參數(shù)資料
型號(hào): TL431C
廠商: ON SEMICONDUCTOR
英文描述: programmable precision references
中文描述: 可編程精確參考
文件頁數(shù): 12/19頁
文件大小: 176K
代理商: TL431C
TL431, A, B Series, NCV431A
http://onsemi.com
12
Figure 31. Simplified TL431 Device Model
+
R
L
V
CC
C
L
15 k
9.0 F
Input
8.25 k
3
Cathode
500 k
V
ref
1.78 V
R
ref
16
G
M
Anode
2
R
GM
1.0 M
Ref
1
Go
1.0 mho
C
P2
0.265 pF
R
P2
10 M
R
Z1
15.9 k
C
P1
20 pF
f, FREQUENCY (Hz)
10
2
10
1
20
30
20
60
0
A
Figure 32. Example 1 Circuit Open Loop Gain Plot
Example 2.
I
C
= 7.5 mA, R
L
= 2.2 k , C
L
= 0.01 F. Cathode tied to
reference input pin. An examination of the data sheet
stability boundary curve (Figure 15) shows that this value of
load capacitance and cathode current is on the boundary.
Define the transfer gain.
The DC gain is:
TL431 OPENLOOP VOLTAGE GAIN VERSUS FREQUENCY
40
10
4
10
3
10
7
10
5
10
6
10
10
50
G
GMRGMGoRL
(2.323)(1.0 M)(1.25 )(2200)
The resulting open loop Bode plot is shown in Figure 33.
The asymptotic plot may be expressed as the following
equation:
6389
76 dB
Av
615
1
jf
500 kHz
1
jf
8.0 kHz
1
jf
60 kHz
1
jf
7.2 kHz
Note that the transfer function now has an extra pole
formed by the load capacitance and load resistance.
Note that the crossover frequency in this case is about
250 kHz, having a phase margin of about 46 degrees.
Therefore, instability of this circuit is likely.
f, FREQUENCY (Hz)
10
2
10
1
20
40
20
80
0
A
Figure 33. Example 2 Circuit Open Loop Gain Plot
With three poles, this system is unstable. The only hope
for stabilizing this circuit is to add a zero. However, that can
only be done by adding a series resistance to the output
capacitance, which will reduce its effectiveness as a noise
filter. Therefore, practically, in reference voltage
applications, the best solution appears to be to use a smaller
value of capacitance in low noise applications or a very
large value to provide noise filtering and a dominant pole
rolloff of the system.
TL431 OPENLOOP BODE PLOT WITH LOAD CAP
60
10
4
10
3
10
6
10
5
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