1.5a low dropout positive voltage regulator september 2005 inv 426 description the ams1086m series of positive adjust able and fixed regulators are designed to pr ovide 1.5a with high efficiency. all internal circuitry is designed to operate dow n to 1.3v input to output differential. on-chip trimming adjusts the reference voltage to 1%. applications ? high efficiency linear regulators ? post regulators for switching supplies ? adjustable power supply features ? adjustable or fixed output ? output current of 1.5a ? low dropout, 1.5v max at 1.5a output current ? 0.04% line regulation ? 0.2 % load regulation ? 100% thermal limit burn-in ? fast transient response typical application data block diagram pin description 4.8v a ms1117s-3.3 ams1086m 4.95v i adj ams1086m-3.3 2 1 2 1 r i r r v v adj ref out + ? ? ? ? ? ? + = beijing estek electronics co.,ltd page 1 of 4 et- ams1086m-xx
absolute maximum ratings symbol parameter value unit v cc power dissipation internally limited w v in input voltage 15 v operation junction temperature range control section 0 to 125 t j power transistor 0 to 150 0 c t stg storage temperature range -65 to +150 0 c t lead lead temperature (soldering 10 sec) 300 0 c electrical characteristics i load = 0ma and t j = +25 0 c (unless otherwise noted) parameter device test conditions min typ max unit v in =5v, i load = 10ma 1.238 1.250 1.262 reference voltage note 1 ams1086m v in ? v out = 1.5v to 10v, i load = 10ma to 1.5a * 1.225 1.250 1.275 v v in ? v out = 1.5v, variator from nominal v out -1 - +1 output voltage note 1 all fixed versions v in ? v out = 1.5v to 10v i load = 0ma to 1.5a, variator from nominal v out * -2 - +2 % line regulation note 1 all i load = 10ma, v in ? v out = 1.5v to 10v * - 0.04 0.20 load regulation note 1 all v in ? v out = 1.5v i load = 10ma to 1.5a * - 0.2 0.40 % minimum load current ams1086m v in =5v, v adj = 0v * - 3 7 ma ground pin current all fixed versions v in ? v out = 1.5v i load = 10ma to 1.5a * - 7 10 ma adjust pin current ams1086m v in ? v out = 1.5v to 10v i load = 10ma * - 40 90 a current limit all v in ? v out = 1.5v * 1.5 2.2 - a ripple rejection note 2 all v in ? v out = 3v i load = 1.5a * 60 65 - db dropout voltage note 1,3 all i load = 1.5a * - 1.3 1.5 v temperature coefficient all v in ? v out = 1.5v, i load = 10ma * - 0.005 - %/ 0 c the * denotes the specifications which apply over the full temperat ure range (see previous table, t j ) notes: 1: low duty pulse testing with kelvin connections required. 2: 120hz input ripple (c adj for adj = 25f, c out = 25f) 3: ? v out , ? v ref = 1% beijing estek electronics co.,ltd page 2 of 4 et- ams1086m-xx
application information the ams1086m series of adj ustable and fixed regulators are easy to use and have all the protection features expected in high performance voltage regulators: short circuit protection and thermal shut-down. pin compatible with older three terminal adjustable regulators, these devices o ffer the advantage of a lower dropout voltage, more precis e reference tolerance and improved reference stabilit y with temperature. stability the circuit design used in the ams1086m series requires the use of an output capacitor as part of the device frequency compensation. the addition of 150f aluminum electrolytic or a 22f solid tantalum on the output will ensur e stability for all operating conditions. when the adjustment terminal is bypassed with a capacitor to improve the rippl e rejection, the requirement for an output capacitor incr eases. the value of 22f tantalum or 150f aluminum covers all cases of bypassing the adjustment termi nal. without bypassing the adjustment terminal smaller capacitors can be used with equally good results. to ensure good transient response with heavy load current changes capacitor va lues on the order of 100f are used in the output of m any regulators. to further improve stability and transient response of these devices larger values of output capacitor can be used. protection diodes unlike older regulators, t he ams1086m family does not need any protection diodes bet ween the adjustment 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 ams1086m adjustment pi n, therefore 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 1000f to 5000f 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 t he input of the ams1086m is used. normal power supply cycling or even plugging and unplugging in the system will not generate current large enough to do any damage. the adjustment pin can be dr iven on a transient basis 25v, with respect to t he output without any device degradation. as with any ic regulator, none the protection circuitry will be functional and the internal transistors will break down if the maximu m input to output voltage differential is exceeded. ripple rejection the ripple rejection values are measured with the adjustment pin bypassed. the impedance of the adjust pin capacitor at the rippl e frequency should be less than the value of r1 (normally 100 ? to 120 ? ) for a proper bypassing and ripple rejection approaching the values shown. the size of the requi red adjust pin capacitor of the input ripple frequency. if r1=100 ? at 120hz the adjust pin capacitor should be 25f. at 10khz only 0.22f is needed. the ripple rejection will be a f unction of output voltage, in circuits without an adjust pin bypass capacitor. the output ripple will increase direct ly as a ratio of the output voltage to the reference voltage (v out / v ref ). ams1086m beijing estek electronics co.,ltd page 3 of 4 et- ams1086m-xx
output voltage the ams1086m 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 7ma. because i adj is very small and constant it represents a small error and it can usually be ignored. load regulation true remote load sensing it is not possible to provide, because the ams1086m is a th ree terminal device. the resistance of the wire connecti ng the regulator to the load will limit the load regulation. the data sheet specificati on for load regulation is measured at the bottom of the package. negative side sensing is a true kelvin connec tion, with the bottom of the output divider returned to t he 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 regulat or and the load would be: connected as shown above, r p is not multiplied by the divider ratio. using 16-gauge wire the parasitic line resistance is about 0.004 ? per foot, translating to 4mv/ft at 1a load current. it is impor tant to keep the positive lead between regulator and load as short as possible and use large wire or pc board traces. thermal considerations the ams1086m series have internal power and thermal limiting circuitry designed to protect the device under overload conditions. however maximum junction temperature ratings s hould not be exceeded under continuous normal load conditions. careful consideration must be given to all sources of thermal resistance from junction to ambient, including junction-to-case, case-to-heat sink interface and heat sink resistance itself. to ensure safe operating temperatures and reflect more accurately the device temperature, new thermal resistance specif ications have been developed. unlike older regulators with a single junction-to-case thermal resistance specificat ion, the data section for these new regulators prov ides a separate thermal resistance and maximum junction temperature for both the control section and t he power transistor. calculations for both te mperatures under certain conditions of ambient te mperature and heat sink resistance and to ensure that both thermal limits are met. junction-to-case thermal resist ance is specified from the ic junction to the bottom of the case directly below the die. this is the lowest resi stance path for the heat flow. in order to ensure the best possible thermal flow from this area of the package to the heat sink proper mounting is required. thermal compound at the case-to-heat sink interface is recommended. a t hermally conductive spacer can be used, if the case of t he device must be electrically isolated, but its added contribut ion to thermal resistance has to be considered. ams1086m ams1086m beijing estek electronics co.,ltd page 4 of 4 et- ams1086m-xx
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