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AAT2556IWP-CA-T1 参数 Datasheet PDF下载

AAT2556IWP-CA-T1图片预览
型号: AAT2556IWP-CA-T1
PDF下载: 下载PDF文件 查看货源
内容描述: 电池充电器和降压型转换器,用于便携式应用 [Battery Charger and Step-Down Converter for Portable Applications]
分类和应用: 转换器电池便携式
文件页数/大小: 29 页 / 796 K
品牌: AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
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AAT2556  
Battery Charger and Step-Down  
Converter for Portable Applications  
The LED should be biased with as little current as  
necessary to create reasonable illumination; there-  
fore, a ballast resistor should be placed between  
the LED cathode and the STAT pin. LED current  
consumption will add to the overall thermal power  
budget for the device package, hence it is good to  
keep the LED drive current to a minimum. 2mA  
should be sufficient to drive most low-cost green or  
red LEDs. It is not recommended to exceed 8mA  
for driving an individual status LED.  
Where:  
PD(MAX) = Maximum Power Dissipation (W)  
θJA  
= Package Thermal Resistance (°C/W)  
TJ(MAX) = Maximum Device Junction Temperature  
(°C) [135°C]  
TA  
= Ambient Temperature (°C)  
Figure 3 shows the relationship of maximum  
power dissipation and ambient temperature of the  
AAT2556.  
The required ballast resistor values can be esti-  
mated using the following formulas:  
3000  
2500  
2000  
1500  
1000  
500  
(VADP  
- VF(LED)  
ILED  
)
R1=  
Example:  
0
(5.5V - 2.0V)  
2mA  
0
20  
40  
60  
80  
100  
120  
R1 =  
= 1.75kΩ  
TA (°C)  
Note: Red LED forward voltage (VF) is typically  
2.0V @ 2mA.  
Figure 3: Maximum Power Dissipation.  
Next, the power dissipation of the battery charger  
can be calculated by the following equation:  
Thermal Considerations  
The AAT2556 is offered in a TDFN33-12 package  
which can provide up to 2W of power dissipation  
when it is properly bonded to a printed circuit board  
and has a maximum thermal resistance of 50°C/W.  
Many considerations should be taken into account  
when designing the printed circuit board layout, as  
well as the placement of the charger IC package in  
proximity to other heat generating devices in a  
given application design. The ambient temperature  
around the IC will also have an effect on the ther-  
mal limits of a battery charging application. The  
maximum limits that can be expected for a given  
ambient condition can be estimated by the follow-  
ing discussion.  
PD = [(VADP - VBAT) · ICH + (VADP · IOP)]  
Where:  
PD = Total Power Dissipation by the Device  
VADP = ADP/USB Voltage  
VBAT = Battery Voltage as Seen at the BAT Pin  
ICH = Constant Charge Current Programmed for  
the Application  
IOP = Quiescent Current Consumed by the  
Charger IC for Normal Operation [0.5mA]  
First, the maximum power dissipation for a given  
situation should be calculated:  
By substitution, we can derive the maximum  
charge current before reaching the thermal limit  
condition (thermal cycling). The maximum charge  
current is the key factor when designing battery  
charger applications.  
(TJ(MAX) - TA)  
θJA  
PD(MAX)  
=
2556.2006.09.1.2  
17  
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