SLVSAX2B September   2011  – June 2020 TPS61170-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Soft Start-up
      2. 7.3.2 Overcurrent Protection
      3. 7.3.3 Undervoltage Lockout
      4. 7.3.4 Thermal Shutdown
      5. 7.3.5 Enable and Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Program Mode
      2. 7.4.2 1-Wire Program Mode
      3. 7.4.3 EasyScale
    5. 7.5 Programming
      1. 7.5.1 Feedback Reference Program Mode Selection
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 12-V to 24-V DC-DC Power Conversion
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Program Output Voltage
          2. 8.2.1.2.2 Maximum Output Current
          3. 8.2.1.2.3 Switch Duty Cycle
          4. 8.2.1.2.4 Inductor Selection
          5. 8.2.1.2.5 Schottky Diode Selection
          6. 8.2.1.2.6 Compensation Capacitor Selection
          7. 8.2.1.2.7 Input and Output Capacitor Selection
        3. 8.2.1.3 Application Curve
      2. 8.2.2 5-V to 12-V DC-DC Power Conversion With Programmable Feedback Reference Voltage
      3. 8.2.3 12-V SEPIC (Buck-Boost) Converter
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.4.1 PWM Program Mode

When the CTRL pin is constantly high, the FB voltage is regulated to 1.229 V typically. However, the CTRL pin allows a PWM signal to lower this regulation voltage. The relationship between the duty cycle and FB voltage is given in Equation 1:

Equation 1. TPS61170-Q1 q1_vfb_lvs789.gif

where

  • Duty = duty cycle of the PWM signal
  • 1.229 V = internal reference voltage

As shown in Figure 11, the IC chops up the internal 1.229-V reference voltage at the duty cycle of the PWM signal. The pulse signal is then filtered by an internal low-pass filter. The output of the filter is connected to the error amplifier as the reference voltage for the FB pin regulation. The regulation voltage is independent of the PWM logic voltage level which often has large variations.

For optimum performance, use the PWM mode in the range of 5 kHz to 100 kHz. The requirement of minimum frequency comes from the EasyScale detection delay and detection time specification for the mode selection. The device can mistakenly enter 1-wire mode if the PWM signal frequency is less than 5 kHz. Because there is an internal fixed ON-time error of 40 nS, the FB voltage absolute value will be different than expected when the PWM frequency is above 100 kHz. For example, the additional duty cycle of 3.2% due to the ON-time error increases the FB voltage when using an 800-kHz PWM signal. A compromise between PWM frequency and FB voltage accuracy extends the frequency range. Adding an external RC filter to the pin serves no purpose.

TPS61170-Q1 fb_v_bd_lvs789.gifFigure 11. Block Diagram of Programmable FB Voltage Using PWM Signal