Thermal monitoring continues throughout the charge
cycle, and the bq2031 enters the Charge Pending state
anytime the temperature is out of range. (There is one
exception; if the bq2031 is in the Fault state—see be
-
low—the out-of-range temperature is not recognized un
-
til the bq2031 leaves the Fault state.) All timers are
suspended (but not reset) while the bq2031 is in Charge
Pending. When the temperature comes back into range,
the bq2031 returns to the point in the charge cycle
where the out-of-range temperature was detected.
When the temperature is valid, the bq2031 performs two
tests on the battery. In test 1, the bq2031 regulates a voltage
of V
FLT
+ 0.25V across the battery and observes I
SNS
.IfI
SNS
does not rise to at least I
COND
within a time-out period (e.g.,
the cell has failed open), the bq2031 enters the Fault state. If
test 1 passes, the bq2031 then regulates current to I
COND
(=
I
MAX
/5) and watches V
CELL
(= V
BAT
-V
SNS
). If V
CELL
does
not rise to at least V
FLT
within a time-out period (e.g., the cell
has failed short), again the bq2031 enters the Fault state. A
hold-off period is enforced at the beginning of qualification
test 2 before the bq2031 recognizes its “pass” criterion. If this
second test passes, the bq2031 begins fast (bulk) charging.
Once in the Fault state, the bq2031 waits until V
CC
is cy
-
cled or a battery insertion is detected. It then starts a new
charge cycle and begins the qualification process again.
Charge Status Display
Charge status is annunciated by the LED driver outputs
LED
1
–LED
3
. Three display modes are available in the bq2031;
the user selects a display mode by configuring pin DSEL. Table
2 shows the three modes and their programming pins.
The bq2031 does not distinguish between an over-voltage
fault and a “battery absent” condition. The bq2031 enters
the Fault state, annunciated by turning on LED
3
, when
-
ever the battery is absent. The bq2031, therefore, gives an
indication that the charger is on even when no battery is
in place to be charged.
4
bq2031
Mode Charge Action State LED
1
LED
2
LED
3
DSEL = 0
(Mode 1)
Battery absent or over-voltage fault Low Low High
Pre-charge qualification Flash Low Low
Fast charging High Low Low
Maintenance charging Low High Low
Charge pending (temperature out of range) X X Flash
Charging fault X X High
DSEL = 1
(Mode 2)
Battery absent or over-voltage fault Low Low High
Pre-charge qualification High High Low
Fast charge Low High Low
Maintenance charging High Low Low
Charge pending (temperature out of range) X X Flash
Charging fault X X High
DSEL = Float
(Mode 3)
Battery absent or over-voltage fault Low Low High
Pre-charge qualification Flash Flash Low
Fast charge: current regulation Low High Low
Fast charge: voltage regulation High High Low
Maintenance charging High Low Low
Charge pending (temperature out of range) X X Flash
Charging fault X X High
Notes: 1 = V
CC
; 0 = V
SS
; X = LED state when fault occurred; Flash =
1
6
s low,
1
6
s high.
In the Pulsed Current algorithm, the bq2031 annunciates maintenance when charging current is off and
fast charge whenever charging current is on.
Table 2. bq2031 Display Output Summary
