LM3914N Dot/Bar Display Driver Technical Summary

Overview

The LM3914N is a monolithic integrated circuit designed to provide a visual display of analog voltage levels through LED illumination. This versatile component drives up to 10 LEDs in either a moving dot or bar graph format, selectable via a single control pin. The device features regulated, programmable current drive to the LEDs, eliminating the need for current-limiting resistors and simplifying system design.

As part of National Semiconductor's (now Texas Instruments) LM391x series, the LM3914N offers linear scaling for accurate analog voltage representation. The device operates across a wide voltage range, making it suitable for various measurement and display applications in both consumer and industrial electronics.

Key Features

• Drives LEDs, LCDs, or vacuum fluorescent displays
• User-selectable bar or dot display mode via external pin
• Programmable LED current (2mA to 30mA) without external resistors
• Internal voltage reference from 1.2V to 12V
• Operates from 3V to 25V supply voltage
• Linear scaling for accurate analog representation
• Input withstands ±35V without damage
• Internal 10-step voltage divider
• Expandable to displays of 20 to 100 segments
• Available in 18-pin PDIP, SOIC, and other packages

Applications

Typical Use Cases

• Battery voltage monitors
• Audio level meters
• Power level indicators
• Analog instrument panels
• Process control displays
• Automotive dashboard indicators
• Test and measurement equipment
• Medical instrumentation

Application Notes

The LM3914N is particularly useful in applications requiring visual representation of analog signals. Its programmable current drive allows direct LED connection without current-limiting resistors, while the selectable display mode provides flexibility in user interface design. When used in expanded configurations with multiple devices, the LM3914N can create displays with higher resolution (20 to 100 segments) while maintaining accurate linear scaling.

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (V+): 25V
• Input Voltage: ±35V
• Power Dissipation: 1365mW (DIP package)
• Operating Temperature Range: 0°C to +70°C
• Storage Temperature Range: -65°C to +150°C
• Lead Temperature (Soldering, 10 sec): 260°C

Recommended Operating Conditions

• Supply Voltage Range: 3V to 25V
• Reference Voltage Output: 1.2V to 12V
• LED Current Range: 2mA to 30mA
• Ambient Temperature: 0°C to +70°C

Electrical Specifications (Typical @ 25°C, V+ = 5V)

• Reference Voltage Accuracy: ±4%
• Comparator Threshold Accuracy: ±0.5dB
• Input Bias Current: 25nA
• Voltage Reference Temperature Coefficient: ±100ppm/°C
• LED Current Match Between Outputs: ±0.5%
• Supply Current (No Load): 6mA

Functional Description

The LM3914N contains a precision voltage divider network that establishes the threshold levels for ten comparators. Each comparator drives an individual LED when the input signal exceeds its specific threshold level. The device offers two display modes:

• Dot Mode: Only one LED (the highest level) is illuminated at any time
• Bar Mode: All LEDs up to the current level are illuminated

The mode selection is controlled by pin 9 (MODE SELECT). The internal voltage reference can be programmed from 1.2V to 12V using external resistors, allowing customization of the full-scale display range. The LED current is set by a single resistor connected to the Iadj pin, with typical values ranging from 2mA to 30mA per LED.

Package Information

18-Pin PDIP (Plastic Dual In-line Package)

• Package Code: N (Narrow)
• Dimensions: 22.86mm x 6.35mm (body)
• Lead Pitch: 2.54mm
• Lead Count: 18
• Material: Molded Plastic
• Operating Temperature: 0°C to +70°C
• Moisture Sensitivity Level (MSL): 1 (Unlimited floor life)

18-Pin SOIC (Small Outline Integrated Circuit)

• Package Code: D
• Dimensions: 11.55mm x 7.50mm (body)
• Lead Pitch: 1.27mm
• Lead Count: 18
• Material: Molded Plastic
• Operating Temperature: 0°C to +70°C
• Moisture Sensitivity Level (MSL): 1 (Unlimited floor life)

Design Considerations

Current Programming

The LED current is set by connecting a resistor between pin 7 (Iadj) and ground. The current follows the relationship: I_LED = 12.5/R_adj, where R_adj is in ohms and I_LED is in amps. For example, a 1.25kΩ resistor will set the current to 10mA per LED.

Voltage Reference Configuration

The internal voltage reference can be adjusted using two external resistors connected to pin 7 (REF OUT) and pin 8 (REF ADJ). The reference voltage is calculated as V_REF = 1.25V (1 + R2/R1) + I_ADJ × R2, where I_ADJ is typically 75µA.

Expanding Display Resolution

Multiple LM3914N devices can be cascaded to create displays with higher resolution. This is achieved by connecting the REF OUT of one device to the REF ADJ of the next, with appropriate resistor networks to establish the correct voltage divisions between devices.

Conclusion

The LM3914N provides a versatile, easy-to-implement solution for analog voltage visualization across numerous applications. Its integrated voltage reference, programmable current drive, and selectable display modes offer designers significant flexibility while reducing component count and board space requirements. With proper configuration, the device can accommodate a wide range of input signals and display requirements, making it a valuable component in measurement and display systems.