参数资料
型号: LTC4057ES5-4.2#TRM
厂商: Linear Technology
文件页数: 8/12页
文件大小: 0K
描述: IC CHARGR BATTERY L-ION TSOT23-5
标准包装: 500
功能: 充电管理
电池化学: 锂离子(Li-Ion)
电源电压: 4.25 V ~ 6.5 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: SOT-23-5 细型,TSOT-23-5
供应商设备封装: TSOT-23-5
包装: 带卷 (TR)
其它名称: LTC4057ES5-4.2
LTC4057ES5-4.2-ND
LTC4057-4.2
APPLICATIO S I FOR ATIO
Using the previous example with an ambient temperature
of 60 ° C, the charge current will be reduced to approxi-
mately:
Table 1. Measured Thermal Resistance
COPPER AREA
BOARD
THERMAL
RESISTANCE
JUNCTION-TO-
I BAT =
120 ° C – 60 ° C
( 4 . 5 V – 3 . 7 V ) ? 150 ° C / W
I BAT = 500 mA
=
60 ° C
120 ° C / A
TOPSIDE*
2500mm 2
1000mm 2
225mm 2
BACKSIDE
2500mm 2
2500mm 2
2500mm 2
AREA
2500mm 2
2500mm 2
2500mm 2
AMBIENT
125 ° C/W
125 ° C/W
130 ° C/W
Moreover, when thermal feedback reduces the charge
current, the voltage at the PROG pin is also reduced
proportionally as discussed in the Operation section.
100mm 2 2500mm 2
50mm 2 2500mm 2
*Device is mounted on topside.
2500mm 2
2500mm 2
135 ° C/W
150 ° C/W
It is important to remember that LTC4057 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
120 ° C.
Thermal Considerations
Because of the small size of the ThinSOT package, it is very
important to use a good thermal PC board layout to
maximize the available charge current. The thermal path
for the heat generated by the IC is from the die to the
copper lead frame, through the package leads, (especially
Increasing Thermal Regulation Current
Reducing the voltage drop across the internal MOSFET
can significantly decrease the power dissipation in the IC.
This has the effect of increasing the current delivered to
the battery during thermal regulation. One method is by
dissipating some of the power through an external compo-
nent, such as a resistor or diode.
Example: An LTC4057-4.2 operating from a 5V wall adapter
is programmed to supply 800mA full-scale current to a
discharged Li-Ion battery with a voltage of 3.75V. Assum-
ing θ JA is 125 ° C/W, the approximate charge current at an
ambient temperature of 25 ° C is:
the ground lead) to the PC board copper. The PC board
copper is the heat sink. The footprint copper pads should
be as wide as possible and expand out to larger copper
I BAT =
120 ° C – 25 ° C
( 5 V – 3 . 75 V ) ? 125 ° C / W
= 608 mA
areas to spread and dissipate the heat to the surrounding
ambient. Feedthrough vias to inner or backside copper
layers are also useful in improving the overall thermal
performance of the charger. Other heat sources on the
board, not related to the charger, must also be considered
By dropping voltage across a resistor in series with a 5V
wall adapter (shown in Figure 2), the on-chip power
dissipation can be decreased, thus increasing the ther-
mally regulated charge current.
when designing a PC board layout because they will affect
overall temperature rise and the maximum charge current.
Table 1 lists thermal resistance for several different board
I BAT =
120 ° C – 25 ° C
( V S – I BAT R CC – V BAT )? θ JA
sizes and copper areas. All measurements were taken in
still air on 3/32" FR-4 board with one ounce copper.
4057f
8
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