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BQ24650 EVM MPPSET

richard laishram
Prodigy 50 points
Other Parts Discussed in Thread: BQ24650

Recently I've ordered a BQ24650 EVM. From what I understood is at 17.8V input, the voltage at MPPSET is 1.2V and if it's less than 17.8V it goes to voltage regulation mode by reducing the charging current. The question is:

1. When input drops below 17.8V, the charging current drops to zero with a 12V Lead Acid battery connected (~12.3V), why?

2. A PV panel will give lesser voltage (say <13V) during morning and evening, so will it still charge a 12V Lead Acid battery?

  • 0
    TI__Mastermind 31120 points

    The MPPSET divider has to be adjusted for your application.

    The MPPTSET pin is monitoring the input voltage scaled down by the divider.

    The way to set the resistor divider is to determine is by taking the solar panel voltage when it puts out maximum power.

    Take this solar panel output voltage and divide it down to 1.2V.  Now the circuit will load the input source until it delivers the programmed charge current or until the MPPT pin drops to 1.2V.

    At this point the converter will only deliver this amount of power (maximum for solar panel).


    If you have a dual source, adapter and solar panel and the adapter is a higher voltage. If the adapter has enough output power to satisfy the charger, then set the MPPT for the solar panel.  When using the adapter, the MPPSET voltage will not drop to 1.2V, which means that the adapter is not being overloaded.

  • 0 in reply to Charles Mauney
    Prodigy 50 points

    Once the voltage sensed on the MPPSET pin drops below 1.2V, the charger maintains the input voltage by reducing the charge current. (datasheet pg. 13, Input Voltage Regulation)

    My main concern is to charge the battery even at lower PV output, so what I got from the datasheet is that if MPPSET drops below 1.2V the charging current drops but it'll still charges the battery and when it drops below 75mV charging is disabled.

    I don't have a dual source. So if I'm using a 12V PV Panel which can reach to ~18V-20V (open circuit) there's no way it can charge a 12V battery if the PV voltage drops below 12V no matter how low the MPPSET pin is kept?

    Please enlighten me if I've missed out something.

  • 0 in reply to richard laishram
    TI__Mastermind 31120 points

    If the voltage at the MPPSET pin drops any below 1.2V, the charging shuts off.

    This circuit works with a resistive source whos output drops the greater the load.  Once the source's voltage drops to 1.2V at the MPPTSET pin the converter does not deliver any more power.  If the source voltage drops such that the voltage that the MPPSET pin is les than 1.2V then the converter does not deliver any power.

    the converter is not a boost converter (just a step down) and one needs a source voltage that is at least one volt above the output regulation voltage for the battery to charge properly.

  • 0 in reply to Charles Mauney
    Prodigy 50 points

    Thanks for replying back in time, now I'm clear on BQ24650. So there is no other way to achieve boosting at lower voltages with other chips also?

  • 0 in reply to richard laishram
    TI__Mastermind 31120 points

    No.  All of our solution are to use a boost converter prior to the buck charger if the input voltage is not sufficient.