BQ27742-G1: Deeply Discharge battery Recovery

JDJ

Part Number: BQ27742-G1

Hello,

We are trying to test a deeply discharged battery recovery using the BQ27742-G1 for a battery that has been discharged to a very low voltage. We measured the battery terminals at 2.7V which I believe should be above V_UVP.

If in low voltage charging mode the charge FET (CHG) is connected to the pack voltage (PACKP). Is this an internal short? If the gate of the CHG FET is not shorted to PACKP, it will follow 2xVPWR as shown in section 6.8?

From section 6.7, is VCHGATT configurable to lower than 2.7V? Our charger provides 2.0 fixed in pre-charge state and might not be enough for the FG to detect charger? Please let me know your comments on this as well .

We are applying 5V to charge the battery.

If we connect the discharged battery to an external power supply, I am able to start charging when I supply ~3.45V. Below this voltage, the battery does not charge. I am not sure what parameter this voltage corresponds to or if it’s configurable.

Thanks

over 3 years ago

0 Shirish over 3 years ago

TI__Guru 57697 points

This may help e2e.ti.com/.../bq27742-g1-bq27742-not-starting-catch-22

0 JDJ over 3 years ago in reply to Shirish

TI__Expert 4456 points

Hi Shirish,

Thank you for the link and I will verify the Fets on the schematic. Also, since the battery voltage is above V_UVP, then this may not be the same exact scenario.

Could you please provide commentary on my above questions in the meantime?

Thanks!

0 Shirish over 3 years ago in reply to JDJ

TI__Guru 57697 points

Hello JDJ,

VCHGATT is not configurable.

Are you using an EVM or a custom design?

0 JDJ over 3 years ago in reply to Shirish

TI__Expert 4456 points

They are using a custom design. I will send you the schematic over email. The FET turn ON gate threshold voltage is 0.8V typical (0.45V minimum). Would this be too high?

0 Shirish over 3 years ago in reply to JDJ

TI__Guru 57697 points

Hello JDJ,

Can you check if this applies?

7.4.1.7 LOW VOLTAGE CHARGING State

In this mode, the fuel gauge shorts the CHG FET gate to PACKP pin if the cell voltage is above the V_LVDET threshold, allowing the battery to be trickle charged with the CHG FET biased in the ohmic region. If below the aforementioned threshold, low voltage charging is prohibited for safety reasons and the cell will likely be permanently unrecoverable due to being dangerously depleted.

0 JDJ over 3 years ago in reply to Shirish

TI__Expert 4456 points

I don't believe this applies as the battery voltage is 2.7V which is above V_UVP and should not be in low charging mode. They are measuring 2xVPWR at the gate of the CHG Fet which also makes me believe we are not in low voltage charging mode.

Thanks,

Power management

Power management forum

BQ27742-G1: Deeply Discharge battery Recovery

7.4.1.7 LOW VOLTAGE CHARGING State