BQ27350 Datasheet, PDF (25/33 Pages) Texas Instruments – Single Cell Li-Ion Battery Manager With Impedance Track Fuel Gauge Technology

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bq27350
Single Cell Li-Ion Battery Manager
With Impedance Track Fuel Gauge Technology
SLUS754 – MARCH 2007
5.7.2 WAKE-UP COMPARATOR
The wake up comparator is used to indicate a change in cell current while the bq27350 is in either Sleep
or Hibernate modes. PackConfiguration( ) uses bits [RSNS1-RSNS0] to set the sense resistor selection.
PackConfiguration( ) uses the [IWAKE] bit to select one of two possible voltage threshold ranges for the
given sense resistor selection. An internal interrupt is generated when the threshold is breached in either
charge or discharge directions. A setting of 0x00 of RSNS1..0 disables this feature.
Table 5-3. I_WAKE Threshold Settings⁽¹⁾
RSNS1
0
0
0
0
1
1
1
1
RSNS0
0
0
1
1
0
0
1
1
IWAKE
0
1
0
1
0
1
0
1
Vth(SRP-SRN)
Disabled
Disabled
+1.25 mV or –1.25 mV
+2.5 mV or –2.5 mV
+2.5 mV or –2.5 mV
+5 mV or –5 mV
+5 mV or –5 mV
+10 mV or –10 mV
(1) The actual resistance value vs. the setting of the sense resistor is not important just the actual voltage
threshold when calculating the configuration.
5.7.3 FLASH UPDATES
Data Flash can only be updated if Voltage( ) ≥ Flash Update OK Voltage. Flash programming current can
cause an increase in LDO dropout. The value of Flash Update OK Voltage should be selected such that
the bq27350 Vcc voltage does not fall below its minimum of 2.4V during Flash write operations. For the
TPS71525 LDO shown in the Reference Schematic, the default value of 2800mV is appropriate.
5.8 AUTOCALIBRATION
The bq27350 provides an autocalibration feature that will measure the voltage offset error across SRP
and SRN from time-to-time as operating conditions change. It subtracts the resulting offset error from
normal sense resistor voltage, Vsr, for maximum measurement accuracy.
The gas gauge performs a single offset calibration when (1) the interface lines stay low for a minimum of
Bus Low Time and (2) Vsr > Deadband.
The gas gauge also performs a single offset when (1) the condition of AverageCurrent( ) ≤ Autocal Min
Current and (2) {voltage change since last offset calibration ≥ Delta Voltage} or {temperature change
since last offset calibration is greater than Delta Temperature for ≥ Autocal Time}.
Capacity and current measurements should continue at the last measured rate during the offset calibration
when these measurements cannot be performed. If the battery voltage drops more than Cal Abort during
the offset calibration, the load current has likely increased considerably; hence, the offset calibration will
be aborted.
6 COMMUNICATIONS
The bq27350 uses I²C communications identical to the bq27200, and interfaces directly with TI-OMAP and
other standard I²C-master devices.
The bq27350 also uses an SDQ interface to communicate with security products, such as the bq26100.
The bq27350 is only acting as a format translator between I²C and SDQ.
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COMMUNICATIONS
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