SNVS872D August   2012  – August 2018 LMZ21700

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency for VIN = 12 V
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 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
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
      1. 7.2.1 Package Construction
    3. 7.3 Feature Description
      1. 7.3.1 Input Undervoltage Lockout
      2. 7.3.2 Enable Input (EN)
      3. 7.3.3 Soft-Start and Tracking Function (SS)
      4. 7.3.4 Power Good Function (PG)
      5. 7.3.5 Output Voltage Setting
      6. 7.3.6 Output Current Limit and Output Short Circuit Protection
      7. 7.3.7 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Mode Operation
      2. 7.4.2 PSM Operation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Input Capacitor (CIN)
        3. 8.2.2.3 Output Capacitor (COUT)
        4. 8.2.2.4 Softstart Capacitor (CSS)
        5. 8.2.2.5 Power Good Resistor (RPG)
        6. 8.2.2.6 Feedback Resistors (RFBB and RFBT)
      3. 8.2.3 Application Curves
        1. 8.2.3.1 VOUT = 1.2 V
        2. 8.2.3.2 VOUT = 1.8 V
        3. 8.2.3.3 VOUT = 2.5 V
        4. 8.2.3.4 VOUT = 3.3 V
        5. 8.2.3.5 VOUT = 5.0 V
    3. 8.3 Do's and Don'ts
  9. 9 Power Supply Recommendations
    1. 9.1 Voltage Range
    2. 9.2 Current Capability
    3. 9.3 Input Connection
      1. 9.3.1 Voltage Drops
      2. 9.3.2 Stability
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Minimize the High di/dt Loop Area
      2. 10.1.2 Protect the Sensitive Nodes in the Circuit
      3. 10.1.3 Provide Thermal Path and Shielding
    2. 10.2 Layout Example
      1. 10.2.1 High Density Layout Example for Space Constrained Applications
        1. 10.2.1.1 35-mm² Solution Size (Single Sided)
  11. 11Device and Documentation Support
    1. 11.1 Device Support
    2. 11.2 Development Support
      1. 11.2.1 Custom Design With WEBENCH® Tools
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Tape and Reel Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • SIL|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.3 Soft-Start and Tracking Function (SS)

When EN is set high for device operation the LMZ21700 starts switching after 50-μs delay and the output voltage will start rising. The VOUT rising slope is controlled by the external capacitor CSS connected to the soft-start (SS) pin. The nano module has a 2.5 μA constant current source internally connected to the SS pin to program the softstart time TSS:

Equation 1. TSS = CSS x 1.25 V / 2.5 μA

The softstart capacitor voltage is reset to zero volts when EN is pulled low and when the thermal protection is active.

If tracking function is desired, the SS pin can be used to track external voltage. If the applied external tracking voltage is between 100 mV and 1.2 V, the FB voltage will follow SS according to the following relationship:

Equation 2. VFB = 0.64 x VSS