When sizing the supercapacitors based on the load requirements and discharge circuitry, the effects of aging, voltage stress, and temperature must be considered. Based on analysis by supercapacitor suppliers, the effective capacitance must be derated significantly; Figure 3-9 shows the results of one such investigation.

Note that as temperature increases, the aging of the supercapacitors is accelerated. The voltage to which the supercapacitors are charged also affects the aging effect; reducing the voltage below the rated 2.7V extends the time for the capacitance to remain close to the initial value.

Figure 3-9 Supercapacitor Degradation Dependence on Temperature and Voltage

For automotive E-latch applications, designers must consider oversizing the capacitance to account for the degradation in effective capacitance as well as other parameters such as equivalent series resistance and self-discharge rate.