SNVS118F december   1999  – may 2023 LM2594 , LM2594HV

PRODUCTION DATA  

  1.   1
  2. Features
  3. Applications
  4. Description
  5. Revision History
  6. Description (continued)
  7. Pin Configuration and Functions
  8. 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
  9. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Delayed Start-Up
      2. 8.3.2 Undervoltage Lockout
      3. 8.3.3 Inverting Regulator
      4. 8.3.4 Inverting Regulator Shutdown Methods
    4. 8.4 Device Functional Modes
      1. 8.4.1 Discontinuous Mode Operation
  10. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Input Capacitor (CIN)
      2. 9.1.2 Output Capacitor (COUT)
      3. 9.1.3 Catch Diode
      4. 9.1.4 Inductor Selection
      5. 9.1.5 Output Voltage Ripple and Transients
      6. 9.1.6 Open Core Inductors
    2. 9.2 Typical Applications
      1. 9.2.1 Series Buck Regulator (Fixed Output)
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Custom Design with WEBENCH® Tools
          2. 9.2.1.2.2 Inductor Selection (L1)
          3. 9.2.1.2.3 Output Capacitor Selection (COUT)
          4. 9.2.1.2.4 Catch Diode Selection (D1)
          5. 9.2.1.2.5 Input Capacitor (CIN)
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Series Buck Regulator (Adjustable Output)
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1 Programming Output Voltage
          2. 9.2.2.2.2 Inductor Selection (L1)
          3. 9.2.2.2.3 Output Capacitor Selection (COUT)
          4. 9.2.2.2.4 Feedforward Capacitor (CFF)
          5. 9.2.2.2.5 Catch Diode Selection (D1)
          6. 9.2.2.2.6 Input Capacitor (CIN)
        3. 9.2.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
      3. 9.4.3 Thermal Considerations
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design with WEBENCH® Tools
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

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

Output Capacitor (COUT)

An output capacitor is required to filter the output and provide regulator loop stability. Low impedance or low ESR Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used. When selecting an output capacitor, the important capacitor parameters are; the 100-kHz Equivalent Series Resistance (ESR), the RMS ripple current rating, voltage rating, and capacitance value. For the output capacitor, the ESR value is the most important parameter.

The output capacitor requires an ESR value that has an upper and lower limit. For low output ripple voltage, a low ESR value is needed. This value is determined by the maximum allowable output ripple voltage, typically 1% to 2% of the output voltage. But if the ESR of the selected capacitor is extremely low, there is a possibility of an unstable feedback loop, resulting in an oscillation at the output. Using the capacitors listed in the tables, or similar types, provides design solutions under all conditions.

If very low output ripple voltage (less than 15 mV) is required, see Section 9.1.5 for a post-ripple filter.

An aluminum electrolytic capacitor ESR value is related to the capacitance value and its voltage rating. In most cases, Higher voltage electrolytic capacitors have lower ESR values (see Figure 9-2). Often, capacitors with much higher voltage ratings can be needed to provide the low ESR values required for low output ripple voltage.

The output capacitor for many different switcher designs often can be satisfied with only three or four different capacitor values and several different voltage ratings. See Figure 9-8 and Table 9-7 for typical capacitor values, voltage ratings, and manufacturers capacitor types.

Electrolytic capacitors are not recommended for temperatures below −25°C. The ESR rises dramatically at cold temperatures and typically rises three times at −25°C and as much as ten times at −40°C (see Figure 9-3).

Solid tantalum capacitors have a much better ESR specifications for cold temperatures and are recommended for temperatures below −25°C.

GUID-80C0FE27-40EC-43BD-ACD6-202EF4B6A433-low.pngFigure 9-2 Capacitor ESR versus Capacitor Voltage Rating (Typical Low-ESR Electrolytic Capacitor)
Table 9-1 Output Capacitor and Feedforward Capacitor Selection Table
OUTPUT VOLTAGE (V)THROUGH-HOLE OUTPUT CAPACITORSURFACE-MOUNT OUTPUT CAPACITOR
PANASONIC HFQ SERIES (µF/V)NICHICON PL SERIES (µF/V)FEEDFORWARD CAPACITORAVX TPS SERIES (µF/V)SPRAGUE 595D SERIES (µF/V)FEEDFORWARD CAPACITOR
1.2220/25220/250220/10220/100
4180/25180/254.7 nF100/10120/104.7 nF
682/2582/254.7 nF100/10120/104.7 nF
982/2582/253.3 nF100/16100/163.3 nF
1282/2582/252.2 nF100/16100/162.2 nF
1582/2582/251.5 nF68/20100/201.5 nF
2482/50120/501 nF10/3515/35220 pF
2882/50120/50820 pF10/3515/35220 pF