Version 4
SHEET 1 1628 964
WIRE 624 80 624 48
WIRE 784 48 624 48
WIRE 784 64 784 48
WIRE 784 112 704 112
FLAG 784 144 0
FLAG 624 160 0
SYMBOL voltage 624 64 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 50 0 20)
SYMBOL PTC_resistor 768 48 R0
SYMATTR InstName U1
SYMATTR SpiceModel PTC_SH120
SYMATTR Value ""
TEXT -184 248 Left 0 !.SUBCKT PTC_SH120 1 2 3\n* Model of Epcos 120 degree PTC thermistor part # B59008C0120A040 http://www.epcos.com/inf/55/db/ptc_03/01770179.pdf\n* PTC is modeled by 4 temperature dependent resistors, 1 in series with a parallel combination of 3\n* terminal 1 and 2 are the thermistor leads, and terminal 3 is the actual die temperature represented as 1 volt per degree C.\n* The thermal response of the die is modeled as an RC time constant fed by a current source representing power.\n* RTH represents the die thermal resistance to ambient and CTH represents the device thermal capacity.\n.param RTH=150 TAU=2 CTH={TAU/RTH} \n* PTC is modeled by 4 temperature dependent resistors, \n* 1 (RT1) in series with a parallel combination of 3 (RT2,RT3, RT4) .\nRT1 7 6 R=exp(4.4502+V(3,0)*-0.001119) \nRT2 6 2 R=exp(-18.9784+V(3,0)*0.2164)\nRT3 6 2 R=exp(2.2403+V(3,0)*0.07727)\nRT4 6 2 R=exp(19.675+V(3,0)*-0.006416)\n* A zero volt source is in series with the thermistor network to act as a current sensor for the power model.\nVRT 1 7 0 \n* V(4) represents ambient temperature\nVAMB 4 0 {TEMP}\n* V(3,4) represents the temperature rise of the thermstor element\n* The temperature limit the highest temperature data is available for.  Actual maximum operating temperature may be less than this.\n.PARAM TLIM=250\n* The current from BTP represents the power dissipated in the die (1 volt represents 1 watt)\n* and is limited to no less than zero and no more than what will push the temperature up to TLIM through RTH.\nBTP 4 3 I=LIMIT(V(1,2)*I(VRT) , (TLIM-TEMP)/RTH , 0)\nRTH 3 4 {RTH}\nCTH 3 4 {CTH}\n.ENDS
TEXT 392 168 Left 0 !;tran 20
TEXT -144 192 Left 0 !.op
TEXT -144 160 Left 0 !.step V1 -30 30 1
TEXT -144 136 Left 0 !.step TEMP -55 250 1