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gm431 2.5v adjustable shunt regulator gm431 v1.07 1 www.gammamicro.com.tw application switching power supplies linear regulator adjustable supplies battery-operated computers computer disk drives instrumentation logic symbol block diagram description the gm431is a three terminal adjustable shunt regulator with thermal stability guaranteed over temperature. the output voltage can be adjusted to any value between 2.5v (v ref ) and 18v by using two external resistors. the gm431 has a typical dynamic output impedance of 0.2 . active output circuitry provides a very unique turn on characteristic, making the gm431an excellent replacement for zener diodes in many applications such as on board regulation and adjustable power supplies. the gm431 is an ideal voltage reference for 3.0 to 3.3v switching power supplies. the gm431 shunt regulator is available with 3 voltage tolerances 0.5%, 1.0% and 2.0% over full temperature range and four package options (sot-23, to-92, sot-89 and so-8). features ? sink current capability 1ma to 100ma ? low dynamic out put impedance, 0.2 typ. ? low output noise ? 0.5%, 1% or 2% reference voltage tolerance ? alternate for tl431, lm431 & as431 ? temperature range -40c to + 125c ? available in sot-23, to-92, sot-89 and sop- 8 packages cathode reference anode v ref cathode anode reference
gm431 v1.07 2 gm431 2.5v adjustable shunt regulators marking information and pin configurations (top view) sot23 to92 sot89 so8 aax: marking code (see table below) rax: marking code (see table below) g: grade code (a: 0.5%, b: 1.0%, c: 2.0%) a: assembly/test site code y: year w: week code ww: week 431g ayww aaxyw 1 re f anode 2 3 cathode 431g ayww ref 1 2 anode 3 cathod e 8. ref 2 anode 3 cathode gm431g ayww 1. cathode 2. anode 3. anode 5. nc 6. anode 7. anode ref 1 4. nc raxyw 1 cathode anode 2 3 ref ( gm431r ) (gm431)
gm431 2.5v adjustable shunt regulator gm431 v1.07 3 ordering information ordering number precision device code grade package shipping gm431at92b 0.5% a to-92 1,000 units/esd bag gm431at92rl 0.5% a to-92 2,000 units/ammo pack (tape) gm431ast23r 0.5% aaa sot-23 3,000 units/tape & reel GM431RAST23R 0.5% raa sot-23 3,000 units/tape & reel gm431as8t 0.5% a so-8 100 units/tube gm431as8r 0.5% a so-8 2,500 units/tape & reel gm431ast89r 0.5% a sot-89 1,000 units/tape & reel gm431bt92b 1.0% b to-92 1,000 units/esd bag gm431bt92rl 1.0% b to-92 2,000 units/ammo pack (tape) gm431bst23r 1.0% aab sot-23 3,000 units/tape & reel gm431rbst23r 1.0% rab sot-23 3,000 units/tape & reel gm431bs8t 1.0% b so-8 100 units/tube gm431bs8r 1.0% b so-8 2,500 units/tape & reel gm431bst89r 1.0% b sot-89 1,000 units/tape & reel gm431ct92b 2.0% a to-92 1,000 units/esd bag gm431ct92rl 2.0% c to-92 2,000 units/ammo pack (tape) gm431cst23r 2.0% aac sot-23 3,000 units/tape & reel gm431rcst23r 2.0% rac so t-23 3,000 units/tape & reel gm431cs8t 2.0% c so-8 100 units/tube gm431cs8r 2.0% c so-8 2,500 units/tape & reel gm431ast89r 2.0% c sot-89 1,000 units/tape & reel
gm431 v1.07 4 gm431 2.5v adjustable shunt regulators absolute maximum ratings parameter symbol ratings units cathode voltage v ka 20 v continuous cathode current range i k -100 to 150 ma reference input current range i ref -50a to 10ma power dissipation at t a = 25 c sot-23 0.23 to-92 0.78 sot-89 0.8 so-8 p d 0.6 w package thermal resistance sot-23 336 to-92 132 sot-89 132 so-8 ja 163 c /w operating ambient temperature range t a -40 - 125 c storage temperature - 65 to 150 c lead temperature (soldering 10 sec.) 260 c recommended operating conditions parameter symbol min max units cathode voltage v ka v ref 18 v cathode current i k 10 100 ma equivalent schematics 10k 20pf 800 800 20pf 3.28k 2.4k 7.2k 4k 1k cathode reference anode
gm431 2.5v adjustable shunt regulator gm431 v1.07 5 electrical characteristics (t a = 2 5 c unless otherwise specified) parameter symbol condition min typ max unit gm431a 2.488 2.500 2.513 gm431b 2.475 2.500 2.525 reference voltage gm431c v ref v ka = v ref , i k = 10ma, test circuit 1 2.450 2.500 2.550 mv v ref deviation over temperature v ref(dev) v ka = v ref , i k = 10ma, full range test circuit 1 4 17 mv ? v ka = 10v to v ref -2.7 -1.0 ratio of change in v ref to change in v ka ? v ref / ? v ka i k = 10ma ? v ka = 18v to 10v -2 -0.4 a reference input current i ref i k = 10ma, r1 = 10k, r2 = test circuit 2 1.3 4 a i ref deviation over temperature v ref(dev) i k = 10ma, r1 = 10k, r2 = full range, test circuit 2 0.4 1.2 a minimum cathode current i k(min) v ka = v ref test circuit 1 0.4 1.0 ma off-state cathode current i k(off) v ka = 18v, v ref = 0v test circuit 3 0.1 1 a dynamic impedance |z ka | v ka = v ref , i k = 1ma to 10ma, f 1khz, test circuit 1 0.2 0.5 ? test circuits v in v in v in v ka v ka v ka i k i k i k(off) v ref v ref r1 r2 v ref i ref test circuit 1 v ka = v ref test circuit 2 v ka > v ref test circuit 3 off-state
gm431 v1.07 6 gm431 2.5v adjustable shunt regulators typical characteristics cathode voltage (v) figure 5. cathode current vs. cathode voltage cathode current (ma) 200 150 100 50 0 -50 -100 -150 -2 -1 0 1 2 3 t a ambient temperature ( ? c) figure 6. reference input current vs. ambient temperature -40 -20 0 20 40 60 80 100 120 i ref , reference input current (ma)) 0.6 0.5 0.4 0.3 0.2 0.1 0 frequency (hz) figure 7. dynamic impedance 0 100k 200k 300k 400k 500k impedance 2.5 2 1.5 1 0.5 0 600k t a ambient temperature ( ? c) figure 8. reference input voltage vs. ambient temperature -20 0 20 40 60 80 100 120 -40 2.500 2.498 2.496 2.494 2.492 2.490 2.488 v ref , reference input voltage (v) 2.486
gm431 2.5v adjustable shunt regulator gm431 v1.07 7 v ref = 2.5v typical design guide for ac-dc smps (switching mode power supply) use of shunt regulator in transformer secondary side control this example is applicable to both forward transforme rs and flyback transformers. a shunt regulator is used on the secondary side as an error amplifier, and feedback to the primary side is provided via a photo-coupler. determination of external constants for the shunt regulator dc characteristic determination: in the application circuit above, r1 and r2 are protection resistors for the light emitting diode in the photo-coupl er, and r2 is a bypass resistor to feed i k minimum, and these are determined as shown below. the photo-co upler specification should be obtained separately from the manufacturer. using the parameters in this circuit, the following formulas are obtained: v k is the gm431 operating voltage, and is set at around 3v, taking into account a margin for fluctuation. r2 is the current shunt resistance for the 1i ght emitting diode, in which a bias current i b of around 1/5 i f f1ows. next, the output voltage can be determined by r3 and r4, and the following formula is obtained: the abso1ute va1ues of r3 and r4 are determi ned by the gm431 reference input current i ref and the ac characteristics described in the next section. the i ref va1ue is around 0.7 a typ. gm384x series transformer sbd r1 r3 output v o (+) (-) r4 v ref r5 c1 r2 i f i b v f light emitting diode phototransistor gm431 figure 9. typical shunt regulator/ error amplifier v o = v ref ( r4 ) r3 + r4 r1 = i f + i b v o ? v f - v k r2 = i b v f
gm431 v1.07 8 gm431 2.5v adjustable shunt regulators g1 * f osc : pwm switching frequency g2 f1 f2 f ac gain g (db) ac characteristic determination: this refers to the determination of the gain frequency characteristic of the shunt regulator as an error amp1ifier. taking the configuration in figure 10, the error amp1ifier char acteristic is as shown in figure 10. in figure 17, the following formulas are obtained: gain g1 = g0 ? 50 db to 60 db (determined by shunt regulator) corner frequencies f 1 = 1/(2 ? pc 1 g 0 r 3 ) f 2 = 1/(2 ? pc 1 r 5 ) g 0 is the shunt regulator open-loop gain; this is given by the reciprocal of the reference voltage fluctuation: ? v ref / ? v ka , and is approximately 50 db . practical example consider the example of a photocoupler, with an internal light emitting diode v f = 1.05 v and i f = 2.5ma, power supply output vo1tage v2 = 5v, and bias resistance r2 current of approximately 1/5 i f at 0.5ma. if the shunt regulator v k = 3v, the following values are found. next, assume that r3 = r4 = 10k. this gives a 5v output. if r5 = 3.3 k, and c1 = 0.022 pf, the following values are found. g2 = 3.3k ? / 10k ? = 0.33 times (-10 db) f 1 = 1 / (2 0.022f 316 10 k) = 2.3 (hz) f 1 = 1 / (2 0.022f 3.3k) = 2.2 (khz) 2 figure 10. gm431 error amplification characteristic when r 5 = 0 when r 5 = 0 f osc frequency f (hz) g 2 = r 3 r 5 1.05v r 2 = 0.54ma = 2.1k ? r 1 = 2.5ma + 0.54ma 5v ? 1.05v ? 3v = 316 ?
gm431 2.5v adjustable shunt regulator gm431 v1.07 9 package outline dimensions ? sot 23 0.003 - 0.007 (0.08 - 0.18) 0.110 - 0.120 (2.80 - 3.04) 0.047 - 0.055 (1.20 - 1.40) (1.91) 0.075 typ. 0.083 - 0.104 (2.11 - 2.62) 0.0150 - 0.0200 (0.382 - 0.508) typ. 0.037 (0.93) 0.0005 - 0.0040 (0.025 - 0.102) 0 - 8 typ 0.013 - 0.017 (0.34 - 0.44) 0.013 - 0.017 (0.34 - 0.44) package outline dimensions ? sot 89 0.084 - 0.090 (2.13 - 2.28) (4.39 - 4.59) 8 0.155 - 0.167 (3.94 - 4.24) (2.28 - 2.59) 0.118 bsc (2.99) bsc 0.059 bsc (1.49) bsc 0.061 ref (1.550 ref) 0.035 - 0.047 (0.89 - 1.19) 0.090 - 0.102 0.016 - 0.023 (0.400 - 0.580) (0.320 - 0.520) 0.013 - 0.021 0.173 - 0.181 0.055 - 0.063 (1.39 - 1.60) 0.014 - 0.017 (0.35 - 0.43)
gm431 v1.07 10 gm431 2.5v adjustable shunt regulators package outline dimensions ? to 92 2.10 - 2.27 4.7 - 5.2 0.4 - 0.55 typ. 3.85 - 4.19 12.7 - 14.2 1.22 - 1.32 4.9 - 5.2 package outline dimensions ? so 8 (0.356 - 0.508) (0.406 - 0.270) 0.016 - 0.050 d 0.189 - 0.197 (4.800 - 5.004) seating plan 0.014 - 0.020 0.150 - 0.157 (3.810 - 3.988) 0.008 - 0.010 (0.203 - 0.254) 8.0 max 0.053 - 0.059 (1.346 - 1.753) 0.004 - 0.010 0.228 - 0.244 (5.791 - 6.198) 0.050 (1.270) typ (0.012 - 0.254) dimensions are in millimeters
gm431 2.5v adjustable shunt regulator gm431 v1.07 1 1 1 1 ordering number g m 431 a t92 r output accuracy package type shipping type apm gamma micro circuit type a: 0.5% b: 1.0% c: 2.0% t92: to-92 st23:sot-23 st89: sot-89 s8: so-8 b: bag rl: ammo pack ( t ape) t: tube r: t ape & reel ordering number g m 431r a st23 r output accuracy package type shipping type apm gamma micro circuit type a: 0.5% b: 1.0% c: 2.0% st23:sot-23 r: t ape & reel

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