BQ2031PN-A5 Datasheet, PDF (9/19 Pages) Texas Instruments – Lead-Acid Fast-Charge IC

bq2031
Second Difference (∆²V)
Second difference is a Unitrode proprietary algorithm
that accumulates the difference between successive sam-
ples of VBAT. The bq2031 takes a sample and makes a
termination decision at a frequency equal to 0.008 *
tMTO. Fast charge terminates when the accumulated dif-
ference is ≤ -8mV. Second difference is used only in the
Two-Step Current algorithm, and is subject to a hold-off
period (see below).
Maximum Voltage
Fast charge terminates when VCELL ≥ VBLK. VBLK is set
per equation 2. Maximum voltage is used for fast charge
termination in the Two-Step Current and Pulsed Cur-
rent algorithms, and for transition from phase 1 to
phase 2 in the Two-Step Voltage algorithm. This crite-
rion is subject to a hold-off period.
Hold-off Periods
Maximum V and ∆²V termination criteria are subject
to a hold-off period at the start of fast charge equal to
0.15 * tMTO. During this time, these termination criteria
are ignored.
Maximum Time-Out
Fast charge terminates if the programmed MTO time is
reached without some other termination shutting off
fast charge. MTO is programmed from 1 to 24 hours by
an R-C network on TMTO (see Figure 9) per the equa-
tion:
Equation 6
tMTO = 0.5 * R * C
where R is in kΩ, C is in µF, and tMTO is in hours. Typi-
cally, the maximum value for C of 0.1µF is used.
Fast-charge termination by MTO is a Fault only in the
Pulsed Current algorithm; the bq2031 enters the Fault
state and waits for a new battery insertion, at which
time it begins a new charge cycle. In the Two-Step Volt-
age and Two-Step Current algorithms, the bq2031 tran-
sitions to the maintenance phase on MTO time-out.
The MTO timer starts at the beginning of fast charge. In
the Two-Step Voltage algorithm, it is cleared and re-
started when the bq2031 transitions from phase 1 (cur-
rent regulation) to phase 2 (voltage regulation). The
MTO timer is suspended (but not reset) during the out-
of-range temperature (Charge Pending) state.
R
1
TM
C
VCC
VCC ¹³
VSS ¹²
bq2031
VSS
FG203112.eps
Figure 9. R-C Network for Setting MTO
Maintenance Charging
Three algorithms are used in maintenance charging:
n Two-Step Voltage algorithm
n Two-Step Current algorithm
n Pulsed Current algorithm
Two-Step Voltage Algorithm
In the Two-Step Voltage algorithm, the bq2031 provides
charge maintenance by regulating charging voltage to
VFLT. Charge current during maintenance is limited to
ICOND.
Two-Step Current Algorithm
Maintenance charging in the Two-Step Current Algo-
rithm is implemented by varying the period (TP) of a
fixed current (ICOND = IMAX/5) and duration (0.2 sec-
onds) pulse to achieve the configured average mainte-
nance current value. See Figure 10.
Maintenance current can be calculated by:
Equation 7
Maintenance current = ^{((0.2) ∗ ICOND )} = ^{((0.04) ∗ IMAX )}
T_P
T_P
where TP is the period of the waveform in seconds.
Table 4 gives the values of P programmed by IGSEL.
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