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LT1513CR 参数 Datasheet PDF下载

LT1513CR图片预览
型号: LT1513CR
PDF下载: 下载PDF文件 查看货源
内容描述: SEPIC Constant-或可编程电流/恒定电压电池充电器 [SEPIC Constant- or Programmable-Current/ Constant-Voltage Battery Charger]
分类和应用: 稳压器开关式稳压器或控制器电源电路电池开关式控制器
文件页数/大小: 16 页 / 303 K
品牌: Linear [ Linear ]
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LT1513/LT1513-2  
U
W U U  
APPLICATIONS INFORMATION  
shown in the maximum charging current graph. Higher  
inductance values give slightly higher maximum charging  
current,butarelargerandmoreexpensive.Alowlosstoroid  
core such as Kool Mµ®, Molypermalloy or Metglas® is  
recommended.Seriesresistanceshouldbelessthan0.04Ω  
for each winding. “Open core” inductors, such as rods or  
barrels are not recommended because they generate large  
magnetic fields which may interfere with other electronics  
close to the charger.  
in Figure 1. These are AVX type TPS or Sprague type 593D  
surface mount solid tantalum units intended for switching  
applications. Donot substituteothertypeswithout ensuring  
that they have adequate ripple current ratings. See Input  
Capacitor section for details of surge limitation on solid  
tantalum capacitors if the battery may be “hot switched” to  
the output of the charger.  
Coupling Capacitor  
C2 in Figure 1 is the coupling capacitor that allows a SEPIC  
converter topology to work with input voltages either higher  
or lower than the battery voltage. DC bias on the capacitor is  
equal to input voltage. RMS ripple current in the coupling  
capacitor has a maximum value of about 1A at full charging  
current. A conservative formula to calculate this is:  
Input Capacitor  
The SEPIC topology has relatively low input ripple current  
compared to other topologies and higher harmonics are  
especially low. RMS ripple current in the input capacitor is  
less than 0.25A with L = 10µH and less than 0.5A with  
L=5µH. AlowESR22µF, 25Vsolidtantalumcapacitor(AVX  
type TPS or Sprague type 593D) is adequate for most  
applications with the following caveat. Solid tantalum  
capacitors can be destroyed with a very high turn-on surge  
currentsuchaswouldbegeneratedifalowimpedanceinput  
source were “hot switched” to the charger input. If this  
condition can occur, the input capacitor should have the  
highestpossiblevoltagerating,atleasttwicethesurgeinput  
voltage if possible. Consult with the capacitor manufacturer  
beforeafinalchoiceismade.A4.7µFceramiccapacitorsuch  
as the one used for the coupling capacitor can also be used.  
Thesecapacitorsdonothaveaturn-onsurgelimitation. The  
inputcapacitormustbeconnecteddirectlytotheVINpinand  
the ground plane close to the LT1513.  
I
(V + V )(1.1)  
BAT  
CHRG IN  
I
=
COUP(RMS)  
2(V )  
IN  
(1.1 is a fudge factor to account for inductor ripple current  
and other losses)  
WithICHRG =1.2A, VIN =15VandVBAT =8.2V, ICOUP =1.02A.  
The recommended capacitor is a 4.7µF ceramic type from  
Marcon or Tokin. These capacitors have extremely low ESR  
and high ripple current ratings in a small package. Solid  
tantalumunitscanbesubstitutediftheirripplecurrentrating  
is adequate, but typical values will increase to 22µF or more  
to meet the ripple current requirements.  
Diode Selection  
Output Capacitor  
The switching diode should be a Schottky type to minimize  
both forward and reverse recovery losses. Average diode  
currentisthesameasoutputchargingcurrent,sothiswillbe  
under2A.A3Adiodeisrecommendedformostapplications,  
although smaller devices could be used at reduced charging  
current. Maximum diode reverse voltage will be equal to  
input voltage plus battery voltage.  
It is assumed as a worst case that all the switching output  
ripple current from the battery charger could flow in the  
output capacitor. This is a desirable situation if it is neces-  
sary to have very low switching ripple current in the battery  
itself. Ferritebeadsorlinechokesareofteninsertedinseries  
with the battery leads to eliminate high frequency currents  
that could create EMI problems. This forces all the ripple  
currentintotheoutputcapacitor. TotalRMScurrentintothe  
capacitor has a maximum value of about 1A, and this is  
handledwiththetwoparalleled22µF,25Vcapacitorsshown  
Diode reverse leakage current will be of some concern  
during charger shutdown. This leakage current is a direct  
drain on the battery when the charger is not powered. High  
Kool Mµ is a registered trademark of Magnetics, Inc.  
Metglas is a registered trademark of AlliedSignal Inc.  
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