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LP3921: Using LP3921 to charge a 3S NiMH battery pack

Rasmus Ågren
Prodigy 10 points
Part Number: LP3921

Hi,


In our product we're currently using the LP3921 to charge a 1S Li-Po battery pack, but we're considering changing the battery pack to a 3S NiMH pack instead (due to mostly easier shipping/handling)

We've studied the datasheet and done some preliminary testing, all of which points towards the possibility to actually continue to use the LP3921 as the charging IC.

We've taken into account the higher V_term (and I_charge) needed for the NiMH pack.


Is there something that we're missing in our assumption that the LP3921 will do a acceptable job in charging a NiMH pack?


Best regards,

Rasmus

  • 0
    TI__Mastermind 23400 points

    Hi Ramsus,

    Rasmus Ågren said:
    We've taken into account the higher V_term (and I_charge)

    Can you elaborate on using the LP3921 for charging 3S pack? The LP3921 can only be configured to charge batteries up to 4.4V.

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    Hi Anthony,

    Yeah, sorry for not being detailed enough.

    We've set the Vterm to 4.4V and Icharge to 450mA (its a 420mA pack). A Nimh cell is supposed to be charged with 1.5V, so we would theoretically need 4.5V to charge. Our theory is that if you supply a 3S NiMH with 4.4 for "long enough" it will still fully charge.

    And the rudimentary tests that we've done so far have shown that the 3S NiMH pack will get fully charged or least near enough to it so that we can't immediately see that it isn't fully charged.

    Regards

  • +1 in reply to Rasmus Ågren
    TI__Mastermind 23400 points

    Hi,

    If you are ok with charging NiMH batteries in a CC / CV phase, then the LP3921 could be used in this manner. The LP3921 is designed for Lithium based batteries and so it uses the CC / CV charge profile. Be aware, this may not be suitable for a NiMH application.