BQ27000 Datasheet, PDF (17/29 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
Max Load Current Registers (MLIL/MLIH) — Address 0x1E/0x1F
This register pair reports the measured maximum load current through sense resistor. The max load current is an
adaptive measurement of the maximum load conditions. If the measured current is ever greater than the initial
Max Load Current programmed in EEPROM, the register pair updates to the new current. MLI is reduced to the
average of the previous value and the initial value in EEPROM whenever the battery is charged to full after a
previous discharge to an RSOC less than 50%. This keeps it from being stuck at an unusually high value. The
value is reported in units of 3.57 µV per count. Use the following equation to convert the value to mA, where R_S
is the sense resistor value in milliohms:
Max Load Current = (256*MLIH + MLIL) * (3.57/ R_S)
The host system has read-only access to this register pair.
Max Load Time to Empty Registers (MLTTEL/MLTTEH) — Address 0x20/0x21
This register pair reports calculated time-to-empty at the maximum measured discharge rate. This value is based
on the temperature and discharge rate compensated available charge at the max load current. MLTTE is
reported in minutes. MLTTE is calculated by:
MLTTE = 60 * CACT/MLI
The host system has read-only access to this register pair.
Available Energy Registers (SAEL/SAEH) — Address 0x22/0x23
SAE is the calculated energy available from the battery. The available energy is computed by multiplying the
compensated available capacity with the average of reported voltage and EDVF threshold voltage while
discharging. SAE is not allowed to increase while discharging, so that if the discharge rate decreases, the
available energy does not increase. This is accomplished by reporting the smaller of the previous and new
computed values. During charging, the available energy uses a computed value for average voltage to avoid an
inflated energy report due to the increased voltage. The value is reported in units of 29.2 µV²h per count. Use the
following equation to convert the value to mWh, where R_S is the sense resistor value in milliohms.
SAE(mWh) = (256*SAEH + SAEL) * 29.2 / Rs(mΩ)
While charging SAE is calculated as:
SAE = 8 * CACT * (3088 +512*NAC/LMD)/65536,
and while discharging SAE is calculated as:
SAE = 4 * CACT * (Reported Voltage + EDVF)/65536
The host system has read-only access to this register pair.
Average Power Registers (APL/APH) — Address 0x24/0x25
Average power is the calculated power delivered during a discharge. It is the product of average current and
reported voltage, reported in units of 29.2 µV² per bit. Use the following formula to convert the value to mW,
where RS is the sense resistor value in milliohms.
AP = (256 * APH + APL) * 29.2 / Rs(mΩ)
AP = 8 * AI * Reported Voltage/65536, while discharging
AP = 0, while charging
The host system has read-only access to this register pair.
Time-to-Empty at Constant Power Registers (TTECPL/TTECPH) — Address 0x26/0x27
TTECP is the time-to-empty in minutes with a constant power load. Because SAE is already scaled for the
average discharge voltage, the result is simply the ratio of SAE to AP:
TTECP = 60 * SAE/AP
The host system has read-only access to this register pair.
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