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samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 1 v1.0 may 17 ,2007 general description the SM8312 is a monolithic integrated circuit that provide all the active functions for a step-down switching regulator, capable of driving a 2a load without additional transistor component. requiring a minimum number of external component, the board space can be saved easily. the external shutdown function can be controlled by ttl logic level and then come into standby mode. the internal compensation makes feedback control have good line and load regulation without external design. regarding protected function, thermal shutdown is to prevent ov er temperature operating from damage, and current limit is against over current operating of the output switch. the SM8312 operates at a switching frequency of 150khz thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. other features include a guaranteed + 4% tolerance on output voltage under specified input voltage and output load conditions, and + 15% on the oscillator frequency. the output version included fixed 3.3v, 5v, 12v, and an adjustable type. the packages are available in a standard 8-lead sop8 package and a 5-lead to-263(u). features - 3.3v, 5v, 12v and adjustable output versions - adjustable version output voltage range, 1.23v to 37v + 4% max over line and load condition - available in to220-5l and to263-5l packages - voltage mode non-synchronous pwm control - thermal-shutdown and current-limit protection - on/off shutdown control input - input voltage range up to 40v - output load current: 2a - 150khz fixed frequency internal oscillator - low power standby mode - built-in switching transistor on chip applications - simple high-efficiency step-down(buck) regulator - efficient preregulator for linear regulators - on-card switching regulators - positive to negative converter - battery charger pin assignments ( top view ) to263-5l 1 v in 5 sd 4 fb 3 gnd 2 output metal tab gnd sop-8 1 3 2 v in fb out gnd gnd gnd 8 6 7 gnd sd 4 5 pin descriptions name description v in operating voltage input output switching output gnd ground fb output voltage feedback control sd on/off shutdown
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 2 v1.0 may 17 ,2007 ordering information package s: sop 8 t:to263-5l output version SM8312 xx x x packing blank : tube a : taping -adj : adjustable -33 : 3.3v -50 : 5.0v -12 : 12v block diagram current source bias 1.235v reference 2.5v regulator 150khz osc. start up + + _ + _ thermal limit pre-driver comp comp gnd output v in sd fb 220mv 200mv 3a switch + _ _ amp comp
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 3 v1.0 may 17 ,2007 absolute maximum ratings symbol parameter rating unit v cc supply voltage +45 v v sd on/off pin input voltage -0.3 to +25 v v fb feedback pin voltage -0.3 to +25 v v out output voltage to ground -1 v p d power dissipation internally limited w t st storage temperature -65 to +150 o c t op operating temperature -40 to +125 o c v op operating voltage +4.5 to +25 v electrical characteristics (all output voltage versions) unless otherwise specified, v in =12v for 3.3v, 5v, adjustable version and v in =24v for the 12v version. i load = 0.2a symbol parameter conditions min. typ. max. unit -50 i b feedback bias current v fb =1.3v (adjustable version only) -10 -100 na 127 150 173 f osc oscillator frequency 110 173 khz fscp oscillator frequency of short circuit protect when current limit occurred and v fb <0.55v 30 70 khz 1.4 v sat saturation voltage i out =2a no outside circuit v fb =0v force driver on 1.25 1.5 v max. duty cycle(on) v fb =0v force driver on 100 dc min. duty cycle(off) v fb =12v force driver off 0 % 3.3 i cl current limit peak current no outside circuit v fb =0 force driver on 2.4 2.8 3.6 a output = 0v no outside circuit v fb =12 force driver off -200 ua i l output= -1v output leakage current v in =24v -5 -30 ma i q quiescent current v fb =12 force driver off 5 10 ma 150 i stby standby quiescent current on/off pin=5v v in =24v 70 200 ua v il low (regulator on) - 0.6 v ih on/off pin logic input threshold voltage high (regulator off) 2.0 1.3 - v i h on/off pin logic input current v logic =2.5v (off) -0.01 i l on/off pin input current v logic =0.5v (on) -0.1 -1 ua tj increasing 175 ts over temperature shutdown threshold tj decreasing 150 o c
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 4 v1.0 may 17 ,2007 electrical characteristics (continued) symbol parameter conditions typ. limit unit fb v output feedback 5v < v in < 40v 0.2a < i load < 2a v out programmed for 3v 1.235 1.193/ 1.18 1.267/ 1.28 v v min v max SM8312-adj efficiency v in = 12v, i load =2a 75 % out v output voltage 5.5v < v in < 40v 0.2a < i load < 2a 3.3 3.168/ 3.135 3.432/ 3.465 v v min v max SM8312-3.3v efficiency v in = 12v, i load =2a 75 % out v output voltage 8v < v in < 40v 0.2a < i load < 2a 5 4.8/ 4.75 5.2/ 5.25 v v min v max SM8312-5v efficiency v in = 12v, i load =2a 80 % out v output voltage 15v < v in < 40v 0.2a < i load < 2a 12 11.52/ 11.4 12.48/ 12.6 v v min v max SM8312-12v efficiency v in = 15v, i load = 2a 90 % specifications with boldface type are for full operating temperature range, the other type are for t j =25oc.
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 5 v1.0 may 17 ,2007 typical performance characteristics typical performance characteristics normalized output voltage 4. 90 4.95 5. 00 5.05 5.10 -50-25 0255075100125 output voltage change v in =20v, i load =2a normalized at t j =25 o c junction temperature( o c) junction temperature( o c) switch current limit (a) switch current limit 0.0 5.0 10.0 15.0 20.0 25.0 -50-25 025 5075100125 junction temperature( o c) supply current (ma) operating quiescent current junction temperature( o c) efficiency (%) efficiency 70 75 80 85 90 95 810152025 30 35 40 5v 3.3v 2a load 1. 2 1. 3 1. 4 1. 5 1. 6 1. 7 2.0 3 45 switch current(a) saturation vol tage (v) 1 2 3 switch saturation voltage 4.5 5.0 5.5 6.0 6.5 -50-25 0255075100125 v in =12v, v out =5v supply volotage (v) current (ua) 0.0 40.0 80.0 120.0 160.0 200.0 shutdown quiescent current 10 20 30 40 v on/off =5v 1 : -40 o c 2 : 25 o c 3 : 125 o c 1 3 2 switch on switch off 100 1 : -40 o c 2 : 25 o c 3 : 125 o c
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 6 v1.0 may 17 ,2007 typical performance characteristics (continued) 1.4 5 10 15 20 22 23 24 25 on/off pin voltage (v) current (ua) on/off pin current (sinking ) 0.0 30.0 60.0 90.0 120.0 150.0 v in =40v -40 o c t j 125 o c 0.0 1.0 2.0 3.0 4.0 5.0 -50 -25 0 25 50 75 100 125 junction temperature ( o c) su ppl y volt age (v) minimum operating supply voltage v out =1.23v i load =120ma junction temperature ( o c) threshold voltage (v) on /off threshold voltage 0.0 1.0 2.0 3.0 4.0 5.0 -50 -25 0 25 50 75 100 125 switch frequency junction temperature ( o c) frequency (khz) 0.0 17.0 34.0 51.0 68.0 -50 -25 0 25 50 75 100 125 junction temperature ( o c) bias current (na) feedback pin bias current 0.0 10.0 20.0 30.0 40.0 50.0 -50 -25 0 25 50 75 100 125 adjustable version only thermal protection 0 2 4 6 8 10 junction temperature ( 50 75 100 125 150 175 200 o c) output voltage vo(v) tsc off tsd on
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 7 v1.0 may 17 ,2007 typical application circuit a fixed type circuit 12 3 5 4 12v dc input c in capacitor fb sd d1 schottky diode vin gnd output SM8312 co capacitor inductor l1 3.3v/2a output load (b) adjustable type circuit 12 3 5 4 12v dc input c in 680uf fb d1 1n5824 vin gnd output SM8312 co 1000 uf 68uf l1 3.3v/2a output load r1 r2 vout = v fb x (1+ r1/r2 ) v fb =1.23v
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 8 v1.0 may 17 ,2007 function description pin functions +v in this is the positive input supply for the ic switching regulator. a suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator. output internal switch and power output. the voltage at this pin switches between (+v in ? v sat ) and approximately ? 0.5v, with a duty cycle of approximately v out / v in . the pc board copper area connected to this pin should be kept a minimum in order to reduc e the coupling sensitivity to the circuitry ground circuit ground. feedback complete the feedback loop by sensing the regulated output voltage on /off allows the switching regulator circuit to be shutdown using logic level signals thus dropping the total input supply current to approximately 100ua. pulling this pin below a threshold voltage of approximately 1.3v turns the regulator on, and pulling this pin above 1.3v (up to a maximum of 25v) shuts the regulator down. if this shutdown feature is not needed, the on /off pin can be wired to the ground pin or it can be left open, in either case the regulator will be in the on condition. thermal considerations the SM8312 is available in two packages, a 8-pin sop 8 and a 5-pin surface mount to-263. the sop 8 package needs a heat sink under most conditions. the size of the heat sink depends on the input voltage, the output voltage, the load current and the ambient temperature. the SM8312 junction temperature rises above ambient temperature for a 2a load and different input and output voltages. the data for these curves was taken with the SM8312 operating as a buck switching regulator in an ambient temperature of 25 o c (still air). these temperature rise numbers are all approximate and there are many factors that can affect these temperatures. higher ambient temperatures require more heat sinking. the to-263 surface mount package tab is designed to be soldered to the copper on a printed circuit board. the copper and the board are the heat sink for this package and the other heat producing components, such as the catch diode and inductor. the pc board copper area that the package is soldered to should be at least 0.8 in 2 , and ideally should have 2 or more square inches of 2 oz. additional copper area improves the thermal characteristics, but with copper areas greater than approximately 6 in 2 , only small improvements in heat dissipation are realized. if further thermal improvements are needed, double sided, multilayer pc board with large copper areas and/or airflow are recommended. function description (continued) the SM8312 (to-263 package) junction temperature rise above ambient temperature with a 2a load for various input and output voltages. this data was taken with the circuit operating as a buck switching regulator with all components mounted on a pc board to simulate the junction temperature under actual operating conditions. this curve can be used for a quick check for the approximate junction temperature for various conditions, but be aware that there are many factors that can affect the junction temperature. when load currents higher than 2a are used, double sided or multilayer pc boards with large copper areas and/or airflow might be needed, especially for high ambient temperatures and high output voltages. for the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (once exception to this is the output (switch) pin, which should not have large areas of copper.) large areas of copper prov ide the best transfer of heat (lower thermal resistance) to the surrounding air, and moving air lowers the thermal resistance even further. package thermal resistance and junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers. some of these factors include board size, shape, thickness, position, location, and even board temperature. other factors are, trace width, total printed circuit copper area, copper thickness,
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 9 v1.0 may 17 ,2007 single or double-sided, multilayer board and the amount of solder on the board. the effectiveness of the pc board to dissipate heat also depends on the size, quantity and spacing of other components on the board, as well as whether the surrounding air is still or moving. furthermore, some of these components such as the catch diode will add heat to the pc board and the heat can vary as the input voltage changes. for the inductor, depending on the physical size, type of core material and the dc resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board. marking information (1) to263-5l "04" = 2004 "03" = 2003 sm 8313fxx output type : 8313f-adj: adj 8313f-33: 3.3v 8313f-50: 5.0v 8313f-12: 12v logo id code year : ( top view ) yy ww ~ xth week : 01~52 ~ (2) sop-8l
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 10 v1.0 may 17 ,2007 package information (1) package type: sop-8l d y a a2 a1 l h e eb c dimensions in millimeters dimensions in inches symbol min. nom. max. min. nom. max. a 1.40 1.60 1.75 0.055 0.063 0.069 a1 0.10 - 0.25 0.040 - 0.100 a2 1.30 1.45 1.50 0.051 0.057 0.059 b 0.33 0.41 0.51 0.013 0.016 0.020 c 0.19 0.20 0.25 0.0075 0.008 0.010 d 4.80 4.85 5.05 0.189 0.191 0.199 e 3.80 3.91 4.00 0.150 0.154 0.157 e - 1.27 - - 0.050 - h 5.79 5.99 6.20 0.228 0.236 0.244 l 0.38 0.71 1.27 0.015 0.028 0.050 y - - 0.10 - - 0.004 0 - 8 0 - 8 package information (continued)
samhop microelectronics corp. SM8312 150khz, 2a pwm buck switching regulator 11 v1.0 may 17 ,2007 (2) package type: to263-5l a c2 c e l1 e b d l f dimensions in millimeters dimensions in inches symbol min. max. min. max. a 4.064 4.826 0.160 0.190 b 0.508 0.991 0.020 0.039 c 0.381 0.737 0.015 0.029 c2 1.143 1.651 0.045 0.065 d 8.382 9.652 0.330 0.380 e 9.652 10.668 0.380 0.420 e 1.702 bsc 0.067 bsc f 6.223 - 0.245 - l 14.605 15.875 0.575 0.625 l1 - 1.676 - 0.066

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