LTC4064 datasheet(13/16 Pages) LINER

13 / 16 page

LTC4064

sn4064 4064fs

Regardless of mode, the voltage at the PROG pin is

proportional to the current being delivered to the battery.

Power Dissipation

The conditions that cause the LTC4064 to reduce charge

current due to the thermal protection feedback can be

approximated by considering the power dissipated in the

IC. For high charge currents, the LTC4064 power dissipa-

tion is approximately:

PD = (VCC – VBAT) • IBAT

where PD is the power dissipated, VCC is the input supply

voltage, VBAT is the battery voltage, and IBAT is the battery

charge current. It is not necessary to perform any worst-

case power dissipation scenarios because the LTC4064

will automatically reduce the charge current to maintain

the die temperature at approximately 105°C. However, the

approximate ambient temperature at which the thermal

feedback begins to protect the IC is:

TA = 105°C – PDθJA

TA = 105°C – (VCC – VBAT) • IBAT • θJA

Example: Consider an LTC4064 operating from a 5V wall

adapter providing 1.2A to a 3.75V Li-Ion battery. The

ambient temperature above which the LTC4064 will begin

to reduce the 1.2A charge current is approximately:

TA = 105°C – (5V – 3.75V) • 1.2A • 40°C/W

TA = 105°C – 1.5W • 40°C/W = 105°C – 60°C = 45°C

The LTC4064 can be used above 45°C, but the charge

current will be reduced below 1.2A. The approximate

charge current at a given ambient temperature can be

approximated by:

BAT

105

–

(–

)• θ

Consider the above example with an ambient temperature

of 55°C. The charge current will be reduced to approxi-

mately:

C W

BAT =

°°

105

3 75

–

(– .

)•

APPLICATIO S I FOR ATIO

Furthermore, the voltage at the PROG pin will change

proportionally with the charge current as discussed in the

Programming Charge Current section.

It is important to remember that LTC4064 applications do

not need to be designed for worst-case thermal conditions

since the IC will automatically reduce power dissipation

when the junction temperature reaches approximately

105°C.

Board Layout Considerations

The ability to deliver maximum charge current under all

conditions require that the exposed metal pad on the

backside of the LTC4064 package be soldered to the PC

board ground. Correctly soldered to a 2500mm2 double-

sided 1oz. copper board the LTC4064 has a thermal

resistance of approximately 40°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 40°C/W. As an example, a

correctly soldered LTC4064 can deliver over 1250mA to a

battery from a 5V supply at room temperature. Without a

backside thermal connection, this number could drop to

less than 500mA.

VCC Bypass Capacitor

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 hot power source. For more information refer to

Application Note 88.

Stability

The constant-voltage mode feedback loop is stable

without any compensation provided that a battery is

connected. However, a 1µF capacitor with a 1Ω series

resistor to GND is recommended at the BAT pin to keep

ripple voltage low when the battery is disconnected.

In the constant-current mode it is the PROG pin that is in

the feedback loop and not the battery. The constant-

current mode stability is affected by the impedance at the

LTC4064 bảng dữ liệu(PDF) 13 Page - Linear Technology

LTC4064 bảng dữ liệu(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

bảng dữ liệu tải về

Link URL