BQ24400: 3 Cell NiMH charger with USB-Power-Supply

Ludger Jansen1

Part Number: BQ24400

We have a design with BQ24400 to charge a 3 cell battery back (NiMH). The schematic is like the reference design in datasheet. Input voltage is 9 volt. Now the customer would like to change the input voltage to 5 volt from an USB power supply.

Is it possible to charge 3 cells with 5 volt (4.75min) input voltage?

If not, which device would you recommend to use for such application?

Thanks in advance.

over 4 years ago

0 Kedar Manishankar over 4 years ago

TI__Mastermind 24075 points

Hi Jansen,

As this is a buck charge controller, VIN has to be greater than VSLP. VSLP is VCC - 1V, so your output voltage should be < VCC -1. If this condition is satisfied, then there is no issue with charging.

0 Ludger Jansen1 over 4 years ago in reply to Kedar Manishankar

Prodigy 20 points

Hi Kedar,
thanks for the fast reply. During charging with 9 Volt input voltage we have VBatt approx. 4,4 Volt. So, input voltage to charge the battery should be minimal 5,4 Volt. Is this right?
Thanks and regards,

Ludger

0 Kedar Manishankar over 4 years ago in reply to Ludger Jansen1

TI__Mastermind 24075 points

Hi Lduger,

Yes, as this is a controller, this is usually done by having an LDO to step down the adapter voltage to provide 5V regulated voltage to VCC of the chip.

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BQ24400: 3 Cell NiMH charger with USB-Power-Supply