1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 features output current of 1.5a fast transient response 0.04% line regulation 0.2% load regulation internal thermal and current limiting adjustable or fixed output voltage(1.5v, 1.8v, 2.5v, 3.3v, 5. 0v) surface mount package to252-3ld & to-263-3ld 100% thermal limit burn-in low dropout voltage 1.5v at 1.5a output current moisture sensitivity level 3 applications battery charger adjustable power supplies constant current regulators portable instrumentation high efficiency linear power supplies high efficiency "green" computer systems smps post-regulator ordering information power pc supplies powering vga & sound card (xx=vout=1.5v, 1.8v, 2.5v, 3.3v, 5.0v, description adjustable) the lm1086 is a low dropout three terminal regulators with 1.5a output current capability. the output voltage is adjustable with the use of a resistor div ider. dropout is guaranteed at a maximum of 500 mv at maximum output current. it's low dro p out volta g e and fast transient res p onse make it ideal for low volta g e micro p rocessor applications. internal current and thermal limiting provides p rotection against any overload condition that would create excessive junction temperature. test & typical application circuit note (1) c1 needed if device is far away from filter capacitors. v ref =v out -v adj =1.25v(typ.) (2) c2 minimum value required for stability v out =v ref x(1+rf2/rf1)+i adj xrf2 i adj =55?(typ.) apr. 2009 - rev1.1 htc -1 - lm1086r-xx device name package to263-3ld LM1086RS-xx to252-3ld 1. adj/gnd 2. output 3. input 1 3 3 1 lm1086 3.3v lm1086 adj to-263 pkg to-252 pkg
1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 block diagram absoulte maximum ratins characteristic supply voltage operating junction temperature range storage temperature range thermal resistance junction to case to-263 thermal resistance junction to ambient to-263 lead temperature (soldering) 10 sec. maximum output current htc - 2 - tjc imax 1.5 vin topr tja tsol a 300 c/w symbol tstg 60 value 3 0 ~ 125 12 c/w -65~150 unit v
1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 electrical characteristics i out =100?, t a =25, unless otherwise specified min. load current(note 3) line regulation (v ref (v in )) load regulation (v ref (v out )) dropout voltage current limit i out (max) thermal regulation (v out (pwr)) output noise, rms htc - 3 - 1.78 1.8 1.82 v output voltage 0 1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 typical performance characteristics figure 1. dropout voltage vs output current figure 2. reference voltage vs temperature figure 3. load regulation vs. output current figure 4. minimum l oad current figure 5. adjust pin current vs temperature figure 6. ripple rej ection vs. frequency (fixed versions) htc - 4 -
1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 figure 9. ripple rejection vs. frequency (adjustable versions) applications information figure 10. resistor divider scheme for the adjustable version figure 11. protection diode scheme for fixed output regulators htc - 5 - lm1086-adj lm1086-xx
1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 application information the lm1086 series of adjustable and fixed regulators are easy to use and have all the protection features expected in high performance voltage regulators : shor t circuit protection and thermal shut-down. pin compatible with older three terminal adjustable regulators, these devices offer the advantage of a lower dropout voltage, more precies reference to lerance and improved reference stability with temperature. stability the circuit design used in the lm1086 series requires the use of an output capacitor as part of the device frequency compensation. the addition of 150uf aluminum electrolytic or a 22uf solid ta ntalum on the output will ensure stability for all operating conditions. when the adjustment ter minal is bypassed with a capacitor to improve the ripple rejection, the requirement for an output cap acitor increases. the value of 22uf tantalum or 150uf aluminum covers all cases of bypassing the ad justment terminal. without bypassing the adjustment terminal smaller capacitors can be use d with equally good results. to ensure good transient response with heavy load current chan ges capacitor values on the order of 100uf are used in the output of many regulators. to fu rther improve stability and transient response of these devices larger values of output capacitor can be used. protection diodes unlike older regulators, the lm1086 family does not need any protection diodies between the adjustment pin and the output and from the output tu the input to prevent over-stressing the die. internal resistors are limiting the internal current paths on the lm1086 adjustment pin, therfore 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 th e internal diode between the input and output pins of the device. in norminal 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 1000uf to 5000uf and the input pin is instantaneo usly shorted to ground, damage can occur. adiode from output to input is recommended, when a c rowbar circuit at the input of the lm1086 is used. normal power supply cycling or even plugging an d unplugging in the system will not generate current large enough to do any damage. the adjustment pin can be driven on a transient basis 25v, wi th respect to the output without any device degradation. as with any ic regulator, none the prot ection circuitry will be functional and the internal transistors will break diwn if the maximum inout t o output voltage differential is exceede d htc - 6 - lm1086
1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 ripple rejection the ripple rejection values are measured with the adjustment p in bypassed. the impedance of the adjust pin capacitor at the ripple frequency should be less tha n the value of r1 (normally 100? to 120?) for a proper bypassing and ripple rejection approachin g the values shown. the size of the required adjust pin capacitor is a function of the input ri pple frequency. if r1=100? at 120hz the adjust pin capacitor should be 25uf. at 10khz only 0.22uf i s 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 (vout/vref) output voltage the lm1086 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 throuth r2 to set the overall output voltage. this current is normally the specified minium load current of 10ma. because i adj is very small and constant it represents a small error and it can usually be ignored. load regulation true remote sheet specification it is not possible to provide, because the lm1086 is a three terminal device. 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)]/r1 , r p = parasitic line resistance connected as shown fig.3 rp is not multiplied by the divider r atio. using 16-gauge wire the parasitic line resistance is about 0.004? per foot, transllatin g to 4mv/ft at 1a load current. htc - 7 - lm1086 lm1086
1.5a l.d.o. voltage regulator (adjustable & fixed) lm1086 thermal considerations the lm1086 series have internal power and thermal limiting cir cuitry designed to protect the device under overload cinditions. however maximum junction temperature ratings should not be exceeded under continous normal load conditions. careful consideration must be given to all sourses of thermal resistance from junction to ambient, including junction-to- ase, case-to-heat sink interface and hea t sink resistance itself. to ensure safe operating temperatures and reflect more accurately the dev ice temperature, new thermal resistance specifications have been developed. unlike order reg uators with a single junction-to- case thermal resistance speccification, the data section for th ese new regulators provides a separate thermal resistance and maximum juntion temperature for both the control section and the power transistor. calculations for both temperatures under cert ain conditions of ambient temperature and heat sink resistance and to ensure that both th ermal limits are met. junction-to-case thermal resistance is specified from the ic j unction to the bottom of the case directly below the die. this is the lowest resistance 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 i s recommended. a thermarlly conductive spacer can be used, if the case of the device must b e electrically isolated, but its added contribution to thermal resistance has to be considered. htc - 8 -
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