SNAS660D June   2015  – May 2021 LM53600-Q1 , LM53601-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison
  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 System Characteristics
    7. 7.7 Timing Requirements
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Control Scheme
      2. 8.3.2 Soft-Start Function
      3. 8.3.3 Current Limit
      4. 8.3.4 Hiccup Mode
      5. 8.3.5 RESET Function
      6. 8.3.6 Forced PWM Operation
      7. 8.3.7 Auto Mode Operation and IQ_VIN
      8. 8.3.8 SYNC Operation
      9. 8.3.9 Spread Spectrum
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown
      2. 8.4.2 FPWM Operation
      3. 8.4.3 Auto Mode Operation
  9. 9 Applications and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Off-Battery 5-V, 1-A Output Automotive Converter with Spread Spectrum
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Inductor Selection
          2. 9.2.1.2.2 Output Capacitor Selection
          3. 9.2.1.2.3 Input Capacitor Selection
          4. 9.2.1.2.4 FB Voltage Divider for Adjustable Versions
          5. 9.2.1.2.5 RPU - RESET Pull Up Resistor
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Off-Battery 3.3 V, 1 A Output Automotive Converter with Spread Spectrum
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Design Procedure
        3. 9.2.2.3 Application Curves
    3. 9.3 Do's and Don't's
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Ground and Thermal Plane Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.3.7 Auto Mode Operation and IQ_VIN

If SYNC/MODE is held low for a period greater than a few microseconds, the LM53600-Q1 and LM53601-Q1 devices will enable automatic power saving light load operation and diode emulation. In this mode, if peak current needed to regulate output voltage drops below a selected value, the clock of the LM53600-Q1 or LM53601-Q1 device slows to maintain regulation. The gain of this clock slowing circuit is low to maintain stability. Output voltage with no load is approximately 1% higher than with a load high enough to allow full frequency operation.

IQ_VIN is the current consumed by a converter utilizing a LM53600-Q1 or LM53601-Q1 device while regulating without a load. While operating without a load, the LM53600-Q1 or LM53601-Q1 is only powering itself. The LM53600-Q1 and LM53601-Q1 device draws power from two sources, its VIN pin, IQ, and either its FB pin for fixed versions or BIAS pin for adjustable versions, IB. Since BIAS or FB is connected to the circuit’s output, the power consumed is converted from input power with an effective efficiency, ηeff, of ~80%. Here, effective efficiency is the added input power needed when lightly loading the converter of the LM53600-Q1 and LM53601-Q1 devices is divided by the corresponding additional load. This allows unloaded current to be calculated as follows:

Equation 1. GUID-5DECA310-AA5C-4A4F-AB68-39DA26C8649A-low.gif

where

  • IQ_VIN is the current consumed by the Buck converter utilizing the LM53600-Q1 or LM53601-Q1 while unloaded.
  • IQ is the current drawn by the LM53600-Q1 or LM53601-Q1 from its VIN terminal. See IQ in section 7.6.
  • IEN is current drawn by the LM53600-Q1 or LM53601-Q1 from its EN terminal. Include this current if EN is connected to VIN. See IEN in section 7.6. Note that this current drops to a very low value if connected to a voltage less than 5 V.
  • IB is bias/feedback current drawn by the LM53600-Q1 or LM53601-Q1 while the Buck converter utilizing it is unloaded. See IB in section 7.6.
  • Idiv is the current drawn by the feedback voltage divider used to set output voltage for adjustable devices. This current is zero for fixed output voltage devices.
  • ηeff is the light load efficiency of the Buck converter with IQ_VIN removed from the Buck converter’s input current. 0.8 is a conservative value that can be used under normal operating conditions

Note that the EN pin consumes a few microamperes when tied to high; see IEN. Add IEN to IQ as shown in the above equation if EN is tied to VIN. If EN is tied to a voltage less than 5 V, virtually no current is consumed allowing EN to be used as a UVL once a voltage divider is added.