LM393MX/NOPB

The LM393MX/NOPB is a dual low-power precision voltage comparator from Texas Instruments, part of the LM193-N series. It contains two independent comparators in a single 8-pin SOIC package, designed to operate from a single 2-V to 36-V supply or dual ±1-V to ±18-V supplies.

The defining characteristic of the LM393 is the input common-mode voltage range that includes ground, even when operating from a single positive supply. This allows the comparator to sense signals at or near ground without requiring a negative supply rail — a critical advantage in single-supply battery-powered and automotive systems.

The PNP input stage provides low input bias current (25 nA typ) and low input offset current (±5 nA), making the LM393 suitable for high-impedance sensor interfaces. The maximum input offset voltage is ±5 mV over temperature, adequate for most threshold detection applications.

The open-collector output can sink up to 16 mA and is compatible with TTL, DTL, ECL, MOS, and CMOS logic levels. The open-collector architecture enables wired-OR connections and level shifting between different voltage domains. A pull-up resistor to the desired logic supply sets the output high level.

The supply current is only 0.4 mA for both comparators combined, independent of supply voltage magnitude. This makes the LM393 one of the most power-efficient general-purpose comparators available, ideal for battery-operated equipment.

The LM393MX/NOPB is the SOIC-8 tape-and-reel version rated for 0°C to 70°C commercial temperature range. The /NOPB suffix indicates lead-free (Pb-free) RoHS-compliant packaging with Sn lead finish, MSL-1 unlimited floor life.

**PNP Input Stage:** Each comparator uses a PNP differential input pair. The PNP structure allows the input common-mode range to extend to ground (0 V) and slightly below (-0.3 V max), which is the key advantage over NPN-input comparators. The input bias current flows out of the input pins (typically 25 nA), setting a minimum source impedance requirement for accurate threshold detection.

**Open-Collector Output:** The output stage is an NPN open-collector transistor that can only sink current to ground. When the inverting input exceeds the non-inverting input, the output transistor turns on (output low, saturation voltage 250 mV at 4 mA). When the non-inverting input is higher, the output transistor turns off and the output floats high via an external pull-up resistor. This allows the output high level to be set independently from the supply voltage, enabling level shifting.

**Comparison Operation:** The comparator has no internal feedback (unlike an op-amp), so it operates in open loop. Any voltage difference between inputs exceeding the offset voltage drives the output to one rail. The typical response time is 1.3 µs for a 5-mV overdrive, making it suitable for moderate-speed signal detection.

**Power Supply:** The LM393 operates from a single 2-36V supply or dual ±1-18V supplies. The supply current (0.4 mA) is essentially constant across the full voltage range because the internal bias network is self-regulating. There is no quiescent current difference between the two output states.