SNVSA45B June   2014  – March 2018 LM46000

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Radiated Emission Graph VOUT = 3.3 V, VIN = 24 V, FS= 500 kHz, IOUT = 0.5 A
  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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Fixed-Frequency, Peak-Current-Mode Controlled Step-Down Regulator
      2. 7.3.2  Light Load Operation
      3. 7.3.3  Adjustable Output Voltage
      4. 7.3.4  Enable (EN)
      5. 7.3.5  VCC, UVLO, and BIAS
      6. 7.3.6  Soft Start and Voltage Tracking (SS/TRK)
      7. 7.3.7  Switching Frequency (RT) and Synchronization (SYNC)
      8. 7.3.8  Minimum ON-Time, Minimum OFF-Time and Frequency Foldback at Dropout Conditions
      9. 7.3.9  Internal Compensation and CFF
      10. 7.3.10 Bootstrap Voltage (CBOOT)
      11. 7.3.11 Power Good (PGOOD)
      12. 7.3.12 Overcurrent and Short-Circuit Protection
      13. 7.3.13 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
      4. 7.4.4 CCM Mode
      5. 7.4.5 Light Load Operation
      6. 7.4.6 Self-Bias Mode
  8. 8 Applications and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      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  Output Voltage Setpoint
        3. 8.2.2.3  Switching Frequency
        4. 8.2.2.4  Input Capacitors
        5. 8.2.2.5  Inductor Selection
        6. 8.2.2.6  Output Capacitor Selection
        7. 8.2.2.7  Feed-Forward Capacitor
        8. 8.2.2.8  Bootstrap Capacitors
        9. 8.2.2.9  VCC Capacitor
        10. 8.2.2.10 BIAS Capacitors
        11. 8.2.2.11 Soft-Start Capacitors
        12. 8.2.2.12 Undervoltage Lockout Setpoint
        13. 8.2.2.13 PGOOD
      3. 8.2.3 Application Performance Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Compact Layout for EMI Reduction
      2. 10.1.2 Ground Plane and Thermal Considerations
      3. 10.1.3 Feedback Resistors
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2 Typical Applications

The LM46000 only requires a few external components to convert from a wide range of supply voltage to output voltage. Figure 44 shows a basic schematic when BIAS is connected to VOUT . This is recommended for VOUT ≥ 3.3 V. For VOUT< 3.3 V, connect BIAS to ground, as shown in Figure 45.

LM46000 Sch_basic01.gifFigure 44. LM46000 Basic Schematic for
VOUT ≥ 3.3 V, Tie BIAS to VOUT
LM46000 Sch_basic02.gifFigure 45. LM46000 Basic Schematic for
VOUT< 3.3 V, Tie BIAS to Ground

The LM46000 also integrates a full list of optional features to aid system design requirements, such as precision enable, VCC UVLO, programmable soft start, output voltage tracking, programmable switching frequency, clock synchronization and power-good indication. Each application can select the features for a more comprehensive design. A schematic with all features utilized is shown in Figure 46.

LM46000 Sch_full_feature.gif
Figure 46. LM46000 Schematic With All Features

The external components must fulfill the needs of the application, but also the stability criteria of the device control loop. The LM46000 is optimized to work within a range of external components. Inductance and capacitance of the LC output filter must be considered in conjunction, creating a double pole, responsible for the corner frequency of the converter. Table 2 can be used to simplify the output filter component selection.

Table 2. L, COUT and CFF Typical Values

FS (kHz) L (µH)(1) COUT (µF)(2) CFF (pF)(3)(4) RT (kΩ) RFBB (kΩ)(3)(4)
VOUT = 1 V
200 22 500 none 200 100
500 10 330 none 80.6 or open 100
1000 4.8 180 none 39.2 100
2200 2.2 100 none 17.8 100
VOUT = 3.3 V
200 68 220 44 200 442
500 27 100 33 80.6 or open 442
1000 15 47 18 39.2 442
2200 6.8 27 12 17.8 442
VOUT = 5 V
200 100 150 66 200 249
500 44 66 33 80.6 or open 249
1000 22 33 22 39.2 249
2200 10 22 18 17.8 249
VOUT = 12 V
200 150 33 see note (5) 200 93.1
500 56 22 47 80.6 or open 93.1
1000 27 15 33 39.2 93.1
VOUT = 24 V
200 270 22 see note (5) 200 44.2
500 120 15 see note (5) 80.6 or open 44.2
1000 56 10 see note (5) 39.2 44.2
(1) Inductor values are calculated based on typical VIN = 24 V. For VOUT of 24 V, VIN = 48 V
(2) All the COUT values are after derating. Add more when using ceramics.
(3) RFBT = 0 Ω for VOUT = 1 V. RFBT = 1 MΩ for all other VOUT settings.
(4) For designs with RFBT other than 1 MΩ, adjust CFF such that (CFF × RFBT) is unchanged and adjust RFBB such that (RFBT / RFBB) is unchanged.
(5) High ESR COUT givse enough phase boost, and CFF not needed.