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 Push-Pull

A Push-Pull (also called Totem-Pole) output consists of both a positive and negative output devices, such that the output can both sink and source current. Since the output can source current, a pull-up resistor is no longer required. Most commonly, the High and Low output voltages are equal to the comparator V+ and V- power supplies.

Push Pull Output StageFigure 2-7 Push Pull Output Stage

High speed devices (<100ns) primarily use Push Pull outputs because symmetrical rise and fall times are required for the fast edges. The rise time is no longer reliant on the pull-up resistor and load capacitance as the push-pull output can now charge and discharge the load capacitance directly, resulting in faster, straighter pulse edges.

Push-Pull outputs are also used for micro and nanopower devices and designs to eliminate wasting power in the pull-up resistor.

A list of Push-Pull output devices is shown in Table 3-1.

Table 2-3 Advantages and Disadvantages of Push-Pull Outputs
Advantages

Disadvantages

  • Output can sink and source current
  • No Pull-up resistor required - saves power
  • Symmetrical rise and fall times
  • No extra current when output high or low.
  • Outputs cannot be tied together
  • Output votlage swing is the same as the supply voltage