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AMS2911CM-15 参数 Datasheet PDF下载

AMS2911CM-15图片预览
型号: AMS2911CM-15
PDF下载: 下载PDF文件 查看货源
内容描述: 1A低压差稳压器 [1A LOW DROPOUT VOLTAGE REGULATOR]
分类和应用: 稳压器
文件页数/大小: 8 页 / 81 K
品牌: ADMOS [ ADVANCED MONOLITHIC SYSTEMS ]
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AMS2911  
APPLICATION HINTS  
The AMS2911 series of adjustable and fixed regulators are easy  
to use and are protected against short circuit and thermal  
overloads. Thermal protection circuitry will shut-down the  
regulator should the junction temperature exceed 165°C at the  
sense point.  
D1  
Pin compatible with older three terminal adjustable regulators,  
these devices offer the advantage of a lower dropout voltage,  
more precise reference tolerance and improved reference stability  
with temperature.  
AMS2911  
VOUT  
VIN  
IN  
OUT  
ADJ  
+
COUT  
R1  
m
F
150  
CADJ  
Stability  
R2  
m
10  
F
The circuit design used in the AMS2911 series requires the use of  
an output capacitor as part of the device frequency compensation.  
The addition of 150mF aluminum electrolytic or a 22mF solid  
tantalum on the output will ensure stability for all operating  
conditions.  
Figure 1.  
When the adjustment terminal is bypassed with a capacitor to  
improve the ripple rejection, the requirement for an output  
capacitor increases. The value of 22mF tantalum or 150mF  
aluminum covers all cases of bypassing the adjustment terminal.  
Without bypassing the adjustment terminal smaller capacitors can  
be used with equally good results.  
To ensure good transient response with heavy load current  
changes capacitor values on the order of 100mF are used in the  
output of many regulators. To further improve stability and  
transient response of these devices larger values of output  
capacitor can be used.  
Output Voltage  
The AMS2911 series develops a 1.25V reference voltage  
between the output and the adjust terminal. Placing a resistor  
between these two terminals causes a constant current to flow  
through R1 and down through R2 to set the overall output  
voltage. This current is normally the specified minimum load  
current of 10mA. Because IADJ is very small and constant it  
represents a small error and it can usually be ignored.  
AMS2911  
VOUT  
VIN  
IN  
OUT  
ADJ  
Protection Diodes  
VREF  
R1  
R2  
IADJ  
Unlike older regulators, the AMS2911 family does not need any  
protection diodes between the adjustment pin and the output and  
from the output to the input to prevent over-stressing the die.  
Internal resistors are limiting the internal current paths on the  
AMS2911 adjustment pin, therefore even with capacitors on the  
adjustment pin no protection diode is needed to ensure device  
safety under short-circuit conditions.  
50  
A
m
VOUT = VREF (1+ R2/R1)+IADJR2  
Figure 2. Basic Adjustable Regulator  
Diodes between the input and output are not usually needed.  
Microsecond surge currents of 50A to 100A can be handled by the  
internal diode between the input and output pins of the device. In  
normal operations it is difficult to get those values of surge  
currents even with the use of large output capacitances. If high  
value output capacitors are used, such as 1000mF to 5000mF and  
the input pin is instantaneously shorted to ground, damage can  
occur. A diode from output to input is recommended, when a  
crowbar circuit at the input of the AMS2911 is used (Figure 1).  
Load Regulation  
True remote load sensing it is not possible to provide, because  
the AMS2911 is a three terminal device. The resistance of the  
wire connecting the regulator to the load will limit the load  
regulation. The data sheet specification for load regulation is  
measured at the bottom of the package. Negative side sensing is a  
true Kelvin connection, with the bottom of the output divider  
returned to the negative side of the load.  
The best load regulation is obtained when the top of the resistor  
divider R1 is connected directly to the case not to the load. If R1  
were connected to the load, the effective resistance between the  
regulator and the load would be:  
RP x ( R2+R1 ) , RP = Parasitic Line Resistance  
R1  
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140