LTC4065EDC#TR Linear Technology, LTC4065EDC#TR Datasheet - Page 14

• Manufacturer Part Number: LTC4065EDC#TR
• Description: IC CHARGER BATT LI-ON 6-DFN
• Manufacturer: Linear Technology

Specifications of LTC4065EDC#TR

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 3.75 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 6-WFDFN Exposed Pad
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIO S I FOR ATIO
LTC4065/LTC4065A
length, however, may add enough series inductance to
require a bypass capacitor of at least 1µF from BAT to
GND. Furthermore, a 4.7µF capacitor with a 0.2Ω to 1Ω
series resistor from BAT to GND is required to keep ripple
voltage low when the battery is disconnected.
High value capacitors with very low ESR (especially ce-
ramic) may reduce the constant-voltage loop phase mar-
gin. Ceramic capacitors up to 22µF may be used in parallel
with a battery, but larger ceramics should be decoupled
with 0.2Ω to 1Ω of series resistance.
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
battery current as shown in Figure 4. A 10K resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
Figure 4. Isolating Capacitive Load on the PROG Pin and Filtering
14
R
PROG
≤
LTC4065
2
GND
π
PROG
•
PROG
10
U
5
1
•
:
C
R
PROG
PROG
U
10k
4065 F04
C
FILTER
W
PROG
CHARGE
CURRENT
MONITOR
CIRCUITRY
, the following
U
Power Dissipation
The conditions that cause the LTC4065/LTC4065A to
reduce charge current through thermal feedback can be
approximated by considering the power dissipated in the
IC. For high charge currents, the LTC4065/LTC4065A
power dissipation is approximately:
Where P
voltage, V
current. It is not necessary to perform any worst-case
power dissipation scenarios because the LTC4065 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:
Example: Consider an LTC4065/LTC4065A operating from
a 5V wall adapter providing 750mA to a 3.6V Li-Ion
battery. The ambient temperature above which the
LTC4065/LTC4065A will begin to reduce the 750mA charge
current is approximately:
The LTC4065/LTC4065A can be used above 70°C, but the
charge current will be reduced from 750mA. The approxi-
mate current at a given ambient temperature can be
calculated:
Using the previous example with an ambient temperature
of 73°C, the charge current will be reduced to approxi-
mately:
P
T
T
T
T
T
I
I
BAT
BAT
A
A
A
A
A
D
= 115°C – P
= 115°C – (V
= 115°C – (5V – 3.6V) • (750mA) • 60°C/W
= 115°C – 1.05W • 60°C/W = 115°C – 63°C
= 52°C
= (V
=
=
D
BAT
CC
(
(
is the power dissipated, V
5
V
V
CC
– V
is the battery voltage and I
115
115
– .
–
3 6
BAT
V
°
D
°
BAT
CC
C T
C
V
) • I
• θ
–
–
)
– V
)
JA
•
73
BAT
• θ
A
60
BAT
°
JA
C
°
C W
) • I
/
BAT
=
84
CC
• θ
42
°
is the input supply
JA
C A
°
BAT
C
/
=
is the charge
500
mA
4065fb