BQ78PL116: CFET Failure

Chetan SL2

Part Number: BQ78PL116

We have 4 cell LiFe battery pack with each cell having 3.6V/2.9Ah capacity. The EUV threshold level is set to 2.55V, the EUV time is set to 2 Secs and EUV recovery is set to 2.9V.

When the battery cell voltages are below 2.98V and the battery is in ship mode, then if the battery cells are charged by-passing the charge FET then the CFETF bit is set.

However I have noticed that the same test condition provided the battery cell voltages are 3V and above wouldn't set the CFETF bit.

How is the CFETF bit dependent on Cell voltages of the battery?

Best Regards,

Chetan.S.L.

over 6 years ago

0 Batt over 6 years ago

TI__Mastermind 42535 points

Hi Chetan,

A CFETF is detected when the CHG fet is supposed to be open but the monitor detects a current. It's unlikely that it has a correspondence to voltage, please check if you have a differential across your sense resistor that is getting detected as a chg current.

0 Chetan SL2 over 6 years ago in reply to Batt

Prodigy 20 points

Hi Batt,

I checked the differential in both the cases, when the cell voltages are <2.9V and >3V. The CFETF bit is not setting when the cell voltages are @ >3V and will set when <2.9V.

Best Regards,

Chetan.S.L.

0 Batt over 6 years ago in reply to Chetan SL2

TI__Mastermind 42535 points

Please check your calibration. If at 0V across Rsns, you have a current, then you need to adjust the offset. An offset seen as chg current can cause chg fet failure to set.

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BQ78PL116: CFET Failure