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BQ2002: Typical SCH

Fandy
Expert 2285 points
Part Number: BQ2002
Other Parts Discussed in Thread: LM317

Hello

My customer have NI-MH battery charger demands, input 5V, 3 NI-MH battery, I find Ti just have BQ2002x for NI-MH charger, but havn't find typical SCH of BQ2002, Could you provides reference SCH ?

  • 0
    TI__Mastermind 24075 points
    Hi Fandy,
    You can take a look at this document showing a reference schematic: www.ti.com/.../sluu007b.pdf
    Can also be found in the user guide section of BQ2002 webpage.
  • 0 in reply to Kedar Manishankar
    Expert 2285 points

    Hi Kedar

    NIMH charger circuit must be one charger IC(BQ2002) combine with one LDO(LM317) ?

    This User Guide just design for 4,5,6,8,10 Cell,  how to renew to support 3 Cell ? Select resistor divider Rtop=(N-1)=200K for 3Cell ?

    Minimum input voltage is Vbat+4V ? 

  • 0 in reply to Fandy
    Expert 2285 points
    Hi Kedar
    any update ？
  • 0 in reply to Fandy
    TI__Mastermind 24075 points

    Hi Fandy,

      1. BQ2002 is a charge controller and the LM317 is a voltage regulator, but by connecting a fixed resistor between the ADJUST and OUTPUT terminals, the LM317 device can function as a precision current regulator, which allows the desired charge current.

      2. For 3 cell configuration see below explanation from datasheet to set desired charge regulation voltage: 

    The voltage presented on the battery sense input, BAT, should represent a single-cell potential for the battery under charge. A resistor-divider ratio of RB2/RB1 = N-1 is recommended to maintain the battery voltage within the valid range, where N is the number of cells, RB1 is the resistor connected to the positive battery terminal, and RB2 is the resistor connected to the negative battery terminal.

      3. 4V headroom between VCC and BAT = (3V dropout voltage of LM317 + forward voltage drop of diode D3). 3-V headroom is recommended (VI – VO) to support maximum current and lowest temperature. For customer's application most likely either higher VIN Is required or lower dropout voltage current regulator is required. Note that this part is old and more efficient drop out regulators are available now, and that LM317 is rated for up to 40V Vi-Vo Input Output Differential Voltage, while customer only needs about 1V dropout.