LMV331SQ3T2G: Key Specifications and Application Circuit Design for a Low-Voltage Comparator
The LMV331SQ3T2G is a single, low-voltage comparator from onsemi, designed to offer high performance while operating from a single supply voltage as low as 2.7V and up to 5V. Its combination of low power consumption, small packaging, and rail-to-rail input capabilities makes it an ideal choice for a vast array of portable, battery-powered, and space-constrained applications.
Key Specifications
Understanding the critical electrical characteristics is paramount for effective circuit design. The LMV331SQ3T2G stands out in several key areas:
Low Supply Voltage Operation: This device is optimized for single-supply operation from 2.7V to 5V, making it perfectly suited for modern digital systems and products powered by two or three-cell battery packs.
Ultra-Low Supply Current: A typical supply current of just 20 µA ensures minimal power drain, which is crucial for extending battery life in portable devices.
Rail-to-Rail Input Common-Mode Range: The input voltage can swing from the negative rail (GND) to the positive supply rail (V+), providing maximum flexibility in sensing signals close to the power supply boundaries. This simplifies biasing and interface circuitry.
Low Input Offset Voltage: With a maximum offset voltage of 5.0 mV, the comparator offers good precision, reducing errors in threshold detection.
Push-Pull Output Stage: The CMOS output stage provides a rail-to-rail swing, ensuring solid logic high and low levels without requiring an external pull-up resistor, which saves board space and components.
Small Package: Housed in a SC-70-5 package, it is one of the smallest available 5-pin packages, addressing the needs of highly miniaturized designs.
Application Circuit Design: A Basic Voltage Monitor
A common use for the LMV331SQ3T2G is as a voltage monitor or undervoltage lockout (UVLO) circuit. The following design illustrates a simple battery voltage monitor that triggers a warning when the battery voltage falls below a predefined threshold.
Circuit Operation:
1. Reference Voltage: A resistive voltage divider (R1 and R2) creates a stable reference voltage (V_REF) at the inverting input (-). This voltage is calculated as V_REF = V+ (R2 / (R1 + R2)). For a 3.6V threshold in a 5V system, example values could be R1=130 kΩ and R2=100 kΩ, giving V_REF ≈ 2.17V.
2. Sensed Voltage: The battery voltage to be monitored is scaled down by another voltage divider (R3 and R4) and fed to the non-inverting input (+). The ratio should be chosen so that when the battery is at the desired threshold voltage, the scaled voltage equals V_REF.
3. Comparison: The LMV331SQ3T2G compares these two voltages.
When V_BATT is high, the voltage at the non-inverting input is greater than V_REF. The output switches to a logic high state (near V+).
When V_BATT drops below the threshold, the voltage at the non-inverting input falls below V_REF. The output switches to a logic low state (near GND).
4. Output Action: The output can directly drive a microcontroller's input pin, an LED (with a current-limiting resistor), or other logic circuitry to signal a low-battery condition.
Design Considerations:
Hysteresis: The basic circuit is susceptible to noise causing the output to chatter when the input voltage is very near the threshold. Adding positive feedback hysteresis is essential for stable operation. This can be achieved by adding a large resistor (R_HYS) from the output back to the non-inverting input. This creates two distinct thresholds: one for turning on and a lower one for turning off, providing noise immunity.
Input Filtering: In electrically noisy environments, small capacitors (e.g., 10-100nF) across the divider resistors or in series with small resistors on the inputs can help filter out noise.
Supply Decoupling: A 0.1 µF ceramic capacitor should be placed as close as possible to the V+ pin and GND to bypass noise on the power supply and ensure stable operation.
ICGOOODFIND: The LMV331SQ3T2G is a highly efficient and compact solution for low-voltage comparison tasks. Its standout features of ultra-low power consumption, rail-to-rail input, and tiny SC-70-5 packaging make it exceptionally well-suited for modern portable and battery-powered electronics. By incorporating simple design techniques like hysteresis, engineers can create robust and reliable circuits for voltage monitoring, sensor interfacing, and threshold detection.
Keywords: Low-Power Comparator, Rail-to-Rail Input, SC-70 Package, Voltage Monitoring, Battery-Powered Applications
