LF398 Sample-and-Hold Circuit

Overview

The LF198/LF298/LF398 are monolithic sample-and-hold circuits that leverage BI-FET technology to deliver ultra-high DC accuracy, fast signal acquisition, and low droop rates. These devices operate as unity gain followers, achieving a typical DC gain accuracy of 0.002% and an acquisition time as low as 6 µs to 0.01%. The bipolar input stage ensures low offset voltage and wide bandwidth, making these circuits suitable for high-precision applications. The input offset can be adjusted using a single pin without compromising input offset drift. With a wide bandwidth, the LF398 can be integrated into the feedback loop of 1 MHz operational amplifiers without stability concerns. The high input impedance (10¹⁰ Ω) allows for use with high-source impedances while maintaining accuracy.

Features

• Wide Supply Voltage Range: Operates from ±5V to ±18V supplies.
• Ultra-High DC Accuracy: Typical DC gain accuracy of 0.002%.
• Fast Acquisition Time: As low as 6 µs to 0.01%.
• Low Droop Rate: Achieves droop rates as low as 5 mV/min with a 1 µF hold capacitor.
• Low Offset Voltage: Bipolar input stage minimizes offset voltage.
• Single-Pin Offset Adjust: Input offset adjustment does not degrade drift performance.
• High Input Impedance: 10¹⁰ Ω input impedance supports high-source impedances.
• No Feed-Through in Hold Mode: Ensures isolation between input and output, even at supply voltage levels.
• Low Noise: JFET-based design reduces noise compared to MOS alternatives.
• Temperature Stability: No high-temperature instabilities due to JFET construction.

Applications

The LF398 is designed for precision applications requiring fast and accurate signal sampling. Key use cases include:

• Data Acquisition Systems: High-speed sampling for analog-to-digital conversion.
• Instrumentation: Precision measurement equipment requiring stable hold modes.
• Audio Processing: Sample-and-hold circuits in analog synthesizers and signal processors.
• Automatic Test Equipment (ATE): Accurate signal capture for testing and validation.
• Medical Electronics: Biomedical signal processing where low noise and high accuracy are critical.
• Industrial Control Systems: Feedback loops and signal conditioning in control applications.

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (V_CC to V_EE): ±18V
• Input Voltage: ±V_CC
• Operating Temperature Range: -55°C to +125°C
• Storage Temperature Range: -65°C to +150°C

Key Performance Parameters (Typical at 25°C, ±15V Supplies)

• DC Gain Accuracy: 0.002%
• Acquisition Time (to 0.01%): 6 µs
• Droop Rate: 5 mV/min (with 1 µF hold capacitor)
• Input Offset Voltage: 1 mV
• Input Bias Current: 30 pA
• Bandwidth: 1 MHz
• Hold Capacitor Range: 0.001 µF to 1 µF

Package Information

The LF398 is available in multiple package options to suit different application requirements. Below are the standard package details:

8-Pin Metal Can (TO-99)

• Package Code: H
• Dimensions: 9.08 mm diameter, 5.33 mm height (excluding leads)
• Pin Configuration:
  • Pin 1: Offset Adjust
  • Pin 2: Input
  • Pin 3: Output
  • Pin 4: V_EE (Negative Supply)
  • Pin 5: Ground (Logic Common)
  • Pin 6: Logic Input
  • Pin 7: V_CC (Positive Supply)
  • Pin 8: Hold Capacitor

8-Pin Plastic DIP (PDIP)

• Package Code: N
• Dimensions: 9.81 mm x 6.35 mm x 3.3 mm
• Pin Configuration: Same as TO-99.

8-Pin SOIC (Surface Mount)

• Package Code: D
• Dimensions: 4.9 mm x 3.9 mm x 1.25 mm
• Pin Configuration: Same as TO-99.

Conclusion

The LF398 sample-and-hold circuit is a high-performance solution for applications demanding precision, speed, and stability. Its BI-FET technology ensures low noise, minimal offset drift, and excellent temperature stability, making it ideal for data acquisition, instrumentation, and control systems. With flexible supply voltage options and multiple package choices, the LF398 can be tailored to a wide range of design requirements.