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LT1763CS8-2.5#TRPBF 参数 Datasheet PDF下载

LT1763CS8-2.5#TRPBF图片预览
型号: LT1763CS8-2.5#TRPBF
PDF下载: 下载PDF文件 查看货源
内容描述: [LT1763 - 500mA, Low Noise, LDO Micropower Regulators; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C]
分类和应用: 线性稳压器IC调节器电源电路光电二极管输出元件
文件页数/大小: 16 页 / 280 K
品牌: Linear [ Linear ]
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LT1763 Series  
U
W U U  
APPLICATIONS INFORMATION  
plus the ADJ pin bias current. The ADJ pin bias current,  
30nA at 25°C, flows through R2 into the ADJ pin. The  
output voltage can be calculated using the formula in  
Figure 2. The value of R1 should be no greater than 250k  
to minimize errors in the output voltage caused by the ADJ  
pinbiascurrent.Notethatinshutdowntheoutputisturned  
off and the divider current will be zero. Curves of ADJ Pin  
Voltage vs Temperature and ADJ Pin Bias Current vs  
Temperature appear in the Typical Performance Charac-  
teristics section.  
10µs, with total output voltage deviation of less than 2.5%  
(see LT1763-5 Transient Response in the Typical Perfor-  
mance Characteristics). However, regulator start-up time  
is inversely proportional to the size of the bypass capaci-  
tor, slowing to 15ms with a 0.01µF bypass capacitor and  
10µF output capacitor.  
Output Capacitance and Transient Response  
The LT1763 regulators are designed to be stable with a  
wide range of output capacitors. The ESR of the output  
capacitor affects stability, most notably with small capaci-  
tors. A minimum output capacitor of 3.3µF with an ESR of  
3or less is recommended to prevent oscillations. The  
LT1763-X is a micropower device and output transient  
response will be a function of output capacitance. Larger  
values of output capacitance decrease the peak deviations  
and provide improved transient response for larger load  
current changes. Bypass capacitors, used to decouple  
individual components powered by the LT1763-X, will  
increase the effective output capacitor value. With larger  
capacitors used to bypass the reference (for low noise  
operation), larger values of output capacitors are needed.  
For 100pF of bypass capacitance, 4.7µF of output capaci-  
tor is recommended. With a 1000pF bypass capacitor or  
larger, a 6.8µF output capacitor is recommended.  
IN  
OUT  
V
OUT  
+
V
IN  
R2  
LT1763  
GND  
R2  
R1  
VOUT = 1.22V 1+  
ADJ = 1.22V  
ADJ = 30nA AT 25°C  
OUTPUT RANGE = 1.22V TO 20V  
+ I  
R2  
(
ADJ)(  
)
ADJ  
V
R1  
I
1763 F02  
Figure 2. Adjustable Operation  
The adjustable device is tested and specified with the ADJ  
pin tied to the OUT pin for an output voltage of 1.22V.  
Specifications for output voltages greater than 1.22V will  
beproportionalto the ratio ofthe desired outputvoltage to  
1.22V: VOUT/1.22V. For example, load regulation for an  
output current change of 1mA to 500mA is 2mV typical  
at VOUT = 1.22V. At VOUT = 12V, load regulation is:  
TheshadedregionofFigure3definestherangeoverwhich  
the LT1763 regulators are stable. The minimum ESR  
needed is defined by the amount of bypass capacitance  
used, while the maximum ESR is 3.  
(12V/1.22V)(–2mV) = 19.6mV  
Bypass Capacitance and Low Noise Performance  
The LT1763 regulators may be used with the addition of a  
bypass capacitor from VOUT to the BYP pin to lower output  
voltage noise. A good quality low leakage capacitor is  
recommended. This capacitor will bypass the reference of  
the regulator, providing a low frequency noise pole. The  
noise pole provided by this bypass capacitor will lower the  
output voltage noise to as low as 20µVRMS with the  
addition of a 0.01µF bypass capacitor. Using a bypass  
capacitor has the added benefit of improving transient  
response. With no bypass capacitor and a 10µF output  
capacitor, a 10mA to 500mA load step will settle to within  
1% of its final value in less than 100µs. With the addition  
of a 0.01µF bypass capacitor, the output will settle to  
within 1% for a 10mA to 500mA load step in less than  
4.0  
3.5  
3.0  
STABLE REGION  
2.5  
2.0  
C
= 0  
BYP  
1.5  
1.0  
0.5  
0
C
= 100pF  
BYP  
C
= 330pF  
BYP  
C
1000pF  
BYP  
1
3
6
9 10  
7 8  
2
4
5
OUTPUT CAPACITANCE (µF)  
1763 F03  
Figure 3. Stability  
1763fa  
12