GENERAL DATA — 500 mW DO-35 GLASS  
					APPLICATION NOTE  
					Since the actual voltage available from a given zener diode  
					temperature and may be found as follows:  
					is temperature dependent, it is necessary to determine junc-  
					tiontemperatureunderanysetofoperatingconditionsinorder  
					to calculate its value. The following procedure is recom-  
					mended:  
					∆T = θ P .  
					JL JL D  
					θ
					may be determined from Figure 3 for dc power condi-  
					JL  
					tions. For worst-case design, using expected limits of I , limits  
					Z
					ofP andtheextremesofT (∆T )maybeestimated.Changes  
					D
					J
					J
					Lead Temperature, T , should be determined from:  
					L
					in voltage, V , can then be found from:  
					Z
					T = θ  
					L
					P
					LA D  
					+ T .  
					A
					∆V = θ  
					∆T .  
					J
					VZ  
					, the zener voltage temperature coefficient, is found from  
					θ
					isthelead-to-ambientthermalresistance(°C/W)andP is  
					LA  
					D
					θ
					VZ  
					Figure 2.  
					Under high power-pulse operation, the zener voltage will  
					the power dissipation. The value forθ willvaryanddepends  
					onthedevicemountingmethod.θ isgenerally30to40°C/W  
					for the various clips and tie points in common use and for  
					printed circuit board wiring.  
					LA  
					LA  
					vary with time and may also be affected significantly by the  
					zenerresistance. Forbestregulation, keepcurrentexcursions  
					as low as possible.  
					Surge limitations are given in Figure 5. They are lower than  
					would be expected by considering only junction temperature,  
					as current crowding effects cause temperatures to be ex-  
					tremely high in small spots, resulting in device degradation  
					should the limits of Figure 5 be exceeded.  
					The temperature of the lead can also be measured using a  
					thermocoupleplacedontheleadascloseaspossibletothetie  
					point. The thermal mass connected to the tie point is normally  
					large enough so that it will not significantly respond to heat  
					surges generated in the diode as a result of pulsed operation  
					once steady-state conditions are achieved. Using the mea-  
					sured value of T , the junction temperature may be deter-  
					L
					mined by:  
					T = T + ∆T .  
					JL  
					J
					L
					∆T is the increase in junction temperature above the lead  
					JL  
					Motorola TVS/Zener Device Data  
					500 mW DO-35 Glass Data Sheet  
					6-118