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bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
The wake up comparator is used to indicate a change in cell current while the bq27500/1 is in eitherSLEEP or HIBERNATE modes. Operation Configuration uses bits [RSNS1-RSNS0] to set the senseresistor selection. Operation Configuration also uses the [IWAKE] bit to select one of two possiblevoltage threshold ranges for the given sense resistor selection. An internal interrupt is generated when thethreshold is breached in either charge or discharge directions. Setting both [RSNS1] and [RSNS0] to "0"disables this feature.
Table 5-4. I
WAKE
Threshold Settings
(1)
RSNS1 RSNS0 IWAKE Vth(SRP-SRN)
0 0 0 Disabled
0 0 1 Disabled
0 1 0 1.25 mV or –1.25 mV
0 1 1 2.5 mV or –2.5 mV
1 0 0 2.5 mV or –2.5 mV
1 0 1 5 mV or –5 mV
1 1 0 5 mV or –5 mV
1 1 1 10 mV or –10 mV
(1) The actual resistance value vs. the setting of the sense resistor is not important just the actual voltagethreshold when calculating the configuration.
Data Flash can only be updated if Voltage( ) ≥Flash Update OK Voltage. Flash programming current cancause an increase in LDO dropout. The value of Flash Update OK Voltage should be selected such thatthe bq27500/1 V
CC
voltage does not fall below its minimum of 2.4V during Flash write operations.
The bq27500 provides an autocalibration feature that measures the voltage offset error across SRP andSRN as operating conditions change. It subtracts the resulting offset error from normal sense resistorvoltage, V
SR
, for maximum measurement accuracy.
Auto calibration of the ADC begins on entry to SLEEP mode, except if Temperature( ) is <= 5 °C orTemperature( ) >= 45 °C.
The fuel gauge also performs a single offset when (1) the condition of AverageCurrent( ) ≤100mA and (2){voltage change since last offset calibration ≥256mV} or {temperature change since last offset calibrationis greater than 80 °C for ≥60s}.
Capacity and current measurements will continue at the last measured rate during the offset calibrationwhen these measurements cannot be performed. If the battery voltage drops more than 32mV during theoffset calibration, the load current has likely increased considerably; hence, the offset calibration will beaborted.
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