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AAT4626IHS-1-T1 参数 Datasheet PDF下载

AAT4626IHS-1-T1图片预览
型号: AAT4626IHS-1-T1
PDF下载: 下载PDF文件 查看货源
内容描述: USB双通道电源开关 [USB Dual-Channel Power Switch]
分类和应用: 开关电源开关
文件页数/大小: 15 页 / 389 K
品牌: AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
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AAT4626  
USB Dual-Channel Power Switch  
die and the board onto which it is mounted. TA(MAX)  
is the maximum ambient temperature for the print-  
ed circuit board assembly under the AAT4626  
when the load switch is not dissipating power.  
Applications Information  
Operation in Current Limit  
If an excessive load is applied to either output of an  
AAT4626, the load current will be limited by the  
device's current limit circuitry. Refer to the "Current  
Limit" curve in the Typical Characteristics section of  
this datasheet. If a short circuit were to occur on the  
load applied to either the A or B output, there would  
be a demand for more current than what is allowed by  
the internal current limiting circuit and the voltage at  
the device output will drop. This causes the AAT4626  
to dissipate more power than in normal operation,  
causing the die temperature to increase. When die  
temperature exceeds the internal over-temperature  
threshold, the AAT4626 will shut down both the A and  
B output channels. After shutting down, the AAT4626  
cools to a level below the over-temperature thresh-  
old, at which point it will start up again. The AAT4626  
will continue to cycle off and on until one of the fol-  
lowing events occurs: the load current of the offend-  
ing output is reduced to a level below the AAT4626's  
current limit setting; the input power is removed; or  
the output is turned off by a logic high level applied to  
the EN pin of the fault channel.  
Equation 1 can be transformed to provide IMAX  
;
Refer to Equation 2.  
TSD(MIN) - TA(MAX)  
DS(ON)(MAX) · RΘJA  
=
IMAX  
Eq. 2:  
R
TSD(MIN) is the minimum temperature required to  
activate the device over-temperature protection.  
The typical thermal limit temperature specification  
is 125°C for the AAT4626. For calculations, 115°C  
is a safe minimum value to use.  
For example, a portable device is specified to oper-  
ate in a 50°C environment. The printed circuit board  
assembly will operate at temperatures as high as  
85°C. This portable device has a sealed case and  
the area of the printed board assembly is relatively  
small, causing RθJA to be approximately 100°C/W.  
RDS(ON)(MAX) = 130W. Using Equation 2,  
115°C - 85°C  
Thermal Considerations  
=
= 1.25A  
IMAX  
Eq. 3:  
130W · 120°C/W  
Since the AAT4626 has internal current limit and  
over-temperature protection, junction temperature  
is rarely a concern. If an application requires a  
large load current in a high temperature operating  
environment, there is the possibility that the over-  
temperature protection circuit rather than the cur-  
rent limit circuit from one of the two outputs will reg-  
ulate the current available to the load. In these  
applications, the maximum current available with-  
out risk of activation of the over-temperature circuit  
can be calculated. The maximum internal temper-  
ature while current limit is not active can be calcu-  
lated using Equation 1:  
If this system requires less than 1.4A, the thermal  
limit will not activate during normal operation.  
Input Capacitor  
The input capacitor serves two purposes. First, it  
protects the source power supply from transient  
current effects generated by the application load cir-  
cuits. If a short circuit is suddenly applied to either  
output of an AAT4626, there is a microsecond long  
period during which a large current can flow before  
the current limit circuit becomes active. Refer to the  
Typical Characteristics curve "Short Circuit Through  
0.3Ω." A properly sized input capacitor can dramat-  
ically reduce the load switch input transient  
response effects seen by the power supply and  
other circuitry upstream from the AAT4626.  
TJ(MAX) = IMAX2 · RDS(ON)(MAX) · RΘJA + TA(MAX)  
Eq. 1:  
In Equation 1, IMAX is the maximum current  
required by the load. RDS(ON)(MAX) is the maximum  
rated RDS(ON) of the AAT4626 at high temperature.  
RθJA is the thermal resistance between the device  
The second purpose of the input capacitor is to pre-  
vent transient events generated by the load circuits  
8
4626.2006.05.1.2