LTC4085 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC4085' PDF : 24 Pages View PDF
LTC4085
APPLICATIONS INFORMATION
Consider the above example with an ambient temperature of
55°C. The charge current will be reduced to approximately:
IBAT
=
105°C –
(5V – 3V) •
55°C
37°C/
W
=
50°C
74°C/A
=
0.675A
Board Layout Considerations
In order to be able to deliver maximum charge current
under all conditions, it is critical that the Exposed Pad on
the backside of the LTC4085 package is soldered to the
board. Correctly soldered to a 2500mm2 double-sided
1oz. copper board the LTC4085 has a thermal resistance
of approximately 37°C/W. Failure to make thermal contact
between the Exposed Pad on the backside of the package
and the copper board will result in thermal resistances far
greater than 37°C/W. As an example, a correctly soldered
LTC4085 can deliver over 1A to a battery from a 5V supply
at room temperature. Without a backside thermal connec-
tion, this number could drop to less than 500mA.
VIN and Wall Adapter Bypass Capacitor
Many types of capacitors can be used for input bypassing.
However, caution must be exercised when using multilayer
ceramic capacitors. Because of the self resonant and high
Q characteristics of some types of ceramic capacitors, high
voltage transients can be generated under some start-up
conditions, such as connecting the charger input to a hot
power source. For more information, refer to Application
Note 88.
Stability
The constant-voltage mode feedback loop is stable without
any compensation when a battery is connected. However,
a 4.7μF capacitor with a 1Ω series resistor to GND is
recommended at the BAT pin to keep ripple voltage low
when the battery is disconnected.
TYPICAL APPLICATION
USB Power Control Application with Wall Adapter Input
5V WALL
ADAPTER
INPUT
5V (NOM)
FROM USB
CABLE VBUS
4.7μF
1Ω*
4.7μF
1Ω*
1k 510Ω 510Ω
4.7μF
IN
CHRG
ACPR
WALL
LTC4085
OUT
GATE
BAT
VNTC
NTC
SUSPEND USB POWER
500mA/100mA SELECT
*SERIES 1W RESISTOR ONLY
NEEDED FOR INDUCTIVE
INPUT SUPPLIES
SUSP
HPWR
PROG
CLPROG
TIMER
GND
RPROG
71.5k
RCLPROG
2.1k
TO LDOs
REGs, ETC
RNTCBIAS
10k
+ Li-Ion
CELL
RNTC
10k
0.15μF
4085 TA02
4085fd
21
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