BQ2031PN-A5 Datasheet, PDF (10/19 Pages) Texas Instruments – Lead-Acid Fast-Charge IC

bq2031
Table 4. Fixed-Pulse Period by IGSEL
IGSEL
L
H
Z
TP (sec.)
0.4
0.8
1.6
Pulsed Current Algorithm
In the Pulsed Current algorithm, charging current is
turned off after the initial fast charge termination until
VCELL falls to VFLT. Full fast charge current (IMAX) is
then re-enabled to the battery until VCELL rises to VBLK.
This cycle repeats indefinitely.
Charge Regulation
The bq2031 controls charging through pulse-width modu-
lation of the MOD output pin, supporting both constant-
current and constant-voltage regulation. Charge current
is monitored by the voltage at the SNS pin, and charge
voltage by voltage at the BAT pin. These voltages are
compared to an internal temperature-compensated refer-
ence, and the MOD output modulated to maintain the de-
sired value.
Voltage at the SNS pin is determined by the value of re-
sistor RSNS, so nominal regulated current is set by:
Equation 8
IMAX = 0.250V/RSNS
The switching frequency of the MOD output is deter-
mined by an external capacitor (CPWM) between the
pin TPWM and ground, per the following:
Equation 9
FPWM = 0.1/CPWM
where C is in µF and F is in kHz. A typical switching
rate is 100kHz, implying CPWM = 0.001µF. MOD pulse
width is modulated between 0 and 80% of the switching
period.
To prevent oscillation in the voltage and current control
loops, frequency compensation networks (C or R-C) are
typically required on the VCOMP and ICOMP pins (respec-
tively) to add poles and zeros to the loop control equations.
A software program, “CNFG2031,” is available to assist in
configuring these networks for buck type regulators. For
more detail on the control loops in buck topology, see the
application note, “Switch-Mode Power Conversion Using
the bq2031.” For assistance with other power supply topolo-
gies, contact the factory.
ICOND
0
ICOND
0
IGSEL = L
Ave. Current
IGSEL = H
Ave. Current
ICOND
0
IGSEL = Z
Ave. Current
TP = 0.4 Sec
TP = 0.8 Sec
0.2 Sec
TP = 1.6 Sec
TD203101.eps
Figure 10. Implementation of Fixed-Pulse Maintenance Charge
10