BQ7718: Battery Charging and Discharging

Henry Wong

Part Number: BQ7718

The part we are thinking to use is: BQ771809DPJT.

We want to use this to charge 5 batteries and then switch to using these batteries in series to power a stepper motor. We are making a PCB and would like to know how to do the connections.

More specifically, I would like to know how to connect BQ7718 for the charging and stepper motor operation. In the datasheet, it looks like we can connect a 3-25 V power source between PACK+ and PACK- to charge the battery pack. How can we get the output voltage to run the stepper motor?

Thank you for your time.

Henry

over 2 years ago

0 Matt Sunna over 2 years ago

TI__Guru* 77423 points

Hi Henry,

This reference design using the BQ7718 may be helpful for you:

https://www.ti.com/tool/TIDA-00108

The BQ7718 connects to the battery cells as shown in the reference design. Most battery packs use the same PACK+ and PACK- pins for the load (stepper motor) or for the charger.

Regards,

Matt

0 Henry Wong over 2 years ago in reply to Matt Sunna

Prodigy 10 points

Thanks Matt. Could you also explain what is the component circled in yellow below? This is from the BQ7718 datasheet.

0 Matt Sunna over 2 years ago in reply to Henry Wong

TI__Guru* 77423 points

This is a 3-terminal Fuse. This component is also present in the TI Reference Design I shared.

Regards,

Matt

0 Henry Wong over 2 years ago in reply to Matt Sunna

Prodigy 10 points

Hi Matt,

Could you also explain how to connect the output pin? Is that a gate/drain/source mosfet? Also since we are connecting five 3.7V batteries in series, the voltage between PACK+ and PACK- will be 18.5V. Our microcontroller operates at 5V. Do we need a level shifter to drop the voltage at the out pin from 18.5V to 5V?

Thanks,

Henry

0 Matt Sunna over 2 years ago in reply to Henry Wong

TI__Guru* 77423 points

Hi Henry,

You would need to reduce the voltage for the microcontroller. The voltage of the OUT pin will be around 7V.

Many users use the OUT pin to control a 3-terminal fuse as shown in the reference design I shared. However, you can also use this to communicate with the microcontroller - you would just need to use a resistor divider to reduce the voltage.

Regards,

Matt

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BQ7718: Battery Charging and Discharging