BQ27000 Datasheet, PDF (16/29 Pages) Texas Instruments – SINGLE CELL Li-Ion AND Li-Pol BATTERY GAS GAUGE IC FOR PORTABLE APPLICATIONS (bqJUNIOR)

bq27000, bq27200
SLUS556B – SEPTEMBER 2004 – REVISED NOVEMBER 2004
www.ti.com
Last Measured Discharge Registers (LMDL/LMDH) — Address 0x12/0x13
Last measured discharge is the measured discharge capacity of the battery from full to empty. LMD is updated
on a valid learning cycle, which occurs when the battery reaches the EDV1 level while the VDQ bit is set. It is
used with NAC to calculate Relative State-Of-Charge (RSOC). The host system has read-only access to this
register pair. LMD is reported in units of 3.57 µVh per count.
Average Current Registers (AIL/AIH) — Address 0x14/0x15
This register pair reports the magnitude of the average current through the sense resistor. The value is reported
with a resolution 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:
Average Current = (256*AIH + AIL) * 3.57/ R_S
The current reported is an average over the last 5.12 seconds. The host system has read-only access to this
register pair.
Time-to-Empty Registers (TTEL/TTEH) — Address 0x16/0x17
This register pair reports calculated time-to-empty at the measured discharge rate. This value is based on the
temperature and discharge rate compensated available charge and the average current. The equation to
calculate TTE is:
TTE = 60 * CACT/AI
TTE is reported in minutes. The host system has read-only access to this register pair.
Time-to-Full Registers (TTFL/TTFH) — Address 0x18/0x19
This register pair reports calculated time-to-full at the measured charge rate. The time computed at the average
current charge rate is extended by 50% to estimate the effect of the current taper. TTF is reported in minutes.
The equation for TTF is:
TTF = 60 * 1.50 * (LMD-NAC)/AI
The host system has read-only access to this register pair.
Standby Current Registers (SIL/SIH) — Address 0x1A/0x1B
This register pair reports measured standby current through the sense resistor. The standby current is an
adaptive measurement. Initially, the register pair reports the standby current programmed in EEPROM and after
spending some time in standby, the register pair reports the measured standby current. The register value is
updated every 5.12 seconds when the measured current is above the DMF threshold and is less than or equal to
2x the initial programmed standby current value. Each new SI value is computed as follows:
SI_NEW = (15/16)*SI_OLD + (1/16)*AI
This filter function allows the reported standby current to shift towards the actual measured current with a time
constant of approximately 67 seconds. The value is reported with a resolution of 3.57 µV per bit. Use the
following equation to convert the value to mA, where R_S is the sense resistor value in milliohms:
Standby Load Current = (256*SIH + SIL) * (3.57/ R_S)
The host system has read-only access to this register pair.
Standby Time-to-Empty Registers (STTEL/STTEH) — Address 0x1C/0x1D
This register pair reports calculated time-to-empty at the measured standby current value. This value is based on
the nominal available charge and the standby current. STTE is reported in minutes. STTE is calculated by:
STTE = 60 * NAC/SI
The host system has read-only access to this register pair.
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