advanced monolithic systems, inc. www.advanced-monolithic.com phone (925) 443-0722 fax (925) 443-0723 advanced ams2908 monolithic 800ma low dropout voltage regulator systems rohs compliant features applications ? three terminal adjustable or fixed voltages* ? high efficiency linear regulators 1.5v, 1.8v, 2.5v, 2.85v, 3.3v and 5.0v ? post re g ulators for switchin g supplies ? output current of 800ma ? 5v to 3.3v linear regulator ? operates down to 1v dropout ? battery chargers ? line regulation: 0.2% max. ? active scsi terminators ? load regulation: 0.4% max. ? power management for notebook ? sot-223 and to-252 package available ? battery powered instrumentation general description the ams2908 series of adjustable and fixed voltage regulator s are designed to provide 800ma output current and to operate down to 1v input-to-output differential. the dropout voltage of the device is guaranteed maximum 1.3v at maximum output current, decreasing at lower load currents. on-chip trimming adjusts the reference voltage to 1%. curre nt limit is also trimmed, minimizing the stress under overload conditions on both the regulator and power source circuitry. the ams2908 devices are pin compatible with other three-termin al regulators and are offered in the low profile surface mount sot-223 package and in the to-252 (dpak) plastic package. ordering information: package type operating junction to-252 sot-223 temperature range ams2908cd ams2908 -40 to 125 c ams2908cd-1.5 ams2908-1.5 -40 to 125 c ams2908cd-1.8 ams2908-1.8 -40 to 125 c ams2908cd-2.5 ams2908-2.5 -40 to 125 c ams2908cd-2.85 ams2908-2.85 -40 to 125 c ams2908cd-3.3 ams2908-3.3 -40 to 125 c ams2908cd-5.0 ams2908-5.0 -40 to 125 c *for additional available fixed voltages contact factory. pin connections fixed version adjustable version 1- v in 2- ground 3- v out 1 - v in 2- adjust 3- v out sot-223 top view 1 2 3 to-252 front view 1 2 3
advanced monolithic systems, inc. www.advanced-monolithic.com phone (925) 443-0722 fax (925) 443-0723 ams2908 absolute maximum ratings (note 1) power dissipation internally limited soldering information input voltage 15v lead temperature (25 sec) 265 c operating junction temperature thermal resistance control section -40 c to 125 c to-252 package ? ja = 80 c/w power transistor -40 c to 150 c sot-223 package ? ja = 90 c/w* storage temperature - 65 c to +150 c * with package soldering to copper area over backside ground plane or internal power plane ? ja can vary from 46 c/w to > 90 c/w depending on mounting technique and the size of the copper area. electrical characteristics electrical characteristics at i out = 0 ma, and t j = +25c unless otherwise specified. parameter device conditions min typ max units reference voltage (note 2) ams2908 i out = 10 ma 10ma i out 800ma, 1.5v (v in - v out ) 12v 1.238 1.225 1.250 1.250 1.262 1.270 v v output voltage (note 2) ams2908-1.5 0 i out 800ma , 4.35v v in 12v 1.485 1.476 1.500 1.500 1.515 1.524 v v ams2908-1.8 0 i out 800ma , 4.35v v in 12v 1.782 1.772 1.800 1.800 1.818 1.828 v v ams2908-2.5 0 i out 800ma , 4.35v v in 12v 2.475 2.460 2.500 2.500 2.525 2.560 v v ams2908-2.85 0 i out 800ma , 4.35v v in 12v 2.82 2.79 2.850 2.850 2.88 2.91 v v ams2908-3.3 0 i out 800ma , 4.75v v in 12v 3.267 3.235 3.300 3.300 3.333 3.365 v v ams2908-5.0 0 i out 800ma , 6.5v v in 12v 4.950 4.900 5.000 5.000 5.050 5.100 v v line regulation ams2908 i load = 10 ma , 1.5v (v in - v out ) 12v 0.015 0.035 0.2 0.2 % % ams2908-1.5 3.0v v in 12v 0.3 0.6 5 6 mv mv ams2908-1.8 3.0v v in 12v 0.3 0.6 5 6 mv mv ams2908-2.5 4.0v v in 12v 0.3 0.6 6 6 mv mv ams2908-2.85 4.35v v in 12v 0.3 0.6 6 6 mv mv ams2908-3.3 4.75v v in 12v 0.5 1.0 10 10 mv mv ams2908-5.0 6.5v v in 12v 0.5 1.0 10 10 mv mv load regulation (notes 2, 3) ams2908 (v in - v out ) =3v, 10ma i out 800ma 0.1 0.2 0.3 0.4 % % ams2908-1.5 v in = 5v, 0 i out 800ma 3 6 10 20 mv mv ams2908-1.8 v in = 5v, 0 i out 800ma 3 6 10 20 mv mv ams2908-2.5 v in = 5v, 0 i out 800ma 3 6 12 20 mv mv
advanced monolithic systems, inc. www.advanced-monolithic.com phone (925) 443-0722 fax (925) 443-0723 ams2908 electrical characteristics electrical characteristics at i out = 0 ma, and t j = +25c unless otherwise specified. parameter device conditions min typ max units load regulation (notes 2, 3) ams2908-2.85 v in = 5v, 0 i out 800ma 3 6 12 20 mv mv ams2908-3.3 v in = 5v, 0 i out 800ma 3 7 15 25 mv mv ams2908-5.0 v in = 8v, 0 i out 800ma 5 10 20 35 mv mv dropout voltage (v in - v out ) ams2908-1.5/-1.8/-2.5/- 2.85/-3.3/-5.0 ? v out , ? v ref = 1%, i out = 800ma (note 4) 1.1 1.3 v current limit ams2908-1.5/-1.8/-2.5/- 2.85/-3.3/-5.0 (v in - v out ) = 5v 900 1,100 1,500 ma minimum load current ams2908 (v in - v out ) = 12v (note 5) 5 10 ma quiescent current ams2908-1.5/-1.8/-2.5/- 2.85/-3.3/-5.0 v in 12v 5 10 ma ripple rejection ams2908 f =120hz , c out = 25 f tantalum, i out = 800ma, (v in -v out ) = 3v, c adj =25 f 60 75 db ams2908-1.5/-1.8/-2.5/- 2.85 f =120hz , c out = 25 f tantalum, i out = 800ma, v in = 6v 60 72 db ams2908-3.3 f =120hz , c out = 25 f tantalum, i out = 800ma v in = 6.3v 60 72 db ams2908-5.0 f =120hz , c out = 25 f tantalum, i out = 800ma v in = 8v 60 68 db thermal regulation ams2908 t a = 25c, 30ms pulse 0.008 0.04 %w adjust pin current ams2908 10ma i out 800ma , 1.5v (v in - v out ) 12v 55 120 a a adjust pin current change ams2908 10ma i out 800ma , 1.5v (v in - v out ) 12v 0.2 5 a temperature stability 0.5 % long term stability t a =125c, 1000hrs 0.3 1 % rms output noise (% of v out ) t a = 25c , 10hz f 10khz 0.003 % thermal resistance junction-to-case 15 c/w parameters identified with boldface type apply over the full operating temperature range. note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. for guaranteed specifications and test co nditions, see the electrical characteristics . the guaranteed specifications apply onl y for the test conditions listed. note 2: line and load regulation are guaranteed up to the maximum power dissipation of 1.2 w. power dissi pation is determined by the i nput/output differential and the output current. guaranteed maximum power dissipation will not be availabl e over the full input/output rang e. note 3: see thermal regulation specifications for cha nges in output voltage due to heating eff ects. line and load regulation are measur ed at a constant junction temperature by low duty cycle pulse testing. load regulation is measured at the output l ead ~1/8? from the package. note 4: dropout voltage is specified over the full output current range of the device. note 5: minimum load current is defined as the minimum output current required to maintain regulation. when 1.5v (v in - v out ) 12v the device is guaranteed to regulate if the output current is greater than 10ma.
advanced monolithic systems, inc. www.advanced-monolithic.com phone (925) 443-0722 fax (925) 443-0723 ams2908 application hints the ams2908 series of adjustable and fixed regulators are easy to use and are protected against shor t circuit and thermal overloads. thermal protection circuitry will shut-down the regulator should the junction temperature exceed 165 c at the sense point. pin compatible with older three terminal adjustable regulators, these devices offer the advantage of a lower dropout voltage, more precise reference tolerance and improved reference stability with temperature. stability the circuit design used in the am s2908 series requires the use of an output capacitor as part of the device frequency compensation. the addition of 150 f aluminum electrolytic or a 22 f solid tantalum on the output will ensure stability for all operating conditions. when the adjustment terminal is bypassed with a capacitor to improve the ripple rejection, the requirement for an output capacitor increases. the value of 22 f tantalum or 150 f aluminum covers all cases of by passing the adjustment terminal. without bypassing the adjustment terminal smaller capacitors can be used with equally good results. to further improve stability and transient response of these devices larger values of output capacitor can be used. protection diodes unlike older regulators, the ams2908 family does not need any protection diodes between the adju stment pin and the output and from the output to the input to prevent over-stressing the die. internal resistors are limiting the internal current paths on the ams2908 adjustment pin, therefor e even with capacitors on the adjustment pin no protection diode is needed to ensure device safety under short-circuit conditions. diodes between the input and output are not usually needed. microsecond surge currents of 50a to 100a can be handled by the internal diode between the input and output pins of the device. in normal operations it is difficult to get those values of surge currents even with the use of large output capacitances. if high value output capacitors are used, such as 1000 f to 5000 f and the input pin is instantaneously shorted to ground, damage can occur. a diode from output to input is recommended, when a crowbar circuit at the input of the ams2908 is used (figure 1). ams2908 in out adj + c out 150 f v out r 1 r 2 c adj 10 f d1 v in figure 1. output voltage the ams2908 series develops a 1. 25v reference voltage between the output and the adjust terminal. placing a resistor between these two terminals causes a constant current to flow through r1 and down through r2 to set the overall output voltage. this current is normally the specified minimum load current of 10ma. because i adj is very small and constant it represents a small error and it can usually be ignored. ams2908 in out adj r1 r2 v out v ref v in i adj 50 a v out = v ref ( 1+ r2/r1)+i adj r2 figure 2. basic adjustable regulator load regulation true remote load sensing it is not possible to provide, because the ams2908 is a three terminal devi ce. the resistance of the wire connecting the regulator to the load will limit the load regulation. the data sheet specification for load regulation is measured at the bottom of the package. negative side sensing is a true kelvin connection, with the bottom of the output divider returned to the negative side of the load. the best load regulation is obtained when the top of the resistor divider r1 is connected directly to the case not to the load. if r1 were connected to the load, the effective resistance between the regulator and the load would be: r p x ( r2+r1 ) , r p = parasitic line resistance r1
advanced monolithic systems, inc. www.advanced-monolithic.com phone (925) 443-0722 fax (925) 443-0723 ams2908 application hints connected as shown , r p is not multiplied by the divider ratio ams2908 in out adj r l r1* r2* v in r p parasitic line resistance * connect r1 to case connect r2 to load figure 3. connections fo r best load regulation in the case of fixed voltage devi ces the top of r1 is connected kelvin internally, and the ground pin can be used for negative side sensing. thermal considerations the ams2908 series have internal power and thermal limiting circuitry designed to protect the device under overload conditions. however maximum junction te mperature ratings of 125 c should not be exceeded under continuous normal load conditions. careful consideration must be gi ven to all sources of thermal resistance from junction to ambient. for the surface mount package sot-223 additional heat s ources mounted near the device must be considered. the heat dissipation capability of the pc board and its copper traces is used as a heat sink for the device. the thermal resistance from the junction to the tab for the ams2908 is 15 c/w. thermal resistance from tab to ambient can be as low as 30 c/w. the total thermal resistance from junction to ambient can be as low as 45 c/w. this requires a reasonable sized pc board with at least on layer of copper to spread the heat across the board and couple it into the surrounding air. experiments have shown that the heat spreading copper layer does not need to be electrically connected to the tab of the device. the pc material can be very effective at transmitting heat between the pad area, attached to the pad of the device, and a ground plane layer either inside or on the opposite side of the board. although the actual thermal resistance of the pc material is high, the length/area ratio of the thermal resistance between layers is small. the data in table 1, was taken using 1/16? fr-4 board with 1 oz. copper foil, and it can be used as a rough guideline for estimating thermal resistance. for each application the thermal resistance will be affected by thermal interactions with other components on the board. to determine the actual value some experimentation will be necessary. the power dissipation of the ams2908 is equal to: p d = ( v in - v out )( i out ) maximum junction temperature will be equal to: t j = t a(max) + p d (thermal resistance (junction-to-ambient)) maximum junction temperature must not exceed 125 c. ripple rejection the ripple rejection values are measured with the adjustment pin bypassed. the impedance of the adjust pin capacitor at the ripple frequency should be less than the value of r1 (normally 100 ? to 200 ? ) for a proper bypassing and ripple rejection approaching the values shown. the size of the re quired adjust pin capacitor is a function of the input ripple frequency. if r1=100 ? at 120hz the adjust pin capacitor should be > 13 f. at 10khz only 0.16 f is needed. the ripple rejection will be a function of output voltage, in circuits without an adjust pin bypass capacitor. the output ripple will increase directly as a ratio of the output voltage to the reference voltage (v out / v ref ). table 1. copper area thermal resistance top side* back side board area (junction-to-ambient) 2500 sq. mm 2500 sq. mm 2500 sq. mm 45 c/w 1000 sq. mm 2500 sq. mm 2500 sq. mm 45 c/w 225 sq. mm 2500 sq. mm 2500 sq. mm 53 c/w 100 sq. mm 2500 sq. mm 2500 sq. mm 59 c/w 1000 sq. mm 1000 sq. mm 1000 sq. mm 52 c/w 1000 sq. mm 0 1000 sq. mm 55 c/w * tab of device attached to topside copper.
advanced monolithic systems, inc. www.advanced-monolithic.com phone (925) 443-0722 fax (925) 443-0723 ams2908 typical performance characteristics minimum operating current (adjustable device) short-circuit current load regulation ripple rejection vs. current adjust pin current temperature stability 0 5 10 15 20 0 3 6 9 12 input/output differential (v) 0 5 10 15 minimum operating current (ma) input/output differential 0 0.25 0.50 0.75 1.00 1.25 short circuit current (a) -50 -25 0 25 50 75 100 125 -0.20 -0.15 -0.10 -0.05 0 0.05 0.10 temperature (c) output voltage deviation (%) 0 0.2 0.4 0.6 0.8 0 10 20 30 40 50 60 70 80 90 100 output current (a) ripple rejection (db) -50 -25 0 25 50 75 100 125 150 -2.0 -1.0 0 1.0 2.0 temperature (c) output voltage change (%) temperature (c) -50 -25 0 25 50 75 100 125 150 0 10 20 30 40 50 60 70 80 90 100 adjust pin current ( a) t j = 125c t j = 25c f ripple = 120hz f ripple = 20hz v ripple 3vp-p v ripple 0.5vp-p ? i load = 800ma v out = 5v c adj = 25 f c out = 25 f t j = 25c t j = 125c
advanced monolithic systems, inc. www.advanced-monolithic.com phone (925) 443-0722 fax (925) 443-0723 ams2908 package dimensions inches (millimeters) unless otherwise noted. to-252 plastic package (d) 0.030 (0.762) typ 0.087-0.094 (2.21-2.39) 0.018-0.023 (0.46-0.58) 0.0200.002 (0.5100.0508) 0.018-0.023 (0.46-0.58) d (d3) ams drw# 011601 0.035-0.050 (0.89-1.27) 0.035-0.045 (0.89-1.14) 0.235-0.245 (5.969-6.223) 0.156-0.204 (3.96-5.18) 0.255-0.265 (6.48-6.73) 0.206-0.214 (5.23-5.44) 0.025 (0.635) typ 7.0 0.380-0.410 (9.65-10.41) 0.045-0.060 (1.14-1.52) 3 lead sot-223 plastic package 0.130-0.146 (3.30-3.71) 0.248-0.264 (6.30-6.71) 0.116-0.124 (2.95-3.15) 0.264-0.287 (6.71-7.29) 0.090 (2.29) nom 0.071 (1.80) max 0.033-0.041 (0.84-1.04) 0.025-0.033 (0.64-0.84) 0.181 (4.60) nom 0.012 (0.31) min 0.025-0.033 (0.64-0.84) 10 max 10-16 10-16 0.010-0.014 (0.25-0.36) (sot-223 ) ams drw# 042292
|
