SLVSDR8B April   2018  – February 2023 TPS62147 , TPS62148

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  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
    6. 7.6 Typical Characteristics
  8. 8 Parameter Measurement Information
    1. 8.1 Schematic
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Precise Enable
      2. 9.3.2 Power Good (PG)
      3. 9.3.3 MODE
      4. 9.3.4 Undervoltage Lockout (UVLO)
      5. 9.3.5 Thermal Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 Pulse Width Modulation (PWM) Operation
      2. 9.4.2 Power Save Mode Operation (PWM/PFM)
      3. 9.4.3 100% Duty-Cycle Operation
      4. 9.4.4 Current Limit And Short Circuit Protection (for TPS62148)
      5. 9.4.5 HICCUP Current Limit And Short Circuit Protection (for TPS62147)
      6. 9.4.6 Soft Start / Tracking (SS/TR)
      7. 9.4.7 Output Discharge Function (TPS62148 only)
      8. 9.4.8 Starting into a Pre-Biased Load
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Programming the Output Voltage
      2. 10.1.2 External Component Selection
      3. 10.1.3 Inductor Selection
      4. 10.1.4 Capacitor Selection
        1. 10.1.4.1 Output Capacitor
        2. 10.1.4.2 Input Capacitor
        3. 10.1.4.3 Soft-Start Capacitor
      5. 10.1.5 Tracking Function
      6. 10.1.6 Output Filter and Loop Stability
    2. 10.2 Typical Applications
      1. 10.2.1 Typical Application with Adjustable Output Voltage
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
        3. 10.2.1.3 Application Curves
    3. 10.3 System Examples
      1. 10.3.1 LED Power Supply
      2. 10.3.2 Powering Multiple Loads
      3. 10.3.3 Voltage Tracking
      4. 10.3.4 Precise Soft-Start Timing
    4. 10.4 Power Supply Recommendations
    5. 10.5 Layout
      1. 10.5.1 Layout Guidelines
      2. 10.5.2 Layout Example
      3. 10.5.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Receiving Notification of Documentation Updates
    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

10.1.3 Inductor Selection

The TPS62147, TPS62148 are designed for a nominal 1-µH inductor if FSEL = high and a 1.5-uH or 2.2-uH inductor if FSEL = low. Larger values can be used to achieve a lower inductor current ripple but they can have a negative impact on efficiency and transient response. Smaller values than 1 µH cause a larger inductor current ripple which causes larger negative inductor current in forced PWM mode at low or no output current. Therefore they are not recommended at large voltages across the inductor as it is the case for high input voltages and low output voltages. With low output current in forced PWM mode this causes a larger negative inductor current peak which can exceed the negative current limit.

The inductor selection is affected by several effects like inductor ripple current, output ripple voltage, PWM-to-PFM transition point and efficiency. In addition, the inductor selected has to be rated for appropriate saturation current and dc resistance (DCR). Equation 11 calculates the maximum inductor current.

Equation 11. GUID-9A8BEC90-932E-4019-BD1C-E0101B7331AE-low.gif
Equation 12. GUID-0F1A9F85-90D0-4FCF-A6CB-1990B039E7C9-low.gif

where

  • IL(max) is the maximum inductor current
  • ΔIL is the Peak to Peak Inductor Ripple Current
  • L(min) is the minimum effective inductor value.

Above equation is valid for FSEL = high. With FSEL = low, the ON-time is doubled from 100 ns to 200 ns so the peak inductor current doubles given the same input voltage and inductor.

Calculating the maximum inductor current using the actual operating conditions gives the minimum saturation current of the inductor needed. A margin of about 20% is recommended to add. A larger inductor value is also useful to get lower ripple current, but increases the transient response time and size as well. The following inductors have been used with the TPS62147, TPS62148 and are recommended for use:

Table 10-2 List of Inductors(1)
TYPEINDUCTANCE [µH]CURRENT [A](2)DIMENSIONS [LxBxH] mmMANUFACTURER(1)
XFL3012-102ME1.0 µH, ±20%2.33 x 3 x 1.3Coilcraft
XFL4015-122ME1.2µH, ±20%4.54 x 4 x 1.6Coilcraft
XFL4020-102ME1.0 µH, ±20%5.44 × 4 x 2.1Coilcraft
XFL4020-152ME1.5 µH, ±20%4.64 x 4 x 2.1Coilcraft
XFL4020-222ME2.2 µH, ±20%3.74 x 4 x 2.1Coilcraft
DFE322512F-2R2M2.2 µH, ±20%2.63.2 x 2.5 x 1.2Murata
DFE322512F-1R5M1.5 µH, ±20%3.03.2 x 2.5 x 1.2Murata
DFE322512F-1R0M1.0 µH, ±20%3.83.2 x 2.5 x 1.2Murata
(2) Lower of IRMS at 40°C rise or ISAT at 30% drop.

The inductor value also determines the load current at which Power Save Mode is entered:

Equation 13. GUID-4A535C30-3C3C-471A-9805-3E1766955FA3-low.gif