TL431, A, B
Series
PROGRAMMABLE
PRECISION REFERENCES
Order this document by TL431/D
(Top View)
3
1
Reference
N/C
N/C
N/C
2
4
8
7
6
5 N/C
Anode
N/C
Cathode
Anode
Anode
LP SUFFIX
PLASTIC PACKAGE
CASE 29
(TO92)
P SUFFIX
PLASTIC PACKAGE
CASE 626
D SUFFIX
PLASTIC PACKAGE
CASE 751
(SOP8)
Pin 1. Reference
2. Anode
3. Cathode
(Top View)
3
1
Reference
N/C
2
4
8
7
6
5
N/C
Cathode
SOP8 is an internally modified SO8 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. SOP8 conforms to all external
dimensions of the standard SO8 package.
DM SUFFIX
PLASTIC PACKAGE
CASE 846A
(Micro8)
8
1
8
1
8
1
SEMICONDUCTOR
TECHNICAL DATA
1
2
3
1
MOTOROLA ANALOG IC DEVICE DATA
Programmable
Precision References
The TL431, A, B integrated circuits are threeterminal 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
. 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
Typical
Sink Current Capability of 1.0 mA to 100 mA
Equivalent FullRange Temperature Coefficient of 50 ppm/
C Typical
Temperature Compensated for Operation over Full Rated Operating
Temperature Range
Low Output Noise Voltage
ORDERING INFORMATION
Device
Operating
Temperature Range
Package
TL431CLP, ACLP, BCLP
T
0
70
C
TO92
TL431CP, ACP, BCP
TA = 0
to +70
C
Plastic
TL431CDM, ACDM, BCDM
TA = 0
to +70
C
Micro8
TL431CD, ACD, BCD
SOP8
TL431ILP, AILP, BILP
T
40
85
C
TO92
TL431IP, AIP, BIP
TA = 40
to +85
C
Plastic
TL431IDM, AIDM, BIDM
TA = 40
to +85
C
Micro8
TL431ID, AID, BID
SOP8
Motorola, Inc. 1998
Rev 6
TL431, A, B Series
2
MOTOROLA ANALOG IC DEVICE DATA
Representative Block Diagram
1.0 k
Cathode
(K)
2.5 Vref
Anode (A)
Reference
(R)
4.0 k
150
Symbol
10 k
20 pF
800
Cathode (K)
3.28 k
Representative Schematic Diagram
Component values are nominal
Anode (A)
+
Anode
(A)
800
Reference
(R)
2.4 k
7.2 k
20 pF
800
Cathode
(K)
Reference
(R)
This device contains 12 active transistors.
MAXIMUM RATINGS
(Full operating ambient temperature range applies, unless
otherwise noted.)
Rating
Symbol
Value
Unit
Cathode to Anode Voltage
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
TA
C
TL431I, TL431AI, TL431BI
40 to +85
TL431C, TL431AC, TL431BC
0 to +70
Storage Temperature Range
Tstg
65 to +150
C
Total Power Dissipation @ TA = 25
C
PD
W
Derate above 25
C Ambient Temperature
D, LP Suffix Plastic Package
0.70
P Suffix Plastic Package
1.10
DM Suffix Plastic Package
0.52
Total Power Dissipation @ TC = 25
C
PD
W
Derate above 25
C Case Temperature
D, LP Suffix Plastic Package
1.5
P Suffix Plastic Package
3.0
NOTE:
ESD data available upon request.
RECOMMENDED OPERATING CONDITIONS
Condition
Symbol
Min
Max
Unit
Cathode to Anode Voltage
VKA
Vref
36
V
Cathode Current
IK
1.0
100
mA
THERMAL CHARACTERISTICS
Characteristic
Symbol
D, LP Suffix
Package
P Suffix
Package
DM Suffix
Package
Unit
Thermal Resistance, JunctiontoAmbient
R
JA
178
114
240
C/W
Thermal Resistance, JunctiontoCase
R
JC
83
41
C/W
TL431, A, B Series
3
MOTOROLA ANALOG IC DEVICE DATA
ELECTRICAL CHARACTERISTICS
(TA = 25
C, unless otherwise noted.)
Ch
i i
S
b l
TL431I
TL431C
Characteristic
Symbol
Min
Typ
Max
Min
Typ
Max
Unit
Reference Input Voltage (Figure 1)
Vref
V
VKA = Vref, IK = 10 mA
TA = 25
C
2.44
2.495
2.55
2.44
2.495
2.55
TA = Tlow to Thigh (Note 1)
2.41
2.58
2.423
2.567
Reference Input Voltage Deviation Over
Vref
7.0
3.0
mV
Temperature Range (Figure 1, Notes 1, 2)
VKA= Vref, IK = 10 mA
Ratio of Change in Reference Input Voltage
D
V
ref
mV/V
to Change in Cathode to Anode Voltage
ref
D
V
KA
IK = 10 mA (Figure 2),
D
V
KA
VKA = 10 V to Vref
1.4
2.7
1.4
2.7
VKA = 36 V to 10 V
1.0
2.0
1.0
2.0
Reference Input Current (Figure 2)
Iref
A
IK = 10 mA, R1 = 10 k, R2 =
TA = 25
C
1.8
4.0
1.8
4.0
TA = Tlow to Thigh (Note 1)
6.5
5.2
Reference Input Current Deviation Over
Iref
0.8
2.5
0.4
1.2
A
Temperature Range (Figure 2, Note 1, 4)
IK = 10 mA, R1 = 10 k, R2 =
Minimum Cathode Current For Regulation
Imin
0.5
1.0
0.5
1.0
mA
VKA = Vref (Figure 1)
OffState Cathode Current (Figure 3)
Ioff
260
1000
2.6
1000
nA
VKA = 36 V, Vref = 0 V
Dynamic Impedance (Figure 1, Note 3)
|ZKA|
0.22
0.5
0.22
0.5
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 = Vref max
Vref min
TA = T2 T1
T2
Ambient Temperature
T1
Vref min
Vref max
The average temperature coefficient of the reference input voltage,
Vref is defined as:
V
ref
ppm
_
C
+
D
V
ref
V
ref
@ 25
_
C
X 106
D
T
A
+
D
V
ref
x 106
D
T
A
(V
ref
@ 25
_
C)
Vref can be positive or negative depending on whether Vref Min or Vref Max occurs at the lower ambient temperature. (Refer to Figure 6.)
Example :
D
V
ref
+
8.0 mV and slope is positive,
V
ref
@ 25
_
C
+
2.495 V,
D
T
A
+
70
_
C
a
V
ref
+
0.008 x 106
70 (2.495)
+
45.8 ppm
_
C
3. The dynamic impedance ZKA is defined as |ZKA|
+
D
V
KA
D
I
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
KA
|
[
|Z
KA
|
1
)
R1
R2
TL431, A, B Series
4
MOTOROLA ANALOG IC DEVICE DATA
ELECTRICAL CHARACTERISTICS
(TA = 25
C, unless otherwise noted.)
Ch
i i
S
b l
TL431AI
TL431AC
TL431B
Characteristic
Symbol
Min
Typ
Max
Min
Typ
Max
Min
Typ
Max
Unit
Reference Input Voltage (Figure 1)
Vref
V
VKA = Vref, IK = 10 mA
TA = 25
C
2.47
2.495
2.52
2.47
2.495
2.52
2.483
2.495
2.507
TA = Tlow to Thigh
2.44
2.55
2.453
2.537
2.475
2.495
2.515
Reference Input Voltage Deviation Over
Vref
7.0
3.0
3.0
mV
Temperature Range (Figure 1, Notes 1, 2)
VKA= Vref, IK = 10 mA
Ratio of Change in Reference Input Voltage
D
V
ref
mV/V
to Change in Cathode to Anode Voltage
ref
D
V
KA
IK = 10 mA (Figure 2),
D
V
KA
VKA = 10 V to Vref
1.4
2.7
1.4
2.7
1.4
2.7
VKA = 36 V to 10 V
1.0
2.0
1.0
2.0
1.0
2.0
Reference Input Current (Figure 2)
Iref
A
IK = 10 mA, R1 = 10 k, R2 =
TA = 25
C
1.8
4.0
1.8
4.0
1.1
2.0
TA = Tlow to Thigh (Note 1)
6.5
5.2
4.0
Reference Input Current Deviation Over
Iref
0.8
2.5
0.4
1.2
0.4
1.2
A
Temperature Range (Figure 2, Note 1)
IK = 10 mA, R1 = 10 k, R2 =
Minimum Cathode Current For Regulation
Imin
0.5
1.0
0.5
1.0
0.5
1.0
mA
VKA = Vref (Figure 1)
OffState Cathode Current (Figure 3)
Ioff
260
1000
260
1000
230
500
nA
VKA = 36 V, Vref = 0 V
Dynamic Impedance (Figure 1, Note 3)
|ZKA|
0.22
0.5
0.22
0.5
0.14
0.3
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 = Vref max
Vref min
TA = T2 T1
T2
Ambient Temperature
T1
Vref min
Vref max
The average temperature coefficient of the reference input voltage,
Vref is defined as:
V
ref
ppm
_
C
+
D
V
ref
V
ref
@ 25
_
C
X 106
D
T
A
+
D
V
ref
x 106
D
T
A
(V
ref
@ 25
_
C)
Vref can be positive or negative depending on whether Vref Min or Vref Max occurs at the lower ambient temperature. (Refer to Figure 6.)
Example :
D
V
ref
+
8.0 mV and slope is positive,
V
ref
@ 25
_
C
+
2.495 V,
D
T
A
+
70
_
C
a
V
ref
+
0.008 x 106
70 (2.495)
+
45.8 ppm
_
C
3. The dynamic impedance ZKA is defined as |ZKA|
+
D
V
KA
D
I
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
KA
|
[
|Z
KA
|
1
)
R1
R2
TL431, A, B Series
5
MOTOROLA ANALOG IC DEVICE DATA
IK
Vref
VKA
Input
Figure 1. Test Circuit for VKA = Vref
Input
IK
R2
Iref
Vref
VKA
R1
Figure 2. Test Circuit for VKA > Vref
V
KA
+
V
ref
1
)
R1
R2
)
I
ref
S
R1
Ioff
Input
VKA
Figure 3. Test Circuit for Ioff
1.0
IMin
200
400
VKA, CATHODE VOLTAGE (V)
200
0
0
1.0
2.0
3.0
800
600
2.0
1.0
0
100
1.0
2.0
3.0
150
50
VKA, CATHODE VOLTAGE (V)
0
50
Figure 4. Cathode Current versus
Cathode Voltage
Figure 5. Cathode Current versus
Cathode Voltage
Input
100
VKA = Vref
TA = 25
C
IK
VKA
I K
, CA
THODE
CURRENT
(mA)
I K
, CA
THODE
CURRENT
(
A
)
125
TA, AMBIENT TEMPERATURE (
C)
3.0
100
50
75
55
0
2.5
0.5
2.0
1.0
25
0
25
1.5
2600
2580
2560
2540
2520
2500
2480
2460
VKA = Vref
IK = 10 mA
TA, AMBIENT TEMPERATURE (
C)
VKA
IK
55
Input
Vref
75
100
125
2440
0
50
Figure 6. Reference Input Voltage versus
Ambient Temperature
Figure 7. Reference Input Current versus
Ambient Temperature
2420
2400
25
25
Input
IK
IK = 10 mA
Iref
10k
VKA
ref
V
,
REFERENCE INPUT
VOL
T
AGE (mV)
I ref
, REFERENCE INPUT
CURRENT
(
A
)
Vref Max = 2550 mV
Vref Typ = 2495 mV
Vref Min = 2440 mV
VKA = Vref
TA = 25
C
Input
VKA
IK
TL431, A, B Series
6
MOTOROLA ANALOG IC DEVICE DATA
NOISE VOL
T
AGE (nV/
Hz)
55
f, FREQUENCY (MHz)
100
10
1.0
100 k
10 M
1.0 M
1.0 k
10 k
0.1
75
25
0
25
50
100
125
TA, AMBIENT TEMPERATURE (
_
C)
0.200
0.220
0.240
0.300
0.320
0.260
0.280
IK
50
1.0 k
+
Output
Gnd
Output
Gnd
IK
50
1.0 k
+
VKA = Vref
IK = 1.0 mA to 100 mA
f
1.0 kHz
TA = 25
_
C
IK = 1.0 mA to 100 mA
|Z
KA
|, DYNAMIC IMPEDANCE (
)
|Z
KA
|, DYNAMIC IMPEDANCE (
)
f, FREQUENCY (Hz)
40
10
10 k
1.0 k
100
0
20
100 k
60
f, FREQUENCY (MHz)
100 k
0
10 M
1.0 M
10
10
20
30
60
50
40
1.0 k
10 k
VKA = Vref
IK = 10 mA
TA = 25
C
IK
Output
Input
80
, OPEN LOOP
VOL
T
AGE GAIN (dB)
230
Gnd
Output
IK
9.0
F
8.25 k
15 k
IK = 10 mA
TA = 25
_
C
55
0.01
100
10
1.0
0.1
TA, AMBIENT TEMPERATURE (5C)
75
25
0
25
50
100
125
40
1.0 k
VKA, CATHODE VOLTAGE (V)
30
10
0
32
8.0
16
20
0
24
R2
Vref
R1
IK
Input
VKA
Input
Ioff
VKA = 36 V
Vref = 0 V
VKA
V
ref
, REFERENCE INPUT
VOL
T
AGE (mV)
I of
f, OFFST
A
TE
CA
THODE
CURRENT
(nA)
IK = 10 mA
TA = 25
C
Figure 8. Change in Reference Input
Voltage versus Cathode Voltage
Figure 9. OffState Cathode Current
versus Ambient Temperature
Figure 10. Dynamic Impedance
versus Frequency
Figure 11. Dynamic Impedance
versus Ambient Temperature
Figure 12. OpenLoop Voltage Gain
versus Frequency
Figure 13. Spectral Noise Density
VOL
A
TL431, A, B Series
7
MOTOROLA ANALOG IC DEVICE DATA
Input
Output
t, TIME (
s)
Pulse
Generator
f = 100 kHz
0
8.0
4.0
20
0
16
2.0
3.0
12
0
1.0
5.0
0
20
40
60
80
100
120
140
1000 pF
0.01
F
0.1
F
1.0
F
10
F
CL, LOAD CAPACITANCE
100 pF
Figure 14. Pulse Response
Figure 15. Stability Boundary Conditions
50
220 Output
Gnd
Input
Monitor
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
TA = 25
_
C
VOL
T
AGE SWING (V)
I K
, CA
THODE
CURRENT
(mA)
A
B
C
D
B
A
Stable
Stable
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
V+
IK
150
IK
V+
150
CL
10 k
CL
Figure 18. Shunt Regulator
Figure 19. High Current Shunt Regulator
V+
Vout
R1
V+
Vout
R1
R2
R2
Vout
+
1
)
R1
R2
V
ref
Vout
+
1
)
R1
R2
V
ref
TYPICAL APPLICATIONS
TL431, A, B Series
8
MOTOROLA ANALOG IC DEVICE DATA
Figure 20. Output Control for a
ThreeTerminal Fixed Regulator
Figure 21. Series Pass Regulator
V+
Vout
R1
R2
Out
In
MC7805
V+
Vout
R2
Common
R1
Vout
+
1
)
R1
R2
V
ref
Vout min
+
V
ref
)
5.0V
Vout
+
1
)
R1
R2
V
ref
Vout min
+
V
ref
)
V
be
Figure 22. Constant Current Source
Figure 23. Constant Current Sink
V+
RCL
Iout
V+
RS
I
Sink
+
V
ref
R
S
Iout
+
V
ref
R
CL
Isink
Figure 24. TRIAC Crowbar
Figure 25. SRC Crowbar
Vout
V+
R2
V+
Vout
R1
R2
R1
V
out(trip)
+
1
)
R1
R2
V
ref
V
out(trip)
+
1
)
R1
R2
V
ref
TL431, A, B Series
9
MOTOROLA ANALOG IC DEVICE DATA
Figure 26. Voltage Monitor
Figure 27. SingleSupply Comparator with
TemperatureCompensated Threshold
Vth = Vref
V+
Vout
Vin
R1
R3
V+
Vout
R2
R4
l
L.E.D. indicator is `on' when V+ is between the
upper and lower limits.
Lower Limit
+
1
)
R1
R2
V
ref
Upper Limit
+
1
)
R3
R4
V
ref
Vin
Vout
< Vref
V+
> Vref
2.0 V
Figure 28. Linear Ohmmeter
Figure 29. Simple 400 mW Phono Amplifier
* Thermalloy
*
THM 6024
*
Heatsink on
*
LP Package
*
Tl = 330 to 8.0
8.0
+
LM11
2.0 mA
25 V
25 V
5.0 V
Vout
Range
V
1.0 M
V
100 k
V
V
1.0 k
RX
5.0 M
1%
500 k
1%
50 k
1%
5.0 k
1%
47 k
Tone
0.05
F
470
F
Volume
1N5305
1.0
F
TI
360 k
330
56 k
10 k
25 k
38 V
+
10 k
10 k
Calibrate
Rx
+
Vout
D W
V
Range
TL431, A, B Series
10
MOTOROLA ANALOG IC DEVICE DATA
Figure 30. High Efficiency StepDown Switching Converter
150
m
H @ 2.0 A
1N5823
0.01
F
+
470
F
51 k
0.1
F
+
2200
F
4.7 k
Vin = 10 V to 20 V
TIP115
MPSA20
1.0 k
4.7 k
4.7 k
10
2.2 k
100 k
Vout = 5.0 V
Iout = 1.0 A
Test
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%
TL431, A, B Series
11
MOTOROLA ANALOG IC DEVICE DATA
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 nonstandard 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)
where IC is the device cathode current and Gm is in mhos
Go = 1.25 (Vcp2)
mhos.
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:
P1
+
1
2
p
R
GM
C
P1
+
1
2
p
* 1.0 M * 20 pF
+
7.96 kHz
P2
+
1
2
p
R
P2
C
P2
+
1
2
p
* 10 M * 0.265 pF
+
60 kHz
Z1
+
1
2
p
R
Z1
C
P1
+
1
2
p
* 15.9 k * 20 pF
+
500 kHz
In addition, there is an external circuit pole defined by the
load:
P
L
+
1
2
p
R
L
C
L
Also, the transfer dc voltage gain of the TL431 is:
G
+
G
M
R
GM
GoR
L
Example 1:
I
C
+
10 mA, R
L
+
230
W
, C
L
+
0. Define the transfer gain .
The DC gain is:
G
+
G
M
R
GM
GoR
L
+
(2.138)(1.0 M)(1.25
m
)(230)
+
615
+
56 dB
Loop gain
+
G
8.25 k
8.25 k
)
15 k
+
218
+
47 dB
The resulting transfer function Bode plot is shown in
Figure 32. The asymptotic plot may be expressed as the
following equation:
Av
+
615
1
)
jf
500 kHz
1
)
jf
8.0 kHz
1
)
jf
60 kHz
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 OpenLoop 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.
TL431, A, B Series
12
MOTOROLA ANALOG IC DEVICE DATA
Figure 31. Simplified TL431 Device Model
+
RL
VCC
CL
15 k
9.0
m
F
Input
8.25 k
3
Cathode
500 k
Vref
1.78 V
Rref
16
GM
Anode
2
RGM
1.0 M
Ref
1
Go
1.0
m
mho
CP2
0.265 pF
RP2
10 M
RZ1
15.9 k
CP1
20 pF
f, FREQUENCY (Hz)
102
101
20
30
20
60
0
A
v
, OPENLOOP
VOL
T
AGE GAIN (dB)
Figure 32. Example 1
Circuit Open Loop Gain Plot
TL431 OPENLOOP VOLTAGE GAIN VERSUS FREQUENCY
40
104
103
107
105
106
10
10
50
Example 2.
IC = 7.5 mA, RL = 2.2 k
W
, CL = 0.01
m
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:
G
+
G
M
R
GM
GoR
L
+
(2.323)(1.0 M)(1.25
m
)(2200)
+
6389
+
76 dB
The resulting open loop Bode plot is shown in Figure 33.
The asymptotic plot may be expressed as the following
equation:
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)
102
101
20
40
20
80
0
A
v
,
OPENLOOP
GAIN (dB)
Figure 33. Example 2
Circuit Open Loop Gain Plot
TL431 OPENLOOP BODE PLOT WITH LOAD CAP
60
104
103
106
105
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, A, B Series
13
MOTOROLA ANALOG IC DEVICE DATA
LP SUFFIX
PLASTIC PACKAGE
CASE 2904
(TO92)
ISSUE AE
P SUFFIX
PLASTIC PACKAGE
CASE 62605
ISSUE K
OUTLINE DIMENSIONS
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.
1
4
5
8
F
NOTE 2
A
B
T
SEATING
PLANE
H
J
G
D
K
N
C
L
M
M
A
M
0.13 (0.005)
B
M
T
DIM
MIN
MAX
MIN
MAX
INCHES
MILLIMETERS
A
9.40
10.16
0.370
0.400
B
6.10
6.60
0.240
0.260
C
3.94
4.45
0.155
0.175
D
0.38
0.51
0.015
0.020
F
1.02
1.78
0.040
0.070
G
2.54 BSC
0.100 BSC
H
0.76
1.27
0.030
0.050
J
0.20
0.30
0.008
0.012
K
2.92
3.43
0.115
0.135
L
7.62 BSC
0.300 BSC
M
10
10
N
0.76
1.01
0.030
0.040
_
_
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.
R
A
P
J
L
F
B
K
G
H
SECTION XX
C
V
D
N
N
X X
SEATING
PLANE
DIM
MIN
MAX
MIN
MAX
MILLIMETERS
INCHES
A
0.175
0.205
4.45
5.20
B
0.170
0.210
4.32
5.33
C
0.125
0.165
3.18
4.19
D
0.016
0.022
0.41
0.55
F
0.016
0.019
0.41
0.48
G
0.045
0.055
1.15
1.39
H
0.095
0.105
2.42
2.66
J
0.015
0.020
0.39
0.50
K
0.500
12.70
L
0.250
6.35
N
0.080
0.105
2.04
2.66
P
0.100
2.54
R
0.115
2.93
V
0.135
3.43
1
TL431, A, B Series
14
MOTOROLA ANALOG IC DEVICE DATA
D SUFFIX
PLASTIC PACKAGE
CASE 75106
(SOP8)
ISSUE T
OUTLINE DIMENSIONS
DM SUFFIX
PLASTIC PACKAGE
CASE 846A02
(Micro8)
ISSUE D
S
B
M
0.08 (0.003)
A
S
T
DIM
MIN
MAX
MIN
MAX
INCHES
MILLIMETERS
A
2.90
3.10
0.114
0.122
B
2.90
3.10
0.114
0.122
C
1.10
0.043
D
0.25
0.40
0.010
0.016
G
0.65 BSC
0.026 BSC
H
0.05
0.15
0.002
0.006
J
0.13
0.23
0.005
0.009
K
4.75
5.05
0.187
0.199
L
0.40
0.70
0.016
0.028
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.
B
A
D
K
G
PIN 1 ID
8 PL
0.038 (0.0015)
T
SEATING
PLANE
C
H
J
L
SEATING
PLANE
1
4
5
8
A
0.25
M
C B
S
S
0.25
M
B
M
h
q
C
X 45
_
L
DIM
MIN
MAX
MILLIMETERS
A
1.35
1.75
A1
0.10
0.25
B
0.35
0.49
C
0.19
0.25
D
4.80
5.00
E
1.27 BSC
e
3.80
4.00
H
5.80
6.20
h
0
7
L
0.40
1.25
q
0.25
0.50
_
_
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.
D
E
H
A
B
e
B
A1
C
A
0.10
TL431, A, B Series
15
MOTOROLA ANALOG IC DEVICE DATA
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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.
TL431, A, B Series
16
MOTOROLA ANALOG IC DEVICE DATA
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