The TI LM4040AIZ-10.0 device model exhibits about 2.1mV/C when looking at DC operating point of the device using Iz=400uA across the span 0-50C in a temperature sweep. The TI LM4040AIZ device datasheet specifies 100ppm max across the full temperature range -40~85C and average of 20ppm with Iz <1mA. Worst case should be 1mV/C and the average should be 200uV/C. Tempco may not be addressed in the model and some default is being used or else internal tempco settings are incorrect. Any suggestions for a correction? Stability simulations are meaningless with a device that doesn't imitate real world behavior....
