BQ25504EVM-674: 296-29834-ND

Luisa Petti

Part Number: BQ25504EVM-674

Hi,

I just wanted to ask if it is possible to charge a charge a 2.4 V NiMH battery from a solar cell by placing the battery directly to the BATT pin or if an additional battery charging current protection circuit is required.

Thank you very much.

Regards,

Luisa

over 8 years ago

0 Raheem over 8 years ago

TI__Mastermind 21590 points

Hello,
You would not be able to use the BQ25504 for this application due to the fact that the minimum battery voltage for that device is 2.5V which is higher than the voltage rating of your battery. you can however use the BQ25570 which has a minimum VBAT of 2V. Best of luck with your design.
-Raheem

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

Hi Raheem,

thank you for your reply. Would it be possible to use a thin battery with 3.7 V nominal voltage (operating between 2.75 and 4.2 V) with the BQ25504? As far as I have seen from the datasheets and the TI TINA simulations, the battery charging and end voltage levels can be tuned from the resistances in the EVM, right? As that thin film batteries would be LiPO (without charging protection circuit), do we need to have an external battery protection circuit?

Thank you.

Kind regards

Luisa

0 Raheem over 8 years ago in reply to Luisa Petti

TI__Mastermind 21590 points

Luisa,
That would be possible with the BQ25504. Yes, the end voltage levels can be tuned using resistors on the EVM. The device comes with User Programmable Undervoltage and Overvoltage Levels and On-Chip Temperature Sensor With Programmable Overtemperature Shutoff so an external protection circuit is not needed.
-Raheem

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

Hi Raheem,

thanks again. As far as I understand the charging current is not limited thus, is that right? Does it need to be limited?

Thanks,
Luisa

0 Raheem over 8 years ago in reply to Luisa Petti

TI__Mastermind 21590 points

Luisa,
This will depend on the power supplied by the harvesting source. The maximim input current is 300 mA.
-Raheem

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

Thank you!

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

Hi Raheem,

is there any chance to change the output voltage (VSTORE) of the bq25504 evm to 3 V? We would have a 1.5 V EH input and a 3.7 V battery.

Thank you!

Regards

Luisa

0 Raheem over 8 years ago in reply to Luisa Petti

TI__Mastermind 21590 points

Luisa,

If you set VSTOR to 3V, the battery will not be charged above 3V. You can do this by changing the external resistor between VRDIV and GND as explained below to change the battery over voltage threshold.

Regards,

Raheem

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

Hi Raheem,

thanks. Not sure this would be fine, we need to charge the battery to 4 V and discharge it to 3 V, but we need to have only 3 V at its output. Is that possible?

Thanks

Luisa

0 Raheem over 8 years ago in reply to Luisa Petti

TI__Mastermind 21590 points

Luisa,

If that's the case, you should set VBAT_OV to 4V and VBAT_UV to 3V as explained below. Since the output voltage isn't regulated, the output voltage will be the battery voltage. You should consider the BQ25570 as that has a regulated output from a buck.

Regards,

Raheem

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

thank you Raheem, this is very useful.

0 Luisa Petti over 8 years ago in reply to Luisa Petti

Prodigy 100 points

Hi Raheem,

we are looking into a dc-dc converter for low-power thermoelectric energy harvesters (120 uW total power but low voltage <50 mV). Are there similar products that can start from lower voltages?

Thank you.

Regards

Luisa

0 Raheem over 8 years ago in reply to Luisa Petti

TI__Mastermind 21590 points

Luisa,
Do you need an Energy harvesting device of just a boost converter?
Regards,
Raheem

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

Hi Raheem,

just an upconverter.

Thanks

Luisa

0 Raheem over 8 years ago in reply to Luisa Petti

TI__Mastermind 21590 points

Hello Luisa,

Unfortunately, I couldn't find any TI Boost converters that supports an input voltage of 50mV.

Regards,

Raheem

0 Luisa Petti over 8 years ago in reply to Raheem

Prodigy 100 points

Thank you for the help anyway!

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BQ25504EVM-674: 296-29834-ND