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LT1587CT-3.3 参数 Datasheet PDF下载

LT1587CT-3.3图片预览
型号: LT1587CT-3.3
PDF下载: 下载PDF文件 查看货源
内容描述: 7A , 4.6A , 3A低压降快速响应正可调稳压器和固定 [7A, 4.6A, 3A Low Dropout Fast Response Positive Regulators Adjustable and Fixed]
分类和应用: 线性稳压器IC调节器电源电路输出元件局域网
文件页数/大小: 12 页 / 278 K
品牌: Linear [ Linear ]
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LT1584/LT1585/LT1587  
U
W U U  
APPLICATIONS INFORMATION  
maximum supply voltage. When power is first applied, the  
inputvoltagerisesandtheoutputvoltagefollowstheinput.  
The input-to-output voltage remains small and the regula-  
tor can supply large output currents. This action permits  
the regulator to start-up into very heavy loads.  
handle microsecond surge currents of 50A to 100A. Even  
with large value output capacitors it is difficult to obtain  
those values of surge currents in normal operation. Only  
with large values of output capacitance, such as 1000µF to  
5000µF, and with the input pin instantaneously shorted to  
ground can damage occur. A crowbar circuit at the input of  
the LT1584/LT1585/LT1587 can generate those levels of  
current, and a diode from output to input is then recom-  
mended. This is shown in Figure 2. Usually, normal power  
supply cycling or system “hot plugging and unplugging”  
will not generate current large enough to do any damage.  
With higher input voltages, a problem can occur where the  
removal of an output short does not permit the output  
voltage to recover. This problem is not unique to the  
LT1584 devices and is present on the LT1083/LT1084/  
LT1085 family and older generation linear regulators. The  
problem occurs with a heavy output load, a high input  
voltage, and a low output voltage. An example is immedi-  
ately after the removal of a short circuit. The load line of  
such a load may intersect the output current curve at two  
points. If this happens, two stable output operating points  
exist for the regulator. With this double intersection, the  
power supply may require cycling down to zero and back  
up again to make the output recover. This situation does  
not occur with the LT1585/LT1587 because no foldback  
circuitry is required to provide safe-area protection.  
The adjust pin can be driven on a transient basis ±7V with  
respect to the output, without any device degradation. As  
with any IC regulator, exceeding the maximum input-to-  
outputvoltagedifferentialcausestheinternaltransistorsto  
break down and none of the protection circuitry is then  
functional.  
D1  
1N4002  
(OPTIONAL)  
Ripple Rejection  
LT1584-3.3  
V
IN  
OUT  
V
OUT  
IN  
+
+
+
C1  
C2  
The typical curve for ripple rejection reflects values for the  
LT1584/LT1585/LT1587 fixed output voltage parts be-  
tween 3.3V and 3.6V. In applications that require improved  
ripple rejection, use the adjustable devices. A bypass  
capacitor from the adjust pin to ground reduces the output  
ripple by the ratio of VOUT/1.25V. The impedance of the  
adjust pin capacitor at the ripple frequency should be less  
than the value of R1 (typically in the range of 100to  
120) in the feedback divider network in Figure 2. There-  
fore, the value of the required adjust pin capacitor is a  
function of the input ripple frequency. For example, if R1  
equals 100and the ripple frequency equals 120Hz, the  
adjust pin capacitor should be 22µF. At 10kHz, only 0.22µF  
is needed.  
GND  
10µF  
22µF  
D1  
1N4002  
(OPTIONAL)  
LT1584  
V
IN  
IN  
OUT  
V
OUT  
+
C1  
10µF  
C2  
22µF  
ADJ  
R1  
+
LT1584 • F02  
R2  
C
ADJ  
Figure 2  
Overload Recovery  
Output Voltage  
The LT1584 devices have safe-area protection similar to  
the LT1083/LT1084/LT1085. The safe-area protection de-  
creases current limit as input-to-output voltage increases.  
This behavior keeps the power transistor inside a safe  
operating region for all values of input-to-output voltage.  
The LT1584 protection circuitry provides some output  
current at all values of input-to-output voltage up to the 7V  
TheLT1584/LT1585/LT1587adjustableregulatorsdevelop  
a 1.25V reference voltage between the output pin and the  
adjust pin (see Figure 3). Placing a resistor R1 between  
these two terminals causes a constant current to flow  
through R1 and down through R2 to set the overall output  
voltage. Normally, this current is the specified minimum  
9