Hello,
I am looking at having 3 series supercaps in my design. The caps are required for fail safe operation of the product in the event of power supply failure, hence they need to be charged quickly when power is available to limit the products start-up time (it cannot operate until the product has enough stored energy to be sure to fail safe).
The input to the product ranges from 10 to 30V. The supercaps will be charged to 7.5 volts and this is the internal voltage that the product will operate off. The supercap bank is effectively 1.667F @ 7.5V. If I charge the bank at 2A on power up the bank will take 6.3 seconds to change. In operation the product sporadically draws 500mA but mostly the current draw will be in the milliamp range. It will also draw 500mA in the fail safe mode.
The bq24640 looks like a really good solution to charge the capacitor bank. But when looking at the EVM module there is a lot of other circuitry to switch the output from the input supply voltage and the supercap backup on the input supply failure.
In my case I would prefer to run the product full time off the output of the bq24640 and charged super caps (constant 7.5V instead of the varying input). This is possible because the product will only operate once the supercaps are charged and the peak current draw is lower than the charge current.
Is this an acceptable use of the bq24640? Will I be appreciably shortening the life of the supercaps by drawing current and having the bq24640 continually topping up the voltage?
Many thanks,
Ian.
