LM385BZ Micropower Adjustable Band-Gap Voltage Reference

Overview

The LM385BZ is a precision micropower 3-terminal adjustable band-gap voltage reference diode designed for applications requiring stable reference voltages. Part of the LM185/LM285/LM385 family, this component operates across a wide voltage range (1.24V to 5.3V) and current range (10µA to 20mA), making it versatile for various low-power applications. The device features excellent temperature stability, low dynamic impedance, and tight voltage tolerance achieved through on-chip trimming. Its band-gap reference architecture, utilizing only transistors and resistors, ensures low noise and reliable performance.

Key Features

• Adjustable Output Voltage: Programmable from 1.24V to 5.30V using external resistors.
• Low Operating Current: Functional from 10µA to 20mA, ideal for battery-powered applications.
• Exceptional Temperature Stability: Tight temperature coefficient ensures stable performance across varying environmental conditions.
• Low Dynamic Impedance: Typically 1Ω, minimizing voltage fluctuations under load variations.
• On-Chip Trimming: Precision trimming during manufacturing guarantees tight voltage tolerance.
• Low Noise: Band-gap architecture with transistors and resistors reduces output noise.
• Wide Operating Range: Suitable for applications requiring reference voltages from 1.24V up to 5.3V.

Applications

The LM385BZ is widely used in precision analog circuits where stable voltage references are critical. Common applications include:

• Portable and Battery-Powered Devices: Due to its low current consumption, it is ideal for handheld meters, medical devices, and IoT sensors.
• Voltage Regulators: Provides a stable reference for linear and switching regulators.
• Data Acquisition Systems: Ensures accurate analog-to-digital conversion in measurement equipment.
• Industrial Control Systems: Used in process control and instrumentation where precision voltage references are required.
• Automotive Electronics: Suitable for sensors and control modules requiring stable references under varying temperatures.
• Consumer Electronics: Found in audio equipment, power management circuits, and display drivers.

Electrical Characteristics

The following table summarizes the key electrical specifications of the LM385BZ under typical operating conditions (unless otherwise noted):

Absolute Maximum Ratings

• Supply Voltage (V_IN): 40V
• Reference Current (I_REF): 20mA (max)
• Operating Temperature Range: -40°C to +85°C (LM385BZ)
• Storage Temperature Range: -65°C to +150°C

Typical Performance Characteristics

• Reference Voltage (V_REF): 1.24V (adjustable up to 5.3V)
• Dynamic Impedance: 1Ω (typical at 100µA)
• Temperature Coefficient: 30ppm/°C (typical over full temperature range)
• Line Regulation: 0.2%/V (typical for 10µA ≤ I_REF ≤ 20mA)
• Load Regulation: 0.3Ω (typical output impedance)
• Long-Term Stability: 20ppm/1000hr (typical)

Package Information

The LM385BZ is available in a standard TO-92 package, which is widely used for through-hole PCB mounting. Key package details include:

• Package Type: TO-92 (3-pin)
• Pin Configuration:
  • Pin 1: Adjust (for setting output voltage with external resistors)
  • Pin 2: Cathode (connected to ground or negative supply)
  • Pin 3: Anode (input supply voltage)
• Dimensions: 4.95mm (L) x 3.94mm (W) x 4.95mm (H)
• Weight: Approximately 0.35 grams
• Mounting Style: Through-hole
• Operating Temperature: -40°C to +85°C (industrial grade)

Design Considerations

Setting the Output Voltage

The LM385BZ's output voltage can be adjusted using two external resistors (R1 and R2) connected between the Adjust pin and ground. The reference voltage (V_REF) is determined by the equation:

V_OUT = V_REF × (1 + R1/R2)

where V_REF is typically 1.24V. For best stability, use low-temperature-coefficient resistors (e.g., metal film).

Noise Reduction

To minimize noise, a bypass capacitor (typically 0.1µF to 10µF) should be placed close to the Adjust pin. For ultra-low-noise applications, an additional RC filter can be added.

Thermal Considerations

Although the LM385BZ has excellent temperature stability, minimizing thermal gradients across the device improves performance. Avoid placing heat-generating components nearby.

Conclusion

The LM385BZ is a versatile, high-performance voltage reference suitable for a wide range of precision analog applications. Its adjustable output, low power consumption, and excellent stability make it ideal for portable, industrial, and automotive systems. Engineers can rely on its consistent performance in demanding environments, ensuring accurate voltage references for critical circuits.