SLVS052J April   1988  – September 2026 TL594

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Switching Characteristics
    7. 5.7 Typical Characteristics
  7. 6 Parameter Measurement Information
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 5V Reference Regulator
      2. 7.3.2 Undervoltage Lockout
      3. 7.3.3 Oscillator
      4. 7.3.4 Dead-Time Control
      5. 7.3.5 Comparator
      6. 7.3.6 Pulse-Width Modulation (PWM)
      7. 7.3.7 Error Amplifiers
      8. 7.3.8 Output-Control Input
      9. 7.3.9 Output Transistors
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Power Source
        2. 8.2.2.2 Control Circuits
          1. 8.2.2.2.1 Oscillator
          2. 8.2.2.2.2 Error Amplifier
          3. 8.2.2.2.3 Current-Limiting Amplifier
          4. 8.2.2.2.4 Soft Start
          5. 8.2.2.2.5 Setting the Dead Time
        3. 8.2.2.3 Inductor Calculations
        4. 8.2.2.4 Output Capacitance Calculations
        5. 8.2.2.5 Transistor Power-Switch Calculations
      3. 8.2.3 Application Curve
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Feedback Traces
        2. 8.4.1.2 Input or Output Capacitors
        3. 8.4.1.3 Compensation Components
        4. 8.4.1.4 Traces and Ground Planes
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

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8.2.2.5 Transistor Power-Switch Calculations

The constructions of the transistor power switch is with an NTE153 pnp drive transistor and an NTE331 npn output transistor. These two power devices connect in a pnp hybrid Darlington circuit configuration (see Figure 8-8).

TL594 Power-Switch SectionFigure 8-8 Power-Switch Section

Saturate the hybrid Darlington circuit at a maximum output current of IO + ΔIL/2, or 10.8 A. The Darlington hFE at 10.8A must be high enough not to exceed the 250mA maximum output collector current of the TL594. Based on published NTE153 and NTE331 specifications, calculate the required power-switch minimum drive using Equation 21 through Equation 23, resulting in 144mA.

Equation 21. h F E Q 1   a t   I C   o f   3 A = 1 5
Equation 22. h F E Q 2   a t   I C   o f   10.0 A = 5
Equation 23. i B ≥ I O + I L 2 h F E Q 2 × h F E Q 1 ≥ 144 m A

Use Equation 24 to calculate the value of R10.

Equation 24. R 10 ≤ V I - V B E Q 1 + V C E T L 494 i B = 32 - 1.5 + 0.7 0.144 R 10 ≤ 207 Ω

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

The power supply described demonstrates the flexibility of the TL594 PWM control circuit. This power-supply design demonstrates many of the power-supply control methods the TL594 provides, as well as the versatility of the control circuit.