TI LM311 Comparator: Collector/Emitter Output and Strobe | Texas Instruments

Design LM311 threshold circuits around its separate output transistor connections, pullup loading, input range and strobe behavior.

TI LM311 Comparator: Collector/Emitter Output and Strobe

Design LM311 threshold circuits around its separate output transistor connections, pullup loading, input range and strobe behavior.

LM311 is a single comparator whose output transistor exposes collector and emitter connections. This gives flexibility in referencing the output to the receiving circuit, but it also means the output is not a self-driven CMOS logic pin. A conventional logic connection needs an appropriate collector pullup and an intentional emitter reference.

The pullup value trades current against rise time. A larger resistor reduces low-state current but charges the output capacitance more slowly; a smaller resistor increases the required sink current and dissipation. Assess the comparator’s switching behavior together with that external network, rather than treating the response-time headline as the complete digital edge specification.

LM311 also provides offset-balance and strobe functions. The strobe can force the output transistor off regardless of the input comparison, which makes its wiring relevant even in a basic threshold detector. For slowly varying or noisy inputs, design the hysteresis and verify common-mode limits at the selected supply; operation from a 5 V rail does not imply rail-to-rail analog inputs.

Key Features

Separate collector and emitterDefine the receiving-side voltage reference and pullup path.
Load-dependent output edgeBalance pullup current against capacitance and rise time.
Balance/strobe controlsAccount for auxiliary pins instead of copying an op-amp connection.

Target Applications

Threshold and limit detection
Oscillator and peak-detector circuits
Logic interfacing from analog comparison signals

Compare LM311 Variants

Comparison of 10 selected variants from Texas Instruments

Parameter	LM311PWRG4	LM311PWLE	LM311DG4	LM311DRG4	LM311DRE4	LM311PG4	LM311H/NOPB	LM311P-NG	LM311PW	LM311PE4
Package / Case	8-TSSOP (0.173", 4.40mm Width)	-	8-SOIC (0.154", 3.90mm Width)	8-SOIC (0.154", 3.90mm Width)	8-SOIC (0.154", 3.90mm Width)	8-DIP (0.300", 7.62mm)	TO-99-8 Metal Can	8-DIP (0.300", 7.62mm)	8-TSSOP (0.173", 4.40mm Width)	8-DIP (0.300", 7.62mm)
Max Operating Temp	+ 70 C	-	+ 70 C	-	+ 70 C	-	+ 70 C	-	-	+ 70 C
Min Operating Temp	0 C	-	0 C	-	0 C	-	0 C	-	-	0 C
Operating Temperature	0°C ~ 70°C	-	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C
Comparator Type	Differential	-	Differential	-	Differential	-	General Purpose	-	-	Differential
Current Input Bias Max	0.25µA @ ±15V	-	0.25µA @ ±15V	0.25µA @ ±15V	0.25µA @ ±15V	0.25µA @ ±15V	0.25µA @ ±15V	0.25µA @ ±15V	0.25µA @ ±15V	0.25µA @ ±15V
Current Quiescent Max	7.5mA	-	7.5mA	7.5mA	7.5mA	7.5mA	7.5mA	5mA, 7.5mA	7.5mA	5mA, 7.5mA
Dual Supply Voltage	+/- 3 V, +/- 5 V, +/- 9 V, +/- 12 V	-	+/- 3 V, +/- 5 V, +/- 9 V, +/- 12 V	-	+/- 3 V, +/- 5 V, +/- 9 V, +/- 12 V	-	+/- 3 V, +/- 5 V, +/- 9 V, +/- 12 V, +/- 15 V	-	-	+/- 3 V, +/- 5 V, +/- 9 V, +/- 12 V
Ib Input Bias Current	250 nA	-	250 nA	-	250 nA	-	250 nA	-	-	250 nA
Lifecycle Status	Active	Active	Active	Active	Active	Obsolete	Active	Active	Active	Active
Maximum Dual Supply Voltage	+/- 15 V	-	+/- 15 V	-	+/- 15 V	-	+/- 18 V	-	-	+/- 15 V
Minimum Dual Supply Voltage	1.75 V	-	1.75 V	-	1.75 V	-	+/- 2.5 V	-	-	1.75 V
Number of Channels	1 Channel	-	1 Channel	1	1 Channel	-	1 Channel	-	1	1 Channel
Number of Elements	1	-	1	1	1	1	1	1	1	1
Operating Supply Current	7.5 mA	-	7.5 mA	-	7.5 mA	-	7.5 mA	-	-	7.5 mA
Output Type	DTL, MOS, Open-Collector, Open-Emitter, RTL, TTL	-	MOS, Open-Collector, Open-Emitter, TTL	MOS, Open-Collector, Open-Emitter, TTL	MOS, Open-Collector, Open-Emitter, TTL	DTL, MOS, Open-Collector, Open-Emitter, RTL, TTL	DTL, MOS, Open-Collector, Open-Emitter, RTL, TTL	Open-Collector, Open-Emitter	DTL, MOS, Open-Collector, Open-Emitter, RTL, TTL	Open-Collector, Open-Emitter
Package	8-TSSOP	-	8-SOIC	SOIC (D)-8	8-SOIC	8-DIP (0.300", 7.62mm)	TO-99-8	-	TSSOP (PW)-8	8-PDIP
Response Time	115 ns	-	115 ns	-	115 ns	-	200 ns	-	-	115 ns
Series	LM311	-	LM311	-	LM311	-	LM311-N-MIL	-	-	LM311
Shutdown	No Shutdown	-	No Shutdown	-	No Shutdown	-	Shutdown	-	-	No Shutdown
Supplier Device Package	8-TSSOP	-	8-SOIC	8-SOIC	8-SOIC	8-PDIP	TO-99-8	8-PDIP	8-TSSOP	8-PDIP
Supply Type	Single, Dual	-	Single, Dual	-	Single, Dual	-	Single, Dual	-	-	Single, Dual
Supply Voltage	3.5 V to 30 V	-	3.5 V to 30 V	-	3.5 V to 30 V	-	9 V, 12 V, 15 V, 18 V, 24 V, 28 V	-	-	3.5 V to 30 V
Supply Voltage Max	30 V	-	30 V	-	30 V	-	36 V	-	-	30 V
Supply Voltage Min	3.5 V	-	3.5 V	-	3.5 V	-	5 V	-	-	3.5 V
Technology	Bipolar	-	Bipolar	-	Bipolar	-	Bipolar	-	-	Bipolar
Type	General Purpose	-	General Purpose	General Purpose	General Purpose	General Purpose	General Purpose	Differential	General Purpose	Differential
Unit Weight	0.001376 oz	-	0.002561 oz	-	0.002561 oz	-	0.007654 oz	-	-	0.015535 oz
Vcm Common Mode Voltage	500 mV	-	500 mV	-	500 mV	-	500 mV	-	-	500 mV
Voltage Gain Db	106.02 dB	-	106.02 dB	-	106.02 dB	-	106.02 dB	-	-	106.02 dB
Voltage Input Offset Max	7.5mV @ ±15V	-	7.5mV @ ±15V	7.5mV @ ±15V	7.5mV @ ±15V	7.5mV @ ±15V	7.5mV @ ±15V	7.5mV @ ±15V	7.5mV @ ±15V	7.5mV @ ±15V
Voltage Supply Single Dual	3.5V ~ 30V, ±1.75V ~ 15V	-	3.5V ~ 30V, ±1.75V ~ 15V	3.5V ~ 30V, ±1.75V ~ 15V	3.5V ~ 30V, ±1.75V ~ 15V	3.5V ~ 30V, ±1.75V ~ 15V	5V ~ 36V, ±2.5V ~ 18V	3.5V ~ 30V, ±1.75V ~ 15V	3.5V ~ 30V, ±1.75V ~ 15V	3.5V ~ 30V, ±1.75V ~ 15V
Vos Input Offset Voltage	7.5 mV	-	7.5 mV	-	7.5 mV	-	7.5 mV	-	-	7.5 mV
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Selection Guide

📦Package

8-TSSOP (0.173", 4.40mm Width)→LM311PWRG4LM311PW

8-SOIC (0.154", 3.90mm Width)→LM311DG4LM311DRG4LM311DRE4

8-DIP (0.300", 7.62mm)→LM311PG4LM311P-NGLM311PE4

TO-99-8 Metal Can→LM311H/NOPB

Technical Specifications

Use the exact LM311 variant and supply conditions; output-transistor capability is separate from analog input range.

Documented parameters and selection boundaries

Output architecture

Separate collector and emitter connections

Control functions

Offset balancing and strobe

Supply examples

Single 5 V or split supplies, subject to recommended limits

Frequently Asked Questions

Common technical questions about the LM311 series.

Will LM311 generate a high logic output without an external pullup?

Not in the usual open-collector logic connection; provide the required pullup and emitter reference.

Why can changing a pullup alter observed response time?

The resistor and output capacitance determine the rising edge after the transistor releases the node.

Does a 5 V supply allow comparison at either rail?

Check the input common-mode range; supply compatibility does not imply rail-to-rail input operation.