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BQ25172: Problem connecting it to a load

Fernando Carazo
Prodigy 20 points
Part Number: BQ25172
Other Parts Discussed in Thread: BQ25171-Q1

When I connect it to a circuit (load), after 4 hours the charger continues charging, the LED remains on. But if I disconnect the charger and reconnect it, the LED is off, indicating that the batteries are charged. If I don't connect it to the circuit(load), the charger works perfectly, charges the batteries after 4 hours without any problem and the LED turns off.Do you have any recommendations?

  • 0
    TI__Guru* 75556 points

    Hello

    Can you send a schematic of the circuit and description of the test set up?

  • 0 in reply to Bill Johns
    Prodigy 20 points

    At first I had Vbatt connected to F500, but when I removed a battery the fault diode flashed so fast that it could hardly be seen. When I add the Mosfet in and separated it from the rest of the circuit (load) the LED blinked at its frequency. But I still have the problem that it won't stop loading

  • 0 in reply to Fernando Carazo
    TI__Guru* 75556 points

    Hi Fernado 

    Thanks for the schematic.

    Fernando Carazo said:
    If I don't connect it to the circuit(load), the charger works perfectly, charges the batteries after 4 hours without any problem and the LED turns off.

    The charge current is set to 300mA, is the load possibly greater than the charge current?

    Fernando Carazo said:
    At first I had Vbatt connected to F500, but when I removed a battery the fault diode flashed so fast that it could hardly be seen.

    The BQ25172 has OUT overvoltage protection, at 1.7V per cell the unit will turn off until voltage drops below 1.45V per cell.  With battery disconnect the output voltage will overshoot to 10.2V (1.7V X 6).  Voltage will drop, charge will restart overshoot and shutdown again.

  • 0 in reply to Bill Johns
    Prodigy 20 points

    I increased the current to 400mA and the charger stops after 4 hours, as it should. But it is too much current to charge the batteries, the batteries are 2500mA each. Do you have any suggestions to separate the circuit (load) from the charger?, now I have the Q506 Mosfet.

    Thanks

  • 0 in reply to Fernando Carazo
    TI__Guru* 75556 points

    Hi Fernado

    Fernando Carazo said:
    Do you have any suggestions to separate the circuit (load) from the charger?

    Take a look at BQ25171-Q1 datasheet figure 8-14 page 29.  This is a circuit that will separate system load from charger.