SNVSB35C May   2018  – November 2024 LM26420-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics Per Buck
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Soft Start
      2. 6.3.2 Power Good
      3. 6.3.3 Precision Enable
    4. 6.4 Device Functional Modes
      1. 6.4.1 Output Overvoltage Protection
      2. 6.4.2 Undervoltage Lockout
      3. 6.4.3 Current Limit
      4. 6.4.4 Thermal Shutdown
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Programming Output Voltage
      2. 7.1.2 VINC Filtering Components
      3. 7.1.3 Using Precision Enable and Power Good
      4. 7.1.4 Overcurrent Protection for HTSSOP-20 Package
      5. 7.1.5 Current Limit and Short-Circuit Protection for WQFN-16 Package
    2. 7.2 Typical Applications
      1. 7.2.1 2.2-MHz, 0.8-V Typical High-Efficiency Application Circuit
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 7.2.1.2.2 Inductor Selection
          3. 7.2.1.2.3 Input Capacitor Selection
          4. 7.2.1.2.4 Output Capacitor
          5. 7.2.1.2.5 Calculating Efficiency and Junction Temperature
        3. 7.2.1.3 Application Curves
      2. 7.2.2 2.2-MHz, 1.8-V Typical High-Efficiency Application Circuit
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
        3. 7.2.2.3 Application Curves
      3. 7.2.3 LM26420-Q12.2-MHz, 2.5-V Typical High-Efficiency Application Circuit
        1. 7.2.3.1 Design Requirements
        2. 7.2.3.2 Detailed Design Procedure
        3. 7.2.3.3 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Power Supply Recommendations - HTSSOP-20 Package
      2. 7.3.2 Power Supply Recommendations - WQFN-16 Package
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
      3. 7.4.3 Thermal Considerations
        1. 7.4.3.1 Method 1: Silicon Junction Temperature Determination
        2. 7.4.3.2 Thermal Shutdown Temperature Determination
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Custom Design With WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

7.1.3 Using Precision Enable and Power Good

The LM26420-Q1 device precision EN and PG pins address many of the sequencing requirements required in challenging applications. Each output can be controlled independently and have independent power good. This allows for a multitude of ways to control each output. Typically, the enables to each output are tied together to the input voltage and the outputs ratiometrically ramp up when the input voltage reaches above UVLO rising threshold. There can be instances where the second output (VOUT2) not turning on until the first output (VOUT1) has reached 90% of the desired setpoint is desired. This is easily achieved with an external resistor divider attached from VOUT1 to EN2, see Figure 7-3.

LM26420-Q1 VOUT1 Controlling VOUT2 With Resistor DividerFigure 7-3 VOUT1 Controlling VOUT2 With Resistor Divider

If having a resistor divider to control VOUT2 with VOUT1 is not desired, then the PG1 can be connected to the EN2 pin to control VOUT2, see Figure 7-4. RPG1 is a pullup resistor on the range of 10 kΩ to 100 kΩ. 50 kΩ is the suggested value. This turns on VOUT2 when VOUT1 is approximately 85% of the programmed output.

Note:

Using PG1 to control VOUT2 also turns off VOUT2 when VOUT1 is outside the of the programmed output.

LM26420-Q1 PG1 Controlling VOUT2Figure 7-4 PG1 Controlling VOUT2

Another example is that the output is not to be turned on until the input voltage reaches 90% of desired voltage setpoint. This verifies that the input supply is stable before turning on the output. Select REN1 and REN2 so that the voltage at the EN pin is greater than 1.12 V when reaching the 90% desired set-point.

LM26420-Q1 Vin Controlling VOUTFigure 7-5 Vin Controlling VOUT

The power-good feature of the LM26420-Q1 is designed with hysteresis to make sure no false power-good flags are asserted during large transient. After power good is asserted high, power good is not pulled low until the output voltage exceeds ±15% of the setpoint for a during of approximately 7.5 µs (typical), see Figure 7-6.

LM26420-Q1 Power-Good Hysteresis Operation Figure 7-6 Power-Good Hysteresis Operation