SNVSB70F May   2019  – June 2021 LM61460-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Characteristics
    7. 8.7 Systems Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  EN/SYNC Uses for Enable and VIN UVLO
      2. 9.3.2  EN/SYNC Pin Uses for Synchronization
      3. 9.3.3  Clock Locking
      4. 9.3.4  Adjustable Switching Frequency
      5. 9.3.5  PGOOD Output Operation
      6. 9.3.6  Internal LDO, VCC UVLO, and BIAS Input
      7. 9.3.7  Bootstrap Voltage and VCBOOT-UVLO (CBOOT Pin)
      8. 9.3.8  Adjustable SW Node Slew Rate
      9. 9.3.9  Spread Spectrum
      10. 9.3.10 Soft Start and Recovery From Dropout
      11. 9.3.11 Output Voltage Setting
      12. 9.3.12 Overcurrent and Short Circuit Protection
      13. 9.3.13 Thermal Shutdown
      14. 9.3.14 Input Supply Current
    4. 9.4 Device Functional Modes
      1. 9.4.1 Shutdown Mode
      2. 9.4.2 Standby Mode
      3. 9.4.3 Active Mode
        1. 9.4.3.1 CCM Mode
        2. 9.4.3.2 Auto Mode - Light Load Operation
          1. 9.4.3.2.1 Diode Emulation
          2. 9.4.3.2.2 Frequency Reduction
        3. 9.4.3.3 FPWM Mode - Light Load Operation
        4. 9.4.3.4 Minimum On-time (High Input Voltage) Operation
        5. 9.4.3.5 Dropout
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1  Choosing the Switching Frequency
        2. 10.2.2.2  Setting the Output Voltage
        3. 10.2.2.3  Inductor Selection
        4. 10.2.2.4  Output Capacitor Selection
        5. 10.2.2.5  Input Capacitor Selection
        6. 10.2.2.6  BOOT Capacitor
        7. 10.2.2.7  BOOT Resistor
        8. 10.2.2.8  VCC
        9. 10.2.2.9  BIAS
        10. 10.2.2.10 CFF and RFF Selection
        11. 10.2.2.11 External UVLO
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Ground and Thermal Considerations
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

9.3.5 PGOOD Output Operation

The PGOOD function is implemented to replace a discrete reset device, reducing BOM count and cost. The PGOOD pin voltage goes low when the feedback voltage is outside of the specified PGOOD thresholds (see Figure 8-8). This can occur in current limit and thermal shutdown, as well as while disabled and during normal start-up. A glitch filter prevents false flag operation for short excursions of the output voltage, such as during line and load transients. Output voltage excursions that are shorter than tPGDFLT_FALL do not trip the power-good flag. Power-good operation can be best understood by referring to Figure 9-6.

The power-good output consists of an open-drain NMOS, requiring an external pullup resistor to a suitable logic supply or VOUT. When EN is pulled low, the flag output is also forced low. With EN low, power good remains valid as long as the input voltage is ≥ 1 V (typical).

GUID-5735B504-37B7-42F5-AA42-46FEA95D7E29-low.gifFigure 9-6 PGOOD Timing Diagram (Excludes OV Events)
Table 9-1 Conditions That Cause PGOOD to Signal a Fault (Pull Low)
FAULT CONDITION INITIATEDFAULT CONDITION ENDS (AFTER WHICH tPGDFLT(rise) MUST PASS BEFORE PGOOD OUTPUT IS RELEASED)(1)
VOUT < VOUT-target × PGDUV AND t > tPGDFLT(fall)Output voltage in regulation:
VOUT-target × (PGDUV + PGDHYST) < VOUT < VOUT-target × (PGDOV - PGDHYST) (See Figure 8-8)
VOUT > VOUT-target × PGDOV AND t > tPGDFLT(fall)Output voltage in regulation
TJ > TSD_RTJ < TSD_F AND output voltage in regulation
EN < VEN FallingEN > VEN Rising AND output voltage in regulation
VCC < VCC_UVLO - VCC_UVLO_HYSTVCC > VCC_UVLO AND output voltage in regulation
(1) As an additional operational check, PGOOD remains low during soft start, defined as until the lesser of either full output voltage reached or tSS2 has passed since initiation.