BQ27000 Datasheet, PDF (19/29 Pages) Texas Instruments – SINGLE CELL Li-Ion AND Li-Pol BATTERY GAS GAUGE IC FOR PORTABLE APPLICATIONS (bqJUNIOR)

bq27000, bq27200
www.ti.com
SLUS556B – SEPTEMBER 2004 – REVISED NOVEMBER 2004
Scaled EDVF Threshold (SEDVF) — Address 0x77
This register contains the scaled value of the threshold for zero battery capacity. To calculate the value to
program, use the following equation:
SEDVF = Design EDVF(mV)/8 – 256
Scaled EDV1 Threshold (SEDV1) — Address 0x78
This register contains the scaled value of the voltage when the battery has 6.25% remaining capacity. When the
battery reaches this threshold during a valid discharge, the device learns the full battery capacity, including the
remaining 6.25%. See the bqJUNIOR Capacity Learning section for more information on the learning cycles of
the device. To calculate the value to program, use the following equation:
SEDV1 = Design EDV1(mV)/8 – 256
Initial Standby Load Current (ISLC) — Address 0x79
This register contains the scaled, end-equipment-design standby current. On a full reset or POR, this value is
transferred to the SI register and is used to calculate Standby Time-to-Empty. The gauge learns a new standby
load if the discharge activity is above the DMF threshold and less than or equal to 2 times the initial standby
load.
A capacity learning cycle is disqualified if average current is less than or equal to 2 times the initial standby load
when the EDV1 threshold voltage is reached. The equation for programming this value is:
ISLC = Design Standby Current (mA) * R_S(mΩ) / 7.14
where R_S is the value of the sense resistor used in the system.
Digital Magnitude Filter and Self-Discharge Values (DMFSD) — Address 0x7A
NAME
BIT 7
DMF[3]
BIT 6
DMF[2]
BIT 5
DMF[1]
BIT 4
DMF[0]
BIT 3
SD[3]
BIT 2
SD[2]
BIT 1
SD[1]
BIT 0
SD[0]
DMF[3:0]
Sets the digital magnitude filter threshold. See the bqJUNIOR Digital Magnitude Filter section for
more information on the function of the DMF. The value to be programmed is:
DMF[3:0] = Design Threshold/4.9
SD[3:0]
Sets the self-discharge rate %/day value at 25°C. The value to be programmed is:
SD[3:0] = 1.61/Design SD
NAC is reduced with an estimated self-discharge correction to adjust for the expected self-discharge of the
battery. This estimation is performed only when the battery is not being charged. The rate programmed in
EEPROM for DMFSD determines the self-discharge when 20°C ≤ TEMP < 30°C. The self-discharge estimation is
doubled for each 10°C decade hotter than the 20-30°C decade, up to a maximum of 16 times the programmed
rate for TEMP ≥ 60°C and is halved for each 10°C decade colder than the 20-30°C decade, down to a minimum
of 1/4th the programmed rate for TEMP < 0°C. The self-discharge estimation is performed by reducing NAC by
NAC/512 at a time interval that achieves the desired estimation. If DMFSD is programmed with 8 decimal, the
self-discharge rate is 0.195% per day in the 20-30°C decade. This is accomplished by reducing NAC by
NAC/512 (100/512 = 0.195%) a single time every 23.3 hours (0.195 * 24/23.3 = 0.2). If temperature rises by
10°C, the 0.195% NAC reduction is made every 11.65 hours for a 0.4% per day reduction. If TAPER[7] = 1,
capacity aging is enabled, and there is an LMD reduction of 0.01% (Design Capacity/1024) every time there are
8 NAC self-discharge estimate reductions without charging the battery to full.
Taper Current (TAPER) — Address 0x7B
This register contains the enable bit for the capacity aging estimate and the charge taper current value. The
taper current value, in addition to battery voltage, is used to determine when the battery has reached a full
charge state. The equation for programming the taper current is:
TAPER[6-0] = Design Taper Current (mA) * R_S(mΩ)/228 µV
where R_S is the value of the sense resistor used in the system.
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