SLVS074I January   1983  – July 2022 TL494

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Block Diagram
  5. 5 Revision History
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics, Reference Section
    6. 7.6  Electrical Characteristics, Oscillator Section
    7. 7.7  Electrical Characteristics, Error-Amplifier Section
    8. 7.8  Electrical Characteristics, Output Section
    9. 7.9  Electrical Characteristics, Dead-Time Control Section
    10. 7.10 Electrical Characteristics, PWM Comparator Section
    11. 7.11 Electrical Characteristics, Total Device
    12. 7.12 Switching Characteristics
    13. 7.13 Typical Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 5-V Reference Regulator
      2. 9.3.2 Oscillator
      3. 9.3.3 Dead-time Control
      4. 9.3.4 Comparator
      5. 9.3.5 Pulse-Width Modulation (PWM)
      6. 9.3.6 Error Amplifiers
      7. 9.3.7 Output-Control Input
      8. 9.3.8 Output Transistors
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Input Power Source
        2. 10.2.2.2 Control Circuits
          1. 10.2.2.2.1 Oscillator
          2. 10.2.2.2.2 Error Amplifier
          3. 10.2.2.2.3 Current-Limiting Amplifier
          4. 10.2.2.2.4 Soft Start and Dead Time
        3. 10.2.2.3 Inductor Calculations
        4. 10.2.2.4 Output Capacitance Calculations
        5. 10.2.2.5 Transistor Power-Switch Calculations
      3. 10.2.3 Application Curves for Output Characteristics
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Feedback Traces
      2. 12.1.2 Input/Output Capacitors
      3. 12.1.3 Compensation Components
      4. 12.1.4 Traces and Ground Planes
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Trademarks
    2. 13.2 Electrostatic Discharge Caution
    3. 13.3 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

10.2.2.5 Transistor Power-Switch Calculations

The transistor power switch was constructed with an NTE153 pnp drive transistor and an NTE331 npn output transistor. These two power devices were connected in a pnp hybrid Darlington circuit configuration (see Figure 10-7).

GUID-9D2F4858-4361-401F-A1D2-A95D3F69CBD1-low.gifFigure 10-7 Power-Switch Section

The hybrid Darlington circuit must be saturated at a maximum output current of IO + ΔIL/2 or 10.8 A. The Darlington hFE at 10.8 A must be high enough not to exceed the 250-mA maximum output collector current of the TL494. Based on published NTE153 and NTE331 specifications, the required power-switch minimum drive was calculated by Equation 16 through Equation 18 to be 144 mA:

Equation 16. GUID-4193C51B-057D-4A10-AFD6-0D726BE5B2CB-low.gif
Equation 17. GUID-3210A025-72D7-4B8D-BA33-53EC81E665E9-low.gif
Equation 18. GUID-C9ABCBF3-A440-4DB0-BF2B-E1EE18EAB53B-low.gif

The value of R10 was calculated by:

Equation 19. GUID-0F7F10C5-BF92-4F3C-BA16-8A0E9B8ACDC3-low.gif

Based on these calculations, the nearest standard resistor value of 220 Ω was selected for R10. Resistors R11 and R12 permit the discharge of carriers in switching transistors when they are turned off.

The power supply described demonstrates the flexibility of the TL494 PWM control circuit. This power-supply design demonstrates many of the power-supply control methods provided by the TL494, as well as the versatility of the control circuit.