SNVSCQ8B November   2025  – July 2026 LM654A5-Q1 , LM654B0-Q1

PRODMIX  

  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
    6. 6.6 Typical 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  Mode Selection
        1. 7.3.4.1 MODE/SYNC Pin Uses for Synchronization
        2. 7.3.4.2 Clock Locking
      5. 7.3.5  Adjustable Switching Frequency and Phase Shift
      6. 7.3.6  Dual Random Spread Spectrum (DRSS)
      7. 7.3.7  Internal LDO, VCC UVLO, and BIAS Input
      8. 7.3.8  Bootstrap Voltage (BST Pin)
      9. 7.3.9  Soft Start and Recovery From Dropout
      10. 7.3.10 Safety Features
        1. 7.3.10.1 Power-Good Monitor
        2. 7.3.10.2 Overcurrent and Short-Circuit Protection
        3. 7.3.10.3 Hiccup
        4. 7.3.10.4 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
    2. 8.2 Typical Application
      1. 8.2.1 Design Example Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Choosing the Switching Frequency
        2. 8.2.2.2 Inductor Selection
        3. 8.2.2.3 Output Capacitors
        4. 8.2.2.4 Input Capacitor Selection
        5. 8.2.2.5 Setting the Output Voltage
        6. 8.2.2.6 Compensation Components
        7. 8.2.2.7 Feed-forward Capacitor (CFF)
        8. 8.2.2.8 Maximum Ambient Temperature
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    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

7.3.10.2 Overcurrent and Short-Circuit Protection

The LM654xx-Q1 is protected from overcurrent conditions by cycle-by-cycle current limiting on both the high-side and the low-side MOSFETs.

High-side MOSFET overcurrent protection is implemented by the nature of the peak current mode control. The high-side switch current is sensed when the high-side FET is turned on after a short blanking time. The high-side switch current is compared to the minimum of a fixed current set-point, or the output of the voltage regulation loop minus slope compensation, every switching cycle. Because of this, the high-side peak current limit drops slightly with increasing switch duty cycle. See Figure 7-8 for typical variations of the high side current limit with duty cycle.

LM654A5-Q1 LM654B0-Q1 High Side Current Limit vs Duty Cycle Figure 7-8 High Side Current Limit vs Duty Cycle

When the low-side switch is turned on, the current is also sensed. Like the high-side MOSFET, the low-side MOSFET turn-off is commanded by the voltage control loop. For the low-side FET, turn-off is prevented if the low-side current limit is exceeded, even if the oscillator normally starts a new switching cycle; see the Electrical Characteristics for values. If the low-side current limit is exceeded, the low-side MOSFET stays on and the high-side switch is not turned on. The low-side switch is turned off after the low-side current falls below the limit. The high-side switch is turned on again as long as at least one clock period has passed since the last time the high-side device has turned on.

LM654A5-Q1 LM654B0-Q1 Current Limit Waveforms Figure 7-9 Current Limit Waveforms

The maximum output current is therefore controlled by both the high-side and low-side peak current limit. Use Equation 6 to provide an approximate value of maximum load current. With severe overloads or short circuit on the output, the device goes into hiccup current limit mode. In this case, the output current "folds-back" and falls to a very low level to prevent excessive device temperature. See also Section 7.3.10.3.

Equation 6. I O U T - M A X ≅ I H S - L I M + I L S - L I M 2

The above considers the effect of the current limits on the maximum available output current. However, the maximum output current can be limited by thermal considerations. This possibility can be checked by referring to Section 8.2.2.8. In any case, paralleling two or more LM654xx regulators can mitigate issues with current limit and thermal constraints.

After the overload condition is removed, the device recovers as though in soft start; see Electrical Characteristics. Note that hiccup can be triggered if output voltage drops below approximately 0.4 times the intended output voltage.