BQ27750 Datasheet, PDF (17/34 Pages) Texas Instruments – Impedance Track Battery Gas Gauge and Protection Solution for 1-Series Cell Li-Ion Battery Packs

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Feature Description (continued)
NTC
V_REG
R_NTC
ADx
bq27750
SLUSCM7 – JUNE 2017
Figure 18. External Thermistor Biasing
7.3.9 Power Supply Control
The bq27750 device manages its supply voltage dynamically according to operating conditions. When V_BAT >
V_{SWITCHOVER–} + V_HYS, the AFE connects an internal switch to BAT and uses this pin to supply power to its internal
1.8-V LDO, which subsequently powers all device logic and flash operations. Once BAT decreases to V_BAT <
V_{SWITCHOVER–}, the AFE disconnects its internal switch from BAT and connects another switch to PACK, allowing
sourcing of power from a charger (if present). An external capacitor connected to PBI provides a momentary
supply voltage to help guard against system brownouts due to transient short-circuit or overload events that pull
BAT below V_{SWITCHOVER–}.
7.3.10 Power-On Reset
In the event of a power-cycle, the bq27750 AFE holds its internal RESET output pin high for t_RST duration to
allow its internal 1.8-V LDO and LFO to stabilize before running the AGG. The AFE enters power-on reset when
the voltage at V_REG falls below V_REGIT– and exits reset when V_REG rises above V_REGIT– + V_HYS for t_RST time. After
t_RST, the bq27750 AGG will write its trim values to the AFE.
1.8-V Regulator ^VIT+
t_OSU
t_RST
normal operation
(untrimmed)
normal operation
(trimmed)
VIT–
LFO
AFE RESET
AGG writes trim values to
AFE
Figure 19. POR Timing Diagram
7.3.11 Bus Communication Interface
The bq27750 device has an I²C bus communication interface. This device has the option to broadcast
information to a smart charger to provide key information to adjust the charging current and charging voltage
based on the temperature or individual cell voltages.
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