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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  
W
BLOCK DIAGRAM  
V
IN  
SW  
SHUTDOWN  
DELAY AND RESET  
LOW DROPOUT  
2.3V REG  
S/S  
ANTISAT  
500kHz  
LOGIC  
COMP  
DRIVER  
SWITCH  
SYNC  
OSC  
+
I
FBA  
4k  
50k*  
I
FB  
+
+
V
EA  
IA  
0.04Ω  
FB  
A
V
6  
V
C
1.245V  
REF  
LT1513 • BD  
*REMOVE ON LT1513-2  
Figure 2  
U
OPERATION  
The LT1513 is a current mode switcher. This means that  
switch duty cycle is directly controlled by switch current  
rather than by output voltage or current. Referring to the  
BlockDiagram,theswitchisturnedonatthestartofeach  
oscillator cycle. It is turned “off” when switch current  
reaches a predetermined level. Control of output voltage  
and current is obtained by using the output of a dual  
feedback voltage sensing error amplifier to set switch  
current trip level. This technique has the advantage of  
simplified loop frequency compensation. A low dropout  
internal regulator provides a 2.3V supply for all internal  
circuitry on the LT1513. This low dropout design allows  
input voltage to vary from 2.7V to 25V. A 500kHz oscillator  
is the basic clock for all internal timing. It turns “on” the  
output switch via the logic and driver circuitry. Special  
adaptive antisat circuitry detects onset of saturation in the  
powerswitchandadjustsdrivercurrentinstantaneouslyto  
limit switch saturation. This minimizes driver dissipation  
and provides very rapid turn-off of the switch.  
1.245V bandgap reference biases the noninverting input.  
Thefirstinvertinginputoftheerroramplifierisbroughtout  
for positive output voltage sensing. The second inverting  
input is driven by a “current” amplifier which is sensing  
output current via an external current sense resistor. The  
current amplifier is set to a fixed gain of 12.5 which  
provides a 100mV current limit sense voltage.  
The LT1513-2 option removes the feedback resistors  
around the IFB amplifier and connects its output to the FB  
signal. This provides a ground referenced current sense  
voltage suitable for external current programming and  
makes amplifier input and output available for external  
loop compensation.  
The error signal developed at the amplifier output is  
brought out externally and is used for frequency compen-  
sation. During normal regulator operation this pin sits at a  
voltage between 1V (low output current) and 1.9V (high  
outputcurrent). SwitchdutycyclegoestozeroiftheVC pin  
is pulled below the VC pin threshold, placing the LT1513 in  
an idle mode.  
A unique error amplifier design has two inverting inputs  
which allow for sensing both output voltage and current. A  
6