SLCA006 June   2025 LM339 , LM393 , LMH7322 , TL331 , TLV1812 , TLV1871 , TLV1872 , TLV3601 , TLV3604

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Output Types
    1. 2.1 Open Collector or Open Drain
      1. 2.1.1 Selectable Open Collector or Open Emitter Output
    2. 2.2 Push-Pull
      1. 2.2.1 Push-Pull with Separate Supplies
    3. 2.3 Differential
      1. 2.3.1 Differential Push Pull
      2. 2.3.2 ECL, RSECL, PECL, RSPECL, and LVPECL
      3. 2.3.3 Low Voltage Differential Signaling
      4. 2.3.4 Current Mode Logic
  6. 3Summary
  7. 4References

2.2.1 Push-Pull with Separate Supplies

The Push-Pull with separate output supplies has the advantage of the floating OC/OE output while providing the advantages of a push-pull output with a defined output swing.

Push-Pull with Separate SuppliesFigure 2-8 Push-Pull with Separate Supplies

A problem arises when the comparator inputs require a wide supply voltage or a split power supply to accept large or bipolar signals. For most push-pull output comparators, this results in an output swing that is equal to the power supplies (such as 0 and 12V or ±5V) and is not compatible with digital logic. This requires external level shifting or clamping to feed digital logic.

This problem is solved with a push-pull output with seporate input and output power supplies, such as the TLV1871/2 shown above. This allows the output swing to be directly set by the output power supply pins (VCCO and VEEO), and the input voltage range set by the input power supplies (VCCI and VEEI).

An example is where the input supplies (VCCI and VEEI) can be a split supply of +12V and -12V to accept bipolar input signals. The output supplies (VCCO and VEEO) can be set to +3.3V and ground, creating a 0 to 3.3V ground referenced output swing compatible with 3.3V digital logic. No level shifting required!

Another advantage is that the input range is not set by the required output swing, which requires attenuation of the input signal. Instead, input supply pins can be powered from a larger supply voltage to accept a direct, or a lesser attenuated input signal, improving accuracy.

The TLV1871/2 (Push-Pull) and TLV3801/2 (LVDS) have separate output power supplies.

Table 2-4 Advantages and Disadvantages of Push-Pull with Separate Supplies Outputs
AdvantagesDisadvantages
  • Output swing set by output supply pins
  • Separate input power supplies allow wider input range or split supplies.
  • Output can sink and source current
  • No Pull-up resistor required - saves power
  • Symmetrical rise and fall times
  • Outputs cannot be tied together