Datasheet

V
IN
V
UVLO
I
CHG
I
MAX-CHG
I
TAPER
V
BAT
V
BOOST
V
FLOAT
V
RCH
V
BI
ISNSQ6
PGOOD Q7
STAT1 Q8
STAT2Q9
OFF
ON
OFF
OFF
ON
ON
OFF
ON
OFF
OFF
ON
ON
OFF
ON
OFF
ON
ON
OFF
ON
STATE#
STATE#1 STATE#3
STATE#2
#1
#2
1
2
3
5 6 7
4
bq24450
www.ti.com SLUS929C –APRIL 2009– REVISED FEBRUARY 2012
As charging proceeds, the voltage at the VFB pin increases further to V
REF
. At this point, the voltage regulating
amplifier prevents the voltage at the VFB pin from rising further, maintaining the battery voltage at V
BOOST
. [(4) in
Figure 4].
V
BOOST
= V
REF
× (R
A
+ R
B
//R
C
) ÷ R
B
//R
C
I
CHG
keeps flowing into the battery. As the battery approaches full charge, the current into the battery decreases,
while the battery terminal voltage is maintained at V
BOOST
.
At (5), the charging current I
CHG
reduces to a value I
TAPER
such that the voltage across R
ISNS
becomes less than
V
ISNS
(25mV typical)
I
TAPER
= V
ISNS
÷ R
ISNS
Q6 at the output of the current sense comparator turns OFF. The internal current source pulls the BSTOP pin
HIGH, latch L1 is forced to SET, in turn forcing L2 to SET. The reference voltage on the voltage sense
comparator is now 0.9V
REF
. STAT1 turns OFF, and the voltage on the battery settles to:
V
FLOAT
= V
REF
× (R
A
+ R
B
) ÷ R
B
As long as the peak load current is less than I
MAX-CHG
, it will be supplied by Q
EXT
, and the voltage across the
battery will be maintained at V
FLOAT
. But if the peak load current exceeds I
MAX-CHG
, the battery will have to
provide the excess current, and the battery terminal voltage will drop. Once it drops below 0.9V
REF
, at (6) in
Figure 4, a new charge cycle is initiated. The battery voltage V
BAT
at this point, V
RCH
, is given by:
V
RCH
= 0.9V
REF
× (R
A
+ R
B
) / R
B
Figure 5.
Copyright © 2009–2012, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Link(s) :bq24450