欢迎访问ic37.com |
会员登录 免费注册
发布采购

LP2951CMX/NOPB 参数 Datasheet PDF下载

LP2951CMX/NOPB图片预览
型号: LP2951CMX/NOPB
PDF下载: 下载PDF文件 查看货源
内容描述: LP2950 -N / LP2951 -N系列的可调微功耗电压调节器 [LP2950-N/LP2951-N Series of Adjustable Micropower Voltage Regulators]
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: 43 页 / 1949 K
品牌: TI [ TEXAS INSTRUMENTS ]
 浏览型号LP2951CMX/NOPB的Datasheet PDF文件第9页浏览型号LP2951CMX/NOPB的Datasheet PDF文件第10页浏览型号LP2951CMX/NOPB的Datasheet PDF文件第11页浏览型号LP2951CMX/NOPB的Datasheet PDF文件第12页浏览型号LP2951CMX/NOPB的Datasheet PDF文件第14页浏览型号LP2951CMX/NOPB的Datasheet PDF文件第15页浏览型号LP2951CMX/NOPB的Datasheet PDF文件第16页浏览型号LP2951CMX/NOPB的Datasheet PDF文件第17页  
LP2950-N, LP2951-N  
www.ti.com  
SNVS764N JANUARY 2000REVISED MAY 2013  
APPLICATION HINTS  
Output Capacitor Requirements  
A 1.0 μF (or greater) capacitor is required between the output and ground for stability at output voltages of 5V or  
higher. At lower output voltages, more capacitance is required (2.2 μF or more is recommended for 3.0V and  
3.3V versions). Without this capacitor the part will oscillate. Most types of tantalum or aluminum electrolytic work  
fine here; even film types work but are not recommended for reasons of cost. Many aluminum electrolytics have  
electrolytes that freeze at about 30°C, so solid tantalums are recommended for operation below 25°C. The  
important parameters of the capacitor are an ESR of about 5Ω or less and a resonant frequency above 500 kHz.  
The value of this capacitor may be increased without limit.  
Figure 44. Output Capacitor ESR Range  
The reason for the lower ESR limit is that the loop compensation of the feedback loop relies on the capacitance  
value and the ESR value of the output capacitor to provide the zero that gives added phase lead (See  
Figure 44).  
fZ = (1 / (2 x π x COUT x ESR) )  
(1)  
Using the 2.2 µF value from the Output Capacitor ESR Range curve (Figure 44), a useful range for fZ can be  
estimated:  
fZ(MIN)= (1 / (2 x π x 2.2 µF x 5) ) = 14.5 kHz  
fZ(MAX)= (1 / (2 x π x 2.2 µF x 0.05) ) = 318 kHz  
(2)  
(3)  
For ceramic capacitors, the low ESR produces a zero at a frequency that is too high to be useful, so meaningful  
phase lead does not occur. A ceramic output capacitor can be used if a series resistance is added  
(recommended value of resistance about 0.1to 2) to simulate the needed ESR. Only X5R, X7R, or better,  
MLCC types should be used, and should have a DC voltage rating at least twice the VOUT(NOM) value.  
At lower values of output current, less output capacitance is required for stability. The capacitor can be reduced  
to 0.33 μF for currents below 10 mA or 0.1 μF for currents below 1 mA. Using the adjustable versions at voltages  
below 5V runs the error amplifier at lower gains so that more output capacitance is needed. For the worst-case  
situation of a 100 mA load at 1.23V output (Output shorted to Feedback) a 3.3 μF (or greater) capacitor should  
be used.  
Unlike many other regulators, the LP2950-N will remain stable and in regulation with no load in addition to the  
internal voltage divider. This is especially important in CMOS RAM keep-alive applications. When setting the  
output voltage of the LP2951-N versions with external resistors, a minimum load of 1 μA is recommended.  
Applications having conditions that may drive the LP2950-N/51 into nonlinear operation require special  
consideration. Nonlinear operation will occur when the output voltage is held low enough to force the output  
stage into output current limiting while trying to pull the output voltage up to the regulated value. The internal loop  
response time will control how long it takes for the device to regain linear operation when the output has returned  
to the normal operating range. There are three significant nonlinear conditions that need to be considered, all can  
force the output stage into output current limiting mode, all can cause the output voltage to over-shoot with low  
Copyright © 2000–2013, Texas Instruments Incorporated  
Submit Documentation Feedback  
13  
Product Folder Links: LP2950-N LP2951-N