TL431 Reference Tables, Pins & Specifications

Pin reference

Signal names, electrical functions and connection guidance

TO-92

Physical pin numbers3 pins

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TL431 pin functions and connections
Signal	Type	Function & connection
K	Cathode / shunt node	The regulator sinks current from the cathode to the anode to control this voltage. Connection guidance Feed through a current-limiting series resistor; connect the upper feedback resistor here. Do not connect directly across an unrestricted supply. Recommended cathode current is 1–100 mA.
A	Anode / reference return	Common reference for the internal amplifier and cathode voltage. Connection guidance Connect to the circuit ground and the lower divider resistor. TO-92 physical pin 2; SOT-23 physical pin 3.
REF	Reference input	Compares the external divider node against approximately 2.495 V relative to the anode. Connection guidance Connect to the junction of the two output-setting resistors. TO-92 physical pin 3; SOT-23 physical pin 2. Reference-input current slightly raises the nominal setpoint.

TI TL431C standard-accuracy grade

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Cathode voltage	VREF to 36 V	Referenced to the anode
Cathode current	1–100 mA	Recommended range; power dissipation may impose a lower maximum
Ambient temperature	0–70°C	Selected commercial C grade
Initial accuracy	±2% at 25°C	A: ±1%; B: ±0.5% are different grades
Selected through-hole part	TL431CLP	Bulk straight-lead TO-92
Selected SMD part	TL431CDBZR	SOT-23-3; different physical pin map

A shunt-current rating is not a load-current rating.

Electrical-characteristic test conditions

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Reference at 25°C	2.440 / 2.495 / 2.550 V	Minimum / typical / maximum; VKA = VREF, IKA = 10 mA
Reference current	2 µA typical; 4 µA maximum	IKA = 10 mA; R1 = 10 kΩ, R2 open
Minimum regulation current	0.4 mA typical; 1 mA maximum	Do not design only around the typical value
Dynamic impedance	0.2 Ω typical; 0.5 Ω maximum	f ≤ 1 kHz; IKA = 1–100 mA; VKA = VREF
Off-state cathode current	0.1 µA typical; 1 µA maximum	VKA = 36 V; VREF input = 0 V
Output setting	VOUT ≈ VREF × (1 + RUP/RLOW) + IREF × RUP	Resistor tolerance and device errors remain

Initial tolerance, drift, loading and divider errors all contribute to real output accuracy.

Do not merge limits from different packages

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
C-grade ambient	0 to +70°C	The two orderables shown here
I-grade ambient	−40 to +85°C	Requires an I-grade orderable
Q-grade ambient	−40 to +125°C	Requires a Q-grade orderable
C reference change: TO-92	4 mV typical; 25 mV maximum	VKA = VREF; IKA = 10 mA; over C ambient range
C reference change: SOT-23-3	6 mV typical; 16 mV maximum	Different package-specific limits in the same table
Thermal check	TJ ≈ TA + P × θJA	Use the exact package and PCB thermal conditions

Temperature drift does not replace the initial reference-voltage tolerance.

12 V input · SOT-23-3 physical circuit

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Feed resistor	680 Ω, at least 0.25 W	12 V to K1 / output node
Upper divider resistor	10 kΩ	K1 to REF2
Lower divider resistor	10 kΩ	REF2 to A3 / GND
Example load	1 kΩ	Output to GND; approximately 5 mA
Anode	Pin 3 to GND	The TO-92 equivalent is pin 2
Output capacitor	None in this teaching circuit	Capacitive-load stability must be checked before adding one

The diagram is a low-voltage teaching circuit, not a mains-connected power supply.

Illustrative typical-value arithmetic

Manufacturer-referenced values7 parameters

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Parameter	Value	Conditions / notes
Ideal divider output	4.990 V	2.495 × (1 + 10/10)
Reference-current correction	+0.020 V	2 µA × 10 kΩ
Illustrative output	5.010 V	Before tolerances, temperature and load errors
Feed current	10.279 mA	(12 − 5.01) / 680
Load / upper-divider currents	5.010 mA / 0.2515 mA	1 kΩ load; lower-divider current plus 2 µA
Remaining cathode current	Approximately 5.018 mA	Feed minus load minus upper-divider current
Feed resistor / TL431 power	71.9 mW / 25.1 mW	Nominal arithmetic; include worst-case input/load margins

These are calculations, not live readings or an electrical simulation.

Check orientation before connecting

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Cathode K	TO-92: 1 · SOT-23: 1	Controlled shunt/output node
Anode A	TO-92: 2 · SOT-23: 3	Common return
Reference REF	TO-92: 3 · SOT-23: 2	Divider sense input
TO-92 pinout picture	Bottom view, flat edge below	Left-to-right: 3 REF, 2 A, 1 K; top-side PCB view is mirrored
SOT-23 pinout picture	Top view	K1 upper left, REF2 lower left, A3 at right
TL432	Same function; different small-package pinouts	Do not substitute by name alone

The straight-lead TO-92 footprint is not the wider formed-lead footprint.

Stress limits are not operating targets

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Cathode absolute voltage	37 V	Recommended maximum remains 36 V
Cathode absolute current	−100 to +150 mA	Do not use as a normal operating range
Reference absolute current	−0.05 to +10 mA	Input stress limit
Junction / storage	150°C / −65 to +150°C	Absolute limits
Capacitive load	Can destabilize the shunt loop	Check the manufacturer stability curves for voltage, current and capacitance
Worst-case power	VKA × IKA	Evaluate high input / light load, not only the nominal circuit

Allow electrical and thermal margin, and verify stability in the actual circuit.