DS2780 Standalone Fuel Gauge IC
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“learn cycle”. First, the Active Empty Point must be detected. The Learn Flag (LEARNF) is set at this point. Then,
once charging starts, the charge must continue uninterrupted until the battery is charged to full. Upon detecting full,
LEARNF is cleared, the Charge to Full (CHGTF) flag is set and the Age Scalar (AS) is adjusted according to the
learned capacity of the cell.
ACR Housekeeping
The ACR value is adjusted occasionally to maintain the coulomb count within the model curve boundaries. When
the battery is charged to full (CHGTF set), the ACR is set equal to the age scaled full lookup value at the present
temperature. If a learn cycle is in progress, correction of the ACR value occurs after the age scalar (AS) is updated.
When an empty condition is detected (AEF or LEARNF set), the ACR adjustment is conditional. If AEF is set and
LEARNF is not, then the Active Empty Point was not detected and the battery is likely below the Active Empty
capacity of the model. The ACR is set to the Active Empty model value only if it is greater than the Active Empty
model value. If LEARNF is set, then the battery is at the Active Empty Point and the ACR is set to the Active Empty
model value.
Full Detect
Full detection occurs when the Voltage (VOLT) readings remain above the VCHG (Charge Voltage) threshold for
the duration of two Average Current (IAVG) readings, where both IAVG readings are below IMIN (Terminating
Current). The two consecutive IAVG readings must also be positive and non-zero. This ensures that removing the
battery from the charger does not result in a false detection of full. Full Detect sets the Charge to Full (CHGTF) bit
in the Status register.
Active Empty Point Detect
Active Empty Point detection occurs when the Voltage register drops below the VAE threshold and the two
previous Current readings are above IAE. This captures the event of the battery reaching the Active Empty Point.
Note that the two previous Current readings must be negative and greater in magnitude than IAE, that is, a larger
discharge current than specified by the IAE threshold. Qualifying the Voltage level with the discharge rate ensures
that the Active Empty Point is not detected at loads much lighter than those used to construct the model. Also, the
Active Empty Point must not be detected when a deep discharge at a very light load is followed by a load greater
than IAE. Either case would cause a learn cycle on the following charge to include part of the Standby capacity in
the measurement of the Active capacity. Active Empty Point detection sets the Learn Flag (LEARNF) bit in the
Status register. DO NOT confuse the Active Empty Point with the Active Empty Flag. The Active Empty Flag is set
only when the VAE threshold is passed.
RESULT REGISTERS
The DS2780 processes measurement and cell characteristics on a 440ms interval and yields seven result
registers. The result registers are sufficient for direct display to the user in most applications. The host system can
produce customized values for system use, or user display by combining measurement, result and User EEPROM
values.
FULL(T) [ ]: The Full capacity of the battery at the present temperature is reported normalized to the 40°C Full
value. This 15-bit value reflects the cell model Full value at the given temperature. FULL(T) reports values between
100% and 50% with a resolution of 61ppm (precisely 2
-14
). The register is clamped to a maximum value of 100%
even though the format permits values greater than 100%,.
Active Empty, AE(T) [ ]: The Active Empty capacity of the battery at the present temperature is reported
normalized to the 40°C Full value. This 13-bit value reflects the cell model Active Empty Point at the given
temperature. AE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2
-14
).
Standby Empty, SE(T) [ ]: The Standby Empty capacity of the battery at the present temperature is reported
normalized to the 40°C Full value. This 13-bit value reflects the cell model Standby Empty value at the current
temperature. SE(T) reports values between 0% and 49.8% with a resolution of 61ppm (precisely 2
-14
).
Remaining Active Absolute Capacity (RAAC) [mAh] – RAAC reports the remaining battery capacity under the
current temperature conditions at the Active Empty discharge rate (IAE) to the Active Empty Point in absolute units
of milli-amp-hours. RAAC is 16 bits.
