8.3.4.1 Autonomous Charging Cycle

When battery charging is enabled (EN_CHG = 1 and CD pin is LOW;), the device autonomously completes a charging cycle without host involvement. The device default charging parameters are listed in Table 2 below. On BQ25887, the host can always control the charging operation and optimize the charging parameters by writing to the corresponding registers through I²C.

A new charge cycle starts when the following conditions are valid:

1. Converter starts
2. Battery charging is enabled by I²C register bit (EN_CHG = 1 and CD pin is LOW and ICHG register is not 0 mA)
3. No thermistor fault on TS
4. No safety timer fault

The charger automatically terminates the charging cycle when the charging current is below termination threshold, charge voltage is above recharge threshold, and device is not in DPM mode or thermal regulation. When a full battery voltage is discharged below recharge threshold (threshold selectable via VCELL_RECHG[1:0] bits on BQ25887), the device automatically starts a new charging cycle. After the charge is done, toggle CD pin or EN_CHG bit can initiate a new charging cycle.

The STAT output indicates the charging status of: charging (LOW), charging complete or charge disable (HIGH) or charging fault (Blinking). If no battery is connected, the STAT pin blinks as capacitance connected at BAT charges, discharges, then recharges. The STAT output can be disabled by setting STAT_DIS bit. In addition, the status register (CHRG_STAT) indicates the different charging phases as:

• 000 – Not Charging
• 001 – Trickle Charge (VBAT < V_{BAT_SHORT})
• 010 – Pre-charge (V_{BAT_SHORT} < VBAT < V_{BAT_LOWV})
• 011 – Fast-charge (CC mode)
• 100 – Taper Charge (CV mode)
• 101 – Top-off Timer Charging
• 110 – Charge Termination Done

When the charger transitions to any of these states, including when charge cycle is completed, an INT is asserted to notify the host.