Temperature Compensation/Protection 1 Scope ! " ! " !#" $ 2 Table of Contents 1 Scope............................................................................................................................................1 2 Table of Contents .........................................................................................................................1 3 PTC compensation + NTC Overtemperature protection ................................................................2 3.1 Define PTC value ..................................................................................................................2 3.2 Define NTC value..................................................................................................................3 3.3 Conclusion.............................................................................................................................4 4 NTC based compensation example for amber LEDs .....................................................................5 4.1 Application Schematic review................................................................................................5 4.2 Calculation examples .............................................................................................................6 5 PTC based protection....................................................................................................................7 6 Compensation and Protection for the Buck-Boost Topology .........................................................8 6.1 Temperature protection ..........................................................................................................8 6.2 ‘Active’ Temperature compensation ......................................................................................8 7 Conclusions................................................................................................................................10 390111080333 Rev 001, DLM Page 1 of 10 4-Sept-08 Temperature Compensation/Protection 3 PTC compensation + NTC Overtemperature protection % % & ' ( % • • '$ VREF ROSC IREF1 PTC IREF2 MLX10803 Vbat VS/ PWM DRV GND RSENSE NTC R1 3.1 Define PTC value & ' + ) ,' / 0 • • * !. 0$/ !. ' / ' • • 2/ 3 #/ 3 % % 1 ' #4 ' 5 6 /*! & 5 5 % 8 / 0 >?@> 5 4 & 5 - /;<= A /! !. / / '7 & ' 390111080333 Rev 001, DLM ,'7 ,'7 2,# 3 / 0 9 2,# 43 #4 #4 2 - !. 2 '$ ! $ '$ 5 : 9 @> 5 $ Page 2 of 10 4-Sept-08 1 Temperature Compensation/Protection 3.2 Define NTC value @> 5/ % B ': '= C & ': '= A 4 @ ( @> 5 . $ 9 % B ' ( > > - !. A 4* % . & ' R_IREF1 4* PTC R0 = 4* 3000 Temp Coeff = 3900 = 4 * PTC ppm/C '$ B'& -D % -4 $ >' % B ' '$ R_IREF2 = NTC + R3 NTC 150000 4500 Beta 10130124 2200688 597934 194091 72745 30676 14265 7202 3898 Ohm Ohm Ohm Ohm Ohm Ohm Ohm Ohm Ohm R = R0*(1+K*(T0-T)) -40 -20 0 20 40 60 80 100 120 9192 10128 11064 12000 12936 13872 14808 15744 16680 390111080333 Rev 001, DLM Ohm Ohm Ohm Ohm Ohm Ohm Ohm Ohm Ohm Page 3 of 10 4-Sept-08 Temperature Compensation/Protection 3.3 Conclusion % % % % 0 3 / ' $ PTC Compens. + NTC protection LED Temp -40C -20C 0C T0 = 20C 40C 60C 80C 100C 120 Min (R_IREF1, R_IREF2) 9192 ohm 10128 ohm 11064 ohm ILED reduction -23% -16% -8% 12000 12936 13872 14808 7744 4440 0% 8% 16% 23% -35% -63% VREF [V] VREF [%] 0.80 VREF[V] 0.70 %Correction 0.60 0.50 ohm ohm ohm ohm ohm ohm 0.40 0.30 0.20 0.10 0.00 -40 390111080333 Rev 001, DLM -20 Page 4 of 10 0 20 40 60 80 30% 20% 10% 0% -10% -20% -30% -40% -50% -60% -70% Temp [C] 100 120 4-Sept-08 Temperature Compensation/Protection 4 NTC based compensation example for amber LEDs % 3 / '7 1 =$ & ') ' : % #4 ' #0 3 % $ 9 B ' $ 4.1 Application Schematic review VREF ROSC IREF1 R3 NTC1 R1 • • > IREF2 R2 VS/ PWM DRV GND RSENSE NTC2 >/ ! MLX10803 Vbat $ > A>/A0 ! :8> 5 E 8 / '=$ > 4 $ 4 3 - - 3 % > $ B ' % > > $ ! • % $ ( $ 390111080333 Rev 001, DLM Page 5 of 10 '7 B '/ B '/ % 4-Sept-08 Temperature Compensation/Protection 4.2 Calculation examples VREF[V] IREF2[V] 2.00 100k NTC//(R3=330k3) Compensation + 200k NTC Protection 1.80 V(VREF) 1 • • • • 1%/C Linear Fit 1.60 Min(VREF, IREF2) > A 0 !. >/ A 0 !. > A !. B ' A !. " A4/- 1.40 ' • • 1.20 1.00 0.80 0.60 0.40 • 0.20 Temp [C] 0.00 -40 -20 0 20 40 60 80 100 D > A FB ' #4 ' ': 8> 5 1 B '/ A /F !. " A4/& = 0 ' 120 VREF[V] IREF2[V] 2.00 100k NTC//(R3=220k3) Compensation + 300k NTC Protection 1.80 V(VREF) 1 • • • • 1%/C Linear Fit 1.60 #4+3 2-03 Min(VREF, IREF2) > A 0 !. >/ A 0 !. > A // !. B ' A !. " A4/- 1.40 ' • • 1.20 1.00 0.80 0.60 0.40 • 0.20 Temp [C] 0.00 -40 -20 0 20 40 60 80 100 # 3 24 3 D > A /FB ' #4 ' ' 1 B '/ A F !. " A4/& ' 120 % • • > B '/ , , % 390111080333 Rev 001, DLM $ Page 6 of 10 4-Sept-08 Temperature Compensation/Protection 5 PTC based protection @ % 7 H & ' ! B ' $ &>5 & ' " 4* G" >" 4* . 7 % ! ( & ' 7 /-' &>5 % . 8> 5 % 8 = % $ " 4* G" >"7 $ A - 8 : $ VREF PTC ROSC IREF1 R3 NTC1 R1 390111080333 Rev 001, DLM IREF2 MLX10803 Vbat VS/ PWM DRV GND RSENSE R2 Page 7 of 10 4-Sept-08 Temperature Compensation/Protection 6 Compensation and Protection for the Buck-Boost Topology 6.1 Temperature protection " !#" ! 9 I ' < " !#" C* ! % % -40 -20 0 20 40 60 80 100 120 690000 4500 46598572 10123166 2750497 892818 334627 141109 65621 33127 17929 1 // ! >?@> 5 ) !$ > B ' '$ % / ' R0 Beta # * 3 B ' A // ! 2 4* !$ ' ILED reduction Ohm Ohm Ohm Ohm Ohm Ohm Ohm Ohm Ohm -48% -73% 4* ! 8 ! %$ J '$ ( 7 % 00!. % B ' % % $ 6.2 ‘Active’ Temperature compensation ( % @> 5 ! % - $ % @> 5$ " ( % 9 % $ 390111080333 Rev 001, DLM Page 8 of 10 4-Sept-08 Temperature Compensation/Protection VREF ROSC IREF1 IREF2 R3 NTC1 R2 R1 MLX10803 Vbat VS/ PWM DRV GND RSENSE NTC2 ! " # % >/$ 5 >/ A !. 9 8> 5 A $-8$ % > 7> NTC on Voltage source • • • 200% % 180% 160% B ' $ > A 4* . > A !. B ' A 4* . " A - 140% % 120% 3,' 100% 80% / '$ NTConly NTC//R3 60% 1%/CLinear Fit 40% 20% Temp (C) • • 0% -40 -20 0 20 40 60 80 100 #0 3 2- 3 2/ ' #4 ' ' 1 1 • B ' 1 • • B ',,> 1 1 > A % $ !$ $ $ 390111080333 Rev 001, DLM Page 9 of 10 4-Sept-08 Temperature Compensation/Protection 7 Conclusions 9 ! 7 7 % ! " !#" $ 390111080333 Rev 001, DLM Page 10 of 10 4-Sept-08