ltc4065l Linear Technology Corporation, ltc4065l Datasheet - Page 13

• Manufacturer Part Number: ltc4065l
• Description: Standalone 250ma Li-ion Battery Charger In 2 ? 2 Dfn
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
In constant-current mode, the PROG pin is in the feedback
loop, not the battery. Because of the additional pole
created by the PROG pin capacitance, capacitance on this
pin must be kept to a minimum. With no additional
capacitance on the PROG pin, the charger is stable with
program resistor values as high as 25k. However, addi-
tional capacitance on this node reduces the maximum
allowed program resistor. The pole frequency at the PROG
pin should be kept above 100kHz. Therefore, if the PROG
pin is loaded with a capacitance, C
equation should be used to calculate the maximum resis-
tance value for R
Average, rather than instantaneous, battery current may
be of interest to the user. For example, if a switching power
supply operating in low current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
filter can be used on the PROG pin to measure the average
R
PROG
≤
2
π
•
PROG
10
U
5
1
•
:
C
PROG
U
Figure 4. Isolating Capacitive Load on the PROG Pin and Filtering
W
PROG
, the following
LTC4065L
GND
PROG
U
R
PROG
10k
4065L F04
battery current as shown in Figure 4. A 10K resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
Power Dissipation
Due to the low charge currents, it is unlikely that the
LTC4065L will reduce charge current through thermal
feedback. Nonetheless, the LTC4065L power dissipation
can be approximated by:
Where P
voltage, V
current. It is not necessary to perform any worst-case
power dissipation scenarios because the LTC4065L will
automatically reduce the charge current to maintain the
die temperature at approximately 115°C. However, the
approximate ambient temperature at which the thermal
feedback begins to protect the IC is:
C
P
T
T
FILTER
A
A
D
= 115°C – P
= 115°C – (V
= (V
D
CHARGE
CURRENT
MONITOR
CIRCUITRY
BAT
CC
is the power dissipated, V
– V
is the battery voltage and I
BAT
LTC4065L/LTC4065LX
D
CC
) • I
• θ
– V
JA
BAT
BAT
) • I
BAT
CC
• θ
is the input supply
JA
BAT
is the charge
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4065lxfa