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Original question:

BQ77915: BQ77915 OV and UV

BQ77915: CHRG, DSG FETS

Tomas Havel
Prodigy 150 points
Part Number: BQ77915

Hello,

I just encountered a little issue. When my board with BQ77915 isnt connected to charger or load, CHARGING FET seems to be ON (measured about 12V on a pin) and DSG FET seems to be OFF( 0 V).

Once I connect charger, both FETS seems to be high suddenly (12V on both) and charging works.

But when I try to connect load, CHARGE FET is ON but DSG FET is still OFF, so there is no discharging happening.

Could u help me?

Havel

  • 0 in reply to Tomas Havel
    TI__Expert 7455 points

    Hi Tomas,

    I reviewed your schematic and for the most part everything looks ok. The only recommendation I would make is to increase your Rgs_chg resistor from 1M oHm to 3.3mOhm. We recommend a value of 3.3MOhm if load removal is required to recover from a UV fault, see page 37 of the datasheet for details. I would also add a 10K Ohm pull down resistor on the CBI pin. I do not believe that will solve your issue though. 

    If changing the Rgs_chg resistor does not work, I would recommend taking a look at Table 5 in the datasheet. This table outlines how the device behaves in the various fault modes. In particular, you are going to want to look at the faults that cause the DSG fet to turn off and the CHG fet to stay on. This is mainly going to be the UV fault. Check your cell voltages and related pins to determine if this condition is occurring.