The LM2903 is a dual voltage comparator with open-collector outputs, specified from −40 °C to +125 °C. It shares its design and pinout with the LM393; the part number identifies a temperature grade rather than a different circuit. That grade is the reason it appears on automotive and industrial bills of materials, and it is also the reason its guaranteed accuracy is looser than the LM393’s.
LM2903 Pin Configuration
| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | 1OUT | Output | Comparator 1 output, open collector |
| 2 | 1IN− | Input | Comparator 1 inverting input |
| 3 | 1IN+ | Input | Comparator 1 non-inverting input |
| 4 | GND | Supply | Negative supply |
| 5 | 2IN+ | Input | Comparator 2 non-inverting input |
| 6 | 2IN− | Input | Comparator 2 inverting input |
| 7 | 2OUT | Output | Comparator 2 output, open collector |
| 8 | VCC | Supply | Positive supply |
Two details in this map cause most of the wiring errors.
The halves are mirrored about the centre of the package. Reading down the left side, comparator 1 gives output, inverting, non-inverting. Reading up the right side, comparator 2 gives non-inverting, inverting, output. Copying the first comparator’s connections to the second without re-reading the pin numbers inverts it.
Pin 4 is the negative supply, not a signal ground. In split-supply operation it connects to the negative rail, and the supply-voltage limit applies to the difference between pin 8 and pin 4 — not to either pin measured against system ground.
LM2903 CAD Layout
The SOIC-8 land pattern uses 1.55 mm × 0.60 mm pads on a 1.27 mm pitch, with 5.40 mm between the centres of the two rows. That footprint is shared with most 8-pin SOIC parts, so an existing library part will normally drop in.
The LM2903 is offered in five packages, and they are not interchangeable on the board:
| Package | Body size | Junction-to-ambient thermal resistance |
|---|---|---|
| PDIP-8 | 9.81 mm × 6.35 mm | 114.9 °C/W |
| SO-8 | 6.20 mm × 5.30 mm | — |
| SOIC-8 | 4.90 mm × 3.91 mm | 148.5 °C/W |
| TSSOP-8 | 3.00 mm × 4.40 mm | 200.6 °C/W |
| VSSOP-8 | 3.00 mm × 3.00 mm | 193.7 °C/W |
Thermal resistance rarely constrains this part — both comparators together draw about 0.8 mA — but it becomes relevant when the outputs sink current continuously. At the 20 mA absolute-maximum output current on a 12 V rail, a saturated output dissipates enough to matter in TSSOP.
Download the LM2903 datasheet (Texas Instruments, PDF) — document SLCS005AH, which covers the LM193, LM293, LM393 and LM2903 together with the newer B-versions. 2 V to 30 V recommended supply, −40 °C to +125 °C, 1.3 µs typical response time.
Overview and Analysis of the LM2903
The device contains two independent comparators that share only the supply pins. Each compares the voltage on its two inputs and drives an open-collector transistor: the output sinks current when the inverting input is above the non-inverting input, and is high impedance otherwise. There is no internal pull-up, so the high level is defined entirely by an external resistor and whatever rail that resistor connects to.
Three properties define where the part is used. The common-mode input range includes the negative supply, so it can compare signals sitting at ground without a level-shifting front end. The supply range is wide enough to run directly from a 12 V or 24 V rail. And the open-collector output allows the comparator to run on that high rail while presenting a 3.3 V or 5 V logic level to a microcontroller.
One number is frequently misread. The 36 V figure that appears in most summaries of this part is the absolute maximum supply rating — a stress limit, not an operating condition. The recommended supply range for the plain LM2903 is 2 V to 30 V; 32 V applies to V-suffix devices and 36 V to the B-version. Designing a 24 V system against the 36 V number leaves less margin than it appears to.
Technical Specifications
Values at VCC = 5 V and TA = 25 °C unless a full-range figure is given.
| Parameter | Value |
|---|---|
| Supply voltage, recommended | 2 V to 30 V (32 V for V-suffix devices) |
| Supply voltage, absolute maximum | 36 V |
| Operating ambient temperature | −40 °C to +125 °C |
| Input offset voltage | 2 mV typ, 7 mV max; 15 mV max over temperature |
| Input bias current | −25 nA typ, −250 nA max; −500 nA over temperature |
| Input offset current | 5 nA typ, 50 nA max; 200 nA over temperature |
| Common-mode input range | 0 V to VCC − 1.5 V; 0 V to VCC − 2 V over temperature |
| Differential input voltage | Equal to the supply voltage; ±36 V absolute maximum |
| Large-signal voltage gain | 25 V/mV min, 100 V/mV typ (VCC = 15 V, RL ≥ 15 kΩ) |
| Output saturation voltage | 150 mV typ, 400 mV max at 4 mA sink; 700 mV over temperature |
| Output sink current | 6 mA at VOL = 1.5 V |
| Output leakage, high state | 0.1 nA typ, 50 nA max at VOH = 5 V |
| Output current, absolute maximum | 20 mA |
| Supply current, both comparators | 0.8 mA typ, 1 mA max |
| Response time | 1.3 µs typ (100 mV step, 5 mV overdrive); 0.3 µs for a TTL-level step |
| ESD, human body model | ±2000 V |
| Storage temperature | −65 °C to +150 °C |
The common-mode limit deserves attention before the rest. The inputs must sit at least 2 V below the positive supply across the full temperature range. A divider tap or reference placed near VCC is outside the specified range and the comparison result is not guaranteed.
Comparable Parts
Six part numbers share one die and one pinout. What separates them is the temperature range over which parameters are tested and how tightly those parameters are held.
| Part | Temperature range | Offset voltage, max over temperature | Recommended supply |
|---|---|---|---|
| LM393 | 0 °C to +70 °C | ±9 mV | 2 V to 30 V |
| LM293 | −25 °C to +85 °C | ±9 mV | 2 V to 30 V |
| LM393B | −40 °C to +85 °C | ±4 mV | 2 V to 36 V |
| LM2903 | −40 °C to +125 °C | ±15 mV | 2 V to 30 V |
| LM2903B | −40 °C to +125 °C | ±4 mV | 2 V to 36 V |
| LM193 | −55 °C to +125 °C | ±9 mV | 2 V to 30 V |
The LM2903 holds one of the widest ranges in the group and the loosest offset specification of any member. That combination is deliberate: it is the high-volume automotive and appliance grade, sorted for temperature rather than for accuracy.
The LM2903B changes the trade. It keeps the −40 °C to +125 °C range while guaranteeing ±4 mV, raises the supply limit to 36 V, cuts maximum input bias current to 25 nA and brings response time down to 1 µs. Texas Instruments specifies it as a drop-in replacement for the LM2903 in both A and V grades.
The same number is not the same part at every manufacturer
The LM2903 is second-sourced widely, and the datasheets do not agree.
| Texas Instruments | STMicroelectronics | onsemi | |
|---|---|---|---|
| Rated ambient temperature | −40 °C to +125 °C | −40 °C to +125 °C | −40 °C to +105 °C (LM2903V: +125 °C) |
| Supply voltage, recommended | 2 V to 30 V | 2 V to 36 V | 2 V to 36 V |
| ESD, human body model | ±2000 V | 800 V | 1500 V; 250 V for LM2903DG and LM2903DR2G |
| Offset voltage, 25 °C max | 7 mV | 7 mV | 7 mV |
| Offset voltage over temperature | 15 mV | 15 mV | 15 mV |
| Bias current over temperature | 500 nA | 400 nA | 500 nA |
| Voltage gain, min / typ | 25 / 100 V/mV | 25 / 200 V/mV | 25 / 200 V/mV |
| Response time, typ | 1.3 µs | 1.3 µs | 1.5 µs |
| PDIP-8 available | Yes | No | Yes |
| AEC-Q100 qualified variant | LM2903-Q1 | Y-suffix codes, e.g. LM2903YDT | NCV2903 |
Three of these change designs. The temperature rating is the most consequential: an onsemi LM2903 is specified to +105 °C, and onsemi’s +125 °C device is the LM2903V. A design validated on TI or ST silicon and later filled with onsemi stock loses 20 °C of guaranteed range with no change to the number on the BOM.
ESD ratings differ by nearly an order of magnitude, which matters wherever a comparator input reaches a connector rather than staying on the board. And the supply ceiling differs: running a 24 V rail with transient headroom sits inside ST’s specification and outside TI’s.
The guaranteed numbers converge — all three hold 25 V/mV minimum gain and the same 7 mV and 15 mV offset limits. Only typical values differ, and typical values are not design constraints.
LM2903 Circuitry
Each comparator is a three-stage chain. The input stage is a PNP Darlington differential pair, which is what allows the common-mode range to include the negative supply — and also what sets the upper limit two volts below VCC, since the stage needs headroom above the inputs to bias correctly.
The gain stage provides the specified 25 V/mV minimum. The output stage is a single NPN transistor with its collector brought to the pin and its emitter at the negative supply. Nothing pulls the output high.
The saturation voltage of that output transistor is resistive: it rises with sink current rather than clamping at a fixed value. At 4 mA it is 150 mV typical and 400 mV maximum, rising to 700 mV over temperature. Where the output drives a logic input directly, that low level must stay below the receiver’s input-low threshold at the sink current actually used.
Characteristics of the LM2903
Open-collector output. The high level is set by an external pull-up and its rail, independent of VCC. Outputs from both comparators can be tied together to form a wired-AND: any comparator pulling low pulls the shared node low, which builds a multi-input fault flag with no logic gates.
Common-mode limit and its failure mode. With both inputs inside the range the output follows the comparison normally. If the inverting input rises above the range while the non-inverting input stays inside it, the output goes low; the reverse case gives a high-impedance output. Both inputs above the range is the case to avoid, and it is where unexpected output states come from.
Differential input voltage equal to the supply. Either input may be driven to the supply rail without damage, so a comparator sensing a rail directly does not need input clamps for the normal case.
No internal hysteresis. The device switches at the crossing point. Around that point a slow or noisy input produces multiple transitions, and the high gain combined with stray coupling from output to inverting input can sustain oscillation. Positive feedback of around 10 mV is the standard fix; a supply bypass capacitor close to pin 8 is the other.
Response time depends on overdrive. The specified 1.3 µs is for a 100 mV step with 5 mV of overdrive. Larger overdrive is faster — a TTL-level step gives 0.3 µs. A comparator fed a slowly ramping input is not a 1.3 µs device.
Applications of LM2903
Texas Instruments lists server power supplies, single-phase UPS systems, cordless power tools, motor drives, appliances, building and factory automation, and automotive infotainment and cluster among the target applications. The circuit patterns behind those uses are the following.
Voltage Monitoring
Comparing a divided rail against a reference produces an undervoltage or overvoltage flag. The wide supply range means the comparator can run from the rail it monitors, and the open-collector output reports to a controller on a different rail.
Window Comparators
Two comparators in one package make a window detector: one trips above the upper limit, one below the lower limit, and their outputs are tied together as a wired-AND to give a single in-range signal. Battery management and supply-sequencing supervision use this directly.
Zero-Crossing Detectors
For AC-referenced work the comparator marks the instant the input crosses a reference, producing a logic edge locked to the mains or to a pickup coil. This is the standard front end for phase-angle control and for synchronising a converter to line frequency. Both single-supply and split-supply versions appear in the manufacturer datasheets.
Oscillators
With a resistor–capacitor network and positive feedback, one comparator forms a relaxation oscillator producing a square wave. Datasheet examples extend this to crystal-controlled oscillators, time-delay generators and a two-decade voltage-controlled oscillator.
Level Shifters
Because the output stage is isolated from VCC, a comparator running at 12 V or 24 V can present 3.3 V or 5 V logic simply by choosing the pull-up rail. No dedicated translator is needed in either direction.
Automotive Systems
The −40 °C to +125 °C grade and the tolerance of supply variation suit under-hood and cabin electronics. Note that the temperature grade alone does not make the part automotive-qualified; that requires the Q1, NCV or Y-suffix versions covered below.
Control Systems
Threshold detection on a sensor output — a thermistor divider, a current-sense voltage, a photodiode transimpedance stage — converts an analogue quantity into a control decision without occupying an ADC channel.
Application Circuit of LM2903
R1 and R2 scale the monitored rail down to the 2.5 V reference. RH feeds the output back to the non-inverting input, separating the falling and rising thresholds so the output does not chatter while the rail decays. R4 pulls the output up to 3.3 V, which is what makes this a level shifter as well as a detector.
With the values shown the divider presents about 22.5 % of the rail at the input. The falling threshold is the rail voltage at which the divided rail plus the current injected through RH from the pulled-up output equals 2.5 V — 10.6 V. Once the output pulls low, RH sinks toward the saturation voltage instead, and the rail must recover to 11.1 V before the output releases. That is roughly 0.46 V of hysteresis. Raising RH narrows the band; lowering it widens it.
The grade choice shows up in the error budget. The input node presents a source impedance of about 7.4 kΩ, so the 500 nA bias-current limit over temperature contributes about 3.7 mV and the 15 mV offset limit contributes 15 mV. Referred back to the rail through the inverse divider ratio of 4.44, that is roughly ±83 mV of threshold uncertainty at temperature extremes. The same circuit built around an LM2903B holds it below ±20 mV. For a 10.6 V threshold neither matters. For a tolerance-band monitor on a regulated 5 V rail, the difference decides the design.
Functional Design of LM2903
Four checks cover most designs.
Input range. Confirm both inputs stay between the negative supply and VCC − 2 V across the temperature range, not just at room temperature. This usually decides the divider ratio and the reference value before anything else.
Overdrive. The differential voltage must exceed the offset voltage before the comparison is valid — 15 mV over temperature for the LM2903, so a design whose signal only ever moves 10 mV past the threshold does not work. Overdrive also sets speed.
Pull-up sizing. The pull-up resistor sets the rise time, approximately its resistance multiplied by the load capacitance. A 100 kΩ pull-up into 50 pF gives a 5 µs edge, four times slower than the comparator itself. Values between 4.7 kΩ and 10 kΩ keep edges fast while holding sink current well inside the 20 mA maximum. The fall time is set by the output transistor’s saturation resistance and is much shorter.
Layout. Keep a bypass capacitor between pin 8 and pin 4, close to the device. Do not route an output trace parallel to an inverting-input trace without a supply or ground trace between them; that coupling is the usual source of output oscillation. Keep input series resistors small and place them next to the device.
Manufacturer Information
Texas Instruments, STMicroelectronics and onsemi all produce the LM2903, and Diodes Incorporated supplies it as part of the LM2901/LM2903 family. Original documents differ, so the manufacturer belongs on the BOM line alongside the part number whenever the design uses the top of the temperature or supply range.
For qualified automotive production the number itself must change. Temperature grade and automotive qualification are separate axes, and treating the LM2903’s −40 °C to +125 °C rating as equivalent to AEC-Q100 qualification is the most common error with this part. The qualified devices are the LM2903-Q1 and LM2903B-Q1 at Texas Instruments, NCV2903 at onsemi, and the Y-suffix ordering codes at STMicroelectronics.
Frequently Asked Questions
Are the LM2903 and LM393 interchangeable? Not in both directions. They share a die, a pinout and their room-temperature specifications, so an LM2903 will work anywhere an LM393 works. The reverse is not true: the LM393 is only specified from 0 °C to +70 °C, so substituting it into an LM2903 socket removes the temperature guarantee the design was based on.
What supply voltage can the LM2903 actually run from? 2 V to 30 V for the plain part, 32 V for V-suffix versions, and 36 V for the LM2903B. The 36 V figure quoted for the base part is an absolute maximum stress rating.
Why does the output stay high when it should switch? The most common cause is an input outside the common-mode range, which extends only to VCC − 2 V over temperature. The second is a missing pull-up resistor: the open-collector output cannot drive a high level by itself.
Can both comparators share one pull-up resistor? Yes, and that is the wired-AND configuration. The shared node goes low when either comparator pulls low, which is useful for combining fault conditions, but it also means the individual comparator states can no longer be read separately.