LM331 Reference Tables, Pins & Specifications

Pin reference

Signal names, electrical functions and connection guidance

PDIP-8

Physical pin numbers8 pins

Scroll within the table to see all columns and rows.

LM331 pin functions and connections
Signal	Type	Function & connection
IOUT	Switched current source	Delivers reference-controlled charge pulses to the integration network. Connection guidance Join THRESH6 at the RL/CL top node. Not the logic frequency output.
IREF	Reference current setting	Approximately1.89V at the current-setting contact. Connection guidance Connect12kΩ plus5kΩ gain-adjust rheostat in series toGND. Tie rheostat wiper to its unused end for reliable adjustment.
FOUT	Open-collector pulse output	Outputs a pulse train whose frequency follows the input. Connection guidance Pull up through10kΩ to+5V; connect a frequency counter. Requires a pull-up; do not assume a push-pull HIGH.
GND	Supply return	Common analog and logic reference. Connection guidance Connect all ground symbols here.
RC	Timing node	Charges toward the internal timer threshold and then resets. Connection guidance Connect6.8kΩ to+15V and10nF toGND. Use stable, low-leakage timing parts.
THRESH	Comparator threshold	Monitors the integrated feedback voltage. Connection guidance Join IOUT1; RL100kΩ and CL1µF in parallel connect to the47Ω return node.
COMPIN	Comparator signal input	Receives the filtered voltage to convert. Connection guidance Apply VIN through100kΩ; bypass this pin toGND with100nF. Keep normal input below VS−2V.
VS	Positive supply	Powers the converter. Connection guidance Apply+15V in this example; bypass locally with100nF. Recommended device supply4–40V; circuit limits also matter.

TI LM331 commercial grade

Manufacturer-referenced values6 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Supply	4–40V	15V in the example
Ambient	0–70°C	LM331; LM231 grade differs
Comparator common-mode range	−0.2V toVS−2V	Over rated temperature
Supply current at5V	3mA typical;6mA max	LM331, stated test circuit
Supply current at40V	4mA typical;8mA max	Stated test circuit
Full-scale frequency capability	1Hz to100kHz feature range	Requires an appropriate application circuit

The shown circuit is calibrated for10kHz full scale, not automatically for100kHz.

Keep the test circuit distinction

Manufacturer-referenced values6 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Figure16 precision circuit nonlinearity	±0.003% typical;±0.01% max	4.5–20V,25°C, stated calibrated conditions
Shown Figure14 circuit nonlinearity	±0.024% typical;±0.14% max	15V;10Hz to11kHz
Untrimmed LM331 scale factor	0.9–1.1kHz/V	Figure16 conditions;RS14kΩ
Gain temperature drift	±30ppm/°C typical;±150ppm/°C max	Non-A LM331;4.5–20V
Comparator offset	±3mV typical;±10mV max	25°C
Comparator bias current	−80nA typical;−300nA max	Stated conditions

The precision-circuit headline is not the guaranteed accuracy of this simpler stand-alone example.

25°C unless stated

Manufacturer-referenced values6 parameters

Scroll within the table to see all columns and rows.

No load should force output or input terminals beyond their specified limits.

Adapted from TI Figure14

Manufacturer-referenced values8 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Analog supply / output pull-up	15V /5V	100nF local supply bypass;FOUT through10kΩ to5V
RT / CT	6.8kΩ /10nF	RT from15V toRC5;CT fromRC5 toGND
RIN / CIN	100kΩ /100nF	VIN throughRIN toCOMPIN7;CIN toGND
RL / CL	100kΩ /1µF in parallel	From joinedIOUT1/THRESH6 toRETURN
Hysteresis return	47Ω fromRETURN toGND	Shared lower end ofRL andCL
RS	12kΩ plus5kΩ rheostat	IREF2 toGND; trim gain
Logic output	FOUT3 tofrequency counter	Open collector with10kΩ pull-up
Offset adjustment	Optional manufacturer network omitted	Gain calibration retained

Use a film or other suitable low-absorption integration capacitor and stable timing components. Matching labels identify connected nodes.

Ideal charge balance

Manufacturer-referenced values6 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Frequency	fOUT=(VIN/2.09V)×(RS/RL)×1/(RTCT)	Manufacturer application equation
Gain for1kHz/V	RS≈14.212kΩ	RL100kΩ,RT6.8kΩ,CT10nF; then calibrate
Timed current pulse	t≈1.1RTCT≈74.8µs	Nominal timing interval
Example input	2.5V→2.5kHz	After calibration
Pulse count in100ms	250 pulses at2.5V	Quantization step≈10mV per count
Response time	Filter and integration dependent	Do not treat one pulse as an instant precision reading

Values are nominal calculations; device gain, offset and component tolerance require calibration.

LM331N/NOPB · PDIP-8

Manufacturer-referenced values7 parameters

Scroll within the table to see all columns and rows.

Parameter	Value	Conditions / notes
Pitch	2.54 mm	Through-hole
Verified TI package	8-pinPDIP(P)	No TI SMD option in the cited orderable table
Absolute supply	40V	Same numerical upper limit as recommended; do not exceed
Absolute input	−0.2V toVS	Stress rating
Maximum junction	150°C	Apply thermal derating
Junction-to-ambient	100°C/W	Specified PDIP reference
Storage	−65 to+150°C	Unpowered

Verify the exact manufacturer and ordering suffix when sourcing parts.