SNVS119D March   1998  – May 2016 LM2597 , LM2597HV


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Description (continued)
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics - 3.3 V
    6. 7.6  Electrical Characteristics - 5 V
    7. 7.7  Electrical Characteristics - 12 V
    8. 7.8  Electrical Characteristics - Adjustable
    9. 7.9  Electrical Characteristics - All Output Voltage Versions
    10. 7.10 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Bias Supply Feature
      2. 8.3.2 SHUTDOWN and Soft-Start
      3. 8.3.3 Inverting Regulator
      4. 8.3.4 Undervoltage Lockout
      5. 8.3.5 Negative Voltage Charge Pump
    4. 8.4 Device Functional Modes
      1. 8.4.1 Discontinuous Mode Operation
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Soft-Start Capacitor, CSS
      2. 9.1.2 Delay Capacitor, CDELAY
        1. RPULLUP
      3. 9.1.3 Input Capacitor, CIN
      4. 9.1.4 Output Capacitor, COUT
      5. 9.1.5 Catch Diode
      6. 9.1.6 Inductor Selection
      7. 9.1.7 Output Voltage Ripple and Transients
      8. 9.1.8 Open Core Inductors
    2. 9.2 Typical Applications
      1. 9.2.1 Series Buck Regulator (Fixed Output)
        1. Design Requirements
        2. Detailed Design Procedure
          1. Inductor Selection (L1)
          2. Output Capacitor Selection (COUT)
          3. Catch Diode Selection (D1)
          4. Input Capacitor (CIN)
        3. Application Curves
      2. 9.2.2 Series Buck Regulator (Adjustable Output)
        1. Design Requirements
        2. Detailed Design Procedure
          1. Programming Output Voltage
          2. Inductor Selection (L1)
          3. Output Capacitor Selection (COUT)
          4. Feedforward Capacitor (CFF)
          5. Catch Diode Selection (D1)
          6. Input Capacitor (CIN)
        3. Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

6 Pin Configuration and Functions

D or P Package
8-Pin SOIC or PDIP
Top View

Pin Functions(1)

1 Error Flag O Open collector output that provides a low signal (flag transistor ON) when the regulated output voltage drops more than 5% from the nominal output voltage. On start up, Error Flag is low until VOUT reaches 95% of the nominal output voltage and a delay time determined by the Delay pin capacitor. This signal can be used as a reset to a microprocessor on power up.
2 Delay O At power-up, this pin can be used to provide a time delay between the time the regulated output voltage reaches 95% of the nominal output voltage, and the time the error flag output goes high.
3 Bias Supply I This feature allows the regulators internal circuitry to be powered from the regulated output voltage or an external supply, instead of the input voltage. This results in increased efficiency under some operating conditions, such as low output current or high input voltage.
4 Feedback I Senses the regulated output voltage to complete the feedback loop.
5 Shutdown/Soft-Start I This dual function pin provides the following features: (a) Allows the switching regulator circuit to be shut down using logic level signals thus dropping the total input supply current to approximately 80 μA. (b) Adding a capacitor to this pin provides a soft-start feature which minimizes start-up current and provides a controlled ramp up of the output voltage.
6 Ground Circuit ground
7 +VIN I This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents required by the regulator.
8 Output O Internal switch. The voltage at this pin switches between (+VIN − VSAT) and approximately −0.5 V, with a duty cycle of VOUT/VIN. To minimize coupling to sensitive circuitry, the PCB copper area connected to this pin must be kept to a minimum.
(1) If any of the above four features (Shutdown/Soft-start, Error Flag, Delay, or Bias Supply) are not used, the respective pins must be left open.