SNOAA35F April   2019  – December 2024 LM2901 , LM2901B , LM2901B-Q1 , LM2903 , LM2903-Q1 , LM2903B , LM2903B-Q1 , LM339 , LM339-N , LM393 , LM393-N , LM393B , LM397 , TL331 , TL331-Q1 , TL331B

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Devices Covered in Application Note
    1. 1.1 Base Part Numbers
    2. 1.2 Input Voltage Offset Grades
    3. 1.3 Maximum Supply Voltage
    4. 1.4 High Reliability Options
  5. 2 The New TL331B, TL391B, LM339B, LM393B, LM2901B and LM2903B B Versions
  6. 3 PCN's to Change Classic Die to a New Die Design
    1. 3.1 PCN #1 for Single and Dual (TL331 and LMx93/LM2903)
    2. 3.2 PCN #2 for Single and Dual (TL331 and LMx93/LM2903)
    3. 3.3 PCN For Quad (LMx39, LM2901)
    4. 3.4 PCN for B Devices (including -Q1's)
    5. 3.5 Device PCN Summary
    6. 3.6 Determining Die Version Used
      1. 3.6.1 Determine Die Used for Single TL331 and Dual LM293, LM393, and LM2903 - PCN #1 (Ji3)
      2. 3.6.2 Determine Die Used for Single TL331 and Dual LM293, LM393, and LM2903 - PCN #2 (TiB)
      3. 3.6.3 Determine Die Used for Quad LM139, LM239, LM339, and LM2901
      4. 3.6.4 Determine Die Used for Post-PCN B Devices
  7. 4 Changes to Package Top Markings
  8. 5 Roughened Leadframe Finish
  9. 6 Input Considerations
    1. 6.1  Input Stage Schematic – The Classic LM339 Family
    2. 6.2  Input Stage Schematic - New "B" and TiB Devices
    3. 6.3  Differences Between the Classic, "B" and Tib Die Devices
    4. 6.4  Input Voltage Range
    5. 6.5  Input Voltage Range vs. Common Mode Voltage Range
    6. 6.6  Reason for Input Range Headroom Limitation
    7. 6.7  Input Voltage Range Feature
    8. 6.8  Both Inputs Above Input Range Behavior
    9. 6.9  Negative Input Voltages
      1. 6.9.1 Maximum Input Current
      2. 6.9.2 Phase Reversal or Inversion
      3. 6.9.3 Protecting Inputs from Negative Voltages
        1. 6.9.3.1 Simple Resistor and Diode Clamp
        2. 6.9.3.2 Voltage Divider with Clamp
          1. 6.9.3.2.1 Split Voltage Divider with Clamp
    10. 6.10 Power-Up Behavior
    11. 6.11 Capacitors and Hysteresis
    12. 6.12 Output to Input Cross-Talk
  10. 7 Output Stage Considerations
    1. 7.1 Output VOL and IOL
    2. 7.2 Pull-Up Resistor Selection
    3. 7.3 Short Circuit Sinking Current
    4. 7.4 Pulling Output Up Above Vcc
    5. 7.5 Negative Voltages Applied to Output
    6. 7.6 Adding Large Filter Capacitors To Output
  11. 8 Power Supply Considerations
    1. 8.1 Supply Bypassing
      1. 8.1.1 Low VCC Guidance
      2. 8.1.2 Split Supply use
  12. 9 General Comparator Usage
    1. 9.1 Unused Comparator Connections
      1. 9.1.1 Do Not Connect Inputs Directly to Ground
      2. 9.1.2 Unused Comparator Input Connections
      3. 9.1.3 Leave Outputs Floating
      4. 9.1.4 Prototyping
  13. 10PSpice and TINA TI Models
  14. 11Conclusion
  15. 12Related Documentation
    1. 12.1 Related Links
  16. 13Revision History
6.9.3.2.1 Split Voltage Divider with Clamp

To improve upon the voltage divider described above, the upper voltage divider resistor can be split and apply the clamp diode at the higher tap voltage, as shown in Figure 6-9. The idea is that two bottom resistors (R1B and R2) further divide down the diode clamped voltage to bring the clamped voltage to a safe level at the input.

Split Voltage Divider Negative Voltage ProtectionFigure 6-9 Split Voltage Divider Negative Voltage Protection

The upper common voltage divider resistor R1 is split into two resistors, R1A and R1B, providing a higher voltage tap sample point for the clamp diode. The clamp diode maintains that the tap voltage does not exceed -600mV as the input voltage moves further negative.

With a positive input voltage, the diode is reverse biased and does not conduct, effectively removing the diode from the circuit (except for some small leakage current). The voltage divider R1A + R1B combine create the upper R1 voltage divider resistor against R2.

When the input voltage is negative, the diode clamps the node between R1A and R1B to -600mV. R1B and R2 then create a 3x voltage divider, which results in a safer -200mV on the input. Note that R1A now has the full input voltage across the resistor and needs to be sized appropriately.

The design procedure is fairly simple. The full divider is calculated as a normal two resistor voltage divider, deriving the needed R1 and R2 values. The desired secondary negative R1B divider is then calculated from the existing R2 and required portion of R1.