The device charges NiMH batteries in constant current mode only. The charge current programmed by ISET is the only current applied over the charging cycle, as shown in Figure 7-1. The charge termination method for the device is timer-based. The charge safety timer, t_SAFETY, sets the charging duration. Programming the charge safety timer is done with a pulldown resistor on the TMR pin.

Intermittent charging is designed to replenish the natural self-discharge of NiMH cells by restarting a short charge cycle (20% of t_SAFETY) when the output voltage falls below the V_RECHG threshold. If the intermittent charging function is disabled and a full charge cycle has been completed (safety timer expired with V_OUT above V_RECHG), the device does not start a new charge cycle automatically and requires input supply or TS pin toggle to initiate a new charge cycle.

If battery voltage is above V_RECHG at power up, the battery is considered full and the device does not charge. Once the battery voltage falls below V_RECHG, the device automatically begins charging. If the intermittent charging function is disabled, a single charge cycle is initiated with the safety timer duration programmed by the TMR pin. If intermittent charging is enabled, an intermittent charge cycle is initiated for 20% of the TMR programmed value.

When the charge timer (full-length or intermittent) expires, the battery voltage is checked again. If the battery voltage is below V_RECHG, a fault is reported through the STAT pin and further charging is prevented. If the charge timer expires with V_OUT above V_RECHG, the STAT pin indicates charge completed. In the case where the TS fault is within the cool threshold, V_{OUT_OVP} is automatically reduced to V_{OUT_OVP_TSCOOL} voltage.

If the charger is in thermal regulation during charging, the actual charging current will be less than the programmed value. Termination by timer is still enabled, but the charging safety timer is counted at half the clock rate. For more information, refer to Section 7.3.2.2.