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BQ24105 Thermistor and Stop Charging Questions

Vu
Prodigy 200 points
Other Parts Discussed in Thread: BQ24105

Hello Everyone,

I am currently designing a battery charger using the BQ24105 charge management IC. However, the batteries i am using don't have any built-in temperature sensor. So i included a thermistor in my layout that connects to the voltage divider to the TS pin (12). The problem I'm facing right now is i couldn't get the BQ24105 IC to stop charging the batteries.

I set the batteries voltage regulation at 5.9V via a resistors network and the rechargeable batteries measured voltage at the time of the test was  6.3V and the power supply bench (Vin about 10Vdc) showed that the system was pulling about 60mA even the batteries voltage exceeded the regulated voltage.  My overall design is very similar to Figure 3 Page 8 of the datasheet.

 

Best Regards,

Vu

  • 0
    TI__Prodigy 720 points

    TS pin voltage if it is in range, then charger qulify temperature and will charge battery. If you like to use TS pin function, use proper themistor and resistor divider, if you like to disable TS function, just use two same value resistor, so TS pin voltage is in the middle of VTSB.

    Your test resuld does not make sense. The EVM default set point is 4.2V regulation voltage, recharge threshold is 4.1V. If set to other regulation voltage, the ratio is same.

    For example, for two cell case, set regulation point to 8.4V, then recharge threshold is 8.2V. If you set the regulation at 5.9V, then recharge voltage threshold is 5.76V. Recharge voltage threhold must and always below regulation point.

    When battery voltage is at regulation voltage, then current should taper down, when current is termination current (1/10 of charge current), then terminate charge. When battery voltage drops to recharge voltage, resume charging.

    Please measure FB pin voltage, during CV mode, this pin is 2.1V.

    From 60mA current, it looks like not in sleep mode. When battery voltage is too low, short circuit current is 50mA which is close to it. Or the current tapers down to this point.

    In charge done mode, the input current should be very small.

    Also please keep in mind, this charger is for Li-Ion battery CC-CV charing profile, can not be used for other chemistry unless you understand what the change need to be done.

  • 0 in reply to Mao Ye35
    Prodigy 200 points

    Hello Mao,

    I solved the above problem by changing the FB resistors network. However, i have another question i would like to ask you. Let's say i accidentally insert in the non rechargeable batteries into the charger. Does this chip have the ability not to charge the non rechargeable batteries after a few tries of charging the batteries or are there anything on the chip that i can enable/disable to make it not to charge the non rechargeable batteries ? 

     

    Regards,

    Vu

  • 0 in reply to Vu
    TI__Prodigy 720 points

    No, the charger only rely on output voltage, if it is too low ( <2V/cell) then short circuit protection allow 50mA to charge .From 2V/cell to 3V/cell is precharge current, above 3V/cell is fast charing current.

    If output voltage is too high, then stop charging. There's no other special function to do the chemistry detection.

    There're two ways to enable or disable charge, one is /CE pin, pull low enable, pull high disable, safety timer will be reset. Another way is pull TS pin out of range, it pause charging, if TS pin voltage fall back normal, it resume charging, the difference is the safety timer is in hold not reset.