BQ2014H Datasheet, PDF (7/22 Pages) Texas Instruments – Low-Cost NiCd/NiMH Gas Gauge IC

Preliminary bq2014H
Select:
PFC = 27648 counts or 173mVh
PROG₁ = low
PROG₂ = high
PROG₃ = float
PROG₄ = low
PROG₅ = low
The initial full battery capacity is 173mVh
(3460mAh) until the bq2014H “learns” a new capac-
ity with a qualified discharge from full to EDV1.
3. Nominal Available Capacity (NAC):
NAC counts up during charge to a maximum value
of LMD and down during discharge and self-dis-
charge to 0. NAC is reset to 0 on initialization and
on the first valid charge following discharge to
EDV1. To prevent overstatement of charge during
periods of overcharge, NAC stops incrementing
when NAC = LMD or 0.94 ∗ LMD if T < 0°C.
4. Discharge Count Register (DCR):
The DCR counts up during discharge independent
of NAC and could continue increasing after NAC
has decremented to 0. Prior to NAC = 0 (empty
battery), both discharge and self-discharge in-
crement the DCR. After NAC = 0, only discharge
increments the DCR. The DCR resets to 0 when
NAC ≥ 0.94 ∗ LMD and a discharge is detected. The
DCR does not roll over but stops counting when it
reaches FFh.
The DCR value becomes the new LMD value on the
first charge after a valid discharge to V_EDV1 if all
the following conditions are met:
I No valid charge initiations (charges greater than
2 NAC updates where V_SRO > V_SRQ) occurred
during the period between NAC ≥ 0.94 ∗ LMD and
EDV1.
I The self-discharge is less than 6.25% of NAC.
I The temperature is ≥ 0°C when the EDV1 level
is reached during discharge.
I The discharge begins when NAC ≥ 0.94 ∗ LMD.
I VDQ is set.
The valid discharge flag (VDQ) indicates whether
the present discharge is valid for LMD update. If
the DCR update value is less than 0.94 ∗ LMD,
LMD will only be modified by 0.94 ∗ LMD. This pre-
vents invalid DCR values from corrupting LMD.
5. Scaled Available Energy (SAE):
SAE is useful in determining the available energy
within the battery, and may provide a more useful
capacity reference in battery chemistries with
sloped voltage profiles during discharge. SAE may
be converted to an mWh value using the following
formula:
E(mWh) = (SAEH ∗ 256 + SAEL) ∗
1.2 ∗ SCALE ∗ (RB1 + RB2)
RS ∗ RB2
where R_B1, R_B2, and R_S are resistor values in
ohms, as shown in Figure 1. SCALE is the selected
scale from Table 2.
6. Compensated Available Capacity (CACT)
CACT counts similarly to NAC, but contains the
available capacity compensated for discharge rate
and temperature.
Charge Counting
Charge activity is detected based on a positive voltage
on the SR input. If charge activity is detected, the
bq2014H increments NAC at a rate proportional to V_SR
and, if enabled, activates the LED display.
The bq2014H counts charge activity when the voltage at
the SR input (V_SRO) exceeds the minimum charge
threshold (V_SRQ). A valid charge is detected when NAC
has been updated twice without discharging or reaching
the digital magnitude filter time-out. Once a valid
charge is detected, charge counting continues until V_SR,
including offset, falls below V_SRQ.
Discharge Counting
Discharge activity is indicated by a negative voltage on
the SR input. All discharge counts where V_SRO is less
than the minimum discharge threshold (V_SRD) cause
the NAC register to decrement and the DCR to
increment.
Self-Discharge Counting
The bq2014H continuously decrements NAC and incre-
ments DCR for self-discharge on the basis of time and tem-
perature.
Charge/Discharge Current
The bq2014H current-scale registers, VSRH and VSRL,
can be used to determine the battery charge or dis-
charge current. See the Current Scale Register descrip-
tion for details.
7