ZHCSHU8F October   2008  – July 2019 LM5575-Q1

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
  3. 3 说明
    1.     Device Images
      1.      简化原理图
  4. 4 修订历史记录
  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
    3. 7.3 Feature Description
      1. 7.3.1 Shutdown and Standby
      2. 7.3.2 Current Limit
      3. 7.3.3 Soft Start
      4. 7.3.4 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 High-Voltage Start-Up Regulator
      2. 7.4.2 Oscillator and Sync Capability
      3. 7.4.3 Error Amplifier and PWM Comparator
      4. 7.4.4 Ramp Generator
      5. 7.4.5 BOOST Pin
      6. 7.4.6 Maximum Duty Cycle and Input Dropout Voltage
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Bias Power Dissipation Reduction
    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  External Components
        3. 8.2.2.3  R3 (RT)
        4. 8.2.2.4  L1
        5. 8.2.2.5  C3 (CRAMP)
        6. 8.2.2.6  C9, C10
        7. 8.2.2.7  D1
        8. 8.2.2.8  C1, C2
        9. 8.2.2.9  C8
        10. 8.2.2.10 C7
        11. 8.2.2.11 C4
        12. 8.2.2.12 R5, R6
        13. 8.2.2.13 R1, R2, C12
        14. 8.2.2.14 R7, C11
        15. 8.2.2.15 R4, C5, C6
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
    3. 10.3 Thermal Considerations
  11. 11器件和文档支持
    1. 11.1 器件支持
      1. 11.1.1 使用 WEBENCH® 工具创建定制设计
    2. 11.2 接收文档更新通知
    3. 11.3 社区资源
    4. 11.4 商标
    5. 11.5 静电放电警告
    6. 11.6 Glossary
  12. 12机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

10.1 Layout Guidelines

The circuit in Functional Block Diagram serves as both a block diagram of the LM5575-Q1 and a typical application board schematic for the LM5575-Q1. In a buck regulator, there are two loops where currents are switched very fast. The first loop starts from the input capacitors, to the regulator VIN pin, to the regulator SW pin, and then to the inductor then out to the load. The second loop starts from the output capacitor ground, to the regulator PGND pins, to the regulator IS pins, to the diode anode, to the inductor and then out to the load. The user can minimize the loop area of these two loops to reduce the stray inductance and to minimize noise and possible erratic operation. A ground plane in the printed-circuit board (PCB) is recommended as a means to connect the input filter capacitors to the output filter capacitors and the PGND pins of the regulator. Connect all of the low-power ground connections (CSS, RT, CRAMP) directly to the regulator AGND pin. Connect the AGND and PGND pins together through the top-side copper area that covers the entire underside of the device. Place several vias in this underside copper area to the ground plane.

The two highest power-dissipating components are the re-circulating diode and the LM5575-Q1 regulator IC. The easiest method to determine the power dissipated within the LM5575-Q1 is to measure the total conversion losses (Pin – Pout) then subtract the power losses in the Schottky diode, output inductor, and snubber resistor.

Equation 17 calculates an approximation for the Schottky diode loss.

Equation 17. P = (1 – D) × IOUT × Vfwd

Equation 18 calculates an approximation for the output inductor power.

Equation 18. P = IOUT2 × R x 1.1

where

  • R is the DC resistance of the inductor and the 1.1 factor is an approximation for the AC losses

If a snubber is used, Equation 19 calculates an approximation for the damping resistor power dissipation.

Equation 19. P = VIN2 × Fsw × Csnub

where

  • Fsw is the switching frequency and Csnub is the snubber capacitor

The regulator has an exposed thermal pad to help power dissipation. Add several vias under the device to the ground plane to greatly reduce the regulator junction temperature. Select a diode with an exposed pad to help the power dissipation of the diode.

The most significant variables that affect the power dissipated by the LM5575-Q1 are the output current, input voltage, and operating frequency. The power dissipated while the device operates near the maximum output current and maximum input voltage can be appreciable. The operating frequency of the LM5575-Q1 evaluation board has been designed for 300 kHz. When the device operates at 1.5-A output current with a 70-V input, the power dissipation of the LM5575-Q1 regulator is approximately 1.25 W.