SLUSDK0A August 2020 – March 2021 BQ25171-Q1
The device charges a NiMH battery in two phases: constant current and intermittent charge (optional). The duration for constant current charing is controlled by the charge timer, which is programmed using the CHM_TMR pin. Intermittent charging is designed to replenish the natural self-discharge of NiMH by restarting a short charge cycle (25% of programmed charge timer) when the output voltage falls below VRECHG threshold. If the intermittent charging function is disabled, the device will charge a battery once, and not start a recharge cycle automatically. In this case, a new charge cycle can be initiated by toggling the input supply or the CE pin.
Before initiating a NiMH charge cycle, the device checks for a full battery. If battery voltage is above VRECHG, the battery is considered full and the device does not charge. Once the battery voltage falls below VRECHG, the device automatically begins charging. If the intermittent charging function is disabled, a single charge cycle is initiated with the charge timer as programmed by CHM_TMR pin. If intermittent charging is enabled, an intermittent charge cycle is initiated with charge timer as 25% of CHM_TMR programmed value.
If the charger is in thermal regulation during charging, the actual charging current will be less than the programmed value. For NiMH charging, termination by timer is still enabled, but the charging safety timer is counted at half the clock rate. For more information, refer to Section 18.104.22.168.