BQ27750 Datasheet, PDF (18/34 Pages) Texas Instruments – Impedance Track Battery Gas Gauge and Protection Solution for 1-Series Cell Li-Ion Battery Packs

bq27750
SLUSCM7 – JUNE 2017
Feature Description (continued)
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CAUTION
If the device is configured as a single-master architecture (an application processor)
and an occasional NACK is detected in the operation, the master can resend the
transaction. However, in a multi-master architecture, an incorrect ACK leading to
accidental loss of bus arbitration can cause a master to wait incorrectly for another
master to clear the bus. If this master does not get a bus-free signal, then it must have
in place a method to look for the bus and assume it is free after some period of time.
Also, if possible, set the clock speed to be 100 kHz or less to significantly reduce the
issue described above for multi-mode operation.
7.3.12 N-Channel Protection FET Drive
The bq27750 device controls two external N-Channel MOSFETs in a back-to-back configuration for battery
protection. The charge (CHG) and discharge (DSG) FETs are automatically disabled if a safety fault (AOLD,
ASSC, ASCD, SOV) is detected, and can also be manually turned off using AFE_CONTROL[CHGEN, DSGEN]
= 0, 0. When the gate drive is disabled, an internal circuit discharges CHG to BAT and DSG to PACK.
7.3.13 Low Frequency Oscillator
The bq27750 AFE includes a low frequency oscillator (LFO) running at 262.144 kHz. The AFE monitors the LFO
frequency and indicates a failure via LATCH_STATUS[LFO] if the output frequency is much lower than normal.
7.3.14 High Frequency Oscillator
The bq27750 AGG includes a high frequency oscillator (HFO) running at 16.78 MHz. It is synthesized from the
LFO output and scaled down to 8.388 MHz with 50% duty cycle.
7.3.15 1.8-V Low Dropout Regulator
The bq27750 AFE contains an integrated 1.8-V LDO that provides regulated supply voltage for the device CPU
and internal digital logic.
7.3.16 Internal Voltage References
The bq27750 AFE provides two internal voltage references with V_REF1, used by the ADC and CC, while V_REF2 is
used by the LDO, LFO, current wake comparator, and OCD/SCC/SCD1/SCD2 current protection circuitry.
7.3.17 Overcurrent in Discharge Protection
The overcurrent in discharge (OCD) function detects abnormally high current in the discharge direction. The
overload in discharge threshold and delay time are configurable via the OCD_CONTROL register. The thresholds
and timing can be fine-tuned even further based on a sense resistor with lower resistance or wider tolerance via
the PROTECTION_CONTROL register. The detection circuit also incorporates a filtered delay before disabling
the CHG and DSG FETs. When an OCD event occurs, the LATCH_STATUS[OCD] bit is set to 1 and is latched
until it is cleared and the fault condition has been removed.
7.3.18 Short-Circuit Current in Charge Protection
The short-circuit current in charge (SCC) function detects catastrophic current conditions in the charge direction.
The short-circuit in charge threshold and delay time are configurable via the SCC_CONTROL register. The
thresholds and timing can be fine-tuned even further based on a sense resistor with lower resistance or wider
tolerance via the PROTECTION_CONTROL register. The detection circuit also incorporates a blanking delay
before disabling the CHG and DSG FETs. When an SCC event occurs, the LATCH_STATUS[SCC] bit is set to
1 and is latched until it is cleared and the fault condition has been removed.
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