SNVSCF0 October   2024 LM65680-Q1

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Descriptions
      1. 7.3.1  Output Voltage Selection
      2. 7.3.2  EN Pin and Use as VIN UVLO
      3. 7.3.3  Device Configuration
      4. 7.3.4  Single-Output Dual-Phase Operation
      5. 7.3.5  Mode Selection
        1. 7.3.5.1 MODE/SYNC Pin Uses for Synchronization
        2. 7.3.5.2 Clock Locking
      6. 7.3.6  Adjustable Switching Frequency
      7. 7.3.7  Dual Random Spread Spectrum (DRSS)
      8. 7.3.8  Internal LDO, VCC UVLO, and BIAS Input
      9. 7.3.9  Bootstrap Voltage (BST Pin)
      10. 7.3.10 Soft Start and Recovery From Dropout
      11. 7.3.11 Safety Features
        1. 7.3.11.1 Power-Good Monitor
        2. 7.3.11.2 Overcurrent and Short-Circuit Protection
        3. 7.3.11.3 Hiccup
        4. 7.3.11.4 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
        1. 7.4.2.1 Peak Current Mode Operation
        2. 7.4.2.2 Auto Mode Operation
          1. 7.4.2.2.1 Diode Emulation
        3. 7.4.2.3 FPWM Mode Operation
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Power Train Components
        1. 8.1.1.1 Buck Inductor
        2. 8.1.1.2 Output Capacitors
        3. 8.1.1.3 Input Capacitors
        4. 8.1.1.4 EMI Filter
      2. 8.1.2 Error Amplifier and Compensation
      3. 8.1.3 Maximum Ambient Temperature
        1. 8.1.3.1 Derating Curves
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Inductor Selection
        2. 8.2.2.2 Output Capacitors
        3. 8.2.2.3 Feed-forward Capacitor (CFF)
        4. 8.2.2.4 Input Capacitor Selection
        5. 8.2.2.5 Choosing the Switching Frequency
        6. 8.2.2.6 Setting the Output Voltage
        7. 8.2.2.7 Compensation Components
        8. 8.2.2.8 CBST
        9. 8.2.2.9 External UVLO
      3. 8.2.3 Application Curves
    3. 8.3 Best Design Practices
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 Ground and Thermal Considerations
      2. 8.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Development Support
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
        1. 9.2.1.1 PCB Layout Resources
        2. 9.2.1.2 Thermal Design Resources
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape and Reel Information

Package Options

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

7.3.7 Dual Random Spread Spectrum (DRSS)

Table 7-3 Errata 1
Observation Root Cause Recommendation
DRSS pin functionality is different between the prototype device and the final device. Definition change based on the prototype results. See Table 7-5 and Table 7-4. If DRSS disabled is a desired setting, connect a 49.9kΩ to GND on the DRSS pin to have the same device behavior when transitioning from the prototype device to the final device.
If DRSS enabled is a desired setting, tie the DRSS pin to the VCC pin to have a similar device behavior when transitioning from the prototype device to the final device.

The LM656x0-Q1 provides a Dual Random Spread Spectrum (DRSS) function, which reduces EMI of the power supply over a wide-frequency range. The DRSS function combines a low-frequency triangular modulation profile with a high-frequency cycle-by-cycle pseudo-random modulation profile. The low frequency triangular modulation improves performance in the lower radio frequency bands, while the high frequency random modulation improves performance in the higher radio frequency bands.

As shown in Table 7-5, the two low frequency triangular modulation profiles are pin-selectable on the prototype device. The standard low-frequency modulation profile spreads the switching frequency by ±5% with a 12kHz modulation frequency while the wide low frequency modulation profile spreads the switching frequency by ±10% with a 6kHz modulation frequency. The slew rate control is always enabled on the prototype device.

As shown in Table 7-4, the final LM656x0-Q1 device provides a switch-node waveform shaping feature that, when enabled, adjusts the switch-node waveform rising transition for reduced ringing and overshoot. The final device provides the wide low frequency modulation profile which spreads the switching frequency by ±10% with a 6kHz modulation frequency.

Table 7-4 DRSS and Slew-Rate Control - Final Device
DRSS / MODECOMM Pin DRSS Slew Rate Control
Short to VCC(1) Enabled, ±10%, 6kHz Enabled
Float Enabled, ±10%, 6kHz Enabled
150kΩ to GND Enabled, ±10%, 6kHz Disabled
49.9kΩ to GND Disabled Enabled
Short to GND(1) Disabled Disabled

(1) This configuration is only valid for single-phase operation.

Table 7-5 DRSS and Slew-Rate Control - Prototype Device
DRSS / MODECOMM Pin DRSS Slew Rate Control
Short to VCC(1) Enabled, ±5%, 12kHz Enabled
Float Enabled, ±5%, 12kHz Enabled
150kΩ to GND Enabled, ±10%, 6kHz Enabled
49.9kΩ to GND Disabled Enabled
Short to GND(1) Disabled Enabled

Spread spectrum works by converting a narrowband signal into a wideband signal, which spreads the energy over multiple frequencies. Industry standards require different spectrum analyzer resolution bandwidth (RBW) settings for different frequency bands. The RBW has an impact on the spread spectrum performance. For example, the CISPR-25 requires 9kHz RBW for the 150kHz to 30MHz frequency band. For frequencies greater than 30MHz, the required RBW is 120kHz. DRSS is able to simultaneously improve the EMI performance in the high and low RBWs with the low frequency triangular modulation and high-frequency cycle-by-cycle pseudo-random modulation. In the low-frequency band (150kHz -30MHz), the DRSS function can reduce the conducted emissions by as much as 15dBμV, and in the high-frequency band (30MHz - 108MHz) by as much as 5dBμV. The DRSS function is disabled when an external clock is applied to the MODE/SYNC pin.

LM65680-Q1 Dual Random Spread Spectrum Implementation Figure 7-7 Dual Random Spread Spectrum Implementation