Manualshelf

Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - battery management Charge management VRLA SOIC 16 Surface-mount
12345678910
V
REF
250mV
25mV
+
+
0.90V
REF
0.95V
REF
V
REF
Voltage
Reference
V
IN
V
REF
V
VFB
ChargingState Logic
1
23 4
5
6
8
9
10
11
12
13
14
1516
7
Q1
Q2
Q3
Q4
Q5
Q
EXT
External
Supply
R
ISNS
VRLA
Battery
R
A
R
B
R
C
Q6
Q7
Q8
Q9
COMP
VFB
STAT1
BSTOP
IN
DRVE
DRVC
IFBISNSMISNSP
ISNS
GND
CE
Connect
toIN
I
CHG
V
BAT
bq24450
SLUS929C –APRIL 2009– REVISED FEBRUARY 2012
www.ti.com
DETAILED OPERATION AND APPLICATION INFORMATION
A Simple Dual-Level Float-Cum-Boost Charger
Figure 4 shows the bq24450 configured as a simple dual-level float-cum-boost charger. Figure 5 shows the
sequence of events that occur in a normal charge cycle. At (1) in Figure 5, power is switched ON. As long as the
input voltage V
IN
is below the undervoltage lockout threshold UVLO, Q2 is ON, disabling the driver transistor Q1.
As the input voltage V
IN
ramps up and rises above UVLO Q2 turns OFF. This enables Q1 and thus the external
transistor Q
EXT
. At the same time, Q7 turns ON, latch L1 is forced to RESET and latch L2 is SET (see Figure 2
for the internals of the Charging State Logic).
The voltage regulating amplifier tries to force the voltage at the VFB pin to V
REF
by turning Q1 and thus Q
EXT
fully
ON, but the current limiting amplifier limits the charging current I
CHG
to I
MAX-CHG
such that the voltage across
R
ISNS
is V
ILIM
– 250mV typical. Thus I
MAX-CHG
is given by:
I
MAX-CHG
= V
ILIM
÷ R
ISNS
As I
CHG
flows into the battery, the battery terminal voltage increases. The voltage at the VFB pin is the battery
voltage scaled by the resistive divider formed by R
A
and R
B
//R
C
(because Q8 is ON). At (3), the voltage on the
VFB pin exceeds 0.95V
REF
, and the output of the voltage sense comparator goes HIGH. This forces L2 to
RESET, and STAT2 turns ON. The battery voltage V
BI
at this point when STAT2 indicates boost is given by:
V
BI
= 0.95V
REF
× (R
A
+ R
B
//R
C
) ÷ R
B
//R
C
Other than STAT2 changing state at this point, there is no externally observable change in the charging
conditions. I
MAX-CHG
continues to flow into the battery.
Figure 4.
8 Submit Documentation Feedback Copyright © 2009–2012, Texas Instruments Incorporated
Product Folder Link(s) :bq24450