BQ2970: No power output with battery protector.

George Michalis

Part Number: BQ2970
Other Parts Discussed in Thread: BQ24210,

Hello everyone. Preface: i am not an electronics engineer so i may have done something...suboptimal.

I have designed a lipo solar charger using the BQ24210 solar charging IC, and at the same time i wanted to have overdischarge protection so i tried to use the BQ2970.

The charger circuit works as expected, but the problem i am facing is that the battery protection doesn't seem to activate the discharge gate so i dont see any voltage on the output of the system.

I designed the solar charger according to the schematic on the datasheet.

And similarly i integrated the battery protector by referencing the schematic from the datasheet

The Full schematic is the following. The Battery is connected to B+ and B- respectively. the B- becomes the ground of the system.

Cout is 2V so the charge mosfet is active. Dout is 0V. I dont see anything particularly wrong with the schematic, but again, it doesn't work so obviously i am doing a mistake somewhere.

Any ideas?

www.ti.com/.../bq24210.pdf

Double Mosfet

eu.mouser.com/.../SSM6N61NU_datasheet_en_20160831-938862.pdf

over 2 years ago

0 Matt Sunna over 2 years ago

TI__Guru* 77353 points

Hi George,

You say the COUT pin is driving 2V? What is the voltage of your battery cell?

The typical output voltage for COUT is 3.7V (with 3.8V at the BAT pin). 2V seems to indicate a very low cell voltage - in this case the DSG FET will be disabled to protect the cell from discharging further (under-voltage protection).

Best regards,

Matt

0 George Michalis over 2 years ago in reply to Matt Sunna

Prodigy 10 points

Hi Matt.
Battery voltage is 3.8V, which is also the value that i measure in "BAT" pin. I left the battery intentionally half charged before testing to test both the charging and the discharging.

0 Matt Sunna over 2 years ago in reply to George Michalis

TI__Guru* 77353 points

Hi George,

I think the problem is the charger is connecting directly to the cell and is not going through the protected path. I think OUT- should connect to GND and the cell negative connect to an isolated terminal at U2-4, C3 bottom, U3 pin 1. Those pins are now at GND but should be "B-"

Regards,

Matt

0 George Michalis over 2 years ago in reply to Matt Sunna

Prodigy 10 points

Hi Matt. You are right, the battery is indeed directly connected to the charger, which will stop the overvoltage anyway so i only wanted the discharge protection, that's why i have it connected like this.

The GND and B- is connected already. Moreover if you ignore the solar charger, the schematic is a carbon copy of the BQ29700 application note. I can always make a board with only the protection portion just to test, but i dont see how this would affect it

+1 Matt Sunna over 2 years ago in reply to George Michalis

TI__Guru* 77353 points

Since the charger is always connected, the circuit is not waking the device. There is a note in the datasheet (Section 9.4) about waking the device after first connecting it to the battery. This thread explains more: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/886537/bq2970-cout-dout-pin-low-state

0 George Michalis over 2 years ago in reply to Matt Sunna

Prodigy 10 points

Thank you. As you said i had to wake up the device.

I will probably change the layout, but alternative is there any suggested way to automatically wake up the system with the current layout?

+1 Matt Sunna over 2 years ago in reply to George Michalis

TI__Guru* 77353 points

Hi George,

I'm not sure if there is a way to do this automatically with the current design.

0 George Michalis over 2 years ago in reply to Matt Sunna

Prodigy 10 points

Thank you. I will do the other version. Thanks for your support

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BQ2970: No power output with battery protector.