LM339QT - Low-Power Quad Open-Collector Comparator | STMicroelectronics
MPN: LM339QT ✓ ActiveLM339QT Overview
A voltage comparator is a semiconductor device that compares two input voltages and produces a logic-level output indicating which input is higher. The LM339QT belongs to the comparator hierarchy within analog and mixed-signal integrated circuits. Its four open-collector channels can be used independently, allowing several threshold, sensing, window-detection, or protection functions to be implemented in one compact package. Open-collector outputs also provide flexibility for wired logic, level shifting, and interface designs when an external pull-up is used.
Key characteristics include low power consumption, an input offset voltage specified as low as 2 mV maximum for the related LM339A, LM239A, and LM139A precision versions, and input bias current listed as 25 nA in the product listing. The device is compatible with CMOS, DTL, ECL, MOS, open-collector, and TTL logic environments. Each channel provides substantial flexibility in voltage comparison because the inputs can operate across the supply range while the output stage operates from the positive supply.
The open-collector output architecture is a central technical feature. Unlike a totem-pole output, an open-collector transistor can pull the output low but cannot actively drive it high. Designers therefore add a pull-up resistor to establish the high state. Multiple comparator outputs can share a pull-up when the application requires wired-AND behavior. Output speed is not its principal strength; instead, the LM339QT emphasizes low power, wide input common-mode capability, flexible logic interfacing, and four independent channels in one small package.
Typical uses include monitoring multiple power rails, detecting overvoltage or undervoltage conditions, comparing sensor outputs with adjustable references, implementing window comparators, generating system-reset signals, and translating between different logic voltage domains. The compact 16-QFN footprint is useful in space-constrained industrial, consumer, and embedded-control designs where four comparison functions are required without allocating separate components.
The primary design consideration is the open-collector output. Select an external pull-up resistor to suit the required speed, current, and logic level, and place it close enough to the relevant output to limit rise time and susceptibility to noise. Input filtering may also be necessary when the comparator handles slow or high-impedance signals. Verify absolute maximum voltage, common-mode limits, output-current limits, and timing requirements in the manufacturer datasheet for the final operating environment.
This product page combines the exact LM339QT package and headline electrical characteristics with practical interface guidance, sourcing guidance, and a focused comparison of technically relevant alternatives. It is intended to help engineers identify whether the four-channel, low-power, open-collector architecture matches the required voltage sensing and logic interface before committing to a PCB layout.
Drop-in alternatives for LM339QT — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
LM339QDT
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
LM339QT Maximum Ratings & Electrical Characteristics
| Comparator Type | Quad general-purpose voltage comparator |
| Number of Comparator Channels | 4 independent channels |
| Output Type | Open-collector |
| Supply Current | 1.1 mA typical |
| Input Bias Current | 25 nA |
| Input Offset Voltage | 250 mV maximum for the listed LM339QT configuration |
| Precision Version Input Offset Voltage | 2 mV maximum for LM339A, LM239A, and LM139A |
| Common-Mode Input Range | 0 V to VCC − 1.5 V |
| Logic Compatibility | CMOS, DTL, ECL, MOS, open-collector, and TTL |
| Package | 16-QFN (3 x 3 mm) |
| Mounting Type | Surface mount |
| Number of Pins | 16 pins |
LM339QT 16-qfn (3 x 3 mm) Pin Configuration Guide
Pin configuration for LM339QT (16-qfn (3 x 3 mm) package). This analog component features input, output, and power supply pins. Refer to the manufacturer datasheet for offset null, compensation, and enable pin configurations. Ideal for signal conditioning and amplifier circuits.
No detailed pinout data available for LM339QT.
Refer to the datasheet for full pin configuration.
Typical Applications
LM339QT is suitable for 6 applications: Industrial Power-Rail Monitoring, Sensor Threshold Detection, Window Voltage Comparator, Overvoltage and Undervoltage Protection, Battery-Powered Equipment, Logic-Level Interface and Translation.
Industrial Power-Rail Monitoring
The LM339QT is suitable for monitoring several supply rails because it combines four independent comparator channels with a 0 V to VCC − 1.5 V common-mode input range. Each channel can compare a divided rail voltage against a reference, with an open-collector output driving a fault input or system-reset network. The 1.1 mA typical supply current supports low-power supervision, while the 16-QFN 3 x 3 mm package conserves board area. Add input filtering and hysteresis when the monitored rail contains ripple or crosses the threshold slowly.
Recommended
Sensor Threshold Detection
The LM339QT can implement four independent threshold decisions for temperature, light, pressure, or analog sensor conditioning. Its input bias current of 25 nA is useful when the preceding circuit presents appreciable source impedance, and the four channels reduce the component count in a compact sensing module. The open-collector output can pull up to the system logic level through an external resistor. Use hysteresis around the switching threshold and verify that the sensor voltage remains within the 0 V to VCC − 1.5 V common-mode range.
Recommended
Window Voltage Comparator
Two LM339QT channels can monitor the lower and upper limits of a signal, while the other two channels provide auxiliary comparisons or status outputs. The device supports inputs from 0 V through VCC − 1.5 V and accepts signals from CMOS, TTL, DTL, ECL, MOS, and open-collector logic environments. Because the outputs are open collector, pull-up resistors and optional wired-AND logic can implement a fault indication. Select resistor values for the intended logic threshold and add hysteresis to prevent chatter.
Recommended
Overvoltage and Undervoltage Protection
The LM339QT can detect rail excursions by comparing scaled supply voltages with internal or external references. Four independent channels allow simultaneous monitoring of multiple rails, and each open-collector output can directly pull down a reset, inhibit, or fault line. The device's low 1.1 mA typical supply current is advantageous in continuously supervised systems. Account for the maximum input of VCC − 1.5 V, use resistor dividers with suitable tolerances, and test the complete protection system under dynamic load conditions.
Recommended
Battery-Powered Equipment
LM339QT is appropriate for battery-operated monitoring equipment when four low-power decision channels are useful and open-collector fault outputs are acceptable. The 1.1 mA typical supply current is substantially higher than the 9 µA typical consumption listed for the micro-power CMOS TS339, so current budget remains an important trade-off. The LM339QT instead provides broad CMOS, TTL, DTL, ECL, MOS, and open-collector compatibility. Use a pull-up that does not prevent the equipment from entering its intended low-power state.
Recommended
Logic-Level Interface and Translation
The LM339QT's open-collector outputs allow a pulled-up logic output to be referenced to a voltage selected by the system designer, making the device useful for interfacing to a logic domain not directly driven by a push-pull output. Four channels can perform level translation, polarity detection, or fault signaling. The common-mode input limit remains 0 V to VCC − 1.5 V, so input level translation may still be required. Choose the pull-up voltage and resistor for the receiving logic and verify output timing against the system requirement.
Recommended
Recommended Products Summary
Engineering reference data for LM339QT — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | LM339QDT |
|---|---|---|
| Brand | STMicroelectronics | STMicroelectronics |
| Package | 16-QFN (3 x 3 mm) | 16-QFN (3 x 3 mm) |
| Comparator Channels | 4 independent channels | 4 independent channels |
| Output Type | Open-collector | Open-collector |
Key Differentiators
- Four independent channels in a compact 3 x 3 mm package (vs LM339QDT)
- Open-collector interface flexibility (vs TS339)
- Broad logic-environment compatibility (vs LM339LV)
Design Notes
Do not treat an open-collector output as a push-pull logic output. The output transistor pulls the node low but requires an external pull-up resistor to establish the high state. Select the resistor after checking the destination logic voltage, output sink-current rating, capacitive load, and required rise time. A lower resistance gives a faster edge and greater sink current, while a higher resistance reduces current but increases sensitivity to leakage and capacitive noise.
Add positive feedback or another defined hysteresis network when the compared voltages converge slowly or contain noise. Without hysteresis, small input fluctuations around the threshold can cause repeated comparator transitions. Keep the hysteresis network close to the relevant input and verify that its added offset remains acceptable for the measurement or protection function. This is especially important when one LM339QT channel controls a relay, reset signal, or system-wide fault indication.
Place the pull-up resistor near the open-collector output and the associated receiving input, not near a distant source device. This shortens the high-impedance interval during which the node is susceptible to coupling. Maintain a compact ground return for the comparator and evaluate the 16-QFN assembly process against the manufacturer land pattern. Confirm whether the package has an exposed pad and follow the datasheet's thermal and copper requirements exactly.
Check every input against the 0 V to VCC − 1.5 V common-mode range before finalizing signal conditioning. The common-mode range is not the same as the supply-voltage rating, and an input exceeding the allowed range may damage the device even if the output pull-up remains within range. Use resistor dividers or level-shifting stages for higher voltages, and verify the absolute maximum ratings and supply limits in the manufacturer datasheet.
Compliance Information
The LM339QT is a surface-mount integrated circuit, but explicit material-compliance declarations were not identified. AEC-Q100 is treated as not applicable because this is not documented as an automotive-qualified variant.
