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TL431ACLP 参数 Datasheet PDF下载

TL431ACLP图片预览
型号: TL431ACLP
PDF下载: 下载PDF文件 查看货源
内容描述: 可编程精密基准 [PROGRAMMABLE PRECISION REFERENCES]
分类和应用: 输出元件
文件页数/大小: 16 页 / 261 K
品牌: MOTOROLA [ MOTOROLA ]
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TL431, A, B Series  
APPLICATIONS INFORMATION  
The TL431 is a programmable precision reference which  
1
1
P2  
Z1  
60 kHz  
2
R
C
2 * 10 M * 0.265 pF  
is used in a variety of ways. It serves as a reference voltage  
in circuits where a non–standard reference voltage is  
needed. Other uses include feedback control for driving an  
optocoupler in power supplies, voltage monitor, constant  
current source, constant current sink and series pass  
regulator. In each of these applications, it is critical to  
maintain stability of the device at various operating currents  
and load capacitances. In some cases the circuit designer  
can estimate the stabilization capacitance from the stability  
boundary conditions curve provided in Figure 15. However,  
these typical curves only provide stability information at  
specific cathode voltages and at a specific load condition.  
Additional information is needed to determine the  
capacitance needed to optimize phase margin or allow for  
process variation.  
A simplified model of the TL431 is shown in Figure 31.  
When tested for stability boundaries, the load resistance is  
150 . The model reference input consists of an input  
transistor and a dc emitter resistance connected to the  
device anode. A dependent current source, Gm, develops a  
current whose amplidute is determined by the difference  
between the 1.78 V internal reference voltage source and the  
input transistor emitter voltage. A portion of Gm flows through  
P2 P2  
1
1
500 kHz  
2
R
C
2 * 15.9 k * 20 pF  
Z1 P1  
In addition, there is an external circuit pole defined by the  
load:  
1
P
L
2
R C  
L L  
Also, the transfer dc voltage gain of the TL431 is:  
G R GoR  
G
M GM  
L
Example 1:  
10 mA, R  
I
230 , C  
0. Define the transfer gain.  
C
L
L
The DC gain is:  
G
G R  
M GM  
GoR  
L
(2.138)(1.0 M)(1.25 )(230)  
615  
218  
56 dB  
47 dB  
8.25 k  
Loop gain  
G
8.25 k 15 k  
The resulting transfer function Bode plot is shown in  
Figure 32. The asymptotic plot may be expressed as the  
following equation:  
compensation capacitance, C . The voltage across C  
drives the output dependent current source, Go, which is  
connected across the device cathode and anode.  
P2  
P2  
1
jf  
500 kHz  
jf  
8.0 kHz 60 kHz  
Model component values are:  
V
= 1.78 V  
ref  
Gm = 0.3 + 2.7 exp (–I /26 mA)  
Av  
615  
1
1
jf  
C
where I is the device cathode current and Gm is in mhos  
C
The Bode plot shows a unity gain crossover frequency of  
approximately 600 kHz. The phase margin, calculated from  
the equation, would be 55.9 degrees. This model matches  
the Open–Loop Bode Plot of Figure 12. The total loop would  
have a unity gain frequency of about 300 kHz with a phase  
margin of about 44 degrees.  
Go = 1.25 (V 2) µmhos.  
cp  
Resistor and capacitor typical values are shown on the  
model. Process tolerances are ±20% for resistors, ±10% for  
capacitors, and ±40% for transconductances.  
An examination of the device model reveals the location of  
circuit poles and zeroes:  
1
1
P1  
7.96 kHz  
2
R
C
2 * 1.0 M * 20 pF  
GM P1  
11  
MOTOROLA ANALOG IC DEVICE DATA