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TL431CDR2G 参数 Datasheet PDF下载

TL431CDR2G图片预览
型号: TL431CDR2G
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:
文件页数/大小: 18 页 / 176 K
品牌: ONSEMI [ ONSEMI ]
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TL431, A, B Series, NCV431A  
APPLICATIONS INFORMATION  
1
1
The TL431 is a programmable precision reference which  
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.  
P2 +  
+
+
+ 60 kHz  
2p R  
C
2p * 10 M * 0.265 pF  
P2 P2  
1
1
Z1 +  
+ 500 kHz  
2p R  
C
2p * 15.9 k * 20 pF  
Z1 P1  
In addition, there is an external circuit pole defined by the  
load:  
1
P
+
L
2p R C  
L L  
Also, the transfer dc voltage gain of the TL431 is:  
G + G R  
GoR  
M GM  
L
Example 1:  
A simplified model of the TL431 is shown in Figure 31.  
When tested for stability boundaries, the load resistance is  
150 W. 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 amplitude 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  
I
+10mA, R + 230 W, C + 0. Define the transfer gain.  
C
L
L
The DC gain is:  
G + G R  
GoR +  
M GM  
L
(2.138)(1.0 M)(1.25 m)(230) + 615 + 56 dB  
8.25 k  
8.25 k ) 15 k  
compensation capacitance, C . The voltage across C  
P2  
P2  
Loop gain + G  
+ 218 + 47 dB  
drives the output dependent current source, Go, which is  
connected across the device cathode and anode.  
The resulting transfer function Bode plot is shown in  
Figure 32. The asymptotic plot may be expressed as the  
following equation:  
Model component values are:  
V
= 1.78 V  
ref  
Gm = 0.3 + 2.7 exp (−I /26 mA)  
C
jf  
ǒ1 )  
Ǔ
where IC is the device cathode current and Gm is in mhos  
500 kHz  
Av + 615  
jf  
jf  
Go = 1.25 (V 2) mmhos.  
cp  
ǒ
Ǔǒ1 )  
Ǔ
1 )  
8.0 kHz  
60 kHz  
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:  
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.  
1
1
P1 +  
+
+ 7.96 kHz  
2p R  
C
2p * 1.0 M * 20 pF  
GM P1  
http://onsemi.com  
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