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1 www.semtech.com SC4250 negative voltage hot swap controller power management revision: april 6, 2005 ? programmable slew of the inrush current when used for hot insertion in the negative 24v and 48v backplane ? closed loop operation limits the maximum current even in short circuit condition ? built in timer prevents false shutdown when the closed loop operation limits the current ? sensing the drain voltage allows for immediate shutdown in short circuit conditions where current spikes and noise are ignored ? power good signal ? input uvlo and ovlo sensing ? circuit breaker and retry ? so-8 package ? central office switching ? -48v distributed power systems ? power supply hotswap & inrush control description features applications typical application circuit the SC4250 is a negative voltage hotswap controller that allows the insertion of line cards into a live backplane. the inrush current is programmable, and the closed loop operation limits the maximum current even under short circuit conditions. a built-in timing circuit prevents false shutdown. the signal from the drain voltage is fed to the timer, providing safety for the mosfet when in linear mode. the SC4250 latches off under abnormal condi- tions the power has to be recycled in order to resume operation. the device comes in two options, pwrgd (SC4250h) and pwrgd (SC4250l). these high or low signals can be directly used to enable power modules. figure 1 q1 c3 0.33 c5 150 gnd -- 48v r5 10 r1 562k r3 10.2k r4 0.01 r6 18k r2 9.31k c4 3.3nf drain 7 uv 3 vee 4 gate 6 pwrgd 1 sense 5 vcc 8 ov 2 u1 SC4250 gnd(remote) c2 0.001 c1 0.1 vee pwrgd/pwrgd /pwrgd vee
2 ? 2005 semtech corp. www.semtech.com SC4250 power management 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 c i t s i r e t c a r a h c c d e g n a r g n i t a r e p o y l p p u sv c c 0 10 8 v t n e r r u c y l p p u si c c v = v 0 , v 3 = v u e e v = e s n e s , e e 35 a m e g a t l o v p i r t r e k a e r b t i u c r i cv b c v b c v ( = e s n e s v - e e ) 0 50 60 7 v m t n e r r u c p u - l l u p n i p e t a gi u p v , n o e v i r d e t a g e t a g v = e e 0 5 -a t n e r r u c n w o d - l l u p n i p e t a gi d p n o i t i d n o c t l u a f y n a0 4a m t n e r r u c n i p e s n e si e s n e s v e s n e s v m 0 5 =5 0 . 0 -a e v i r d e t a g l a n r e t x e ? v e t a g v ( e t a g v - e e v 0 2 , ) < v d d v 0 8 93 16 1 v v ( e t a g v - e e v 0 1 , ) v d d v 0 2 8 e g a t l o v d l o h s e r h t h g i h n i p v uv h v u n o i t i s n a r t h g i h o t w o l v u 1 4 2 . 13 7 2 . 15 0 3 . 1 v e g a t l o v d l o h s e r h t w o l n i p v uv l v u n o i t i s n a r t w o l o t h g i h v u 2 9 1 . 13 2 2 . 13 5 2 . 1 v s i s r e t s y h n i p v uv y h v u 0 5 v m t n e r r u c t u p n i n i p v ui v u n i v v u v = e e 1 . 0 -a e g a t l o v d l o h s e r h t h g i h n i p v ov h v o n o i t i s n a r t h g i h o t w o l v o 2 9 1 . 13 2 2 . 13 5 2 . 1 v e g a t l o v d l o h s e r h t w o l n i p v ov l v o n o i t i s n a r t w o l o t h g i h v o 3 5 1 . 18 8 1 . 13 2 2 . 1 v s i s r e t s y h n i p v ov y h v o 5 3v m t n e r r u c t u p n i n i p v oi v o n i v v o v 5 . 15 0 . 0 -a unless specified: t a = 25c, v cc = 48v, v ee = 0v. values in bold apply over full operating temperature range. absolute maximum ratings electrical characteristics exceeding the specifications below may result in permanent damage to the device or device malfunction. operation outside of the parameters specified in the electrical characteristics section is not implied. 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 sv c c 0 0 1 o t 3 . 0 -v d g r w p / d g r w p , n i a r d 0 0 1 o t 3 . 0 -v e t a g , e s n e s 0 2 o t 3 . 0 -v v o , v u 0 6 o t 3 . 0 -v 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 a j 8 6 1c 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 c j 8 . 8 3c 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 ot j 5 2 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 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
3 ? 2005 semtech corp. www.semtech.com power management SC4250 electrical characteristics (cont.) unless specified: t a = 25c, v cc = 48v, v ee = 0v. values in bold apply over full operating temperature range. note: (1) this device is esd sensitive. use of standard esd handling precaution is required. 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 d l o h s e r h t d o o g r e w o pv g p v n i a r d v - e e n o i t i s n a r t w o l o t h g i h ,5 . 15 7 . 10 . 2v s i s e r e t s y h d l o h s e r h t d o o g r e w o pv y h g p 4 . 0v t n e r r u c s a i b t u p n i n i a r di n i a r d v n i a r d v 8 4 = 5 10 5 a e g a t l o v w o l t u p t u ov l o v , h 0 5 2 4 c s l o v - d g r w p = n i a r d v @ n i a r d i , v 5 = o a m 1 = 1v v , l 0 5 2 4 c s l o v - d g r w p = e e v @ n i a r d i , v 1 = o a m 1 = 1v e g a k a e l t u p t u oi h o v , h 0 5 2 4 c s n i a r d v - e e v , v 1 = d g r w p v 0 8 = 0 . 10 1 a v , l 0 5 2 4 c s n i a r d v - e e v 5 = 0 . 10 1 a s c i t s i r e t c a r a h c c a w o l e t a g o t h g i h v ot v o l h p 7 . 1s w o l e t a g o t w o l v ut v u l h p 5 . 1s h g i h e t a g o t w o l v ot v o h l p 5 . 5s h g i h e t a g o t w o l v ut v u h l p 5 . 6s w o l e t a g o t h g i h e s n e st e s n e s l h p 3s w o l d g r w p o t w o l n i a r d ) n i a r d - d g r w p ( o t w o l n i a r d h g i h t g p l h p 5 . 0 s h g i h d g r w p o t h g i h n i a r d ) n i a r d - d g r w p ( o t h g i h n i a r d w o l t g p h l p 5 . 0s y a l e d e m i t - e m i t n o e t a gt 1 _ n o v n i a r d t i u c r i c t r o h s r e t f a , v 8 >5s y a l e d e m i t - e m i t n o e t a gt 2 _ n o v n i a r d t i u c r i c t r o h s r e t f a , v 7 <0 5 2s
4 ? 2005 semtech corp. www.semtech.com SC4250 power management 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. r e b m u n t r a pe g a k c a p ) 1 ( r t s i h 0 5 2 4 c s 8 - o s t r t s i h 0 5 2 4 c s ) 2 ( r t s i l 0 5 2 4 c s t r t s i l 0 5 2 4 c s ) 2 ( pin configuration ordering information pin descriptions 1 2 3 4 vcc pwrgd/pwrgd top view (so-8) 5 6 7 8 drain ov gate uv sense vee n i pe m a n n i pn o i t c n u f n i p 1d g r w p / d g r w pv n e h w e l g g o t l l i w n i p s i h t . n i p t u p t u o d o o g r e w o p n i a r d v n i h t i w s i g p v f o e e n a c n i p s i h t . . l a n o i t p o s i e e v o t f 1 . 0 , e l u d o m r e w o p a f o n i p e l b a n e e h t o t y l t c e r i d d e t c e n n o c e b 2v o e g a t l o v r e v o n a , d l o h s e r h t v 3 2 2 . 1 e h t e v o b a d e l l u p s i v o n e h w . t u p n i e g a t l o v r e v o g o l a n a l l i w n i p e t a g e h t . w o l d e l l u p y l e t a i d e m m i e b l l i w n i p e t a g e h t d n a d e t c e t e d s i n o i t i d n o c . d l o h s e r h t w o l o t h g i h v 8 8 1 . 1 e h t w o l e b s p o r d v o l i t n u w o l n i a m e r 3v u n a , d l o h s e r h t v 3 2 2 . 1 e h t w o l e b d e l l u p s i v u n e h w . t u p n i e g a t l o v r e d n u g o l a n a e h t . w o l d e l l u p y l e t a i d e m m i e b l l i w n i p e t a g e h t d n a d e t c e t e d s i n o i t i d n o c e g a t l o v r e d n u o s l a s i n i p v u e h t . d l o h s e r h t 3 7 2 . 1 e h t e v o b a s e s i r v u l i t n u w o l n i a m e r l l i w n i p e t a g s i n i p v u e h t f i . n o i s r e v " f f o h c t a l " e h t n i r e k a e r b t i u c r i c c i n o r t c e l e e h t t e s e r o t d e s u d n a t e s e r s i r e k a e r b t i u c r i c e h t , r e k a e r b t i u c r i c e h t f o p i r t e h t g n i w o l l o f h g i h d n a w o l d e l c y c . r u c c o l l i w e c n e u q e s p u - r e w o p l a m r o n a 4e e v . y l p p u s r e w o p e h t f o l a i t n e t o p r e w o l e h t o t t c e n n o c . t u p n i e g a t l o v y l p p u s e v i t a g e n 5e s n e s v n e e w t e b h t a p y l p p u s e h t n i d e c a l p r o t s i s e r e s n e s a h t i w . n i p e s n e s r e k a e r b t i u c r i c e e s d e e c x e r o t s i s e r e h t s s o r c a e g a t l o v e h t n e h w p i r t l l i w r e k a e r b t i u c r i c e h t , e s n e s d n a f i . r e k a e r b t i u c r i c e h t p i r t t o n l l i w d n a t u o d e r e t l i f e r a s 2 n a h t s s e l f o s e k i p s e s i o n . v m 0 6 s i v m 5 2 y l n o , t n e r r u c g n i t a r e p o l a m r o n e h t e c i w t o t t e s s i t n e r r u c p i r t r e k a e r b t i u c r i c e h t , r e k a e r b t i u c r i c e h t e l b a s i d o t . n o i t a r e p o l a m r o n g n i r u d r o t s i s e r e s n e s e h t s s o r c a d e p p o r d v e e . r e h t e g o t d e t r o h s e b n a c e s n e s d n a 6e t a g g n i w o l l o f e h t n e h w h g i h o g l l i w n i p e t a g e h t . l e n n a h c - n l a n r e t x e r o f t u p t u o e v i r d e t a g v ( d n a w o l s i n i p v o e h t , h g i h s i n i p v u e h t : t e m e r a s n o i t i d n o c p u - t r a t s e s n e s v - e e < ) a m 0 4 a h t i w w o l d e l l u p d n a e c r u o s t n e r r u c a 0 5 a y b h g i h d e l l u p s i n i p e t a g e h t . v m 0 6 . e c r u o s t n e r r u c 7n i a r d t e f l e n n a h c - n l a n r e t x e e h t f o n i a r d e h t o t n i p s i h t t c e n n o c . t u p n i e s n e s n i a r d g o l a n a v w o l e b s i n i p n i a r d e h t n e h w . e l u d o m r e w o p e h t f o n i p ) - ( v e h t d n a g p r o d g r w p e h t , . e l g g o t l l i w n i p d g r w p 8c c v y l p p u s r e w o p e h t f o l a i t n e t o p r e h g i h e h t o t n i p s i h t t c e n n o c . t u p n i e g a t l o v y l p p u s e v i t i s o p e l u d o m r e w o p e h t f o n i p ) + ( v e h t d n a t u p n i
5 ? 2005 semtech corp. www.semtech.com power management SC4250 block diagrams active high pwrgd active low pwrgd 60mv + _ _ + _ + _ + + _ +7v delay drain gate sense vee vcc 12.5v reg 1.223v 1.75v pwrgd 50ua uv ov 60mv + _ _ + _ + _ + + _ +7v delay drain gate sense vee vcc 12.5v reg 1.223v 1.75v pwrgd 50ua uv ov
6 ? 2005 semtech corp. www.semtech.com SC4250 power management applications information insertion of a power circuit board into a live backplane would draw enormous inrush currents. this is mostly due to the charging of the bulk electrolytic capacitors at the input of the power module being plugged in. the transient currents would send glitches all over the power system and could cause corruption of the signals and even a power down if the source isn?t able to handle these high surges. this section describes the components selection needed for a typical application utilizing the SC4250. let?s assume the following requirements for a representative system: input voltage range: 36v to 72v nominal current: 2a typ. over-current condition: 5a bulk capacitance: cload = 150f the schematic in figure 2 combines internal function blocks along with the external components of the application circuit. resistors r1, r2 and r3 make up a voltage divider to set the under-voltage (uv) and over-voltage (ov) trip points. when the input power supply ramps up the uv trips at 1.273v and ov trips at 1.223v; during the ramp down transition the uv trips at 1.223v and ov trips at 1.198v. the 50mv hysteresis for uv and 25mv hysteresis for ov provide the necessary guard-bands to prevent false tripping during power up and power down conditions. as an additional noise killing and stabilizing measure, the capacitor c1 should be placed at the ov terminal with the value in range from 1,000 to 10,000pf. for the uv=38v and ov=70v the values of the resistor can be calculated as follows: vuv = 1.273v (r1+r2+r3) (r2+r3) vov = 1.223v (r1+r2+r3) r3 with the input bias current of the uv and ov comparators in the range of 20-30na, let?s choose the r1 to be 562k ? . this yields the values of r2=9.31k ? and r3 = 10.2k ? . with these values the accuracy is about 1% which is quite acceptable for those functions. figure 2 60mv + _ _ + _ + _ + + _ +7v delay q1 drain gate r4 sense vee vcc 12.5v reg 1.223v 1.75v pwrgd 50ua cloa d 150uf c3 r5 r1 r2 r3 c2 uv ov -48v +48v c 1 r6
7 ? 2005 semtech corp. www.semtech.com power management SC4250 applications information (cont.) resistor r4 sets the over-current trip. to choose r4, the user must determine the level of the current where it should trip. as a rule of thumb, the over-current is set to be 200-300% of the nominal value. in our case, we assumed this value to be 5a. considering the minimum trip voltage is 50mv the value of r4 is 50mv 5a = 10 m ? . the tolerance of this resistor is usually price driven and 5% is an adequate range of accuracy. the actual position and layout of the circuitry around the sense resistor r4 is critical to avoid a false over-current tripping. the trace routing between r4 and SC4250 should be as short as possible and wide enough to handle the maximum current with zero current in the sense lines ? ideally ?kelvin? like. additionally, there is a short delay circuit at the comparator to filter out unwanted noise and otherwise induced transients. inrush current is being controlled by the r5c3 network and swamping capacitor c2 . when a board is plugged into a live backplane, the input bulk capacitance of the board?s power supply produces large current transients due to the rush of the currents charging those capacitors. the main feature of the SC4250 is to provide an orderly and well-controlled inrush current. since the minimum trip voltage is 50mv, let?s choose the inrush current to be 3a. imax = cload ? vmax /dt dt = cload ? vmax /imax = 150f 70v / 3a = 3.5ms this would be the minimum time for the gate voltage plateau during which the vdd linearly decreases maintaining 3a charge current of the cload. the inrush can be calculated using the following equation: i max = (50 a ? c load ) / c3 with the values shown in the schematic the actual inrush current will be about 2a, which is within the limits we have chosen. resistor r5 will produce a time constant which prevents q1 from turning on when power is initially applied and the circuit is not ready to actively pull the gate low. it?s value is not critical and 18k ensures the adequate delay. the value of c2 is chosen to prevent false turn-on of the fet due to the current flowing via c3 into the gate of the fet when the circuit initially connects to the power source. capacitors c2 and c3 form a divider from vin to gnd. c2 must keep the initial voltage at the gate below vth minimum. for the typical fet, this threshold is around 1v to 2v, therefore c2 = 100 ? c3 will keep gate voltage at 0.7v, even at the ?worst? case of vin = 70v. the choice of the q1 is quite straightforward and is guided mostly by thermal considerations due to the power dissipation in the steady state. for instance, in our case, the nominal current is 2a, the power dissipation due to the conducting losses will be pdis = inom2 ? rds_on. the mosfet should be able to withstand vdss 100v with continuous drain current id 6a. device sud06n10 or similar fits this application. it has an rds_on = 0.2 ? , and will dissipate pdis = 22 ? 0.2 = 0.8w, which can be handled by this dpak device. if there is a consideration of reducing the temperature of the mosfet then the lower rds_on device should be chosen or a different style (d2pak) which has lower junction-to-ambient thermal characteristics. the r6 has a function of dumping high frequency oscillations. the value of it is not critical and can be in the range of 5 ? to 20 ? .
8 ? 2005 semtech corp. www.semtech.com SC4250 power management typical characteristics below are the snap-shots taken at start-up with different loading conditions and during the application of the over- current at the output of the circuit. for all figures, ch1: v drain ; ch2: v gate ; ch3: pwrgd; ch4: v r4 (input current) figure 3. start-up with no load. figure 4. start-up with 1a load. figure 5. start-up with ?over the limit? load. figure 6. over-current/short circuit.
9 ? 2005 semtech corp. www.semtech.com power management SC4250 typical characteristics (cont.) the following set of snapshots demonstrates effectiveness of SC4250 circuit in the case where connection to the live back plane is very ?bouncy?, which is usually the situation with manual replacements of the power cards. for all figures, ch1: v drain ; ch2: v gate ; ch3: pwrgd (referenced to v drain ); ch4: v r4 (input current) figure 7. start-up with no load. figure 8. start-up with 1a load. figure 9. start-up with ?over the limit? load. figure 10. over-current/short circuit.
10 ? 2005 semtech corp. www.semtech.com SC4250 power management evaluation board schematic figure 12 evaluation board c3 0.33 c5 150 +vout -vout gnd -- 48v r5 10 r1 562k r3 10.2k r4 0.01 r6 18k r2 9.31k c4 3.3nf drain 7 uv 3 vee 4 gate 6 pwrgd/pwrgd 1 sense 5 vcc 8 ov 2 u1 SC4250h/l gnd(remote) c2(opt) 0.01 +vin -vin on/off power module c1 0.1 c6(opt) 0.1 r7 (opt) copt 0.1 q1 irf1310 figure 11
11 ? 2005 semtech corp. www.semtech.com power management SC4250 f e ry t qr o t a n g i s e de u l a vn o i t p i r c s e dt n i r p t o o f 111 cv 0 0 1 / 1 . 0p a c c i m a r e c0 1 2 1 21 ) . t p o ( 2 c1 0 . 0p a c c i m a r e c5 0 8 0 313 c3 3 . 0p a c c i m a r e cs 6 0 2 1 414 cv 0 0 1 / 3 3 0 0 . 0p a c c i m a r e c5 0 8 0 515 cv 0 8 / 0 5 1p a c m u n i m u l ah - l a - p a c 61 ) . t p o ( 6 cv 0 0 1 / 1 . 0p a c c i m a r e c0 1 2 1 711 q0 1 3 1 f r it e f s o mk a p 2 d 811 rk 2 6 5r o t s i s e r5 0 8 0 912 rk 1 3 . 9r o t s i s e r5 0 8 0 0 113 rk 2 . 0 1r o t s i s e r5 0 8 0 1 114 r1 0 . 0r o t s i s e rs c 0 1 0 2 2 115 r0 1r o t s i s e r5 0 8 0 3 116 rk 8 1r o t s i s e r5 0 8 0 4 117 rk 1 . 5r o t s i s e rs 6 0 2 1 5 111 u0 5 2 4 c sc i h c e t m e s8 - o s evaluation board - bill of materials
12 ? 2005 semtech corp. www.semtech.com SC4250 power management outline drawing - so-8 minimum land pattern - so-8 semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 contact information 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.

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