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BQ24640: Charging Problem

Arnold KIM
Prodigy 20 points
Part Number: BQ24640
When the super capacitor charge is not intermittent, and STAT-turns on / PG-turns on even when charging is not possible.
Figure 11. Typical Application Schematic of Datasheets

Changes in the reference circuit

Input voltage (Adapter): 19V -> 12V

Output voltage (Super Capacitor): 8.1V-> 10.5V (R1: 105K-> 175K, R2: 300K-> 470K)
1. I was wondering if the input voltage is too low compared to the charging voltage, which is causing the problem.
    Is there a problem with the output voltage versus the input voltage I designed?
2. Why is it not charging intermittently?
  • 0
    TI__Mastermind 24075 points
    Hi Arnold,
    According to the equation to set output voltage regulation, with R1=175k, R2=470k, the charge regulation voltage would be set to 7.74V. If you want 10.5V charge regulation voltage you can just change R2 = 420k, R1 = 105k. I am not sure what you mean by charging intermittently? BQ24640 will charge according to the charge profile shown in figure 8. of the datasheet. When looking if input voltage is high enough, you want to focus on the SLEEP parameter mentioned in the datasheet, which describes the condition when charger will enter a low quiescent current mode if input voltage is not high enough relative to output voltage.
  • 0 in reply to Kedar Manishankar
    Prodigy 20 points

    Dear, Kedar

    charge intermittently mean sometime don,t charge.

    The voltage setting resistor I mistook.
    We are a company that manufactures and sells medical devices.
    Up to now, 2000 units have been sold with BQ24640.
    We are experiencing a problem with our recently produced products.
    1. Can you tell me how much input voltage is enough to use an output voltage of 10.5V?
    2. Can the status indicator (STAT) be in Sleep mode when it is not Sleep?