Datasheet

Functional Description
The bq2954 functional operation is described in terms of
the following (Figure 1):
■
Charge algorithm
■
Charge qualification
■
Charge status display
■
Configuring the display and termination
■
Voltage and current monitoring
■
Battery insertion and removal
■
Temperature monitoring
■
Maximum time--out
■
Charge regulation
■
Recharge after fast charge
Charge Algorithm
The bq2954 uses a two-phase fast-charge algorithm. In
phase 1, the bq2954 regulates constant current until the
voltage on the BAT pin, V
BAT
, rises to the internal
threshold, V
REG
. The bq2954 then transitions to phase 2
and regulates constant voltage (V
BAT
=V
REG
) until the
charging current falls below the programmed I
MIN
threshold. Fast charge then terminates, and the bq2954
enters the Charge Complete state. (See Figure 2.)
Charge Qualification
The bq2954 starts a charge cycle when power is applied
while a battery is present or when a battery is inserted.
Figure 2 shows the state diagram for the bq2954. The
bq2954 first checks that the battery temperature is
within the allowed, user-configurable range. If the tem-
perature is out of range, the bq2954 remains in the
QUALIFICATION state (S01) and waits until the battery
temperature and voltage are within the allowed range.
If during any state of charge, a temperature excursion
occurs HOT, the bq2954 proceeds to the DONE state
(S04) and indicates this state on the LED outputs and
provides no current. If this occurs, the bq2954 remains
in the DONE state unless the following two conditions
are met:
■
Temperature falls within valid charge range
■
V
BAT
falls below the internal threshold,V
RCHG
If these two conditions are met, a new charge cycle be
-
gins. During any state of charge, if a temperature ex
-
cursion occurs COLD, the bq2954 terminates charge and
returns to the QUALIFICATION state (S01). Charge re
-
starts if V
BAT
and temperature are in valid range.
When the temperature and voltage are valid, the bq2954
enters the CONDITIONING state (S02) and regulates
current to I
COND
(=I
MAX
/10). After an initial holdoff pe
-
riod t
HO
(which prevents the IC from reacting to tran
-
sient voltage spikes that may occur when charge current
is first applied), the IC begins monitoring V
BAT
.IfV
BAT
does not rise to at least V
MIN
before the expiration of
3
bq2954
BD2954.eps
Voltage
Reference
Charge
Control
State
Machine
PWM
Regulator
Display
Control
Power-On
Reset
MTO
Timer
Oscillator
DSEL
CSEL
LED
1
LED
2
BTST
CHG
LCOM
MOD
ICOMP
V
CC
TM TPWMITERM
V
SS
TS
VCOMP
BAT
SNS
Figure 1. Functional Block Diagram