DS 1302 super capacitor calculator-meixin

Original article address:

Http://china.maxim-ic.com/design/tools/calculators/product-design/supercap.cfm

The original address must be used for calculation...

Used for streaming and charging rtc

The calculator determines the working time of the super capacitor when the power is supplied Based on the starting voltage and ending voltage of the capacitor, discharge current and current capacity.

Where:

• The maximum vcap corresponds to the maximum value of VCC. For more information, see (maximum value of VCC)-(diode pressure drop)
• The minimum vcap is the minimum operating voltage of the RTC oscillator. For more information, see relevant data.
• The maximum ibat value is the maximum current of the battery. You can view the relevant data.
• The typical ibat value is a typical battery current defined at 25 °C and nominal power supply voltage. For more information, see relevant data.
• The maximum vbat voltage is the maximum voltage of the vbat pin. For more information, see relevant data.

The maximum ibat value and the typical ibat value are used to calculate the maximum ibat and the working hours (hours) of a typical ibat ). When calculating the working time, assuming that the ibat current remains constant, you do not need to consider the voltage of the battery input pin.

When calculating the working time of a linear ibat, it is assumed that the oscillator current is proportional to the input voltage, that is, the characteristic of resistance. Calculate the equivalent resistance of the circuit by using the ibat and vbat values provided in the data. This resistance is used to calculate the battery backup time.

For more information about the formula used in this calculator, see application note 3517 to estimate the super capacitor backup time of the Real-Time Streaming clock.Instance type table

Recommended DC operating conditions (TA =-40 °C to + 85 °C)

Parameters	Symbol	Condition	Minimum value	Typical values	Maximum Value	Potential
Power supply voltage	VCC		2.7	3.0	3.3	V
Battery voltage	Vbat		1.3	3.0	3.7	V
Table 1

DC electrical characteristics (TA =-40 °C to + 85 °C)

Parameters	Symbol	Condition	Minimum value	Typical values	Maximum Value	Potential
Battery current	Ibat			600	1000	Na
Table 2

Internal circuit of typical RTC cell chargerFigure 1 Note: The diode selection circuit of some devices allows the selection of 1 or 2 series diodes, and some devices can select 0 or 1 diode. Assume that the voltage drop of each diode is 0.7 V. Typical RTC circuit with super capacitor backup power supplyFigure 2