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Need help building battery charger using bq2000

awan2010
Prodigy 40 points
Other Parts Discussed in Thread: BQ2000, BQ2002

Hi,

I am building simple battery charger using bq2000 for my project and it is partly working. It is charging my lithium battery, but there are some features that are not functioning:

* time out (MTO) does not work. I have flashing LED run indefinitely when there is no battery

* When the battery is pulled out, the state does not change: still in charging state (LED ON)

I attach my schematic here. Any ideas what is going wrong?

Thanks in advance.

 

 

 

  • 0
    TI__Guru**** 150900 points

    The bq2000 is not designed to be a linear charger.  It is designed to be a switching charger.  If you are looking for a linear charger, please look at the bq2407x family or the bq2408x family.

     

  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Chris Glaser said:

    The bq2000 is not designed to be a linear charger.  It is designed to be a switching charger.  If you are looking for a linear charger, please look at the bq2407x family or the bq2408x family.

    thanks for your info. I guess it is my linear-mode charger schematic that causes this problem. Do you have any reference design for charging 3V 45 mAh li-ion battery other than one in datasheet? or I just follow what's in there and change Rsns accordingly?

    Thanks.

  • 0 in reply to awan2010
    TI__Guru**** 150900 points

    What battery chemistry do you have?  The most common rechargeable lithium cells I have come across are either 4.2V or 4.1V.  If you have a 3V coin cell lithium primary battery, those are not rechargeable.

  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Chris Glaser said:

    What battery chemistry do you have?  The most common rechargeable lithium cells I have come across are either 4.2V or 4.1V.  If you have a 3V coin cell lithium primary battery, those are not rechargeable.

    I use this battery:

    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P046-ND

     

    do you have any reference schematic because I believe my schematic is for linear-mode and I need efficient charging method for my project. Thanks again Chris.

     

  • 0 in reply to awan2010
    TI__Guru**** 150900 points

    Thank you for sending the link to your battery.  Assuming these are rechargeable, which contradicts page 2 of this document http://panasonic.com/industrial/includes/pdf/Panasonic_LithiumML_Info.pdf , and assuming that these require a CC/CV charge algorithm as other Lithium batteries do, a simple resistor + LDO charger would be easiest.  I am not guaranteeing that this is a safe way to charge these types of batteries, as I could not find any documentation on how they need to be charged.  I would definitely check with the manufacturer on their recommendations.

    The resistor + LDO charger does not provide any protection--it just limits both the charge current or charge voltage to achieve a CC/CV algorithm.  The LDO would clamp the maximum voltage to the battery, while the resistor would limit the maximum charge current.  Assuming a +/-2% voltage tolerance is acceptable to the battery, the TLV70030 LDO would work.  Just give it >3.1V through a resistor.  The resistor would be sized to limit the current at the maximum input voltage to the minimum battery voltage by:

    R = (Vinmax - Vbattmin) / Ichg

     

  • 0 in reply to awan2010
    Prodigy 10 points

    I would use the one in the data sheet. BQ2002 AND 2004 have worked for me direct from the datasheet schematic.

    Especially have a look at C4 reference to the BQ2000 datasheet schematic and its relationship to the gate of Q3.

    I assume you have not damaged your IC, but would use another to check. I also have not looked at your charge termination values set by your discretes, haven't had another coffee yet, but sure if you stuck to the dtatasheet schematic, you will be problem free