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Original question:

BQ24640 Charge Current requirements >10A

BQ24640: BQ24640 Charge Current requirements

Solomon Kalbore
Prodigy 10 points
Part Number: BQ24640
Other Parts Discussed in Thread: BQ25640,

Hi,

I am a little bit confused with the parameter charge current, which is calculated according to the given formula in the datasheet. I would like to use this IC for charging 2 supercapacitors (45F/5.6V) rated from Visay. I have a +10V supply delivering 3A max. limit as input to my circuit. Since I would somehow use some two schottkey diodes in series for reverse protection. The supply votlage is a little bit down to 9.6-9.7V.

From the datasheet of the supercaps 196 HVC ENYCAP in Table 3 (Part. Nr: MAL219690202E3) it says, the recommeded charge current is 30-300mA and 0.5A is the maximum for both charge and discharge.

Does that mean that I have to set the charge current setting to only 0.5A max. for this supercapacitor stack. I want to charge the supercaps each to 4.8V (9.6V). which means I have almost equal to 0.98 duty cycle from my half bridge configuration.

Thank you.

  • 0
    TI__Intellectual 1910 points
    The 10V input may not provide enough head room to charger supercap upto 9.6V.
  • 0
    TI__Guru 57621 points
    Hi,

    The charge current should not exceed the max charge current specified by the super capacitors.

    The BQ25640 charger is basically a step-down DC-DC (buck) converter. It requires the input voltage to be higher than the output voltage with some headroom for normal operations. It may support 99.5% typical Maximum Effective Duty Cycle.

    It is highly recommended to get familiar with the BQ24640 charger operations by testing the BQ24640 EVM first before designing custom board.

    Thanks!
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