SNOAA35D April   2023  – December 2023 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.   Application Design Guidelines for LM339, LM393, TL331 Family Comparators Including the New B-versions
  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
    1. 2.1 PCN to Change Classic Die to a New Die Design
      1. 2.1.1 Determine Die Used for Single TL331 and Dual LM293, LM393, and LM2903
      2. 2.1.2 Determine Die Used for Quad LM139, LM239, LM339, and LM2901
      3. 2.1.3 Device PCN Summary
    2. 2.2 Changes to Package Top Markings
  6. 3 Input Considerations
    1. 3.1  Input Stage Schematic – The Classic LM339 Family
    2. 3.2  Input Stage Schematic - New B Devices
    3. 3.3  Differences Between the Classic and B Die Devices
    4. 3.4  Input Voltage Range
    5. 3.5  Input Voltage Range vs. Common Mode Voltage Range
    6. 3.6  Reason for Input Range Headroom Limitation
    7. 3.7  Input Voltage Range Feature
      1. 3.7.1 Both Inputs Above Input Range Behavior
    8. 3.8  Negative Input Voltages
      1. 3.8.1 Maximum Input Current
      2. 3.8.2 Phase Reversal or Inversion
      3. 3.8.3 Protecting Inputs from Negative Voltages
        1. 3.8.3.1 Simple Resistor and Diode Clamp
        2. 3.8.3.2 Voltage Divider with Clamp
          1. 3.8.3.2.1 Split Voltage Divider with Clamp
    9. 3.9  Power-Up Behavior
    10. 3.10 Capacitors and Hysteresis
    11. 3.11 Output to Input Cross-Talk
  7. 4 Output Stage Considerations
    1. 4.1 Output VOL and IOL
    2. 4.2 Pull-Up Resistor Selection
    3. 4.3 Short Circuit Sinking Current
    4. 4.4 Pulling Output Up Above VCC
    5. 4.5 Negative Voltages Applied to Output
    6. 4.6 Adding Large Filter Capacitors To Output
  8. 5 Power Supply Considerations
    1. 5.1 Supply Bypassing
      1. 5.1.1 Low VCC Guidance
      2. 5.1.2 Split Supply use
  9. 6 General Comparator Usage
    1. 6.1 Unused Comparator Connections
      1. 6.1.1 Do Not Connect Inputs Directly to Ground
      2. 6.1.2 Unused Comparator Input Connections
      3. 6.1.3 Leave Outputs Floating
      4. 6.1.4 Prototyping
  10. 7 PSPICE and TINA TI Models
  11. 8 Conclusion
  12. 9 Related Documentation
    1. 9.1 Related Links
  13. 10Revision History

3.8 Negative Input Voltages

The LM339 family does not like negative input voltage on any I/O pins, and this is mentioned several times in the data sheets. The LM339 family is built using a junction-isolated die process, wherein all the individual on-die devices are electrically separated from the substrate by a reversed PN junction. This can be thought of as a reversed diode under every circuit node to a common die substrate. These junctions are commonly referred to as the Body Diode or Substrate Diode. For this junction isolation to function properly, the substrate must be maintained at the most negative potential. The die substrate is electrically tied to the GND pin, and thus the GND pin must be at the most negative circuit potential for proper operation.

If any pin is brought more negative than the GND pin (substrate), these various substrate junctions and parasitic transistors will start to conduct. Reverse currents now flow in paths that were not designed for current flow and this can cause parasitic devices to appear, leading to malfunctions, or worse, latch-up if the input current is high enough.

Figure 3-5 shows the input current of the input pin with a +5 V supply, sweeping the input from -1 V to +7 V. Noticeable nanoamp currents will start to flow when the input is at -0.3 V, and will increase to several tens of milliamps as the diodes start to conduct.

GUID-34B03344-3769-4768-B95D-267481C6B45C-low.gifFigure 3-5 Classic Input Pin I/V Curve with 5 V Supply

Section A shows the substrate diode knee starting to conduct at -400mV, with the subsequent increase in reverse current as the negative input voltage is increased.

Section B shows the normal operating Input Bias Current from 0 V up to 3.5 V. The gray zone can be seen as the current heads up towards zero after 4 V.

Section C shows the near zero (picoamp) bias currents as the input devices are reversed and cut off and no base current flows.

When the LM339 Family was originally designed in the early 70's, Electrostatic Discharge (ESD) damage was not as prevalent due to the high breakdown voltages of these older processes, so dedicated ESD protection structures were not included in the LM339 family. Without dedicated ESD structures, there is not a defined current path for reverse currents back to the GND pin. The new B devices do have dedicated ESD structures added to the inputs and output pins for more robust ESD performance.