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AAT2834 参数 Datasheet PDF下载

AAT2834图片预览
型号: AAT2834
PDF下载: 下载PDF文件 查看货源
内容描述: 240毫安共用于便携式设备的显示解决方案 [240mA Total Display Solution for Portable Devices]
分类和应用: 便携式便携式设备
文件页数/大小: 20 页 / 474 K
品牌: ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
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AAT2833/34  
240mA Total Display Solution  
for Portable Devices  
LED Selection  
PCB Layout  
The AAT2833/34 is designed to drive high-intensity  
white LEDs. It is particularly suitable for LEDs with  
an operating forward voltage in the range of 4.2V  
to 1.5V.  
To achieve adequate electrical and thermal per-  
formance, careful attention must be given to the  
printed circuit board (PCB) layout. In the worst-case  
operating condition, the chip must dissipate consid-  
erable power at full load. Adequate heat-sinking  
must be achieved to ensure intended operation.  
The AAT2833/34 can also drive other loads that  
have similar characteristics to white LEDs. For var-  
ious load types, the AAT2833/34 provides a high  
current, programmable, ideal constant current  
channel/sink.  
Figures 6 and 7 illustrate an example PCB layout.  
The bottom of the package features an exposed  
metal pad. The exposed pad acts, thermally, to  
transfer heat from the chip and, electrically, as a  
ground connection.  
Capacitor Selection  
The junction-to-ambient thermal resistance (θJA) for  
the AAT2833/34 package can be significantly  
reduced by following a couple of important PCB  
design guidelines. The PCB area directly under-  
neath the package should be plated so that the  
exposed pad can be mated to the top layer PCB  
copper during the reflow process. Multiple copper  
plated thru-holes should be used to electrically and  
thermally connect the AAT2833/34’s exposed pad  
area to additional ground plane(s).  
Careful selection of the four external capacitors  
CIN, C1, C2, and COUT are important because they  
will affect turn-on time, output ripple, and transient  
performance. Optimum performance will be  
obtained when low equivalent series resistance  
(ESR) ceramic capacitors are used. In general, low  
ESR is defined as a resistance that is less than  
100mΩ.  
X7R and X5R ceramic capacitors are highly rec-  
ommended over all other types of capacitors for  
use with the AAT2833/34. For the input (CIN) and  
output (COUT) capacitors, a 2.2µF or greater value  
is recommended, and a 1µF or greater value is rec-  
ommended for the flying (C1/C2) capacitors.  
Ceramic capacitors offer many advantages over  
their tantalum and aluminum electrolytic counter-  
parts. A ceramic capacitor typically has very low  
ESR, is lowest cost, has a smaller PCB footprint,  
and is non-polarized. Low ESR ceramic capacitors  
help maximize charge pump transient response.  
The chip ground is internally connected to both the  
paddle and to the AGND and PGND pins. It is good  
practice to connect the GND pins to the exposed  
pad area with traces as shown in Figure 5.  
The flying capacitors (C1 and C2), input capacitor  
(C4), and output capacitor (C3) should be connect-  
ed as close as possible to the IC. In addition to the  
external passive components being placed as  
close as possible to the IC, all traces connecting  
the AAT2833/34 should be as short and wide as  
possible to minimize path resistance and potential  
coupling.  
16  
2833.2007.09.1.0  
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