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LM3405A: Using the LM3405A as a NiMH CC charger

Kevin Braun47
Intellectual 450 points
Part Number: LM3405A
Other Parts Discussed in Thread: BQ2002E,

Hello,

I want to use the LM3405A as a constant current driver for NiMH cells.  In my configuration, I have 2 NiMH cells, and a BQ2002E that regulates the battery charge profile.  I want to charge the batteries at 800mA and my lowest possible Vin is 4.2-4.5V.  The NiMH voltage ranges from 1.8V-3.2V during charge and spends the majority of the charge cycle between 2.8-2.9V.

Summary:

Icharge = 800mA

Vin =  4.2V - 4.8V

Vload = 1.8V - 3.2V (the majority of the time between 2.8V - 2.9V)

BQ2002E configured for a 2xNiMH charge controller

I have an Eval board for the LM305A. Questions:

1. Is it possible to use the LM3405A in this configuration?

2. I understand that I have to change R1 to 0.25 ohms for 800mA.  What other optimization should be done?

Regards,

...kevin

  • 0
    TI__Mastermind 25500 points

    Hello Kevin,

    If you need a constant current source then an LED driver is a good option, that is what they are set up for. The LM3405A should work well for you.

    As for other optimizations that kind of depends. But it's a relatively simple circuit so your main concern may be the current ripple, although the charger PSRR may compensate for that. So really just follow the datasheet regarding input/output capacitor and inductor selection and you should be fine. If you have particular concerns let me know and I can probably help.

    Regards,

    Clint