SLVSB64I November 2011 – March 2018 TPS65217
When the charger is enabled (the CH_EN bit is set to 1b), it first checks for a short circuit on the BAT pin by sourcing a small current and monitoring the BAT voltage. If the voltage on the BAT pin increases to more than the BAT pin short-circuit detection threshold (VBAT(SC)), a battery is present and charging can start. The battery is charged in three phases: precharge, constant-current fast charge (current regulation), and constant-voltage (CV) charge (voltage regulation). In all charge phases, an internal control loop monitors the device junction temperature and decreases the charge current if an internal temperature threshold is exceeded. Figure 13 shows a typical charging profile. Figure 14 shows a modified charging profile.
In the precharge phase, the battery is charged at the precharge current (IPRECHG), which is typically 10% of the fast-charge current rate. The battery voltage starts rising. After the battery voltage crosses the precharge-to-fast-charge transition threshold (VLOWV), the battery is charged at the fast charge current (ICHG). The battery voltage continues to rise. When the battery voltage reaches the battery charger voltage (VOREG), the battery is held at a constant value of VOREG. The battery current now decreases as the battery approaches full charge. When the battery current reaches the charge current for termination detection threshold (ITERM), the TERMI bit in the CHGCONFIG0 register is set to 1b. To avoid false termination when the charger goes to either the dynamic power path management (DPPM) loop or thermal loop, termination is disabled when either loop is active.
The charge current cannot exceed the input current limit of the power path minus the load current on the SYS pin because the power-path manager decreases the charge current to support the system load if the input current limit is exceeded. Whenever the nominal charge current is decreased by action of the power-path manger, the DPPM loop, or the thermal loop, the safety timer is clocked with half the nominal frequency to extend the charging time by a factor of 2.