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BQ24650 System power

Lijo Thomas
Intellectual 540 points
Other Parts Discussed in Thread: BQ24650

I am planning to design a Li Ion battery charge circuit using IC BQ24650.

I need to take power from the battery  while charging it with out disturbing the charging parameters.Is it possible?

Can I take  system power from "up side" of the current sense resistor-(SRP pin.) From which point of the application circuit , I can connect the load?

And also in all the application notes of Li-Ion charging,  lower value current of constant current phase is not mentioned. Can you please suggest a minimum current setting in constant current phase.

thank u.

 

  • 0
    TI__Guru**** 166416 points

    Yes, you can take power from the battery while charging it.  However, if the input source cannot provide the total power to the system (connected to the battery) and the charger, the input voltage will drop and the input voltage regulation loop may reduce the available current to zero.

    The battery pre-charge and charge termination/re-charge current levels are 1/10 of the charge current set by R(SR) as explained on page 13.

  • 0 in reply to Jeff F
    Intellectual 540 points

    One more question.

    Suppose I am charging a single 1800mAh battery from a solar pannel with 390mW power (5V 80mA). So I can choose the R(SR) to set CC charge of 75mA.

    My question is whether I can use BQ24650 to charge the cell fully in such a low rate.

  • 0 in reply to Lijo Thomas
    TI__Guru**** 166416 points

    The charger's efficiency drops at lower charging currents but it should be able to provide the 75mA charge current.  However, the pre-charge current will only be 7.5mA.  If battery discharges below the VLOWV threshold, causing the charger to enter pre-charge mode, such a large battery will likely not charge enough at 7.5mA charging current to exit pre-charge mode before the timer expires.

  • 0 in reply to Jeff F
    Intellectual 540 points

    We designed a single cell Li Ion Charger PCB using BQ24650 as per the application circuit given in the data sheet. Assembled the PCB and powered the circuit with 12V DC supply.

    We are getting 4.16V at battery connect point (Open circuit - with out battery). Getting PWM output correctly at MOSFET drive  circuits.

    When connecting the battery the  output voltage suddenly drops to 0.7V and the PWM output drive circuit also goes to off mode. The status LED is always in off condition. The Battery used is  4.2V 900mah charging at 400mA - 0.1 ohm current sense resistor.  Can you please help me to solve the issue.

    The measured voltages at some of the pins are notes as REGN - 6V, VREF- 3.3V, MPPSET - 1.2V

  • 0 in reply to Lijo Thomas
    TI__Guru**** 166416 points

    If only the battery is connected, then it sounds like the battery may be too deeply discharged (or damaged) for the charger to re-charge.  When this occurs, if Ipre-charge (=40mA in your application) cannot increase the battery voltage above the V(LOWV)  (~=0.74X4.16V=3.1V for you) threshold before the 30 minute timer expires, the IC suspends charging.  What voltage do you measure across the battery when it is not connected to the charger?

  • 0 in reply to Jeff F
    Intellectual 540 points

    We solved the problem. The charged battery was in good condition. The problem was - TS pin voltage set to 2.8V. So the charger was in suspend mode.

    Now the circuit is working perfectly from an Aplab variable Voltage source.(Set 12V as input)

    I have one more doubt.We are using a 12V Solar Cell as the input to the charger Circuit.

    What are the procedures to set MPPSET pin Voltage?
    How does it work? Whether it will terminate the charge current after a predefined Solar voltage.

  • 0 in reply to Lijo Thomas
    TI__Guru**** 166416 points

    You use  the resistor divider connected to the MPPSET pin to tell the charger where the solar panel's maximum power point is.  If the solar cell voltage drops below that point then the charger slowly reduces the input current drawn from cell, in order to keep the solar cell output at that voltage.    Eventually, with not enough input current,  the charger's output  current will be reduced.  If the solar cell voltage drops signficantly, then the charger will turn off.  See bottom of datasheet page 12 and top of page 13 for details. 

  • 0 in reply to Jeff F
    Intellectual 540 points

    Suppose I had set MPPSET voltage as 17V. What is the charger turn off voltage as the solar panel voltage decreases?

  • 0 in reply to Lijo Thomas
    TI__Guru**** 166416 points

    Can you send me your phone number and time to call via email so we can discuss this further? Given your small solar panel, small charge rate but 1800mAh battery, perhaps the the bq24650 is not the best solution for you.  We have smaller, linear regulator based chargers that might work better but none of them have integrated MPPT circuitry. 

  • 0 in reply to Jeff F
    Expert 2920 points

    Dear jeff,

    If I use this Charging IC with a 5800mAh battery I would have trouble pre charging the battery from the solar. is it possible to disable the timer? 

  • 0 in reply to Harry
    Intellectual 520 points

    Hi Jeff, Amalinda-

    I also have a large battery bank that may not charge to above the precharge threshold within 30 minutes.  Being able to disable or extend this timer would make my design more robust.  Or perhaps it is possible for the system to try to charge again x minutes after the timeout occurs?  Have either of you determined if this is possible?

    Thanks!