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Order this document by TL431/D

Programmable

Precision References

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

• Sink Current Capability of 1.0 mA to 100 mA

• Equivalent Full–Range Temperature Coefficient of 50 ppm/°C Typical

• Temperature Compensated for Operation over Full Rated Operating

Temperature Range

• Low Output Noise Voltage

TL431, A, B

Series

PROGRAMMABLE

PRECISION REFERENCES

SEMICONDUCTOR

TECHNICAL DATA

LP SUFFIX

PLASTIC PACKAGE

CASE 29

(TO–92)

123

Pin 1. Reference

2. Anode

3. Cathode

8

1

8

1

P SUFFIX

PLASTIC PACKAGE

CASE 626

DM SUFFIX

PLASTIC PACKAGE

CASE 846A

(Micro–8)

ORDERING INFORMATION

Device

Operating

Temperature Range

TL431CLP, ACLP, BCLP

TL431CP, ACP, BCP

TL431CDM, ACDM, BCDM

TA = 0° to +70°C

TL431CD, ACD, BCD

TL431ILP, AILP, BILP

TL431IP, AIP, BIP

TL431IDM, AIDM, BIDM

TA = –40° to +85°C

TL431ID, AID, BID

MOTOROLA ANALOG IC DEVICE DATA

Package

TO–92

Plastic

Micro–8

SOP–8

TO–92

Plastic

Micro–8

SOP–8

Cathode 1

N/C 2

N/C 3

N/C 4

8 Reference

7 N/C

6 Anode

5 N/C

(Top View)

D SUFFIX

PLASTIC PACKAGE

CASE 751

(SOP–8)

8

1

Cathode 1

Anode

2

3

N/C 4

8 Reference

7

Anode

6

5 N/C

(Top View)

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.

© Motorola, Inc. 1998

Rev 6

1

Figure 1. Test Circuit for VKA = Vref

Input IK VKA

Vref

TL431, A, B Series

Figure 2. Test Circuit for VKA > Vref

Figure 3. Test Circuit for Ioff

Input

R1 Iref

R2

Vref

VKA

IK

ǒ Ǔ+ ) )VKA

Vref 1

R1

R2

Iref S R1

Input

Ioff VKA

Figure 4. Cathode Current versus

Cathode Voltage

150

VKA = Vref

TA = 25°C

100 Input

VKA

IK

50

0

–50

–100

–2.0

–1.0 0 1.0

VKA, CATHODE VOLTAGE (V)

2.0

3.0

Figure 5. Cathode Current versus

Cathode Voltage

800

VKA = Vref

TA = 25°C

600 Input

IKVKA

IMin

400

200

0

–20–01.0

0 1.0 2.0

VKA, CATHODE VOLTAGE (V)

3.0

Figure 6. Reference Input Voltage versus

2600

2580 Input

2560 Vref

Ambient Temperature

VKA

IKVKA = Vref

IK = 10 mA

Vref Max = 2550 mV

2540

2520

2500 Vref Typ = 2495 mV

2480

2460

2440 Vref Min = 2440 mV

2420

2400

–55 –25 0 25 50 75 100 125

TA, AMBIENT TEMPERATURE (°C)

Figure 7. Reference Input Current versus

Ambient Temperature

3.0

2.5

2.0

1.5

IK = 10 mA

1.0 Input

VKA

10k Iref IK

0.5

0–55 –25 0 25 50 75 100 125

TA, AMBIENT TEMPERATURE (°C)

MOTOROLA ANALOG IC DEVICE DATA

5

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

W150 . 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) 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:

+ + +p pP1

1

2 RGM CP1

1

2 * 1.0 M * 20 pF

7.96 kHz

+ + +p pP2

1

2 RP2CP2

1

2 * 10 M * 0.265 pF

60 kHz

+ + +p pZ1

1

2 RZ1CP1

1

2 * 15.9 k * 20 pF

500 kHz

In addition, there is an external circuit pole defined by the

load:

+PL

2p

1

RLCL

Also, the transfer dc voltage gain of the TL431 is:

+G GMRGMGoRL

Example 1:

+ + +WIC 10 mA, RL 230 , CL 0. Define the transfer gain.

The DC gain is:

+ +G GMRGMGoRL

+ +m(2.138)(1.0 M)(1.25 )(230) 615 56 dB

+ ) + +Loop gain

G

8.25

8.25 k

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:

)1 jf

ǒ Ǔ500 kHz

+Av 615

ǒ ) Ǔǒ ) Ǔ1 jf 1 jf

8.0 kHz 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 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.

MOTOROLA ANALOG IC DEVICE DATA

11