BQ2040_15 Datasheet, PDF (8/36 Pages) Texas Instruments – Gas Gauge IC With SMBus Interface

Not Recommended For New Designs
bq2040
Charge Counting
Charge activity is detected based on a positive voltage
on the SR input. If charge activity is detected, the
bq2040 increments RM at a rate proportional to VSRO
and, if enabled, activates an LED display. Charge ac-
tions increment the RM after compensation for charge
state and temperature.
The bq2040 determines charge activity sustained at a
continuous rate equivalent to VSRO > +VSRD. A valid
charge equates to sustained charge activity
greater than 10 mAh. Once a valid charge is detected,
charge threshold counting continues until VSRO falls be-
low VSRD. VSRD is a programmable threshold as de-
scribed in the Digital Magnitude Filter section.
Discharge Counting
All discharge counts where VSRO < -VSRD cause the RM
register to decrement and the DCR to increment. VSRD
is a programmable threshold as described in the Digital
Magnitude Filter section.
Self-Discharge Estimation
The bq2040 continuously decrements RM and incre-
ments DCR for self-discharge based on time and temper-
ature provided that the discharge flag in BatteryStatus
is set (charge not detected). The bq2040 self-discharge
estimation rate is programmed in EE 0x4f and can be
set from 0 to 25% per day for 20–30°C. This rate approx-
imately doubles for every 10°C increase until the tem-
perature is ≥ 70°C or halves every 10°C decrease until
the temperature is < 10°C.
Charge Control
The bq2040 supports SBS charge control by broadcast-
ing the ChargingCurrent and the ChargingVoltage to
the Smart Charger address. The bq2040 broadcasts
charging commands every 10 seconds; the broadcasts
can be disabled by writing bit 14 of BatteryMode to 1.
On reset, the initial charging current broadcast to the
charger is set to the value programmed in EE 0x08-
0x09. The bq2040 updates the value used in the charg-
ing current broadcasts based on the battery’s state of
charge, voltage, and temperature.
The bq2040 internal charge control is compatible with
nickel-based and Li-Ion chemistries. The bq2040 uses
current taper detection for Li-Ion primary charge termi-
nation and ∆T/∆t for nickel based primary charge termi-
nation. The bq2040 also provides a number of safety
terminations based on battery capacity, voltage, and
temperature.
Current Taper
For Li-Ion charge control, the ChargingVoltage must be
set to the desired pack voltage during the constant volt-
age charge phase. The bq2040 detects a current taper
termination when it measures the pack voltage to be
within 128mV of the requested charging voltage and
when the AverageCurrent is less than the programmed
threshold in EE 0x38—0x39 and non-zero for at least
100s.
∆T/∆t
The ∆T/∆t used by the bq2040 is programmable in both
the temperature step (1.6°C–4.6°C) and time step (20
seconds–320seconds). Typical settings for 1°C/min in-
clude 2°C over 120 seconds and 3°C over 180 seconds.
Longer times are required for increased slope resolution.
∆T _{is set by the formula:} ∆T ₌
∆t
∆t
[(lower nibble of EE 0x4a)∗2 + 16] / 10  ^oC
[320 − (EE 0x62) ∗ 20)]
 s 
In addition to the ∆T/∆t timer, there is a hold-off timer,
which starts when the battery is being charged at more
than 255mA and the temperature is above 25°C. Until
this timer expires, ∆T/∆t is suspended. If the tempera-
ture falls below 25°C, or if charging current falls below
255mA, the timer is reset and restarts only if these con-
ditions are once again within range. The hold-off time is
programmed in EE 0x63.
Charge Termination
Once the bq2040 detects a valid charge termination, the
Fully_Charged, Terminate_Charge_Alarm, and the
Over_Charged_Alarm bits are set in BatteryStatus, and
the requested charge current is set to zero. Once the
terminating conditions cease, the Termi-
nate_Charge_Alarm and the Over_Charged_Alarm are
cleared, and the requested charging current is set to the
maintenance rate. The bq2040 requests the mainte-
nance rate until RM falls below the amount determined
by the programmable full- charge percentage. Once this
occurs, the Fully_Charged bit is cleared, and the re-
quested charge current and voltage are set to the
fast-charge rate.
Bit 4 (CC) in FLAGS2 determines whether RM is modi-
fied after a ∆T/∆t or current taper termination occurs. If
CC = 1, RM may be set from 0 to 100% of the FullChar-
geCapacity as defined in EE 0x4c. If RM is below the
full-charge percentage, RM is set to the full-charge per-
centage of FCC. If RM is above the full-charge percent-
age, RM is not modified.
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