ltc4054x-4.2 Linear Technology Corporation, ltc4054x-4.2 Datasheet - Page 12

• Manufacturer Part Number: ltc4054x-4.2
• Description: Standalone Linear Li-ion Battery Charger With Thermal Regulation In Thinsot
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC4054-4.2/LTC4054X-4.2
Solving for I
Using R
charge current to be:
While this application delivers more energy to the battery
and reduces charge time in thermal mode, it may actually
lengthen charge time in voltage mode if V
12
Note 2: Large values of R
will not generate enough heat to require thermal regulation.
JA
Figure 3. A Circuit to Maximize Thermal Mode Charge Current
I
I
(
BAT
BAT
V
= 125 C/W we can calculate the thermally regulated
S
–
= 708.4mA
CC
V
BAT
= 0.25 , V
BAT
) –
CC
using the quadratic formula
will result in no solution for I
1 F
U
(
V
S
S
LTC4054-4.2
= 5V, V
–
GND
V
U
V
CC
2
V
S
R
R
BAT
PROG
CC
CC
BAT
BAT
)
2
4
= 3.75V, T
BAT
W
R
R
. This indicates that the LTC4054
405442 F03
PROG
CC
(
120
CC
Li-Ion
CELL
1000
JA
800
600
400
200
becomes low
A
2
0
C T
.
= 25 C and
0
U
V
THERMAL
Figure 4. Charge Current vs R
–
S
MODE
= 5V
0.25
A
)
V
0.5
S
= 5.25V
0.75
CONSTANT
CURRENT
R
CC
V
enough to put the LTC4054 into dropout. Figure 4 shows
how this circuit can result in dropout as R
large.
This technique works best when R
to keep component size small and avoid dropout. Remem-
ber to choose a resistor with adequate power handling
capability.
V
Many types of capacitors can be used for input bypassing,
however, caution must be exercised when using multi-
layer ceramic capacitors. Because of the self-resonant and
high Q characteristics of some types of ceramic capaci-
tors, high voltage transients can be generated under some
start-up conditions, such as connecting the charger input
to a live power source. Adding a 1.5 resistor in series
with an X5R ceramic capacitor will minimize start-up
voltage transients. For more information, refer to Applica-
tion Note 88.
Charge Current Soft-Start
The LTC4054 includes a soft-start circuit to minimize the
inrush current at the start of a charge cycle. When a charge
cycle is initiated, the charge current ramps from zero to the
full-scale current over a period of approximately 100 s.
This has the effect of minimizing the transient current load
on the power supply during start-up.
( )
S
1.0
CC
= 5.5V
V
T
R
Bypass Capacitor
A
JA
BAT
PROG
1.25
= 25 C
= 125 C/W
= 3.75V
DROPOUT
= 1.25k
1.5
405442 F04
CC
1.75
CC
values are minimized
CC
becomes
405442xf