BQ2970 Datasheet, PDF (18/31 Pages) Texas Instruments – Cost-Effective Voltage and Current Protection Integrated Circuit

bq2970, bq2971, bq2972, bq2973
SLUSBU9C – MARCH 2014 – REVISED MARCH 2016
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Device Functional Modes (continued)
9.4.4 Discharge Overcurrent Status (Discharge Overcurrent, Load Short-Circuit)
When a battery is in normal operation and the V– pin is equal to or higher than the discharge overcurrent
threshold for a time greater than the discharge overcurrent detection delay, the DOUT pin is pulled low to turn
OFF the discharge FET and prevent further discharge of the battery. This is known as the discharge overcurrent
status. In the discharge overcurrent status, the V– and VSS pins are connected by a constant current sink I_V–S.
When this occurs and a load is connected, the V– pin is at BAT potential. If the load is disconnected, the V– pin
goes to VSS (BAT/2) potential.
This device detects the status when the impedance between Pack+ and Pack– (see Figure 26) increases and is
equal to the impedance that enables the voltage at the V– pin to return to BAT – 1 V or lower. The discharge
overcurrent status is restored to the normal status.
Alternatively, by connecting the charger to the system, the device returns to normal status from discharge
overcurrent detection status, because the voltage at the V– pin drops to BAT – 1 V or lower.
The resistance R_V–D between V– and BAT is not connected in the discharge overcurrent detection status.
9.4.5 Charge Overcurrent Status
When a battery is in normal operation status and the voltage at V– pin is lower than the charge overcurrent
detection due to high charge current for a time greater than charge overcurrent detection delay, the COUT pin is
pulled low to turn OFF the charge FET and prevent further charging to continue. This is known as charge
overcurrent status.
The device is restored to normal status from charge overcurrent status when the voltage at the V– pin returns to
charge overcurrent detection voltage or higher by removing the charger from the system.
The charge overcurrent detection feature does not work in the over-discharge status.
The resistance R_V–D between V– and BAT and the current sink I_V–S is not connected in the charge overcurrent
status.
9.4.6 0-V Charging Function (Available)
This feature enables recharging a connected battery that has very low voltage due to self-discharge. When the 0-
V battery charge starting charger voltage V_0CHG or higher voltage is applied to Pack+ and Pack– connections by
the charger, the COUT pin gate drive is fixed by the BAT pin voltage.
Once the voltage between the gate and the source of the charging FET becomes equal to or greater than the
turn ON voltage due to the charger voltage, the charging FET is ON and the battery is charged with current flow
through the charging FET and the internal parasitic diode of the discharging FET. Once the battery voltage is
equal to or higher than the over-discharge release voltage, the device enters normal status.
CAUTION
1. Some battery providers do not recommend charging a depleted (self-discharged) battery.
Consult the battery supplier to determine whether to have the 0-V battery charger function.
2. The 0-V battery charge feature has a higher priority than the charge overcurrent detection
function. In this case, the 0-V charging will be allowed and the battery charges forcibly,
which results in charge overcurrent detection being disabled if the battery voltage is lower
than the over-discharge detection voltage.
9.4.7 0-V Charging Function (Unavailable)
This feature inhibits recharging a battery that has an internal short circuit of a 0-V battery. If the battery voltage is
below the charge inhibit voltage V_0INH or lower, the charge FET control gate is fixed to the Pack– voltage to
inhibit charging. When battery is equal to V_0INH or higher, charging can be performed.
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