general description the max8515a/max8515 shunt regulators simplify the design of voltage regulation and overvoltage protection (ovp) functions in high-accuracy isolated dc-to-dc con- verters with output voltages as low as 0.6v. the devices have supply voltage and feedback inputs separated from the output shunt stage, and can operate directly from the dc-to-dc converter output stage when the output voltage is 1.8v to 18v. alternately, the max8515a/max8515 input stage can be biased from an unregulated 1.7v to 28v supply, independent of dc-to-dc converter output volt- age. the max8515a/max8515 shunts 20ma when the output voltage is as low as 0.2v. the max8515a features an initial output accuracy of 0.5% at +25 c and 1% from -40 c to +85 c and provides the output voltage regulation function for isolated dc-to- dc converters. the max8515 features initial output accuracy of 1% at +25 c and 1.8% from -40 c to +85 c and can provide an output ovp function for isolated dc-to-dc converters. high open-loop bandwidth allows design of high-bandwidth dc-to-dc converters. low-cost, low-dropout linear regulators can be designed with the max8515a/max8515 and an external npn tran- sistor for cost-conscious applications that do not require overcurrent, short-circuit, or overtemperature protection. the max8515/max8515a are available in space-saving 5-pin sc70 and sot23 packages and are specified over the -40 c to +85 c extended temperature range. an eval- uation kit is available to speed designs. applications isolated dc-to-dc converters network, telecom, and cellular base station power supplies low-dropout linear regulators shunt regulator adjustable voltage reference features ? max8515a 0.6v 0.5% initial accuracy at +25? 0.6v 1% accuracy from -40? to +85? ? max8515 0.6v 1% initial accuracy at +25? 0.6v 1.8% accuracy from -40? to +85? ? sinks 20ma at 0.2v to 18v ? input voltage range from 1.7v to 28v ? directly drives optocouplers ? 0.2 dynamic output impedance ? space-saving 5-pin sc70 or sot23 packages max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters ________________________________________________________________ maxim integrated products 1 19-2528; rev 1; 2/03 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ordering information part temp range pin-package max8515a exk-t -40 c to +85 c 5 sc70-5 max8515aezk-t -40 c to +85 c 5 thin sot23-5 max8515 exk-t -40 c to +85 c 5 sc70-5 MAX8515EZK-t -40 c to +85 c 5 thin sot23-5 gnd in out 15 f b pgnd max8515a max8515 sc7o/thin sot23 top view 234 pin configuration max8515a max8515 primary sidepwm converter input supply 1.7v to 28v input 1.7v to 18v isolated dc-dcconverter output (down to 0.6v) out fb gnd pgnd in controlvoltage typical operating circuit 5 - p i n s c 7 0 2 . 0 m m x 2 . 1 m m evaluation kit available functional diagram appears at end of data sheet.selector guide appears at end of data sheet. downloaded from: http:///
max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters 2 _______________________________________________________________________________________ absolute maximum ratings stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. in to gnd ...............................................................-0.3v to +30v out to gnd ...........................................................-0.3v to +20v fb to gnd .................-0.3v to the lower of 5.5v and (v in +0.3v) pgnd to gnd .......................................................-0.3v to +0.3v continuous power dissipation (t a =+70 c) 5-pin sc70 (derate 3.1mw/ c above +70 c) ...........246.9mw 5-pin thin sot23 (derate 9.1mw/ c above +70 c) ....727mw operating temperature range ...........................-40 c to +85 c junction temperature range ............................-40 c to +150 c storage temperature range .............................-65 c to +150 c lead temperature (soldering, 10s) .................................+300 c electrical characteristics(v in = 3.3v, out = fb, i out = 5ma, t a = -40? to +85?, unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units in in voltage range v in 1.7 28 v i out = 0.3ma 0.5 1 in supply current i in v in = 2v to 28v i out = 10ma 2.5 4 ma fb max8515ae_k 0.597 0.6 0.603 t a = +25 c max8515e_k 0.594 0.6 0.606 max8515ae_k 0.595 0.6 0.605 t a = 0 c to +85 c max8515e_k 0.592 0.6 0.608 max8515ae_k 0.594 0.6 0.606 fb threshold accuracy t a = -40 c to +85 c max8515e_k 0.589 0.6 0.608 v fb load regulation i out = 1ma to 20ma 3.8 6 mv v in = 2v to 28v 0.2 1 fb line regulation v in = 1.7v to 28v 1.5 mv fb output voltage regulation v out = 0.2v to 18v, i out = 1ma 0.2 1 mv fb input bias current i fb ( bias ) v in = 28v -0.1 0.02 +0.1 ? out out voltage range v out 0.2 18 v maximum output current i out ( max ) v out = 0.2v, v in = 2v, v fb = 0.63v 20 ma t a = +25 c 0.001 0.1 output leakage current i out ( leak ) v in = 28v, v out = 18v, v fb = 0v t a = +85 c 0.03 ? dynamic output impedance z out i out = 1ma to 20ma, f <1khz 0.2 0.32 note 1: devices are production tested at t a = +25 c, limits over temperature are guaranteed by design. downloaded from: http:///
max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters _______________________________________________________________________________________ 3 fb bias current (na) -25 -20 -15 -10 -5 0 -30 fb bias current vs. temperature max8515 toc01 temperature ( c) 60 35 -15 10 -40 85 v in = 3.3v v in = 10v v in = 28v out-leakage current (na) 0 5 10 15 20 25 30 35 40 -5 out-leakage current vs. temperature max8515 toc02 temperature ( c) 60 35 -15 10 -40 85 v in = 28v v out = 18v fb = gnd 70 7045 0 -45 -90 -135 -180 -30 0.1 1 10 100 1000 gain and phase vs. frequency v out = 0.6v -10 max8515 toc03 frequency (khz) gain (db) phase (degrees) 10 30 5040 20 0 -20 60 figure 2 gain and phase vs. frequency v out = 6v max8515 toc04 frequency (khz) gain (db) 100 10 1 -20 -10 0 10 20 30 40 -30 0.1 1000 figure 2 450 -45 -90 -135 -180 90 phase (degrees) output voltage slew rate max8515 toc05 2 s/div 0.55v 0.66v v out : 2v/div v fb : 200mv/div c2 = open supply current vs. load current max8515 toc07 load current (ma) supply current (ma) 15 10 5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 02 0 v in = 28v v in = 10v v in = 3.3v power-supply rejection ratio vs. frequency max8515 toc06 frequency (hz) psrr (db) 1k 100 10 1 -70 -60 -50 -40 -30 -20 -10 0 10 -80 0.1 10k t a = +25 c t a = -40 c t a = +25 c t a = +85 c typical operating characteristics (v in = 3.3v, i out = 5ma, fb = out, circuit in figure 1, c1 = 0.1?, c2 = 1?, t a = +25 c, unless otherwise specified.) downloaded from: http:///
max8515a/max8515 detailed description the max8515a/max8515 adjustable shunt regulatorsfeature isolated supply inputs and outputs, ideal for isolat- ed power-supply applications using an optocoupler in the feedback path. the max8515a/max8515 sink 20ma with v out at 0.2v. the wide input supply range allows the device to operate from 1.7v to 28v. the max8515a/max8515 compare the fb input to a precision 600mv reference. if the fb input is low, out sinks no current. if fb rises above 600mv, out sinks up to 20ma. applications information shunt regulator/adjustable voltage reference figure 1 shows the max8515a/max8515 configured as ashunt regulator. connect fb to out for an output voltage of 0.6v. connect a 1.0? capacitor from out to gnd when the output voltage is 0.6v. a resistor-divider con-nected from out to gnd produces higher output volt- ages and allows for a smaller output capacitor. the value of the output capacitor is inversely proportional to the output voltage: set the current limit with a resistor connected from in to out. this type of shunt regulator is limited to low-current applications. the max8515a/max8515 can typically sink up to 20ma in this application. figure 2 shows the test circuits for gain and phase plots. v r1 r2 c v out out out =+ ?? ? ?? ? = ?? ? ?? ? 06 1 1 06 . . f wide-input 0.6v shunt regulators for isolated dc-to-dc converters 4 _______________________________________________________________________________________ typical operating characteristics (continued) (v in = 3.3v, i out = 5ma, fb = out, circuit in figure 1, c1 = 0.1?, c2 = 1?, t a = +25 c, unless otherwise specified.) output voltage change vs. load current max8515 toc08 load current (ma) output voltage change (%) 15 10 5 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 -0.3 02 0 output voltage change (%) 0 0.01 0.02 0.03 0.04 0.05 -0.01 output voltage change vs. input voltage max8515 toc09 input voltage (v) 23 18 81 3 32 8 pin name function 1 pgnd power ground. connect pgnd and gnd together. 2 gnd analog ground. connect gnd and pgnd together. 3 out output. connect a ceramic capacitor from out to gnd. see the applications information section. 4 in supply input. connect a 0.1? capacitor to gnd. 5 fb feedback input. regulates to 600mv. pin description downloaded from: http:///
optical feedback setting v out figure 3 displays an application circuit using themax8515a/max8515 in an opto-isolated feedback cir- cuit. the maximum bias current for the photodiode is set with r1. the isolated dc-to-dc converter compen- sation circuit is formed with r2, c3, and c4. resistors r3 and r4 set the isolated dc-to-dc converter output voltage. c1 decouples the input supply and c2 is needed to stabilize the max8515a/max8515. calculate v reg with the following equation: set r4 to 10k and calculate r3 by: for example, given a regulator output voltage of 1.8vand r4 = 10k , r3 is found to be 20k . compensation circuit a typical compensation scheme is depicted in figure 3.c3 provides an integrator function that minimizes out- put regulation error. r2 provides additional phase compensation at the zero frequency f z : the midband gain is given by:add c4 for high-frequency noise rejection. determine r2 based on the midband gain required by the isolated power supply. choose f z based on the power supply small-signal transfer function. calculate c3 once f z is known. a r = 2 r3 f z 2r 2c 3 = 1 r3 v v - out fb = ?? ? ?? ? 14 r v r3r4 reg =+ ?? ? ?? ? 06 1 . max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters _______________________________________________________________________________________ 5 figure 1. max8515a/max8515 typical application circuit,shunt regulator/adjustable voltage reference max8515a max8515 c1 0.1 f out fb gnd in v in 1.8v v out 0.6v/20mar1 = short r2 = open c21.0 f r1 r3 r2 pgnd v in (v) 3.3 1028 r3 ( ) 135470 1.33k figure 2. test circuits for gain and phase plots max8515a max8515 0.1 f out fb gnd in 3.3v 5.6v gain = test/reference network analyzer source 0.82 f ?? 50k 1k v out = 0.6v test circuit 1m 1m 2.2nf 2.2nf test pgnd max8515a max8515 0.1 f out fb gnd in 3.3v 11v gain = test/reference reference reference network analyzer source 50k 115k 1% v out = 6v test circuit 1m 0.1 f 10k 1% 90.1k 1% 1m 160k 2.2nf 2.2nf test pgnd downloaded from: http:///
max8515a/max8515 overvoltage protection figure 4 shows an isolated ovp circuit. r1 limits thecurrent supplied to the photodiode. r2 limits the max8515a/max8515 input current. r3 and r4 set the trip threshold for the ovp. c1 is the input supply decoupling capacitor. values for r3 and r4 are chosen based on the needed ovp threshold. for example, a trip threshold of 25% above the rated output voltage is needed for an ovp circuit. the values of r3 can be determined from the following equation once r4 is chosen; 10k is recom- mended for r4. then, r3 = 6.2k . where v ovp = 0.8v x 1.25 for the given example. linear regulator use an external pass transistor in conjunction with themax8515a/max8515 to create a linear regulator as shown in figure 5. determine the output voltage of the regulator by: choose r1 to maintain load regulation up to a 2a load. use the following equation: where i o_max is the rated maximum output current, which is 2a in this application circuit. v reg is the output voltage of the linear regulator. v be is the base-to-emitter forward voltage of q1, and is the minimum current gain of q1 at rated load current. v in is the minimum input volt- age at in. for the typical application circuit, v in_min = 2.375v, v reg = 1.0v, v be = 0.65v, and = 180. choose r1 = 15 for fast transient response. c1 is the input decoupling capacitor and c2 is the compensationcapacitor. use a 1?, 6.3v capacitor for this application. figure 6 shows a typical load-regulation curve for the cir- cuit in figure 5. this circuit does not provide short-circuit, overcurrent, or overtemperature protection. r1 v- v- v i in_min reg be o_max = v r2r3 reg =+ ?? ? ?? ? 06 1 .v r3 v v - ovp fb = ?? ? ?? ? 14 r wide-input 0.6v shunt regulators for isolated dc-to-dc converters 6 _______________________________________________________________________________________ figure 4. max8515a/max8515 typical application circuit,ovp circuit (set to 1v ovp threshold for 0.8v nominal output) max8515a max8515 out 0.8v dc-dc output 6v to 10v c1 0.1 f 16v fb r36.2k 1% r410k 1% r1 1.2k r2 2k gnd pgnd in feedback optocoupler figure 3. max8515a/max8515 typical application circuit,opto-feedback circuit max8515a max8515 out c1 0.1 f v reg 1.8v c20.1 f fb r3 20k 1% r4 10k 1% r1 47k r2 c3 gnd pgnd in max5003 v+ con pgnd ndrv inputsupply c4 downloaded from: http:///
chip information transistor count: 50process: bicmos max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters _______________________________________________________________________________________ 7 figure 6. load regulation of linear-regulator circuit linear-regulator load regulation load current (a) output voltage (mv) 1.5 1.0 0.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0 -3.5 0 2.0 -4.0-4.5 -5.0 v cc = 1.2v v cc = 2.5v c vcc = 220 f figure 5. max8515a/max8515 typical application circuit,linear regulator max8515a max8515 q1 fzt1049a c21.0 f c1 0.1 f out fb gnd in v cc 1.2v to 2.5v v in r26.65k r1 r310k i o 2a (max) v reg 1v v in (v) 2.53.3 5 r1 ( ) 22.140.2 82.5 max8515a max8515 out pgnd 0.6v reference fb gnd in functional diagram selector guide part initial accuracy top marks max8515aexk-t 0.6v, 0.5% feedback adx max8515aezk-t 0.6v, 0.5% feedback adrk max8515exk-t 0.6v, 1% feedback ady MAX8515EZK-t 0.6v, 1% feedback adrl downloaded from: http:///
max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters 8 _______________________________________________________________________________________ sc70, 5l.eps package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .) downloaded from: http:///
max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters _______________________________________________________________________________________ 9 thin sot23.eps package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .) downloaded from: http:///
max8515a/max8515 wide-input 0.6v shunt regulators for isolated dc-to-dc converters maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2003 maxim integrated products printed usa is a registered trademark of maxim integrated products. package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .) downloaded from: http:///
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