BQ2970 Datasheet, PDF (17/31 Pages) Texas Instruments – Cost-Effective Voltage and Current Protection Integrated Circuit

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Device Functional Modes (continued)
bq2970, bq2971, bq2972, bq2973
SLUSBU9C – MARCH 2014 – REVISED MARCH 2016
CAUTION
When the battery is connected for the first time, the discharging circuit may not be
enabled. In this case, short the V– pin to the VSS pin.
Alternatively, connect the charger between the Pack+ and Pack– terminals in the
system.
9.4.2 Overcharge Status
This mode is detected when the battery voltage measured is higher than the overcharge detection threshold
(V_OVP) during charging. If this condition exists for a period greater than the overcharge detection delay (t_OVPD) or
longer, the COUT output signal is driven low to turn OFF the charging FET to prevent any further charging of the
battery.
The overcharge condition is released if one of the following conditions occurs:
• If the V– pin is higher than the overcharge detection voltage (V_{OCC_Min}), the device releases the overcharge
status when the battery voltage drops below the overcharge release voltage (V_OVP-Hys).
• If the V– pin is higher than or equal to the over-discharge detection voltage (V_OCD), the device releases the
overcharge status when the battery voltage drops below the overcharge detection voltage (V_OVP).
The discharge is initiated by connecting a load after the overcharge detection. The V– pin rises to a voltage
greater than VSS due to the parasitic diode of the charge FET conducting to support the load. If the V– pin
voltage is higher than or equal to the discharge overcurrent detection threshold (V_OCD), the overcurrent condition
status is released only if the battery voltage drops lower than or equal to the overcharge detection voltage (V_OVP).
CAUTION
1. If the battery is overcharged to a level greater than overcharge detection (V_OVP) and the
battery voltage does not drop below the overcharge detection voltage (V_OVP) with a heavy
load connected, the discharge overcurrent and load short-circuit detection features do not
function until the battery voltage drops below the overcharge detection voltage (V_OVP). The
internal impedance of a battery is in the order of tens of mΩ, so application of a heavy load
on the output should allow the battery voltage to drop immediately, enabling discharge
overcurrent detection and load short-circuit detection features after an overcharge release
delay.
2. When a charger is connected after an overcharge detection, the overcharge status does not
release even if the battery voltage drops below the overcharge release threshold. The
overcharge status is released when the V– pin voltage exceeds the overcurrent detection
voltage (V_OCD) by removing the charger.
9.4.3 Over-Discharge Status
If the battery voltage drops below the over-discharge detection voltage (V_UVP) for a time greater than (t_UVPD) the
discharge control output, DOUT is switched to a low state and the discharge FET is turned OFF to prevent
further discharging of the battery. This is referred to as an over-discharge detection status. In this condition, the
V– pin is internally pulled up to BAT by the resistor R_V–D. When this occurs, the voltage difference between V–
and BAT pins is 1.3 V or lower, and the current consumption of the device is reduced to power-down level
I_STANDBY. The current sink I_V–S is not active in power-down state or over-discharge state. The power-down state is
released when a charger is connected and the voltage delta between V– and BAT pins is greater than 1.3 V.
If a charger is connected to a battery in over-discharge state and the voltage detected at the V– is lower than
–0.7 V, the device releases the over-discharge state and allows the DOUT pin to go high and turn ON the
discharge FET once the battery voltage exceeds over-discharge detection voltage (V_UVP).
If a charger is connected to a battery in over-discharge state and the voltage detected at the V– is higher than
–0.7 V, the device releases the over-discharge state and allows the DOUT pin to go high and turn ON the
discharge FET once the battery voltage exceeds over-discharge detection release hysteresis voltage (V_{UVP +Hys}).
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