Rainbow Electronics DS2788 - Manual (Page 16)

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8 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 register 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, 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, 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 continuously above the VCHG threshold for the
period between two average current (IAVG) readings,
where both IAVG readings are below IMIN. The two
consecutive IAVG readings must also be positive and
nonzero. 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 (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 dis-
charge rate ensures that the active empty point is not
detected at loads much lighter than those used to con-
struct the model. Also, active empty 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-full to
include part of the standby capacity in the measure-
ment of the active capacity. Active empty detection
sets the learn flag bit (LEARNF) in STATUS.
Result Registers
The DS2788 processes measurement and cell charac-
teristics on a 3.5s interval and yields seven result regis-
ters. 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 dis-
play 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 +50°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 ). Though the register format permits val-
ues greater than 100%, the register value is clamped to
a maximum value of 100%.
Active Empty, AE(T): The active empty capacity of the
battery at the present temperature is reported normal-
ized to the +50°C full value. This 13-bit value reflects
the cell model active empty 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 nor-
malized to the +50°C full value. This 13-bit value
reflects the cell model standby empty value at the cur-
rent 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 capacity available under the current
temperature conditions at the active empty discharge
rate (IAE) to the active empty point in absolute units of
milliamp/hours (mAh). RAAC is 16 bits.
Remaining Standby Absolute Capacity, RSAC
[mAh]: RSAC reports the capacity available under the
current temperature conditions at the standby empty
discharge rate (ISE) to the standby empty point capaci-
ty in absolute units of mAh. RSAC is 16 bits.
Remaining Active Relative Capacity, RARC [%]:
RARC reports the capacity available under the current
temperature conditions at the active empty discharge
rate (IAE) to the active empty point in relative units of
percent. RARC is 8 bits.
Remaining Standby Relative Capacity, RSRC [%]:
RSRC reports the capacity available under the current
temperature conditions at the standby empty discharge
rate (ISE) to the standby empty point capacity in rela-
tive units of percent. RSRC is 8 bits.
Stand-Alone Fuel-Gauge IC with
LED Display Drivers
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