? semiconductor components industries, llc, 2009 august, 2009 ? rev. 2 1 publication order number: and8391/d and8391/d thermal considerations for the on semiconductor family of discrete constant current regulators (ccr) for driving leds in automotive applications prepared by: mike sweador (ae), david helzer (pe) on semiconductor introduction the on semiconductor constant current regulator (ccr) family of devices offer outstanding regulation for leds and other current based loads, such as battery charging circuits. the ccr reduces the complexity of resistor biased designs for sensitive loads, such as led strings connected in series. the ccr can also be connected in parallel for higher load current applications. the two ? terminal ccr requires no external components to regulate at the specified current. these devices can be used wherever a constant current is needed to maintain luminosity under varying voltage conditions. see application note and8349/d for basic circuit considerations. the purpose of this paper is to explore the temperature and power boundaries for devices in the sod ? 123 and sot ? 223 packages operating from typical currents of 20 ma to 30 ma in automotive applications. the sod ? 123 devices available are rated at 20 ma, 25 ma, and 30 ma. the sot ? 223 devices are rated at 25 ma and 30 ma. see appendix a for device list. reference to datasheet the datasheet describes the devices and defines the following terms that will be used throughout this note: vak = voltage applied between the anode and cathode of the device. v overhead = v in ? v leds i reg(ss) = the current through the device supplied to the leds under steady ? state operating conditions (device on 10 sec) i reg(p) = the current through the device supplied to the leds under pulse test conditions ( 300 sec). v r = reverse voltage p d = device power dissipation, typically in mw. t a = ambient temperature in c t j = device junction temperature in c the sod ? 123 and sot ? 223 datasheet thermal characteristics table lists the thermal performance of each device as related to the heat spreader area and thickness. these datasheet tables and curves show thermal specifications and limits with the device junction temperature (t j ) operating at 150 c, the maximum allowable continuous junction temperature. operating at t j max continuously is not recommended for long term reliability. figure 1 shows power dissipation over changes in ambient temperature for the sod ? 123 package. figure 2 shows ja ( c/w) and p d (w) for various cu areas and thicknesses. these tables and graphs illustrate the effect of cu area, thickness and ambient temperature (t a ) over the range of ? 40 c to 85 c, which encompasses the area of interest for automotive led operation. led data sheets show an extreme reduction in luminosity above 85 c t a . http://onsemi.com application note
and8391/d http://onsemi.com 2 t a , ambient temperature ( c) p d , power dissipation (mw) 100 200 300 400 500 600 700 800 ? 40 ? 200 20406080 500 mm 2 2 oz 500 mm 2 1 oz 300 mm 2 2 oz 300 mm 2 1 oz 100 mm 2 2 oz 100 mm 2 1 oz figure 1. power dissipation vs. ambient temperature (sod ? 123) @ t j = 150 c for variable copper heat spreader p d max @ 85 c 500 mm 2 2 oz cu 241 mw 500 mm 2 1 oz cu 228 mw 300 mm 2 2 oz cu 189 mw 300 mm 2 1 oz cu 182 mw 100 mm 2 2 oz cu 117 mw 100 mm 2 1 oz cu 108 mw figure 2. sod ? 123 nsi14030t1g ja and p d vs. cu area 0 200 400 600 800 1000 1200 0 100 200 300 400 500 600 700 0 0.1 0.2 0.3 0.4 0.5 0.6 pcb copper area (mm 2 ) ja , ( c/w) maximum power (w) power curve 2.0 oz cu power curve 1.0 oz cu ja 1.0 oz cu ja 2.0 oz cu t a = 25 c
and8391/d http://onsemi.com 3 figure 3 shows power dissipation over changes in ambient temperature for the sot ? 223 package. figure 4 shows ja ( c/w) and p d (w) for various cu areas and thicknesses. these tables and graphs illustrate the effect of cu area, thickness and ambient temperature (t a ) over the range of ? 40 c to 85 c which encompasses the area of interest for automotive led operation. note: 300 mm 2 2 oz cu area has better thermal performance than 500 mm 2 1 oz cu for this package. 400 600 800 1000 1200 1400 1600 1800 2000 2200 ? 40 ? 200 20406080 t a , ambient temperature ( c) p d , power dissipation (mw) figure 3. power dissipation vs. ambient temperature (sot ? 223) @ t j = 150 c 500 mm 2 2 oz 500 mm 2 1 oz 300 mm 2 2 oz 300 mm 2 1 oz 100 mm 2 2 oz 100 mm 2 1 oz p d max @ 85 c 500 mm 2 2 oz cu 722 mw 300 mm 2 2 oz cu 676 mw 500 mm 2 1 oz cu 631 mw 300 mm 2 1 oz cu 598 mw 100 mm 2 2 oz cu 559 mw 100 mm 2 1 oz cu 494 mw figure 4. sot ? 223 ja and p d vs. cu area 0 20 40 60 80 100 120 140 160 180 0 100 200 300 400 500 600 700 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 copper heat spreader area (mm 2 ) ja , ( c/w) power curve 2.0 oz cu power curve 1.0 oz cu ja 1.0 oz cu ja 2.0 oz cu t a = 25 c pc board design and the use of multilayer board material will af fect the thermal performance. see on semiconductor application notes and8220/d and and8222/d for further information. ambient operating temperature (t a ) and estimated device power will help determine which package to use. figures 2 and 4 can be used to quickly determine which package and heat sink is a good candidate for the application. current regulation: pulse mode vs. steady ? state note: all curves are based upon a typical 30 ma ccr device. there are two methods of measuring current regulation: pulse mode ( ireg(p) ) testing is applicable for factory and incoming inspection of a ccr where the test times are a minimum (t 300 s). dc steady ? state (i reg(ss) ) testing is applicable for application verification where the ccr will be operational for seconds, minutes or hours. on semiconductor has correlated the difference in i reg(p) to i reg(ss) for stated board material, size, copper area and copper thickness. i reg(p) will always be greater than i reg(ss) due to the die temperature rising during i reg(ss) . this heating effect can be minimized during circuit design with the correct selection of board material, metal trace size and weight for the operating current, voltage, and board operating temperature (t a ) and package. (refer to the thermal characteristics table in datasheet).
and8391/d http://onsemi.com 4 the curves of figure 5 for the sod ? 123 and figure 6 for the sot ? 223 packages show the relationship between i reg and time. i reg decreases with time due to the effect of power on the die. 29 30 31 32 33 34 35 36 37 0 5 10 15 20 25 30 35 figure 5. typical sod ? 123 30 ma, 300 mm 2 , 1 oz cu, in still air time (s) i reg , (ma) t a = 25 c vak = 7.5 v 29 30 31 32 0 5 10 15 20 25 30 35 time (s) i reg , (ma) figure 6. typical sot ? 223 30 ma, 300 mm 2 , 2 oz cu, in still air t a = 25 c vak = 7.5 v 31.5 30.5 29.5 i reg vs. time correlation studies show that for each package steady state i reg there is a corresponding pulsed i reg value. notice on these two ? terminal devices that the sot ? 223 i reg(p) has a lower value than the sod ? 123 i reg(p) , which results in i reg(ss) of 30 ma. this is due to the better r ja of the sot ? 223. see figures 7 and 8. the slope of the line in figures 7 and 8 will change if the actual footprint and board thermal properties differ from the footprint listed in the figures. 25 26 27 28 29 30 31 32 33 34 35 30 31 32 33 34 35 36 37 38 39 40 41 42 43 i reg(p) (ma) i reg(ss) , (ma) figure 7. i reg(ss) vs. i reg(p) testing sod ? 123, 300 mm 2 , 1 oz cu, in still air t a = 25 c vak = 7.5 v 25 26 27 28 29 30 31 32 33 34 35 26 27 28 29 30 31 32 33 34 35 36 37 i reg(p) (ma) i reg(ss) , (ma) t a = 25 c vak = 7.5 v figure 8. i reg(ss) vs. i reg(p) testing sot ? 223, 300 mm 2 , 2 oz cu, in still air steady state current (i reg(ss) ) vs. vak @ 30 ma
and8391/d http://onsemi.com 5 the negative temperature coef ficient trend of a sod ? 123 ccr has a benefit as it avoids thermal runaway. there are two areas of interest on the curves of figure 9. the first is for a given t a. each curve shows a decrease in i reg(ss) as vak increases and therefore p d increases. there also is the ambient temperature af fect on i reg for a fixed vak condition. both the sod ? 123 (figure 9) and sot ? 223 (figure 10) show a decrease in i reg(ss) as t a increases. see on semiconductor application note and8223/d for additional information. sod ? 123 devices exhibit a greater negative temperature coefficient as shown in figure 9 than corresponding sot ? 223 devices as shown in figure 10, due to the difference in the package r ja . the sod ? 123 package reaches thermal saturation with less power applied than the sot ? 223 package. 24 25 26 27 28 29 30 31 32 33 34 35 36 37 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 figure 9. typical sod ? 123 30 ma, 300 mm 2 , 1 oz cu, in still air vak (v) i reg(ss) , (ma) t a = ? 40 c t a = 25 c t a = 85 c ? 0.073 ma/ c typ @ vak = 7.5 v ? 0.059 ma/ c typ @ vak = 7.5 v 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 vak (v) figure 10. typical sot ? 223 30 ma, 300 mm 2 , 2 oz cu, in still air i reg(ss) , (ma) t a = ? 40 c t a = 25 c t a = 85 c t a = 125 c ? 0.088 ma/ c typ @ vak = 7.5 v ? 0.058 ma/ c typ @ vak = 7.5 v ? 0.061 ma/ c typ @ vak = 7.5 v the following design examples will show how to determine which package device and the cu needed for a simple circuit. circuit design example 1: for a series circuit (figure 11), the power dissipation of the ccr is determined by: (v source ? (v leds + v rpd )) x i reg . using the worst case scenario; i.e, highest v source , lowest led v f , and highest target i reg . using a 16 v source (auto voltage regulator high output) driving two white leds with a vf of 4.2 v, a reverse protection diode (rpd) with a v f of 0.2 v and 30 ma i reg would give: (16 v ? (2 x 4.2 v + 0.2 v)) x 0.030 a = 7.4 v x 0.03 a = 222 mw. for an ambient temperature of 85 c, from the p d curves of figures 1 and 3 a sod ? 123 with 500 mm 2 1 oz cu would suffice. a sot ? 223 with 100 mm 2 1 oz cu would also work. example 2: three red leds with each having a v f of 2.0 vdc @ 30 ma. automotive battery voltage of 16 vdc. ambient temperature max of 85 c. available heat sink area for device is 300 mm 2 of 1 oz cu. p d of device = (16 vdc ? (3 x 2.0 vdc) + 0.2 vdc) x 30 ma = 294 mw sod ? 123 p d max @ 85 c, 300 mm 2 of 1 oz cu = 182 mw sot ? 223 p d max @ 85 c, 300 mm 2 of 1 oz cu = 598 mw the sot ? 223 gives a margin of safety in the application. or, knowing that 294 mw of power needs to be dissipated, we can select a sot ? 223 device using 100 mm 2 of 1 oz cu. 1 1 q1 nsi45030t1g d3 led 12 d4 led 12 ? dc +dc d1 mbrs140t3 reverse battery protection diode (rpd) anode cathode d2 led 2 ccr figure 11. automotive led?s (3 mm 2 ? 4 lead)
and8391/d http://onsemi.com 6 the following graphs show the relationship between i reg(ss) and t a for both the sod ? 123 and sot ? 223 for a stated cu area and thickness in still air. they also give the slope of the line which can be used to estimate t j at a specific t a. the formula for estimating t j is: t j = (p d x r ja ) + t a (r ja value from datasheet) for the sod ? 123 @ 25 c, t j = (225 mw x 360 c/w) + 25 c = 106 c (as shown on the graph). p d 260 mw est. t j 54 c p d 225 mw p d 198 mw figure 12. typical sod ? 123 30 ma, 300 mm 2 , 1 oz cu, in still air t a ( c) i reg(ss) , (ma) est. t j 106 c figure 13. typical sot ? 223 30 ma, 300 mm 2 , 2 oz cu, in still air r ja 360 c/w vak = 7.5 v t a ( c) i reg(ss) , (ma) i reg(ss) vs. t a 23 24 25 26 27 28 29 30 31 32 33 34 35 36 ? 40 ? 30 ? 20 ? 10010 20304050607080 between 25 c & 85 c ? 0.059 ma/ c est. t j 156 c 23 24 25 26 27 28 29 30 31 32 33 34 35 36 ? 40 ? 20 0 20 40 60 80 100 120 est. t j 142 c p d 174 mw r ja 96 c/w vak = 7.5 v between 25 c & 85 c ? 0.072 ma/ c est. t j 103 c p d 192 mw est. t j 47 c p d 225 mw p d 268 mw between ? 40 c & 25 c ? 0.088 ma/ c est. t j ? 14 c between ? 40 c & 25 c ? 0.073 ma/ c between 85 c & 125 c ? 0.061 ma/ c ? 30 ? 10 10 30 130 110 90 70 pwm current control the power dissipation of the ccr can be reduced when used in a pulse width modulation (pwm) controlled circuit figure 14. the dc average current will be i reg(ss) x duty cycle %. for a typical 30 ma ccr at 20% duty cycle, t a of 25 c, the average current through the leds will be 6.0 ma. figure 14. output control input lead input ccr anode ccr cathode
and8391/d http://onsemi.com 7 the device and heat sink will require analysis for worst case condition to account for 100% duty cycle. figures 15 and 16 will assist to determine the temperature rise caused by a power pulse. example: if the control input is a 500 hz, 20% duty cycle pwm applied to the three red led circuit of figure 11, the r(t) for 300 mm 2 of 1 oz cu for a sod ? 123 from figure 15 would be 90 c/w. therefore; 216 mw x 90 c/w = 19.4 c temperature rise. 0.1 1 10 100 1000 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 pulse time (s) 50% duty cycle 20% 10% 5% 2% 1% single pulse r(t) ( c/w) figure 15. sod ? 123 nsi45030t1g pcb cu area 300 mm 2 pcb cu thk 1.0 oz 0.1 1 10 100 1000 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 pulse time (s) r(t) ( c/w) figure 16. ccr sot ? 223 nsi45030zt1g pcb cu area 300 mm 2 pcb cu thk 2.0 oz 50% duty cycle 20% 10% 5% 2% single pulse 1% summary: the thermal behavior of a ccr is generalized in the following matrix: heatsink area *in general sod ? 123 for 3 v < vak < 10 v, all other variables con- stant: i reg(ss) changes < 2 ma (less @ t a > 25 c). in general sot ? 223 for 3 v < vak < 10 v, all other variables con- stant: i reg(ss) changes < 3 ma. i reg(ss) t j t a vak nc* figure 17.
and8391/d http://onsemi.com 8 appendix a sod ? 123 devices are: nsi45020t1g, steady state i reg(ss) = 20 ma 15% nsi45025t1g, steady state i reg(ss) = 25 ma 15% nsi45030t1g, steady state i reg(ss) = 30 ma 15% nsi45020at1g, steady state i reg(ss) = 20 ma 10% nsi45025at1g, steady state i reg(ss) = 25 ma 10% nsi45030at1g, steady state i reg(ss) = 30 ma 10% sot ? 223 devices are: nsi45025zt1g, steady state i reg(ss) = 25 ma 15% nsi45030zt1g, steady state i reg(ss) = 30 ma 15% nsi45025azt1g, steady state i reg(ss) = 25 ma 10% nsi45030azt1g, steady state i reg(ss) = 30 ma 10% appendix b application note title and8349/d automotive applications the use of discrete constant current regulators (ccr) for chmsl lighting and8220/d how to use thermal data found in data sheets and8222/d predicting the effect of circuit boards on semiconductor package thermal performance and8223/d predicting thermal runaway on semiconductor and are registered trademarks of semiconductor components industries, llc (scillc). scillc reserves the right to mak e changes without further notice to any products herein. scillc makes no warranty, representation or guarantee regarding the suitability of its products for an y particular purpose, nor does scillc assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including wi thout limitation special, consequential or incidental damages. ?typical? parameters which may be provided in scillc data sheets and/or specifications can and do vary in different application s and actual performance may vary over time. all operating parameters, including ?typicals? must be validated for each customer application by customer?s technical experts. scillc does not convey any license under its patent rights nor the rights of others. scillc products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the scillc product could create a sit uation where personal injury or death may occur. should buyer purchase or use scillc products for any such unintended or unauthorized application, buyer shall indemnify and hold scillc and its of ficers, employees, subsidiaries, af filiates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, direct ly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that scillc was negligent regarding the design or manufacture of the part. scillc is an equal opportunity/affirmative action employer. this literature is subject to all applicable copyright laws and is not for resale in any manner. publication ordering information n. american technical support : 800 ? 282 ? 9855 toll free usa/canada europe, middle east and africa technical support: phone: 421 33 790 2910 japan customer focus center phone: 81 ? 3 ? 5773 ? 3850 and8391/d the products described herein (nsi45020t1g, nsi45025t1g, nsi45030t1g, nsi45020at1g, ns145025a51g, nsi45030at1g, nsi45025zt1g, nsi45030zt1g, nsi45025azt1g, nsi45030azt1g) have patents pending. literature fulfillment : literature distribution center for on semiconductor p.o. box 5163, denver, colorado 80217 usa phone : 303 ? 675 ? 2175 or 800 ? 344 ? 3860 toll free usa/canada fax : 303 ? 675 ? 2176 or 800 ? 344 ? 3867 toll free usa/canada email : orderlit@onsemi.com on semiconductor website : www.onsemi.com order literature : http://www.onsemi.com/orderlit for additional information, please contact your local sales representative
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