BQ27210 Datasheet, PDF (19/30 Pages) Texas Instruments – Li-Ion AND Li-Pol BATTERY GAS GAUGE IC FOR PORTABLE APPLICATIONS (bqJUNIOR)

bq27010, bq27210
www.ti.com
SLUS707B – APRIL 2006 – REVISED JANUARY 2007
Scaled EDV1 Threshold (SEDV1) — Address 0x78
This register contains the scaled value of the voltage when the battery has 6.25% remaining capacity at a very
light load. DEDV and EDVT coefficients can be programmed to reduce the EDVI threshold at heavier loads and
at cold temperatures. When the battery reaches this threshold during a valid discharge, the device learns the full
battery capacity, including the remaining unmeasured 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 and EDV1 Temperature Compensation (ISLC/EDVT) – Address
0x79
Name
BIT 7
0
BIT 6
ISLC[2]
BIT 5
ISLC[1]
BIT 4
ISLC[0]
BIT 3
EDVT[3]
BIT 2
EDVT[2]
BIT 1
EDVT[1]
BIT 0
EDVT[0]
The most significant nibble in this register contains the initial standby load current (ISLC) that is transferred to SI
on all resets. The gauge will use this initial value, but will learn the actual system standby current by averaging
in measured discharge currents above the DMF threshold and less than or equal to 2 times the ISLC value.
ISLC is programmed in units of 57.1 µV per bit.
A capacity learning cycle is disqualified if average current is less than or equal to 2 times the ISLC programmed
value.
The equation for programming ISLC is:
ISLC = Design Standby Current (mA) * R_S (mΩ) / 57.1 µV, where R_S is the sense resistor value.
The least significant nibble in this register contains the EDV1 temperature compensation (EDVT) coefficient. The
temperature compensation is impedance-based, so the resulting compensation is proportional to load current.
EDVT is programmed to increase the EDV1 rate compensation (programmed in the DEDV coefficient) by 0.78%
per count for each degree than temperature is below the T_off threshold programmed in TCOMP. See the
GAF/DEDV section for the complete EDV1 compensation equation.
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 % per 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 0.1% (Design Capacity / 1024)
every time there are 8 NAC self-discharge estimate reductions without charging the battery to full.
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