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BQ2000: BQ2000 or BQ24401 For 2 Cells NiMH Battery Charging From DC5V Power Supply

Fai Leung
Prodigy 135 points
Part Number: BQ2000
Other Parts Discussed in Thread: BQ24401

Hello, how do you do?

May I have some questions below regarding to the BQ2000 or BQ24401 charging ICs ?

Q1) Can both ICs be used for 2 cells NiMH battery charging ? If so, changing the voltage divider value for BAT pin to 750k + 750k must work, right ?

Q2) Can both ICs work directly from a DC5V power supply without the suggested discrete voltage regulator ?

Q3) If the voltage of my DC5V power supply is unstable, will it affect the reference voltage inside the IC and charging performance ?

If both ICs can't be used, would you please suggest us another choice ?

Thank you!

best regards,

Alfred.

  • 0
    TI__Mastermind 24075 points

    Hi Fai,

    A1) Yes both IC can be used for 2 cell NiMH battery charging. The voltage divider value should be 1:1, however you should limit series resistance of RB1 and RB2 <1Mohm.

    A2) You can remove on D3, D6, R10 and Q4 ( which comprise the linear regulator at the input) from the schematic on page 5 of the user guide: http://www.ti.com/lit/ug/sluu270/sluu270.pdf to charge with a 5V input source.

    A3) If you are using separate input to the converter, and input to VCC of IC then there is no issue as this is a charge controller, so as long as the input to VCC is within 4V to 6V, then a different input voltage can be used. If VCC is same as input supply, then it is not ideal to use unstable supply. Recommended to obtain an EVM to perform modifications and test with unstable supply first, to see if it works before designing the board.

  • 0 in reply to Kedar Manishankar
    Prodigy 135 points

    Hello Kedar,

    Thanks for your support. Everything is clear now.

    Best regards,

    Fai.

  • 0 in reply to Kedar Manishankar
    Prodigy 135 points

    Hello Keder,

    After changed the circuit per your suggested, it seems work for 2 cells NiMH charging from 5V power supply but not in all condition.

    In the case when the battery is replaced during it is charging, replaced battery can't be recharged unless battery is reconnected after 10 seconds or reset 5V power supply.

    Is it mean the charging program inside the charging IC has to be reset by reconnect 5V power supply or battery with time longer than the time out timer ?

    Any way can keep charging works 100% after the battery is replaced in a short period.

    Thank you!

    Best regards,

    Alfred.

  • 0 in reply to Fai Leung
    TI__Mastermind 24075 points

    Hi Alfred,

        What is the MTO period? 

  • 0 in reply to Kedar Manishankar
    Prodigy 135 points

    Hello Kedar,

    MTO is set to 5 hours by 150nF cap and 62k resistor.

    I guess the issue may not related to MTO.

    Simply speaking, our user may replace the battery when it's in charging mode but the 5V power adaptor will never been disconnected.

    We want to make sure all replaced battery will still be charged even the user just takes few seconds to replace it.

    Thank you!

    Best regards,

    Alfred.

  • 0 in reply to Fai Leung
    Prodigy 135 points

    Hello Kedar,

    Would you reply my question within today ? Thank you!

    Best regards,

    Alfred.

  • 0 in reply to Fai Leung
    TI__Mastermind 24075 points

    Hi Alfred,

       Figure 12 of the BQ2000 datasheet shows expected operation when inserting a battery. Charge should begin ~1.2s after battery insertion. From figure 2. State machine, battery replacement at any time should restart the charge cycle, with expected behavior as shown in figure 12.

  • 0 in reply to Kedar Manishankar
    Prodigy 135 points

    Hello Kedar,

    Yes. It was what I got from datasheet before. However, it's also not the phenomenon I got from my test board.

    What I got is that....

    - When the battery is disconnected, then reconnected after 10 seconds, replaced battery can be charged.

    - When the battery is disconnected, then reconnected after just < 3 seconds, sometimes the replaced battery can't be charged.

    We did 50 times each to prove above phenomenon.

    Replaced battery must not reached full level voltage before replaced.

    Would you please tell me your email address ? I want to share you my circuit diagram for checking. I don't want to show it on this public area.

    Thank you!

    Best regards,

    Alfred.

  • 0 in reply to Fai Leung
    Prodigy 135 points

    Hello Kedar,

    Enclosed 2 timing diagrams I got from my test board for your reference.

    CH1 is connected to positive pole of battery terminal.

    CH2 is connected to pin 5 of BQ2000.

    When the battery is just disconnected, because of the loading of BQ2000 is lost, positive pole of battery terminal changes from pure DC to switching signal, then retry its output. It takes 3.24s totally.

    When I reconnect the battery within 3.24s, sometimes the battery can't be charged again.

    Is it mean that BQ2000 needs to detect battery condition until charge suspend during this 3.24s before another battery is replaced for new charging ?

    Thank you!

    best regards,

    Alfred.

  • 0 in reply to Fai Leung
    TI__Mastermind 24075 points

    I have sent you a friendship request on E2E. You can send files privately through there.

  • 0 in reply to Kedar Manishankar
    Prodigy 135 points

    Hello Kedar,

    I have sent you a private message. Please check and reply there.

    Thank you!

    best regards,

    Alfred.