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BQ24640: Charging Problem

Brian Wang0928
Genius 12830 points
Part Number: BQ24640

Customer design a 30V/20A charger circuit with bq24640 for special/Sport electrical Car application.

1. ISET problem (ISET pin's Voltage is not stable and goes up)

- During heavy load, the voltage at ISET pin can go up from 0.899V (no load) to 1.01V (20A load) around.

a. Customer tried to add a 0.1uF between the VR resistor, however, the problem is NOT gone!

b.  Customer tried to supply ISET pin voltage by external power supply, however the power supply voltage goes up also!

Is this normal behavior? if not so, why and how to improve it? Customer already implement bq device on the board and urgent to offer the goldern sample to end-customer. pls help on this issue.

2. Can bq24640 support up to 20A charging current?

3. The VCC pin of the bq24640 is connected to the Flyback Aux power of 30V,typ? The application input voltage is 28.5V to 32V aound, and the output voltage is designed to 29.3 around.

In the Recommandation Operating conditions, it says the SRP and SRN need to work with voltage less than 28V. So is this application suitable with bq24640?    

  Pls advice. thanks.

  • 0
    TI__Guru 51991 points
    Hi,

    1. ISET pin is to charge current. Please check the charge current instead of ISET pin voltage.
    2. The device is optimized for 10A, but it may support up to 20A with appropriate designs.
    3. Please follow the recommended operating conditions on the d/s. The charger may support super capacitor pack up to 26V. If the output voltage needs to be 29.3V, the device is not suitable.

    Thanks,

    Ning.
    Please click "This Resolved my issue" button if this post answer your question.
  • 0 in reply to Ning T
    TI__Genius 12830 points
    Hello Ning, since it's an urgent issue in customer side, we need more detailed answers from your team.

    1. Output Charge current is out of control and variation according to the ISET pin voltage during haevy load.

    In the D/S, it just says that the ISET pin is connected to the internal comparator. However, it looks there is a current source inside ISET pin which souring out a current to external cap and make the ISET voltage up. Is it possible to explain the behavior detailed? Please support this. Thanks.

    2. What're the specific designs customer need to pay attention for this 20A charge current instead of 10A?

    3. If 29.3V is a typical value, and the max voltage can be clamped below 31V by TVS or something. is it ok in application? (V,max abs =33V)

    Brian
  • 0 in reply to Brian Wang0928
    TI__Guru 51991 points
    Brian,

    1.Is 29.3V charger input voltage or output voltage?
    2.To do a 20-A design, please make sure
    1) All the components selected may handle the current and voltage for the application.
    2) All the components selected may meet the thermal requirements for the application.
    3) Please use bq246xx Calculation Tool V1.5 (Rev. D) @ www.ti.com/.../toolssoftware to calculate critical component values
    4) It is highly recommended to get familiar with the BQ24640 charger operations by testing the BQ24640 EVM first before designing custom board.

    Thanks,

    Ning.
    Please click "This Resolved my issue" button if this post answer your question.
  • 0 in reply to Ning T
    TI__Guru 51991 points
    Hi,

    We haven’t heard back from you for a while, the thread is considered solved and closed.

    Thanks!
    Please click "This Resolved my issue" button if this post answer your question.