• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 38 subscribers
  • Views 399 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

WEBENCH® Tools/BQ24650EVM-639: Charge current inquiry

KIM RAEHYEON
Prodigy 40 points

Part Number: BQ24650EVM-639
Other Parts Discussed in Thread: BQ24650

Tool/software: WEBENCH® Design Tools

I have a question during the bq24650evm-639 exam.
1. The datasheet says that if the mppset pin voltage is below 1.2v, the charging current decreases to maintain the charging state.
2. The mppset power of bq24650evm is 17.8V.
3. We change the input voltage with the power supply and proceed with the charging test.
4. When the input voltage becomes 17.8V or less, the mppset voltage becomes 1.2V or less, so the charging current must be reduced, but the charging is cut off and then charged again when the input voltage is raised to 17.8V or more.

Questions
-Please tell me how to keep the charging state by decreasing the charging current when the mppset voltage falls below 1.2V

DASHEET(BQ24650)

8.3.2 Input Voltage Regulation A solar panel has a unique point on the V-I or V-P curve, called the Maximum Power Point (MPP), at which the entire photovoltaic (PV) system operates with maximum efficiency and produces its maximum output power. The constant voltage algorithm is the simplest Maximum Power Point Tracking (MPPT) method. The BQ24650 automatically reduces charge current so the maximum power point is maintained for maximum efficiency. If the solar panel or other input source cannot provide the total power of the system and BQ24650 charger, the input voltage drops. When the voltage sensed on the MPPSET pin drops below 1.2 V, the charger maintains the input voltage by reducing the charge current. If the MPPSET pin voltage is forced below 1.2 V, the BQ24650 stays in the input voltage regulation loop while the output current is zero. The STAT1 pin is LOW and STAT2 pin is HIGH.

  • 0
    TI__Mastermind 24075 points

    Hi Kim,

         The MPPSET pin is to regulate current, so that the load on the input supply is reduced. In regulating the charge current, the input voltage sag is reduced so that the IC can maintain the input voltage at the MPPSET setpoint.

    You are forcing the input voltage below the MPPSET point, so no matter how much the charger tries to regulate the charge current it cannot decrease the load on the input supply such that the voltage is regulated at the MPPSET point, so it crashes.

    Example: For 17.8V MPPSET, and when 5A charge current for a 20V VIN, and 16V VOUT results in an ideal 4A input current, this input current across input impedance will cause a voltage drop. The VCC seen by the IC is different from what you are sourcing on your power supply. If VCC seen on IC is less than 17.8V, it will reduce the charge current to reduce load on input supply, until the input voltage is 17.8V (corresponds to 1.2V on MPPSET)

    If you force 17V VIN from a DC supply in above scenario, no matter how much charger will regulate the charge current (to reduce load on input supply), it will not be able to bring VIN back up to 17.8V (MPPSET point) so charge current will reduce to 0A.