rise time vs. junction temperature drive pin fall time vs. junction temperature sc1548csk-1.8 small signal gain and phase shift vs. frequency typical characteristics (cont.) (1) 0 1 2 3 4 5 6 7 8 0 25 50 75 100 125 t j (c) short circuit glitch immunity (ms) v in = 12v v en = 3.3v r out of 0 ? applied to output two representative parts shown 0 200 400 600 800 1000 1200 0255075100125 t j (c) t r (s) v in = 12v v en switched from 0v to 3.3v two representative parts shown sc1548csk-1.5 small signal gain and phase shift vs. frequency sc1548csk small signal gain and phase shift vs. frequency 0 100 200 300 400 500 600 700 800 900 1000 0 25 50 75 100 125 t j (c) t f (s) v in = 12v v en switched from 3.3v to 0v two representative parts shown -80 -60 -40 -20 0 20 40 60 80 1.00e+02 1.00e+03 1.00e+04 1.00e+05 1.00e+06 gain (db) f (hz) -360 -315 -270 -225 -180 -135 -90 -45 0 phase () gain phase i out = 1.8a -80 -60 -40 -20 0 20 40 60 80 1.00e+02 1.00e+03 1.00e+04 1.00e+05 1.00e+06 f (hz) gain (db) -360 -315 -270 -225 -180 -135 -90 -45 0 phase () gain phase i out = 1.8a -80 -60 -40 -20 0 20 40 60 80 1.00e+02 1.00e+03 1.00e+04 1.00e+05 1.00e+06 f (hz) gain (db) -360 -315 -270 -225 -180 -135 -90 -45 0 phase () v out = 2v i out = 1.8a gain phase
9 ? 2004 semtech corp. www.semtech.com sc1548 power management typical characteristics (cont.) (1) trace 1: v out , ac coupled, 50mv/div. trace 2: v drv , 2v/div. trace m3: load stepping from 1a to 0a timebase: 1s/div load transient response, expanded trace 1: v drv , 1v/div. trace 2: v en , 2v/div. timebase: 100ns/div t d(off) 36ns disable delay time, t d(off) load transient response trace 1: v out , ac coupled, 50mv/div. trace 2: v drv , 2v/div. trace m3: load stepping from 0a to 1a to 0a timebase: 10s/div load transient response, expanded trace 1: v out , ac coupled, 50mv/div. trace 2: v drv , 2v/div. trace m3: load stepping from 0a to 1a timebase: 1s/div
10 ? 2004 semtech corp. www.semtech.com sc1548 power management typical characteristics (cont.) (1) trace 1: v drv , 1v/div. trace 2: v en , 2v/div. timebase: 500s/div t r 1ms drive output rise time, t r trace 1: v drv , 5v/div. trace 2: v en , 2v/div. timebase: 2ms/div sc1548 enabled into a short, therefore v out < v th(oc) immediately the device is enabled. this device shuts down after 8ms. power-up output short circuit immunity drive output fall time, t f trace 1: v drv , 1v/div. trace 2: v en , 2v/div. timebase: 100ns/div t f 350ns enable delay time, t d(on) trace 1: v drv , 1v/div. trace 2: v en , 2v/div. timebase: 250ns/div t d(on) 550ns
11 ? 2004 semtech corp. www.semtech.com sc1548 power management theory of operation the sc1548 linear fet controller provides a simple way to drive an n-channel mosfet to produce a tightly regulated output voltage from an available, higher, supply voltage. it takes its power from a 12v supply, drawing typically 2ma while operating. it contains an internal bandgap reference which is compared to the output voltage via a resistor divider. this resistor divider is internal on the fixed output voltage options, and user selectable on the adjustable option. since the drive pin can pull up to a 9v guaranteed minimum, the device can be used to regulate a large range of output voltages by careful selection of the external mosfet (see component selection, below). the sc1548 includes an active high enable control with an internal pullup resistor. if this pin is pulled low, the drive pin is pulled low, turning off the n-channel mosfet. if the pin is left open or pulled up to 2.5v, 3.3v or 5v, then the drive pin will be enabled. also included is an overcurrent protection circuit that monitors the output voltage. if the output voltage drops below 50% of nominal, as would occur during an overcurrent or short condition, the device will pull the drive pin low and latch off. fixed output voltage options please refer to the application circuit on page 1. the fixed output voltage parts have an internal resistor divider that draws a nominal 100a from the output. the voltage at the common node of the resistor divider is then compared to the bandgap reference voltage of 1.263v. the drive pin voltage is then adjusted to maintain the output voltage set by the resistor divider. referring to the block diagram on page 5, the nominal resistor values are: e g a t l o v t u p t u ok ( 1 r ? ? ? ? ? )k ( 2 r ? ? ? ? ? ) v 5 1 5 . 12 5 . 23 6 . 2 1 v 8 1 8 . 15 5 . 53 6 . 2 1 typical characteristics (cont.) (1) output short circuit glitch immunity trace 1: v drv , 5v/div. trace 2: v out , 1v/div. timebase: 1ms/div sc1548 enabled, then shorted, therefore v out < v th(oc) immediately the short is applied. this device shuts down after 5ms. note: (1) see applications circuit on page 1. applications infomation
12 ? 2004 semtech corp. www.semtech.com sc1548 power management it is possible to adjust the output voltage of the fixed voltage options, by applying an external resistor divider to the sense pin (please refer to figure 1 below). since the sense pin sinks a nominal 100a, the resistor values should be selected to allow 10ma to flow through the divider. this will ensure that variations in this current do not adversely affect output voltage regulation. thus a target value for r2 (maximum) can be calculated: ? ma 10 v 2 r ) fixed ( out the output voltage can only be adjusted upwards from the fixed output voltage, and can be calculated using the following equation: volts a 100 1 r 2 r 1 r 1 v v ) fixed ( out ) adjusted ( out ? + ? ? ? ? ? ? + ? = adjustable output voltage option the adjustable output voltage option does not have an internal resistor divider. the adjust pin connects directly to the inverting input of the error amplifier, and the output voltage is set using external resistors (please refer to figure 2 above). in this case, the adjust pin sources a nominal 0.5a, so the resistor values should be selected to allow 50a to flow through the divider. again, a target value for r2 (maximum) can be calculated: ? a 50 v 263 . 1 2 r the output voltage can be calculated as follows: 1 r a 5 . 0 2 r 1 r 1 263 . 1 v out ? ? ? ? ? ? ? ? + ? = applications infomation (cont.) vout vpwr 12v in enable r1 r2 q1 c4 0.1uf + c3 22uf + c2 100uf + c1 100uf u1 sc1548csk-x.x 1 2 3 4 5 sns gnd drv in en figure 1: adjusting the output voltage of fixed output voltage options vout vpwr 12v in enable q1 c4 0.1uf + c1 100uf + c2 100uf + c3 22uf r1 r2 u1 sc1548csk 1 2 3 4 5 adj gnd drv in en figure 2: setting the output voltage of the adjustable output voltage option
13 ? 2004 semtech corp. www.semtech.com sc1548 power management please see table 1 below for recommended resistor values for some standard output voltages. all resistors are 1%, 1/10w. ) v ( t u o v( 1 r ? ? ? ? ? )( 2 r ? ? ? ? ? ) 5 . 17 . 8 10 0 1 8 . 12 . 2 40 0 1 5 . 26 . 7 90 0 1 8 . 24 2 12 0 1 0 . 30 4 12 0 1 3 . 39 6 15 0 1 table 1: recommended resistor values for sc1548 the maximum output voltage that can be obtained from the adjustable option is determined by the input supply voltage and the r ds(on) and gate threshold voltage of the external mosfet. assuming that the mosfet gate threshold voltage is sufficiently low for the output voltage chosen and a worst-case drive voltage of 9v, v out(max) is given by: ) max )( on ( ds ) max ( out ) min ( pwr ) max ( out r i v v ? ? = short circuit protection the short circuit protection feature of the sc1548 is implemented by using the r ds(on) of the mosfet. as the output current increases, the regulation loop maintains the output voltage by turning the fet on more and more. eventually, as the r ds(on) limit is reached, the mosfet will be unable to turn on any further, and the output voltage will start to fall. when the output voltage falls to approximately 50% of nominal, the ldo controller is latched off, setting output voltage to 0v. toggling the enable pin or cycling the power will reset the latch. to prevent false latching due to capacitor inrush currents or low supply rails, the current limit latch is initially disabled. it is enabled at a preset time (nominally 5ms) after both in and en rise above their lockout points. if en is left floating (using the internal resistor pullup), then v pwr should come up before v in , or the device will latch off. if the enable function is not being used, en should be tied to v pwr . to be most effective, the mosfet r ds(on) should not be selected artificially low. the mosfet should be chosen so that at maximum required current, it is almost fully turned on. if, for example, a supply of 1.5v at 4a is required from a 3.3v 5% rail, the maximum allowable r ds(on) would be: () ? ? ? ? = m 400 4 025 . 1 5 . 1 3 . 3 95 . 0 r ) max )( on ( ds to allow for temperature effects 200m ? would be a suitable room temperature maximum, allowing a peak short circuit current of approximately 15a for a short time before shutdown. capacitor selection output capacitors: low esr aluminum electrolytic or tan- talum capacitors are recommended for bulk capacitance, with ceramic bypass capacitors for decoupling high frequency transients. input capacitors: placement of low esr aluminum electrolytic or tantalum capacitors at the input to the mosfet (v pwr ) will help to hold up the power supply during fast load changes, thus improving overall transient response. the 12v supply should be bypassed with a 0.1f ceramic capacitor. layout guidelines one of the advantages of using the sc1548 to drive an external mosfet is that the bandgap reference and control circuitry do not need to be located right next to the power device, thus a very accurate output voltage can be obtained since heating effects will be minimal. the 0.1f bypass capacitor should be located close to the supply pin, and connected directly to the ground plane. the ground pin of the device should also be connected directly to the ground plane. the sense or adjust pin does not need to be close to the output voltage plane, but should be routed to avoid noisy traces if at all possible. power dissipation within the device is practically negligible, requiring no special consideration during layout. applications infomation (cont.)
14 ? 2004 semtech corp. www.semtech.com sc1548 power management outline drawing - sot-23-5 semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 contact information land pattern - sot-23-5 .110 bsc .037 bsc detail aaa c seating plane c ccc c 2x n/2 tips 2x e/2 5 see detail a1 a a2 bxn d a .008 12 n e1 e d .060 .114 .063 .118 .010 - 5 a 0.20 1.60 3.00 2.80 bsc 0.95 bsc .069 1.50 2.90 .020 0.25 1.75 0.50 - ei l (l1) c 01 0.25 plane gage h 2.80 .110 bbb c a-b d a b e 0 .008 - .004 .012 .003 (.024) .018 - .035 .000 .035 - - .045 0.10 0.20 10 0 - 10 1.15 (0.60) 0.45 .024 .009 0.30 0.08 .057 .051 .006 0.00 .90 0.90 0.22 0.60 - 0.15 1.45 1.30 - - 1.90 bsc .075 bsc dimensions "e1" and "d" do not include mold flash, protrusions datums and to be determined at datum plane or gate burrs. controlling dimensions are in millimeters (angles in degrees). notes: 1. 3. 2. -a- -b- -h- dimensions inches l1 aaa bbb ccc 01 n dim e e1 l e e1 c d a a2 b a1 min nom millimeters nom max min max side view dimensions inches y z dim g p x c millimeters p (c) z y g .043 .141 .055 (.098) .037 .024 1.40 (2.50) 0.95 0.60 1.10 3.60 x dimensions inches y z dim g p x c millimeters this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1.

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