I am designing a backup system based on a supercap and an LTC4041. The calculations by the guidlines in the datasheet brought me to the folowing parameters: Capacity:2.4F Charge current: 1A charge voltage: 4.5v

As I researched this field I noticed that the capacitors ESR is important for the charge current.

How can I Know what is the maximum charge current for the supercap? (FT0H225ZF for example)


1 Answer 1


The datasheet includes a chart how to select a charging resistance based on capacitor family and capacitance.

For the FT series 2.2F capacitor you ask, the charging resistor is 51 ohms.

Which means you can't achieve your required 1A charging current.

  • \$\begingroup\$ It doesnt make sens. the LTC4041 requires a minimal charge current of 500mA (it recommends to go above it). that means that I need to have a capacitor with less than a 2Ω ESR. \$\endgroup\$
    – metsik
    Jun 27, 2021 at 9:18
  • \$\begingroup\$ Why doesn't it make sense? You found a part that doesn't fulfill requirements. That happens. So, you'd work around it: different part, or multiple parts in parallel or... Also, during a skimming of the data sheet, I can't find an entry in the table of data that suggests that minimum of 0.5 A - could you refer to a specific page or section in the data sheet? \$\endgroup\$
    – mmmm
    Jun 27, 2021 at 9:26
  • \$\begingroup\$ Yes, the capacitor does not make sense. Choose a capacitor that can handle the charging and discharging current you need. \$\endgroup\$
    – Justme
    Jun 27, 2021 at 10:02
  • \$\begingroup\$ @mmmm analog.com/media/en/technical-documentation/data-sheets/… page 17- "Programming the Supercapacitor Charge Current". this is the first time I design a system with a supercap. I have size restrictions that I tie directly to a 'small capacity' supercap (up to 2.4F). I need to conform to height of 9.6mm (stacked PCB system). what can I find a 5.5v that can be charged with a minimum of 500mA? If my questions are in place, I will edit my main question. \$\endgroup\$
    – metsik
    Jun 27, 2021 at 12:39

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