SNOSBI3B July 2000  – November 2015 LF198-N , LF298 , LF398-N


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1Absolute Maximum Ratings
    2. 6.2Recommended Operating Conditions
    3. 6.3Thermal Information
    4. 6.4Electrical Characteristics, LF198-N and LF298
    5. 6.5Electrical Characteristics, LF398-N
    6. 6.6Typical Characteristics
  7. Parameter Measurement Information
    1. 7.1TTL and CMOS 3 V ≤ VLOGIC (Hi State) ≤ 7 V
    2. 7.2CMOS 7 V ≤ VLOGIC (Hi State) ≤ 15 V
    3. 7.3Operational Amplifier Drive
  8. Detailed Description
    1. 8.1Overview
    2. 8.2Functional Block Diagram
    3. 8.3Feature Description
    4. 8.4Device Functional Modes
  9. Application and Implementation
    1. 9.1Application Information
      1. 9.1.1Hold Capacitor
      2. 9.1.2DC and AC Zeroing
      3. 9.1.3Logic Rise Time
      4. 9.1.4Sampling Dynamic Signals
      5. 9.1.5Digital Feedthrough
    2. 9.2Typical Applications
      1. 9.2.1 X1000 Sample and Hold
        1. Requirements
        2. Design Procedure
        3. Curves
      2. 9.2.2 Sample and Difference Circuit
      3. 9.2.3 Ramp Generator With Variable Reset Level
      4. 9.2.4 Integrator With Programmable Reset Level
      5. 9.2.5 Output Holds at Average of Sampled Input
      6. 9.2.6 Increased Slew Current
      7. 9.2.7 Reset Stabilized Amplifier
      8. 9.2.8 Fast Acquisition, Low Droop Sample and Hold
      9. 9.2.9 Synchronous Correlator for Recovering Signals Below Noise Level
      10. 9.2.102-Channel Switch
      11. 9.2.11DC and AC Zeroing
      12. 9.2.12Staircase Generator
      13. 9.2.13Differential Hold
      14. 9.2.14Capacitor Hysteresis Compensation
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1Layout Guidelines
    2. 11.2Layout Example
  12. 12Device and Documentation Support
    1. 12.1Device Support
      1. 12.1.1Device Nomenclature
    2. 12.2Related Links
    3. 12.3Community Resources
    4. 12.4Trademarks
    5. 12.5Electrostatic Discharge Caution
    6. 12.6Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Orderable Information

1 Features

  • Operates from ±5-V to ±18-V Supplies
  • Less than 10-μs Acquisition Time
  • Logic Input Compatible With TTL, PMOS, CMOS
  • 0.5-mV Typical Hold Step at Ch = 0.01 µF
  • Low Input Offset
  • 0.002% Gain Accuracy
  • Low Output Noise in Hold Mode
  • Input Characteristics Do Not Change During Hold Mode
  • High Supply Rejection Ratio in Sample or Hold
  • Wide Bandwidth
  • Space Qualified, JM38510

2 Applications

  • Ramp Generators With Variable Reset Level
  • Integrators With Programmable Reset Level
  • Synchronous Correlators
  • 2-Channel Switches
  • DC and AC Zeroing
  • Staircase Generators

3 Description

The LF298 and LFx98x devices are monolithic sample-and-hold circuits that use BI-FET technology to obtain ultrahigh DC accuracy with fast acquisition of signal and low droop rate. Operating as a unity-gain follower, DC gain accuracy is 0.002% typical and acquisition time is as low as 6 µs to 0.01%. A bipolar input stage is used to achieve low offset voltage and wide bandwidth. Input offset adjust is accomplished with a single pin and does not degrade input offset drift. The wide bandwidth allows the LF198-N to be included inside the feedback loop of 1-MHz operational amplifiers without having stability problems. Input impedance of 1010 Ω allows high-source impedances to be used without degrading accuracy.

P-channel junction FETs are combined with bipolar devices in the output amplifier to give droop rates as low as 5 mV/min with a 1-µF hold capacitor. The JFETs have much lower noise than MOS devices used in previous designs and do not exhibit high temperature instabilities. The overall design ensures no feedthrough from input to output in the hold mode, even for input signals equal to the supply voltages.

Logic inputs on the LF198-N are fully differential with low input current, allowing for direct connection to TTL, PMOS, and CMOS. Differential threshold is
1.4 V. The LF198-N will operate from ±5-V to ±18-V supplies.

An A version is available with tightened electrical specifications.

Device Information(1)

LF298, LFx98xSOIC (14)8.65 mm × 3.91 mm
TO-99 (8)9.08 mm × 9.08 mm
PDIP (8)9.81 mm × 6.35 mm
  1. For all available packages, see the orderable addendum at the end of the data sheet.

Typical Connection

LF198-N LF298 LF398-N LF198A-N LF398A-N typ_connection_snosbi3.gif

Acquisition Time

LF198-N LF298 LF398-N LF198A-N LF398A-N acquisition_time_snosbi3_a.gif