MOTOROLA TL431

Order this document by TL431/D
The TL431, A, B integrated circuits are three–terminal programmable
shunt regulator diodes. These monolithic IC voltage references operate as a
low temperature coefficient zener which is programmable from Vref to 36 V
with two external resistors. These devices exhibit a wide operating current
range of 1.0 mA to 100 mA with a typical dynamic impedance of 0.22 Ω. The
characteristics of these references make them excellent replacements for
zener diodes in many applications such as digital voltmeters, power
supplies, and op amp circuitry. The 2.5 V reference makes it convenient to
obtain a stable reference from 5.0 V logic supplies, and since the TL431, A,
B operates as a shunt regulator, it can be used as either a positive or
negative voltage reference.
•
•
•
•
•
•
•
Programmable Output Voltage to 36 V
Voltage Reference Tolerance: ±0.4%, Typ @ 25°C (TL431B)
Low Dynamic Output Impedance, 0.22 Ω Typical
PROGRAMMABLE
PRECISION REFERENCES
SEMICONDUCTOR
TECHNICAL DATA
LP SUFFIX
PLASTIC PACKAGE
CASE 29
(TO–92)
1
Sink Current Capability of 1.0 mA to 100 mA
2
Pin 1. Reference
2. Anode
3. Cathode
3
Equivalent Full–Range Temperature Coefficient of 50 ppm/°C Typical
Temperature Compensated for Operation over Full Rated Operating
Temperature Range
Low Output Noise Voltage
P SUFFIX
PLASTIC PACKAGE
CASE 626
8
1
DM SUFFIX
PLASTIC PACKAGE
CASE 846A
(Micro–8)
8
1
8 Reference
Cathode 1
N/C 2
7 N/C
N/C 3
6 Anode
N/C 4
5 N/C
(Top View)
D SUFFIX
PLASTIC PACKAGE
CASE 751
(SOP–8)
ORDERING INFORMATION
Device
Operating
Temperature Range
TL431CLP, ACLP, BCLP
TO–92
TL431CP, ACP, BCP
TL431CDM, ACDM, BCDM
Package
Plastic
TA = 0° to +70°C
70°C
8
1
Cathode 1
8
2
7
3
6
N/C 4
5
Anode
Reference
Anode
N/C
Micro–8
(Top View)
TL431CD, ACD, BCD
SOP–8
TL431ILP, AILP, BILP
TO–92
TL431IP, AIP, BIP
TL431IDM, AIDM, BIDM
Plastic
TA = –40°
40° to +85°C
85°C
TL431ID, AID, BID
Micro–8
SOP–8 is an internally modified SO–8 package. Pins 2,
3, 6 and 7 are electrically common to the die attach flag.
This internal lead frame modification decreases power
dissipation capability when appropriately mounted on a
printed circuit board. SOP–8 conforms to all external
dimensions of the standard SO–8 package.
SOP–8
 Motorola, Inc. 1998
MOTOROLA ANALOG IC DEVICE DATA
Rev 6
1
TL431, A, B Series
Symbol
Representative Schematic Diagram
Component values are nominal
Cathode
(K)
Cathode (K)
Reference
(R)
800
800
Reference
(R)
Anode
(A)
20 pF
Representative Block Diagram
Reference
(R)
4.0 k
20 pF
Cathode
(K)
+
150
3.28 k
2.4 k
10 k
7.2 k
–
1.0 k
2.5 Vref
800
Anode (A)
Anode (A)
This device contains 12 active transistors.
MAXIMUM RATINGS (Full operating ambient temperature range applies, unless
otherwise noted.)
Rating
Symbol
Value
Unit
VKA
37
V
Cathode Current Range, Continuous
IK
–100 to +150
mA
Reference Input Current Range, Continuous
Iref
–0.05 to +10
mA
Operating Junction Temperature
TJ
150
°C
Operating Ambient Temperature Range
TL431I, TL431AI, TL431BI
TL431C, TL431AC, TL431BC
TA
Cathode to Anode Voltage
Storage Temperature Range
Tstg
Total Power Dissipation @ TA = 25°C
Derate above 25°C Ambient Temperature
D, LP Suffix Plastic Package
P Suffix Plastic Package
DM Suffix Plastic Package
PD
Total Power Dissipation @ TC = 25°C
Derate above 25°C Case Temperature
D, LP Suffix Plastic Package
P Suffix Plastic Package
PD
NOTE:
°C
–40 to +85
0 to +70
–65 to +150
°C
W
0.70
1.10
0.52
W
1.5
3.0
ESD data available upon request.
RECOMMENDED OPERATING CONDITIONS
Condition
Cathode to Anode Voltage
Symbol
Min
Max
Unit
VKA
Vref
36
V
IK
1.0
100
mA
Cathode Current
THERMAL CHARACTERISTICS
Symbol
D, LP Suffix
Package
P Suffix
Package
DM Suffix
Package
Unit
Thermal Resistance, Junction–to–Ambient
RθJA
178
114
240
°C/W
Thermal Resistance, Junction–to–Case
RθJC
83
41
–
°C/W
Characteristic
2
MOTOROLA ANALOG IC DEVICE DATA
TL431, A, B Series
ELECTRICAL CHARACTERISTICS (TA = 25°C, unless otherwise noted.)
TL431I
Ch
Characteristic
i i
S b l
Symbol
Reference Input Voltage (Figure 1)
VKA = Vref, IK = 10 mA
TA = 25°C
TA = Tlow to Thigh (Note 1)
Min
Typ
TL431C
Max
Min
Typ
Max
Vref
V
Reference Input Voltage Deviation Over
Temperature Range (Figure 1, Notes 1, 2)
VKA= Vref, IK = 10 mA
∆Vref
Ratio of Change in Reference Input Voltage
to Change in Cathode to Anode Voltage
IK = 10 mA (Figure 2),
∆VKA = 10 V to Vref
∆VKA = 36 V to 10 V
DVref
DVKA
2.44
2.41
2.495
–
2.55
2.58
2.44
2.423
2.495
–
2.55
2.567
–
7.0
–
–
3.0
–
mV
mV/V
–
–
Reference Input Current (Figure 2)
IK = 10 mA, R1 = 10 k, R2 = ∞
TA = 25°C
TA = Tlow to Thigh (Note 1)
Unit
–1.4
–1.0
–2.7
–2.0
–
–
–1.4
–1.0
–2.7
–2.0
µA
Iref
–
–
1.8
–
4.0
6.5
–
–
1.8
–
4.0
5.2
Reference Input Current Deviation Over
Temperature Range (Figure 2, Note 1, 4)
IK = 10 mA, R1 = 10 k, R2 = ∞
∆Iref
–
0.8
2.5
–
0.4
1.2
µA
Minimum Cathode Current For Regulation
VKA = Vref (Figure 1)
Imin
–
0.5
1.0
–
0.5
1.0
mA
Off–State Cathode Current (Figure 3)
VKA = 36 V, Vref = 0 V
Ioff
–
260
1000
–
2.6
1000
nA
|ZKA|
–
0.22
0.5
–
0.22
0.5
Ω
Dynamic Impedance (Figure 1, Note 3)
VKA = Vref, ∆IK = 1.0 mA to 100 mA
f ≤ 1.0 kHz
NOTES: 1. Tlow = –40°C for TL431AIP TL431AILP, TL431IP, TL431ILP, TL431BID, TL431BIP, TL431BILP, TL431AIDM, TL431IDM, TL431BIDM
= 0°C for TL431ACP, TL431ACLP, TL431CP, TL431CLP, TL431CD, TL431ACD, TL431BCD, TL431BCP, TL431BCLP, TL431CDM,
TL431ACDM, TL431BCDM
Thigh = +85°C for TL431AIP, TL431AILP, TL431IP, TL431ILP, TL431BID, TL431BIP, TL431BILP, TL431IDM, TL431AIDM, TL431BIDM
= +70°C for TL431ACP, TL431ACLP, TL431CP, TL431ACD, TL431BCD, TL431BCP, TL431BCLP, TL431CDM, TL431ACDM, TL431BCDM
2. The deviation parameter ∆Vref is defined as the difference between the maximum and minimum values obtained over the full operating ambient
temperature range that applies.
Vref max
∆Vref = Vref max
–Vref min
∆TA = T2 – T1
Vref min
T1
ǒ
Ǔ
T2
Ambient Temperature
The average temperature coefficient of the reference input voltage, αVref is defined as:
D Vref
V
@ 25_C
X 10 6
D
x 10 6
ref
D TA
(V
@ 25_C)
A ref
αVref can be positive or negative depending on whether Vref Min or Vref Max occurs at the lower ambient temperature. (Refer to Figure 6.)
ppm
V
ref _C
+ 8.0 mV and slope is positive,
@ 25_C + 2.495 V, DT + 70_C
ref
A
Example : DV
V
+
ref
ref
3. The dynamic impedance ZKA is defined as |Z KA|
+ DDVIKA
+DT
a
V
ref
V
x 106
+ 45.8 ppmń_C
+ 0.008
70 (2.495)
K
When the device is programmed with two external resistors, R1 and R2, (refer to Figure 2) the total dynamic impedance of the circuit is defined as:
|Z
MOTOROLA ANALOG IC DEVICE DATA
Ȁ| [ |ZKA|
KA
ǒ
1
) R1
R2
Ǔ
3
TL431, A, B Series
ELECTRICAL CHARACTERISTICS (TA = 25°C, unless otherwise noted.)
TL431AI
Ch
Characteristic
i i
S b l
Symbol
Reference Input Voltage (Figure 1)
VKA = Vref, IK = 10 mA
TA = 25°C
TA = Tlow to Thigh
Min
Typ
TL431AC
Max
Min
Typ
TL431B
Max
Min
Typ
Max
Unit
Vref
V
2.47
2.44
2.495
–
2.52
2.55
2.47
2.453
2.495
–
2.52
2.537
2.483
2.475
2.495
2.495
2.507
2.515
–
7.0
–
–
3.0
–
–
3.0
–
∆Vref
Reference Input Voltage Deviation Over
Temperature Range (Figure 1, Notes 1, 2)
VKA= Vref, IK = 10 mA
DVref
DVKA
Ratio of Change in Reference Input Voltage
to Change in Cathode to Anode Voltage
IK = 10 mA (Figure 2),
∆VKA = 10 V to Vref
∆VKA = 36 V to 10 V
mV
mV/V
–
–
Reference Input Current (Figure 2)
IK = 10 mA, R1 = 10 k, R2 = ∞
TA = 25°C
TA = Tlow to Thigh (Note 1)
∆Iref
Reference Input Current Deviation Over
Temperature Range (Figure 2, Note 1)
IK = 10 mA, R1 = 10 k, R2 = ∞
–1.4
–1.0
–2.7
–2.0
–
–
–1.4
–1.0
–2.7
–2.0
–
–
–1.4
–1.0
–2.7
–2.0
µA
–
–
1.8
–
4.0
6.5
–
–
1.8
–
4.0
5.2
–
–
1.1
–
2.0
4.0
∆Iref
–
0.8
2.5
–
0.4
1.2
–
0.4
1.2
µA
Minimum Cathode Current For Regulation
VKA = Vref (Figure 1)
Imin
–
0.5
1.0
–
0.5
1.0
–
0.5
1.0
mA
Off–State Cathode Current (Figure 3)
VKA = 36 V, Vref = 0 V
Ioff
–
260
1000
–
260
1000
–
230
500
nA
|ZKA|
–
0.22
0.5
–
0.22
0.5
–
0.14
0.3
Ω
Dynamic Impedance (Figure 1, Note 3)
VKA = Vref, ∆IK = 1.0 mA to 100 mA
f ≤ 1.0 kHz
NOTES: 1. Tlow = –40°C for TL431AIP TL431AILP, TL431IP, TL431ILP, TL431BID, TL431BIP, TL431BILP, TL431AIDM, TL431IDM, TL431BIDM
= 0°C for TL431ACP, TL431ACLP, TL431CP, TL431CLP, TL431CD, TL431ACD, TL431BCD, TL431BCP, TL431BCLP, TL431CDM,
TL431ACDM, TL431BCDM
Thigh = +85°C for TL431AIP, TL431AILP, TL431IP, TL431ILP, TL431BID, TL431BIP, TL431BILP, TL431IDM, TL431AIDM, TL431BIDM
= +70°C for TL431ACP, TL431ACLP, TL431CP, TL431ACD, TL431BCD, TL431BCP, TL431BCLP, TL431CDM, TL431ACDM, TL431BCDM
2. The deviation parameter ∆Vref is defined as the difference between the maximum and minimum values obtained over the full operating ambient
temperature range that applies.
Vref max
∆Vref = Vref max
–Vref min
∆TA = T2 – T1
Vref min
T1
ǒ
Ǔ
T2
Ambient Temperature
The average temperature coefficient of the reference input voltage, αVref is defined as:
D Vref
V
@ 25_C
X 10 6
D
V
x 10 6
ref
(V
@ 25_C)
A
A ref
αVref can be positive or negative depending on whether Vref Min or Vref Max occurs at the lower ambient temperature. (Refer to Figure 6.)
ppm
V
ref _C
D
T
+ 8.0 mV and slope is positive,
@ 25_C + 2.495 V, DT + 70_C
ref
A
Example : DV
V
+
ref
ref
3. The dynamic impedance ZKA is defined as |Z KA|
+ DDVIKA
+DT
a
V
ref
x 106
+ 45.8 ppmń_C
+ 0.008
70 (2.495)
K
When the device is programmed with two external resistors, R1 and R2, (refer to Figure 2) the total dynamic impedance of the circuit is defined as:
|Z
4
Ȁ| [ |ZKA|
KA
ǒ
1
) R1
R2
Ǔ
MOTOROLA ANALOG IC DEVICE DATA
TL431, A, B Series
Figure 1. Test Circuit for VKA = Vref
Input
Figure 2. Test Circuit for VKA > Vref
VKA
Input
VKA
IK
Iref
R1
Vref
Figure 3. Test Circuit for Ioff
R2
Input
V
KA
VKA
Ioff
IK
ǒ
Ǔ
+ Vref 1 ) R1
) Iref S R1
R2
Vref
Figure 4. Cathode Current versus
Cathode Voltage
Figure 5. Cathode Current versus
Cathode Voltage
800
VKA = Vref
TA = 25°C
100
Input
IK , CATHODE CURRENT ( µA)
IK , CATHODE CURRENT (mA)
150
VKA
IK
50
0
–50
–100
–2.0
–1.0
0
1.0
2.0
3.0
600 Input
VKA = Vref
TA = 25°C
400
200
0
–200
–1.0
0
VKA, CATHODE VOLTAGE (V)
VKA
IKVKA = Vref
IK = 10 mA
Input
2560
Vref
Vref Max = 2550 mV
2540
2520
Vref Typ = 2495 mV
2500
2480
2460
2440
Vref Min = 2440 mV
2420
2400
–55
–25
0
25
50
75
TA, AMBIENT TEMPERATURE (°C)
MOTOROLA ANALOG IC DEVICE DATA
2.0
3.0
Figure 7. Reference Input Current versus
Ambient Temperature
100
125
Iref , REFERENCE INPUT CURRENT ( µA)
Vref , REFERENCE INPUT VOLTAGE (mV)
2580
1.0
VKA, CATHODE VOLTAGE (V)
Figure 6. Reference Input Voltage versus
Ambient Temperature
2600
IMin
VKA
IK
3.0
2.5
2.0
1.5
IK = 10 mA
1.0
Input
10k Iref
VKA
IK
0.5
0
–55
–25
0
25
50
75
125
100
TA, AMBIENT TEMPERATURE (°C)
5
TL431, A, B Series
Figure 9. Off–State Cathode Current
versus Ambient Temperature
0
IK = 10 mA
TA = 25°C
–8.0
–16
Input
VKA
IK
R1
–24
–32
R2
Vref
0
10
20
30
1.0 k
Ioff , OFF–STATE CATHODE CURRENT (nA)
∆ Vref , REFERENCE INPUT VOLTAGE (mV)
Figure 8. Change in Reference Input
Voltage versus Cathode Voltage
100
10
1.0
Input
0.1
0.01
–55
40
–25
0
VKA, CATHODE VOLTAGE (V)
50
10
–
+
Gnd
1.0
0.1
1.0 k
10 k
100 k
1.0 M
10 M
0.280
0.260
125
100
125
0.240
0.220
0.200
–55
–25
0
25
50
75
TA, AMBIENT TEMPERATURE (_C)
Figure 12. Open–Loop Voltage Gain
versus Frequency
Figure 13. Spectral Noise Density
80
60
50
9.0 µF
40
IK
15 k
Output
230
NOISE VOLTAGE (nV/ √Hz)
A VOL, OPEN LOOP VOLTAGE GAIN (dB)
100
VKA = Vref
∆ IK = 1.0 mA to 100 mA
f ≤ 1.0 kHz
Output
1.0 k
IK
50
–
+
Gnd
0.300
f, FREQUENCY (MHz)
8.25 k
Gnd
30
20
10
75
0.320
TA = 25_C
∆ IK = 1.0 mA to 100 mA
Output
IK
50
Figure 11. Dynamic Impedance
versus Ambient Temperature
|ZKA|, DYNAMIC IMPEDANCE (Ω )
|ZKA|, DYNAMIC IMPEDANCE (Ω )
1.0 k
25
TA, AMBIENT TEMPERATURE (5C)
Figure 10. Dynamic Impedance
versus Frequency
100
VKA = 36 V
Vref = 0 V
VKA
Ioff
IK = 10 mA
TA = 25_C
60
40
Input
VKA = Vref
IK = 10 mA
TA = 25°C
20
Output
IK
0
–10
1.0 k
10 k
100 k
f, FREQUENCY (MHz)
6
1.0 M
10 M
0
10
100
1.0 k
10 k
100 k
f, FREQUENCY (Hz)
MOTOROLA ANALOG IC DEVICE DATA
TL431, A, B Series
Figure 14. Pulse Response
TA = 25_C
Input
Monitor
Output
2.0
Pulse
Generator
f = 100 kHz
1.0
220 Output
50
Gnd
0
5.0
0
4.0
120
100
A) VKA = Vref
B) VKA = 5.0 V @ IK = 10 mA
C) VKA = 10 V @ IK = 10 mA
D) VKA = 15 V @ IK = 10 mA
D) TA = 25°C
Stable
A
A
B
B
80
Stable
C
60
D
40
20
Input
0
IK , CATHODE CURRENT (mA)
VOLTAGE SWING (V)
3.0
Figure 15. Stability Boundary Conditions
140
12
8.0
16
20
0
100 pF
1000 pF
0.01 µF
0.1 µF
1.0 µF
10 µF
CL, LOAD CAPACITANCE
t, TIME (µs)
Figure 16. Test Circuit For Curve A
of Stability Boundary Conditions
Figure 17. Test Circuit For Curves B, C, And D
of Stability Boundary Conditions
150
150
IK
IK
V+
10 k
V+
CL
CL
TYPICAL APPLICATIONS
Figure 18. Shunt Regulator
V+
Figure 19. High Current Shunt Regulator
Vout
V+
Vout
R1
R1
R2
V out
ǒ Ǔ
+ 1 ) R1
R2
R2
V
ref
MOTOROLA ANALOG IC DEVICE DATA
V out
ǒ Ǔ
+ 1 ) R1
R2
V
ref
7
TL431, A, B Series
Figure 20. Output Control for a
Three–Terminal Fixed Regulator
Figure 21. Series Pass Regulator
V+
MC7805
Out
In
Common
V+
Vout
R1
Vout
R1
R2
ǒ Ǔ
V out
Figure 22. Constant Current Source
RCL
V+
ǒ Ǔ
+ 1 ) R1
V
ref
R2
V out min + V ) V
ref
be
+ 1 ) R1
V
ref
R2
V out min + V ) 5.0V
ref
V out
R2
Figure 23. Constant Current Sink
V+
Iout
Isink
I
I out
Sink
CL
RS
V+
Vout
Figure 25. SRC Crowbar
V+
Vout
R1
8
out(trip)
S
+ RVref
Figure 24. TRIAC Crowbar
V
+ VRref
ǒ Ǔ
+ 1)
R1
R2
R1 V
ref
R2
V
out(trip)
ǒ Ǔ
+ 1 ) R1
R2
R2
V
ref
MOTOROLA ANALOG IC DEVICE DATA
TL431, A, B Series
Figure 26. Voltage Monitor
V+
Figure 27. Single–Supply Comparator with
Temperature–Compensated Threshold
Vout
l
R1
V+
R3
Vout
Vin
R2
R4
Vth = Vref
L.E.D. indicator is ‘on’ when V+ is between the
upper and lower limits.
ǒ Ǔ
ǒ Ǔ
+ 1 ) R1
R2
Upper Limit + 1 ) R3
R4
Lower Limit
V
V
50 k
1%
10 kΩ
V
1.0 kΩ
V
500 k
1%
100 kΩ
V
25 V
–
LM11
+
Range
RX
Rx
+ Vout D
38 V
Tl = 330 to 8.0 Ω
W
V
–5.0 V
Range
MOTOROLA ANALOG IC DEVICE DATA
330
TI
10 k
Calibrate
1.0 MΩ
V
≈ 2.0 V
Figure 29. Simple 400 mW Phono Amplifier
2.0 mA
5.0 M
1%
> Vref
ref
25 V
5.0 k
1%
Vout
V+
ref
Figure 28. Linear Ohmmeter
1N5305
Vin
< Vref
8.0 Ω
+
470 µF
360 k
1.0 µF
*
Vout
* Thermalloy
* THM 6024
* Heatsink on
* LP Package
56 k
10 k
0.05 µF
Tone
25 k
Volume
47 k
9
TL431, A, B Series
Figure 30. High Efficiency Step–Down Switching Converter
150 mH @ 2.0 A
Vin = 10 V to 20 V
TIP115
Vout = 5.0 V
Iout = 1.0 A
1.0 k
4.7 k
+
4.7 k
MPSA20
1N5823
0.01µF
100 k
2200 µF
470 µF
4.7 k
+
0.1 µF
2.2 k
Test
10
51 k
10
Conditions
Results
Line Regulation
Vin = 10 V to 20 V, Io = 1.0 A
53 mV (1.1%)
Load Regulation
Vin = 15 V, Io = 0 A to 1.0 A
25 mV (0.5%)
Output Ripple
Vin = 10 V, Io = 1.0 A
50 mVpp P.A.R.D.
Output Ripple
Vin = 20 V, Io = 1.0 A
100 mVpp P.A.R.D.
Efficiency
Vin = 15 V, Io = 1.0 A
82%
MOTOROLA ANALOG IC DEVICE DATA
TL431, A, B Series
APPLICATIONS INFORMATION
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.
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 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
compensation capacitance, CP2. The voltage across CP2
drives the output dependent current source, Go, which is
connected across the device cathode and anode.
Model component values are:
Vref = 1.78 V
Gm = 0.3 + 2.7 exp (–IC/26 mA)
Go = 1.25 (Vcp2) µmhos.
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
2p R
C
2
p
*
1.0
M
* 20 pF
GM P1
+
MOTOROLA ANALOG IC DEVICE DATA
+ 2p R 1 C + 2p * 10 M1* 0.265 pF + 60 kHz
P2 P2
Z1
+ 2p R 1 C + 2p * 15.91k * 20 pF + 500 kHz
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
+
+ GMRGMGoRL
Example 1:
I
C
+ 10 mA, RL+ 230 W, CL+ 0. Define the transfer gain.
The DC gain is:
+ GMRGMGoRL +
(2.138)(1.0 M)(1.25 m)(230) + 615 + 56 dB
8.25 k
Loop gain + G
+ 218 + 47 dB
8.25 k ) 15 k
G
The resulting transfer function Bode plot is shown in
Figure 32. The asymptotic plot may be expressed as the
following equation:
1
jf
500 kHz
Av
615
1
jf
1
jf
8.0 kHz 60 kHz
+
where IC is the device cathode current and Gm is in mhos
+
P2
ǒ)Ǔ
ǒ ) Ǔǒ ) Ǔ
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.
11
TL431, A, B Series
Figure 31. Simplified TL431 Device Model
VCC
RL
CL
Input
3
15 k
Cathode
9.0 mF
Ref
RP2
10 M
Vref
1.78 V
+
–
1
500 k
8.25 k
RGM
1.0 M
Anode
Figure 32. Example 1
Circuit Open Loop Gain Plot
RZ1
15.9 k
CP2
0.265 pF
2
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.
TL431 OPEN–LOOP VOLTAGE GAIN VERSUS FREQUENCY
60
50
Figure 33. Example 2
Circuit Open Loop Gain Plot
40
30
TL431 OPEN–LOOP BODE PLOT WITH LOAD CAP
80
20
10
0
–10
–20
101
103
102
104
105
106
107
f, FREQUENCY (Hz)
Example 2.
IC = 7.5 mA, RL = 2.2 kW, CL = 0.01 mF. 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:
+ GMRGMGoRL +
(2.323)(1.0 M)(1.25 m)(2200) + 6389 + 76 dB
G
The resulting open loop Bode plot is shown in Figure 33.
The asymptotic plot may be expressed as the following
equation:
1
jf
500 kHz
Av
615
1
jf
1
jf
1
jf
8.0 kHz 60 kHz 7.2 kHz
+
12
ǒ)Ǔ
ǒ ) Ǔǒ ) Ǔǒ ) Ǔ
Av, OPEN–LOOP GAIN (dB)
Av, OPEN–LOOP VOLTAGE GAIN (dB)
CP1
20 pF
GM
Rref
16
Go
1.0 mmho
60
40
20
0
–20
101
102
103
104
105
106
f, FREQUENCY (Hz)
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.
MOTOROLA ANALOG IC DEVICE DATA
TL431, A, B Series
OUTLINE DIMENSIONS
A
LP SUFFIX
PLASTIC PACKAGE
CASE 29–04
(TO–92)
ISSUE AE
B
R
P
L
F
SEATING
PLANE
K
DIM
A
B
C
D
F
G
H
J
K
L
N
P
R
V
D
X X
G
J
H
V
C
SECTION X–X
1
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. CONTOUR OF PACKAGE BEYOND DIMENSION R
IS UNCONTROLLED.
4. DIMENSION F APPLIES BETWEEN P AND L.
DIMENSION D AND J APPLY BETWEEN L AND K
MINIMUM. LEAD DIMENSION IS UNCONTROLLED
IN P AND BEYOND DIMENSION K MINIMUM.
N
N
INCHES
MIN
MAX
0.175
0.205
0.170
0.210
0.125
0.165
0.016
0.022
0.016
0.019
0.045
0.055
0.095
0.105
0.015
0.020
0.500
–––
0.250
–––
0.080
0.105
–––
0.100
0.115
–––
0.135
–––
MILLIMETERS
MIN
MAX
4.45
5.20
4.32
5.33
3.18
4.19
0.41
0.55
0.41
0.48
1.15
1.39
2.42
2.66
0.39
0.50
12.70
–––
6.35
–––
2.04
2.66
–––
2.54
2.93
–––
3.43
–––
P SUFFIX
PLASTIC PACKAGE
CASE 626–05
ISSUE K
8
5
NOTES:
1. DIMENSION L TO CENTER OF LEAD WHEN
FORMED PARALLEL.
2. PACKAGE CONTOUR OPTIONAL (ROUND OR
SQUARE CORNERS).
3. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
–B–
1
4
F
–A–
NOTE 2
L
C
J
–T–
N
SEATING
PLANE
D
H
M
K
DIM
A
B
C
D
F
G
H
J
K
L
M
N
MILLIMETERS
MIN
MAX
9.40
10.16
6.10
6.60
3.94
4.45
0.38
0.51
1.02
1.78
2.54 BSC
0.76
1.27
0.20
0.30
2.92
3.43
7.62 BSC
–––
10_
0.76
1.01
INCHES
MIN
MAX
0.370
0.400
0.240
0.260
0.155
0.175
0.015
0.020
0.040
0.070
0.100 BSC
0.030
0.050
0.008
0.012
0.115
0.135
0.300 BSC
–––
10_
0.030
0.040
G
0.13 (0.005)
MOTOROLA ANALOG IC DEVICE DATA
M
T A
M
B
M
13
TL431, A, B Series
OUTLINE DIMENSIONS
DM SUFFIX
PLASTIC PACKAGE
CASE 846A–02
(Micro–8)
ISSUE D
–A–
–B–
K
PIN 1 ID
G
D 8 PL
0.08 (0.003)
–T–
NOTES:
6. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
7. CONTROLLING DIMENSION: MILLIMETER.
8. DIMENSION A DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT
EXCEED 0.15 (0.006) PER SIDE.
9. DIMENSION B DOES NOT INCLUDE INTERLEAD
FLASH OR PROTRUSION. INTERLEAD FLASH OR
PROTRUSION SHALL NOT EXCEED 0.25 (0.010)
PER SIDE.
M
T B
S
A
DIM
A
B
C
D
G
H
J
K
L
S
SEATING
PLANE
C
0.038 (0.0015)
INCHES
MIN
MAX
0.114
0.122
0.114
0.122
–––
0.043
0.010
0.016
0.026 BSC
0.002
0.006
0.005
0.009
0.187
0.199
0.016
0.028
L
J
H
MILLIMETERS
MIN
MAX
2.90
3.10
2.90
3.10
–––
1.10
0.25
0.40
0.65 BSC
0.05
0.15
0.13
0.23
4.75
5.05
0.40
0.70
D SUFFIX
PLASTIC PACKAGE
CASE 751–06
(SOP–8)
ISSUE T
D
A
8
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME
Y14.5M, 1994.
2. DIMENSIONS ARE IN MILLIMETER.
3. DIMENSION D AND E DO NOT INCLUDE MOLD
PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 PER SIDE.
5. DIMENSION B DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 TOTAL IN EXCESS
OF THE B DIMENSION AT MAXIMUM MATERIAL
CONDITION.
C
5
0.25
H
E
M
B
M
1
4
h
B
e
X 45 _
q
A
C
SEATING
PLANE
L
0.10
A1
B
0.25
14
M
C B
S
A
S
DIM
A
A1
B
C
D
E
e
H
h
L
q
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
4.80
5.00
3.80
4.00
1.27 BSC
5.80
6.20
0.25
0.50
0.40
1.25
0_
7_
MOTOROLA ANALOG IC DEVICE DATA
TL431, A, B Series
Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty, representation or guarantee regarding
the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and
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arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that
Motorola was negligent regarding the design or manufacture of the part. Motorola and
are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal
Opportunity/Affirmative Action Employer.
MOTOROLA ANALOG IC DEVICE DATA
15
TL431, A, B Series
Mfax is a trademark of Motorola, Inc.
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16
◊
TL431/D
MOTOROLA ANALOG IC DEVICE DATA