Super Capacitor CalculatorFor Trickle Charger RTCs
This calculator determines timekeeping operation using a super capacitor based upon starting and ending capacitor voltages, discharge current, and capacitor size.
The (Linear IBAT) Hours calculation assumes that oscillator current is directly proportional to the voltage input, i.e., resistive in nature. The IBAT Max and VBAT Max values from the data sheet are used to calculate the equivalent resistance of the circuit, which is used in the equation to calculate the backup time.
For details on the formulas used in the calculations, refer to application note 3517, Estimating Super Capacitor Backup Time on Trickle-Charger Real-Time Clocks.
Example Specification TablesRECOMMENDED DC OPERATING CONDITIONS (TA = -40°C to +85°C)
DC ELECTRICAL CHARACTERISTICS (TA = -40°C to +85°C)
Typical RTC trickle-charger internal circuit diagram
Note: Some device diode select circuits allow 1 or 2 series diodes, others allow 0 or 1. Assume 0.7V drop per diode.
Typical RTC with SuperCap on backup supply