Rainbow Electronics DS2784 - Manual (Page 21)

DS2784: 1-Cell Stand-Alone Fuel Gauge IC with Li+ Protector and SHA-1 Authentication
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he ACR value is adjusted occasionally to maintain the coulomb count within the model curve boundaries. When
to full (CHGTF set), the ACR is set equal to the age scaled full lookup value at the present
If the AEF is set and the LEARNF is not set, then the active-empty point was not detected. The battery is likely
t present temp
ƒ
Full Detect
ull detection occurs when the voltage (V) readings remain continuously above the charge voltage (VCHG)
the duration of two average current (IAVG) readings, and both IAVG readings are below terminating
ctive-empty point detection occurs when the voltage register drops below the VAE threshold AND the two
above IAE. This captures the event of the battery reaching the active-empty point.
report the device status. All bits are set internally. The CHGTF, AEF, SEF, and
UVF and PORF bits can be cleared by writing a zero to the bit locations.
BIT 7 BIT 6 BIT 5 BIT 2 BIT 1 BIT 0
CHGTF LEARNF
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
T
the battery is charged
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 (LEARNF and/or AEF set), the ACR adjustment is conditional:
ƒ
below the active-empty capacity of the model. The ACR is set to the active-empty model value a
only if it is greater than the active-empty model value at present temp.
If the AEF is set, the LEARNF is not set, and the ACR is below the active-empty model value at present temp
the ACR is NOT updated.
ƒ If the LEARNF is set, then the battery is at the active-empty point and the ACR is set to the active-empty model
value.
F
threshold for
current (IMIN). The two consecutive IAVG readings must also be positive and nonzero (> 16 LSB). 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
A
previous current readings are
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.
STATUS REGISTER FORMAT
The status register contains bits that
LEARNF bits are read only. The
ADDRESS 01h
BIT 4 BIT 3
AEF SEF X UVF PORF X
GTF —Charg ation Flag. CHGTF is icate an ge current register values
ave persisted above the VCHG and below the IMIN thresholds sufficiently long to detect a fully charged condition.
at or below the active-empty point. AEF is set
hen the voltage register value is less than the VAE threshold. AEF is cleared when RARC is greater than 5%.
pty Flag. SEF is set to indicate RSRC is less than 10%. SEF is cleared when RSRC is greater
an 15%. SEF is read only.
CH
h e-Termin set to ind that the voltage d avera
CHGF is cleared when RARC is less than 90%. CHGF is read only.
AEF
—Active-Empty Flag. AEF is set to indicate that the battery is
w
AEF is read only.
SEF
—Standby-Em
th