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BQ2000: How to disable trickle charge on BQ2000 charging IC ?

Fai Leung
Prodigy 135 points
Part Number: BQ2000


Hello, how do you do ?

This's an engineer from Vtech. We are using your BQ2000SN-B5TR charging IC with 1A charging current to charge a NiMH 7.2V 4000mAh rechargeable battery. To meet the CEC and DoE USA energy saving type approval requirement, we want to disable the top-off trickle charge to save the charging energy.

However, after changed CMTO capacitor value to less than 0.07uF by using 0.047uF for CMTO and 180k for RMTO to set 5.3 hours maximum charging time, trickle charge was still activated frequently when the battery reached full level after fast charging.

Would you please tell us how to change the circuit values to get below result ?

- Battery is connected to the output of charging circuit.
- Provides DC power to charging circuit.
- Charging IC starts charging by fast charge.
- Battery is charged to full level with temperature rise.
- Charging IC detects delta voltage and temperature rise, then stop all charging.
- Charging IC keeps STOP all charging until battery is reconnected or DC power reset.

Thank you!

Best regards,
Fai.

  • 0
    TI__Expert 8130 points

    Hi Fai,

    In order to disable top-off, as mentioned in the datasheet (image you provided), the capacitance value should be less than 0.07μF. Keep in mind that Trickle Charge (after fast charge) is not optional, as the BQ2000 is designed to remain in trickle maintenance charge forever in order to keep the Nickel pack full.
    Also, with R_MTO values near 150kΩ, it can be difficult to tell which state the charger is in (top-off or trickle charge).

    -To get the battery charging in fast-charge make sure that the voltage at BAT & TS pin are within correct range: V_LBAT < VBAT < V_MCV and V_HTF < VTS < VLTF.

    Table 3 in the datasheet also provides various temperature-monitoring conditions.

    Regards,
    Alejandro

  • 0 in reply to iAlejandro
    Prodigy 135 points

    Hello Alejandro,

    Thank you for your reply and noted that the trickle charge can't be disabled on BQ2000. Then, I will put a 5 hours time out timer in MCU to shut down BQ2000 to stop charging.

    From attached diagram, is it safe to turn off BQ2000 power supply by short circuit D6 5.6V zener diode with a NPN transistor which control by the MCU ?

    Best regards,

    Fai.

  • 0 in reply to Fai Leung
    Prodigy 135 points

    May I have your reply today ? Thank you!

  • 0 in reply to Fai Leung
    TI__Expert 8130 points
    Hi Fai,

    Yes; that should be a safe way to turn off the charger.

    Regards,
    Alejandro