Pulsed Current Algorithm
In the Pulsed Current algorithm, charging current is
turned off after the initial fast charge termination until
V
CELL
falls to V
FLT
. Full fast charge current (I
MAX
)is
then re-enabled to the battery until V
CELL
rises to V
BLK
.
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 R
SNS
, so nominal regulated current is set by:
Equation 8
I
MAX
= 0.250V/R
SNS
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
F
PWM
= 0.1/C
PWM
where C is in
µ
F and F is in kHz. A typical switching
rate is 100kHz, implying C
PWM
= 0.001
µ
F. 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.
10
bq2031
IGSEL T
P
(sec.)
L 0.4
H 0.8
Z 1.6
Table 4. Fixed-Pulse Period by IGSEL
TD203101.eps
I
COND
I
COND
I
COND
0
0
0
IGSEL = L
Ave. Current
IGSEL = H
Ave. Current
IGSEL = Z
Ave. Current
T
P
= 1.6 Sec
T
P
= 0.8 Sec
T
P
= 0.4 Sec
0.2 Sec
Figure 10. Implementation of Fixed-Pulse Maintenance Charge
