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BQ2000: Power supply circuit

Yoshinobu Kagawa
Expert 1810 points
Part Number: BQ2000

Regarding the application of the BQ2000, it is to fast charge a 4.8V, 1450mAh NI-MH 4-cell battery within 4 hours (targeting about 2 hours).
At this time, what voltage and capacity of the power supply circuit is optimal for the front stage of the BQ2000?

Best regards,
Kagawa

  • 0
    TI__Mastermind 24075 points

    Hi Kagawa-san,

        For BQ2000, as it is a buck charge controller IC, it requires 5V at VCC pin, but an input voltage higher than output voltage, at the input to the buck power stage. The EVM shows such a configuration where there is an LDO to step down the input voltage such that 5V is seen at VCC.

    The minimum delta required is defined by the Vslp threshold, for which the voltage at BAT <  VCC-1V with a tolerance of +/-0.5V. 

    When selecting input adapter account for voltage drop across input cable, and trace impedance,

    Note that BAT is not actual battery voltage, but the output of a resistor divider from real battery to GND that scales down the battery voltage to be sensed at BAT pin of IC.

  • 0 in reply to Kedar Manishankar
    Expert 1810 points

    The battery pack used in this project does not have a thermistor. Is it possible for the BQ2000 to be controlled without the thermistor?
    Looking at the state transition diagram, temperature comparison processing is included everywhere, and for example, I feel that even if the temperature rises during the trickle, there is no thermistor and the transition cannot be stopped.

    Best regards,

    Kagawa

  • 0 in reply to Yoshinobu Kagawa
    TI__Mastermind 24075 points

    Hi Kagawa-san,

    The thermistor converts the battery temperature to a voltage, and internal TS comparators (TCO, LTF and HTF) will reduce charge depending on sensed TS voltage. As battery pack does not have a thermistor, a fixed voltage (resistor divider) can be sourced on to the TS pin so charger always senses valid TS range and will always charge.

    In this case, as battery temperature is not being monitored, it would be best to use PVD termination.