SNVS686K March   2011  – May 2024 LMZ22005

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
    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 Synchronization Input
      2. 6.3.2 Output Overvoltage Protection
      3. 6.3.3 Current Limit
      4. 6.3.4 Thermal Protection
      5. 6.3.5 Prebiased Start-Up
    4. 6.4 Device Functional Modes
      1. 6.4.1 Discontinuous And Continuous Conduction Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Design Steps
        2. 7.2.2.2 Enable Divider, RENT, RENB and RENH Selection
        3. 7.2.2.3 Output Voltage Selection
        4. 7.2.2.4 Soft-start Capacitor Selection
        5. 7.2.2.5 Tracking Supply Divider Option
        6. 7.2.2.6 CO Selection
        7. 7.2.2.7 CIN Selection
        8. 7.2.2.8 Discontinuous And Continuous Conduction Modes Selection
      3. 7.2.3 Application Curves
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Examples
    3. 9.3 Power Dissipation and Thermal Considerations
    4. 9.4 Power Module SMT Guidelines
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.2.2.2 Enable Divider, RENT, RENB and RENH Selection

Internal to the module is a 2-MΩ pullup resistor connected from VIN to Enable. For applications not requiring precision undervoltage lockout (UVLO), the Enable input may be left open circuit and the internal resistor will always enable the module. In such case, the internal UVLO occurs typically at 4.3 V (VIN rising).

In applications with separate supervisory circuits Enable can be directly interfaced to a logic source. In the case of sequencing supplies, the divider is connected to a rail that becomes active earlier in the power-up cycle than the LMZ22005 output rail.

Enable provides a precise 1.279-V threshold to allow direct logic drive or connection to a voltage divider from a higher enable voltage such as VIN. Additionally there is 21 μA (typical) of switched offset current allowing programmable hysteresis. See Figure 7-2.

The function of the enable divider is to allow the designer to choose an input voltage below which the circuit will be disabled. This implements the feature of programmable UVLO. The two resistors must be chosen based on the following ratio:

Equation 1. RENT / RENB = (VIN UVLO / 1.279 V) – 1

The LMZ22005 typical application shows 12.7 kΩ for RENB and 42.2 kΩ for RENT resulting in a rising UVLO of 5.46 V.

Note:

A midpoint 5.1-V Zener clamp is present to allow setting UVLO to cover an extended range of operation. The Zener clamp is not required if the target application prohibits the maximum Enable input voltage from being exceeded.

Additional enable voltage hysteresis can be added with the inclusion of RENH. It may be possible to select values for RENT and RENB such that RENH is a value of zero allowing it to be omitted from the design.

Rising threshold can be calculated as follows:

Equation 2. VEN(rising) = 1.279 ( 1 + RENT|| 2 meg/ RENB)

Whereas falling threshold level can be calculated using:

Equation 3. VEN(falling) = VEN(rising) – 21 µA ( RENT|| 2 meg || RENTB + RENH )
LMZ22005 Enable Input DetailFigure 7-2 Enable Input Detail