DS2778 Maxim Integrated Products, DS2778 Datasheet - Page 23

• Manufacturer Part Number: DS2778
• Description: 2-Cell Stand-Alone Li+ Fuel-Gauge IC
• Manufacturer: Maxim Integrated Products

count-based estimation is reset after a learn cycle. The
cycle-count-based estimation is used only in the
absence of a learn cycle.
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 AS is updated. When an
empty condition is detected (LEARNF and/or AEF set),
the ACR adjustment is conditional:
• If the AEF is set and the LEARNF is not set, the
• If the AEF is set, the LEARNF is not set, and the ACR
• If the LEARNF is set, the battery is at the active-
Full detection occurs when the average of V
V
charge voltage (VCHG) threshold for the duration of two
average current (IAVG) readings, and both IAVG read-
ings are below terminating current (IMIN). The two con-
secutive IAVG readings must also be positive and
nonzero (>16 LSB). This ensures that removing the bat-
tery from the charger does not result in a false detec-
tion of full. Full detect sets the charge to full (CHGTF)
bit in the Status register.
Active-empty point detection occurs when the average
of V
threshold and the two previous current readings are
above IAE. This captures the event of the battery reach-
ing the active-empty point. Note that the two previous
current readings must be negative and greater in mag-
nitude than IAE (i.e., a larger discharge current than
specified by the IAE threshold). Qualifying the voltage
IN2
active-empty point was not detected. The battery is
likely below the active-empty capacity of the model.
The ACR is set to the active-empty model value at
present temperature only if it is greater than the
active-empty model value at present temperature.
is below the active-empty model value at present
temperature, the ACR is not updated.
empty point and the ACR is set to the active-empty
model value.
IN1
voltage registers remain continuously above the
Protector and Optional SHA-1 Authentication
and V
2-Cell, Stand-Alone, Li+ Fuel-Gauge IC with
IN2
voltage registers drops below the VAE
______________________________________________________________________________________
Active-Empty Point Detect
ACR Housekeeping
Full Detect
IN1
and
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 dis-
charge 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.
Note: 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.
The DS2775–DS2778 process measurement and cell
characteristics on a 3.5s interval and yield seven result
registers. The result registers are sufficient for direct
display to the user in most applications. The host sys-
tem can produce customized values for system use or
user display by combining measurement, result, and
user EEPROM values.
The full capacity of the battery at the present tempera-
ture is reported normalized to the +40°C full value. This
15-bit value reflects the cell model full value at the
given temperature. The FULL(T) register reports values
between 100% and 50% with a resolution of 61ppm
(precisely 2
ues greater than 100%, the register value is clamped to
a maximum value of 100%.
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 value at the given temperature. The AE(T) regis-
ter reports values between 0% and 49.8% with a
resolution of 61ppm (precisely 2
The standby-empty capacity of the battery at the pre-
sent 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. The
SE(T) register reports values between 0% and 49.8%
with a resolution of 61ppm (precisely 2
-14
). Though the register format permits val-
Standby Empty, SE(T)
Result Registers
Active Empty, AE(T)
-14
).
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-14
).
FULL(T)
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