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LT1507CS8-3.3 参数 Datasheet PDF下载

LT1507CS8-3.3图片预览
型号: LT1507CS8-3.3
PDF下载: 下载PDF文件 查看货源
内容描述: 500kHz的单片式降压模式开关稳压器 [500kHz Monolithic Buck Mode Switching Regulator]
分类和应用: 稳压器开关式稳压器或控制器电源电路开关式控制器光电二极管
文件页数/大小: 20 页 / 346 K
品牌: Linear [ Linear ]
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LT1507  
U
W U U  
APPLICATIONS INFORMATION  
Table 1. Representative Surface Mount Units  
be due to a radiated magnetic field coupling into PC  
board traces. But why were some boards bad and  
others good? In a moment of desperation (or divine  
inspiration) I unsoldered a “bad” inductor, rotated it  
180° and resoldered it. Problem fixed!!  
VALUE  
MANUFACTURER (µH)  
DC  
(A)  
CORE SERIES  
HEIGHT  
(mm)  
TYPE  
()  
CORE  
Coiltronics  
CTX5-1  
CTX10-1  
CTX5-1P  
CTX10-1P  
5
10  
5
2.3  
1.9  
1.8  
1.6  
Tor  
Tor  
Tor  
Tor  
0.027 KMµ  
0.039 KMµ  
0.021  
4.2  
4.2  
4.2  
4.2  
52  
52  
It turns out that the inductor was symmetrical in all  
regards except that the polarity of the magnetic field  
reversed when the unit was rotated 180° because  
current flowed in the opposite direction in the coil. In  
one direction, the magnetically induced ripple in the  
boardtracesadded tooutputripple.Rotatingtheinduc-  
tor caused the induced field to reduce output ripple.  
Unfortunately the inductor had no physical package  
assymmetry to indicate rotation, including part mark-  
ing, so we had to visually examine the winding in each  
unit before soldering it to the boards. This little horror  
story should not preclude the use of open core induc-  
tors, but it emphasizes the need to carefully check the  
effect these seductively small, low cost inductors may  
have on regulator or system performances.  
10  
0.030  
Sumida  
CDRH64  
CDRH73  
CD73  
10  
10  
10  
10  
1.7  
1.7  
1.4  
2.4  
SC  
SC  
0.084  
0.055  
Fer  
Fer  
Fer  
Fer  
4.5  
3.4  
3.5  
4.0  
Open 0.062  
Open 0.041  
CD104  
Gowanda  
SM20-102K  
10  
1.3  
Open 0.038  
Fer  
7
Dale  
IHSM-4825  
IHSM-5832  
10  
10  
3.1  
4.3  
Open 0.071  
Open 0.053  
Fer  
Fer  
5.6  
7.1  
SC = Semi-closed geometry  
Fer = Ferrite core material  
52 = Type 52 powdered iron core material  
KMµ = Kool Mµ  
OUTPUT CAPACITOR  
The output capacitor is normally chosen by its effective  
series resistance (ESR), because that is what determines  
output ripple voltage. At 500kHz any polarized capacitor is  
essentially resistive. To get low ESR takes volume; physi-  
cally larger capacitors have lower ESR. The ESR range  
needed for typical LT1507 applications is 0.05to 0.5.  
A typical output capacitor is an AVX type TPS, 100µF at  
10V, with a guaranteed ESR less than 0.1. This is a “D”  
size surface mount solid tantalum capacitor. TPS capaci-  
tors are specially constructed and tested for low ESR so  
they give the lowest ESR for a given volume. The value in  
microfarads is not particularly critical and values from  
22µF to greater than 500µF work well, but you cannot  
cheat mother nature on ESR. If you find a tiny 22µF solid  
tantalum capacitor, it will have high ESR and output ripple  
voltage will be terrible. The chart in Table 2 shows some  
typical solid tantalum surface mount capacitors.  
4. Look for an inductor (see Table 1) which meets the  
requirements of core shape, peak current (to avoid  
saturation), average current (to limit heat) and fault  
current (if the inductor gets too hot, wire insulation will  
melt and cause turn-to-turn shorts). Keep in mind that  
all good things like high efficiency, surface mounting,  
lowprofileandhightemperatureoperationwillincrease  
cost, sometimes dramatically.  
5. Aftermakinganinitialchoice,considersecondarythings  
like output voltage ripple, second sourcing, etc. Use the  
experts in the Linear Technology Applications Depart-  
ment if you feel uncertain about the final choice. They  
haveexperiencewithawiderangeofinductortypesand  
cantellyouaboutthelatestdevelopmentsinlowprofile,  
surface mounting, etc.  
10