BQ2040_15 Datasheet, PDF (9/36 Pages) Texas Instruments – Gas Gauge IC With SMBus Interface

Not Recommended For New Designs
bq2040
Charge Suspension
The bq2040 may temporarily suspend charge if it detects
a charging fault. The charging faults include the follow-
ing conditions:
n Maximum Overcharge: If charging continues for
more than the programmed maximum overcharge
limit as defined in EE 0x3a—0x3b beyond RM=FCC,
the Fully_Charged bit is set, and the requested
charging current is set to the maintenance rate.
n Overvoltage: An over-voltage fault exists when the
bq2040 measures a voltage more than 5% above the
ChargingVoltage. When the bq2040 detects an
overvoltage condition, the requested charge current is
set to 0 and the Terminate_Charge_Alarm bit is set
in BatteryStatus. The alarm bit is cleared when the
current drops below 256mA and the voltage is less
than 105% of ChargingVoltage.
n Overcurrent: An overcurrent fault exists when the
bq2040 measures a charge current more than 25%
above the ChargingCurrent. If the ChargingCurrent
is less than 1024mA, an overcurrent fault exists if the
charge current is more than 1mA above the lowest
multiple of 256mA that exceeds the ChargingCurrent.
When the bq2040 detects an overcurrent condition, the
requested charge current is set to 0 and the
Terminate_Charge_Alarm bit is set in Battery Status.
The alarm bit is cleared when the current drops below
256mA.
n Maximum Temperature: When the battery
temperature equals the programmed maximum
temperature, the requested charge current is set to
zero and the Over_Temp_Alarm and the
Terminate_Charge_Alarm bits are set in Battery
Status. The Over_Temp_Alarm bit is cleared when
the temperature drops to 43°C below the maximum
temperature threshold minus 5°C.
n PSTAT: When the PSTAT input is ≥1.5V, the
requested charge current is set to 0 and the
Terminate_Charge_Alarm bit is set in BatteryStatus
if the Discharging flag is not set. The alarm bit is
cleared when the PSTAT input is <1.0V or the
Discharging flag is set.
n Low Temperature: When the battery temperature
is less than 12°C (LTF bit in FLAGS2 set), the
requested charge current is set to the maintenance
rate. Once the temperature is above 15°C, the
requested charge current is set to the fast rate.
n Undervoltage: When the battery voltage is below
the EDVF threshold, the requested charge current is
set to the EDVF rate stored in EE0x5a/0x5b. Once
the voltage is above EDVF, the requested charge
current is set to the fast or maintenance rate
depending on the state of the LTF bit.
Count Compensations
Charge activity is compensated for temperature and
state-of-charge before updating the RM and/or DCR.
Self-discharge estimation is compensated for tempera-
ture before updating RM or DCR.
Charge Compensation
Charge efficiency is compensated for state-of-charge,
temperature, and battery chemistry. The charge effi-
ciency is adjusted using the following equations:
1.) RM = RM * (Q _EFC − Q _ET )
where RelativeStateOfCharge < FullChargePercentage,
and Q _EFC is the programmed fast-charge efficiency vary-
ing from 0.75 to 1.0.
2.) RM = RM * (Q _ETC − Q _ET )
where RelativeStateOfCharge ≥ FullChargePercentage
and Q _ETC is the programmed maintenance (trickle)
charge efficiency varying from 0.75 to 1.0.
Q _ET is used to adjust the charge efficiency as the battery
temperature increases according to the following:
Q _ET = 0 if T < 30°C
Q _ET = 0.02 if 30°C ≤ T < 40°C
Q _ET = 0.05 if T ≥ 40°C
QET is 0 over the entire temperature range for Li-Ion.
Digital Magnitude Filter
The bq2040 has a programmable digital filter to elimi-
nate charge and discharge counting below a set
threshold, VSRD. Table 2 shows typical digital filter
settings. The proper digital filter setting can be calcu-
lated using the following equation.
DMF = ⁴⁵
VSRD
Table 2. Typical Digital Filter Settings
DMF
75
100
150
175
200
DMF Hex.
4B
64
96
AF
C8
VSRD (mV)
0.60
0.45
0.30
0.26
0.23
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