Nominal Available Charge (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 EDV.
To prevent overstatement of charge during periods
of overcharge, NAC stops incrementing when NAC
NAC is set to the value in LMD when SEG
is pulled low during a reset.
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 incre-
ment the DCR. After NAC = 0, only discharge in-
crements the DCR. The DCR resets to 0 when NAC
= LMD. The DCR does not roll over but stops
counting when it reaches FFFFh.
The DCR value becomes the new LMD value on the
first charge after a valid discharge to V
All discharge counts where V
> 500µV cause the
NAC register to decrement and the DCR to increment.
Exceeding the fast discharge threshold (FDQ) if the rate
is equivalent to V
> 2mV activates the display, if en-
abled. The display becomes inactive after V
The bq2011 continuously decrements NAC and incre-
ments DCR for self-discharge based on time and tempera-
ture. The self-discharge count rate is programmed to be a
* NAC rate per day. This is the rate for a bat-
tery whose temperature is between 20°–30°C. The NAC
register cannot be decremented below 0.
The bq2011 determines fast charge when the NAC up-
dates at a rate of
counts/sec. Charge and discharge
activity is compensated for temperature and charge/dis-
charge rate before updating the NAC and/or DCR. Self-
discharge estimation is compensated for temperature
before updating the NAC or DCR.
No valid charge initiations (charges greater than
256 NAC counts; or 0.006 – 0.01C) occurred dur-
ing the period between NAC = LMD and EDV
The self-discharge count is not more than 4096
counts (8% to 18% of PFC, specific percentage
threshold determined by PFC).
The temperature is
0°C when the EDV level is
reached during discharge.
Two charge efficiency factors are used for trickle charge
and fast charge. Fast charge is defined as a rate of
charge resulting in
2 NAC counts/sec (≥ 0.15C to 0.32C
depending on PFC selections; see Table 2). The compen-
sation defaults to the fast charge factor until the actual
charge rate is determined.
Temperature adapts the charge rate compensation fac-
tors over three ranges between nominal, warm, and hot
temperatures. The compensation factors are shown below.
The valid discharge flag (VDQ) indicates whether
the present discharge is valid for LMD update.
Charge activity is detected based on a negative voltage
on the V
input. If charge activity is detected, the
bq2011 increments NAC at a rate proportional to V
) and, if enabled, activates an LED display
< -1mV. Charge actions increment the NAC af-
ter compensation for charge rate and temperature.
The bq2011 determines a valid charge activity sustained
at a continuous rate equivalent to V
< -400µV. A
valid charge equates to a sustained charge activity
greater than 256 NAC counts. Once a valid charge is de-
tected, charge counting continues until V
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