Application Circuits

The IC measures voltage of the cells and balances the charge using internal FETs and the balancing resistors. It also measures current using a sense resistor that is accumulated to give a coulomb count and measures temperature using an on-chip sensor or up to 4 external thermistors, since the cells are likely to be located far away from the IC. The protector control drives a pair of high-side N-channel FETs. The IC also opens a three-terminal fuse for harsh faults that necessitate the battery to be permanently disabled for safety reasons. To power small loads like real-time clocks or housekeeping microcontrollers that need to be always on, the IC provides a regulated output that stays alive even when the protection FETs are opened. This output powers down only when the cells are severely depleted and, therefore, prevents any further drain for safety reasons.

The IC can permanently open a three-terminal fuse with the PFAIL pin when a permanent failure is detected. A secondary protector can also be included to open the three-terminal fuse.

The IC and the system can share a pushbutton to wake up the system and the IC. The diode on the system interface PMIC blocks the pulldown when there is no supply. This prevents the wakeup for the IC when the system interface PMIC loses power in ship mode. The diode on the ALRT pin prevents the alert pulldown from triggering a button action on the PMIC. This prevents accidental shutdown in the event of an uncleared alert for > 10 seconds. The FET between the IC and the System AP blocks the System AP pulldown from triggering the wakeup when the AP does not have power. The FET acts as a level shifter and passes the pulldown alert signal in both directions when the 1.8V voltage is present.