ZHCSSS7 august   2023 TPS552872-Q1

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 描述
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  VCC Power Supply
      2. 7.3.2  EXTVCC Power Supply
      3. 7.3.3  Input Undervoltage Lockout
      4. 7.3.4  Enable and Programmable UVLO
      5. 7.3.5  Soft Start
      6. 7.3.6  Shutdown
      7. 7.3.7  Switching Frequency
      8. 7.3.8  Switching Frequency Dithering
      9. 7.3.9  Inductor Current Limit
      10. 7.3.10 Internal Charge Path
      11. 7.3.11 Output Voltage Setting
      12. 7.3.12 Output Current Monitoring and Cable Voltage Droop Compensation
      13. 7.3.13 Output Current Limit
      14. 7.3.14 Overvoltage Protection
      15. 7.3.15 Output Short Circuit Protection
      16. 7.3.16 Power Good
      17. 7.3.17 Constant Current Output Indication
      18. 7.3.18 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Mode
      2. 7.4.2 Power Save Mode
  9. 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 Switching Frequency
        2. 8.2.2.2 Output Voltage Setting
        3. 8.2.2.3 Inductor Selection
        4. 8.2.2.4 Input Capacitor
        5. 8.2.2.5 Output Capacitor
        6. 8.2.2.6 Output Current Limit
        7. 8.2.2.7 Loop Stability
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 第三方产品免责声明
    2. 9.2 接收文档更新通知
    3. 9.3 支持资源
    4. 9.4 Trademarks
    5. 9.5 静电放电警告
    6. 9.6 术语表
  11. 10Mechanical, Packaging, and Orderable Information

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机械数据 (封装 | 引脚)
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订购信息

8.2.2.3 Inductor Selection

Since the selection of the inductor affects steady state operation, transient behavior, and loop stability, the inductor is the most important component in power regulator design. There are three important inductor specifications: inductance, saturation current, and DC resistance.

The TPS552872-Q1 is designed to work with inductor values between 1 µH and 10 µH. The inductor selection is based on consideration of both buck and boost modes of operation. For 2 MHz switching frequency, a 1uH or 2.2uH inductor is recommended. For 400kHz switching frequency, a 4.7uH inductor is recommended.

For buck mode, the inductor selection is based on limiting the peak-to-peak current ripple to the maximum inductor current at the maximum input voltage. In CCM, Equation 9 shows the relationship between the inductance and the inductor ripple current.

Equation 9. GUID-74F4F263-8B89-45CF-A892-D2236521FBD5-low.gif

where

  • VIN(MAX) is the maximum input voltage
  • VOUT is the output voltage
  • ΔIL(P-P) is the peak to peak ripple current of the inductor
  • fSW is the switching frequency

For a certain inductor, the inductor ripple current achieves maximum value when VOUT equals half of the maximum input voltage. Choosing higher inductance gets smaller inductor current ripple while smaller inductance gets larger inductor current ripple.

For boost mode, the inductor selection is based on limiting the peak-to-peak current ripple to the maximum inductor current at the maximum output voltage. In CCM, Equation 10 shows the relationship between the inductance and the inductor ripple current.

Equation 10. GUID-CF3A1984-E1EE-4703-9A8B-4D02B331FDF0-low.gif

where

  • VIN is the input voltage
  • VOUT(MAX) is the maximum output voltage
  • ΔIL(P-P) is the peak to peak ripple current of the inductor
  • fSW is the switching frequency

For a certain inductor, the inductor ripple current achieves maximum value when VIN equals to the half of the maximum output voltage. Choosing higher inductance gets smaller inductor current ripple while smaller inductance gets larger inductor current ripple.

In buck mode, the inductor DC current equals to the output current. In boost mode, the inductor DC current can be calculated with Equation 11.

Equation 11. GUID-CC8CB586-8F9F-40A5-B9EF-BA50CC9790ED-low.gif

where

  • VOUT is the output voltage
  • IOUT is the output current
  • VIN is the input voltage
  • η is the power conversion efficiency

For a given maximum output current of the buck-boost converter TPS552872-Q1, the maximum inductor DC current happens at the minimum input voltage and maximum output voltage. Set the inductor current limit of the TPS552872-Q1 higher than the calculated maximum inductor DC current to make sure the TPS552872-Q1 has the desired output current capability.

In boost mode, the inductor ripple current is calculated with Equation 12.

Equation 12. GUID-7A839601-AFCD-4F95-95CD-CE9C127F65B0-low.gif

where

  • ΔIL(P-P) is the inductor ripple current
  • L is the inductor value
  • fSW is the switching frequency
  • VOUT is the output voltage
  • VIN is the input voltage

Therefore, the inductor peak current is calculated with Equation 13.

Equation 13. GUID-2C63B917-81A1-4A2F-8BA5-FBE6A52AE96D-low.gif

Normally, it is advisable to work with an inductor peak-to-peak current of less than 40% of the average inductor current for maximum output current. A smaller ripple from a larger valued inductor reduces the magnetic hysteresis losses in the inductor and EMI, but in the same way, load transient response time is increased. The selected inductor must have higher saturation current than the calculated peak current.

The conversion efficiency is dependent on the resistance of its current path. The switching loss associated with the switching MOSFETs, and the inductor core loss. Therefore, the overall efficiency is affected by the inductor DC resistance (DCR), equivalent series resistance (ESR) at the switching frequency, and the core loss. Table 8-2 lists recommended inductors for the TPS552872-Q1. In this application example, switching frequency is 2 MHz and the Coilcraft inductor XGL5030-102 is selected for its small size, high saturation current, and small DCR.

Table 8-2 Recommended Inductors
PART NUMBERL (µH)DCR (MAXIMUM) (mΩ)SATURATION CURRENT / HEAT RATING CURRENT (A)SIZE (L x W x H mm)VENDOR(1)
XGL5030-102MEC15.814/17.85.5 × 5.3 × 3.1Coilcraft
74438367010111.513.1/11.855.4 × 5.4 × 3.1WE
XGL6060-472MEC4.710.110.2/16.66.7 × 6.5 × 6.1Coilcraft
(1) See the Third-party Products disclaimer.