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

10 Power Supply Recommendations

The LM53600-Q1 and LM53601-Q1 devices are designed for automotive direct off battery applications needing minimal protection. Protection recommended includes reverse battery protection and EMI/ESD filtering. The LM53600-Q1 and LM53601-Q1 devices are able to continue regulating during load dump with peak voltage less than 42 V, double battery (jump start) conditions down to input voltage as low as VDROP above the selected output voltage. In addition, the LM53600-Q1 and LM53601-Q1 devices continue to operate though may be out of regulation with input voltage as low as 3.8 V. This allows the LM53600-Q1 and LM53601-Q1 devices to operate through cranking in all but the most demanding systems.

If the regulator is connected to the input supply through long wires or PCB traces, special care is required to achieve good performance. The parasitic inductance and resistance of the input cables can have an adverse effect on the operation of the regulator. The parasitic inductance, in combination with the low ESR ceramic input capacitors, can form an under-damped resonant circuit. This circuit may cause over-voltage transients at the VIN pin, each time the input supply is cycled on and off. The parasitic resistance will cause the voltage at the VIN pin to dip when the load on the regulator is switched on, or exhibits a transient. If the regulator is operating close to the minimum input voltage, this dip may cause the device to shutdown and/or reset. The best way to solve these kinds of issues is to reduce the distance from the input supply to the regulator and/or use an aluminum or tantalum input capacitor in parallel with the ceramics. The moderate ESR of these types of capacitors will help to damp the input resonant circuit and reduce any voltage overshoots. A value in the range of 20 µF to 100 µF is usually sufficient to provide input damping and help to hold the input voltage steady during large load transients.

Sometimes, for other system considerations, an input filter is used in front of the regulator. This can lead to instability, as well as some of the effects mentioned above, unless it is designed carefully. The Simple Success with Conducted EMI for DC–DC Converters User's Guide (SNVA489) provides helpful suggestions when designing an input filter for any switching regulator

In some cases, a Transient Voltage Suppressor (TVS) is used on the input of regulators. One class of this device has a snap-back V-I characteristic (thyristor type). The use of a device with this type of characteristic is not recommend. When the TVS fires, the clamping voltage drops to a very low value. If this holding voltage is less than the output voltage of the regulator, the output capacitors will be discharged through the regulator back to the input. This uncontrolled current flow could damage the regulator.