When a valid input source is connected to IN or USB and the BQ2416xx is NOT in High Impedance mode, the buck converter enters soft-start and turns on to power the load on SYS. The STAT/INT pin outputs a 128-µs interrupt pulse to alert the host that an input has been connected. The FAULT bits indicate a normal condition, and the Supply Status register indicates that a new supply is connected. The CE bit (bit 1) in the control register (0x02) indicates whether a charge cycle is initiated. By default, the BQ2416xx ( CE = 0) enables a charge cycle when a valid input source is connected. When the CE bit is '1' and a valid input source is connected, the battery FET is turned off and the SYS output is regulated to the V_SYS(REG) programmed by the V_BATREG threshold in the I²C register. A charge cycle is initiated when the CE bit is written to a 0 value (cleared).

When the CE bit is a 0 and a valid source is connected to IN or USB, the buck converter starts up using soft-start. A charge cycle is initiated 64 ms after the buck converter iniates startup. When V_BAT is high enough that V_SYS > V_SYS(REG), the battery FET is turned on and the SYS output is connected to BAT. If the SYS voltage falls to V_SYS(REG), it is regulated to that point to maintain the system output even with a deeply discharged or absent battery. In this mode, the SYS output voltage is regulated by the buck converter and the battery FET linearly regulates the charge current into the battery. The current from the supply is shared between charging the battery and powering the system load at SYS. The dynamic power-path management (DPPM) circuitry of the BQ2416xx monitors the current limits continuously, and if the SYS voltage falls to the V_MINSYS voltage, it adjusts charge current to maintain the minimum system voltage and supply the load on SYS. If the charge current is reduced to zero and the load increases further, the BQ2416xx enters battery-supplement mode. During supplement mode, the battery FET is turned on and the battery supplements the system load.

When an input is connected with no battery attached and termination enabled, the startup process proceeds as normal until the termination deglitch times out. After this, the BQ2416xx enters battery detection and waits for a battery to be connected. Once a battery is connected and passes battery detection, a new charge cycle begins. Once the battery is applied, the HZMODE bit or CD pin must be toggled before writing the BATREG to a higher voltage and beginning a new charge cycle. Failure to do this can result in SYS unexpectedly regulating to 15% above V_BATREG.

Figure 8-2 Example DPPM Response (V_Supply = 5 V, V_BAT = 3.1 V, 1.5 A Input Current Limit)