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BQ2000 - design question

Jeffrey Shih
Prodigy 50 points
Other Parts Discussed in Thread: BQ2000, BQ2002

Hi,

I am going to use the BQ2000  charger IC. I have read the datasheet. I am not good at power design. The datasheet provide the example circuit for Single Cell Li-Ion and 3-Cell NiMH 1A. In my design, I will use 3-cell NiMH 1A, and the input is 5V DC from adaptor (1A). How do I revise the example circuit from datasheet like which components to take out? Please help me, and thank you very much. 

  • 0
    TI__Mastermind 36110 points

    It is important that you read the datasheet and closely analyze the typical application circuit to understand functionality of the IC and its external components.  There is also more information in the EVM.  After you understand this, you will be able to modify the circuit to meet your needs.  Can I ask about the end application and when you will go to production with this design?

  • 0 in reply to Matthew Day
    Prodigy 50 points

    Hi,

    Thanks your reply. Actually I can't understand the example circuit from the pin8 (MOD), which hook up the transistors and DC input.   I know the pin8 (MOD) is to control the charging current to battery. Can I just take out those parts, and just keep the 4.7uF and a series resistor 1.1K to ground? In this case, I am not sure when the pin8 (MOD) is high or low. Furthermore, for the NiMH PVD design, the RB2=(N-1)*RB1. The RB1 is 210K and RB2 is 420K. At the pin4 (BAT), I calculate the voltage, if the full singe-cell NiMH voltage is 1.5V, then at pin4 (BAT) I got 4.5V*(420/210+420)=3V. Am I wrong? It's over the pin4 (BAT) limit 2V. The end application will be the end of July. The whole project is almost done except the power part. Please help me and thanks very much.

  • 0 in reply to Jeffrey Shih
    TI__Guru**** 150950 points

    With your input voltage and charge current, I think a better solution is the bq2002 linear charger.

    But to design with either the bq2002 or bq2000, you will not be able to generate a robust solution overnight.  You need to read the datasheet and user's guide and app notes for the part and have a basic background in understanding fundamental power electronics principles.  Since you are on such a short timeline, I suggest you contact a design services company to do this design for you.

    How many units do you plan to build?

    To address your questions:

    I am not sure what you mean by 'just take out those parts and just keep the 4.7uF and series resistor'.

    The description of the MOD pin's operation is found on page 2 of the datasheet.  It goes high and low to regulate the charging current.

    Your equation is backwards, per page 9 of the datasheet.  It should be Rb1 = (N-1) * Rb2.