For trickle charging RTC
The calculator determines the working time of the supercapacitor when it is powered by the supercapacitor according to the starting and ending voltages, discharge currents and capacities of the capacitor.
- The maximum Vcap corresponds to the maximum value of the VCC, and the relevant data can be consulted, i.e. (VCC maximum) - diode voltage drop.
- The minimum Vcap is the minimum value of the working voltage of the RTC oscillator, and the relevant data can be consulted.
- The maximum value of IBAT is the maximum current of the battery, and the relevant data can be consulted.
- The typical IBAT value is the typical battery current defined at 25 C and nominal power supply voltage, and the relevant data can be consulted.
- The maximum value of VBAT is the maximum voltage of VBAT pin, and the relevant data can be consulted.
IBAT maximum and IBAT typical values are used to calculate the maximum IBAT and the working hours (hours) of typical IBAT. When calculating the working time, it is assumed that the IBAT current is kept constant without considering the voltage of the battery input pin.
When calculating the working time of linear IBAT, it is assumed that the oscillator current is proportional to the input voltage, that is, the resistance characteristic. The equivalent resistance of the circuit is calculated by the IBAT maximum and VBAT maximum provided in the data, which is used to calculate the battery backup time.
Specification table example
Recommended DC working conditions(TA= -40°C to +85°C)
| Supply voltage
| Battery voltage
| Table 1
DC electrical characteristics(TA= -40°C to +85°C)
Typical RTC Trickle Charger internal circuit
| Battery current
| Table 2
Note: Some diode selection circuits allow the selection of 1 or 2 diodes in series, while others allow the selection of 0 or 1 diodes. It is assumed that the voltage drop of each diode is 0.7V.
Typical RTC circuit with super capacitor backup power supply