JAJSFD4A May   2018  – November 2018 LM5122ZA

PRODUCTION DATA.  

  1. 特長
  2. アプリケーション
  3. 概要
    1.     Device Images
      1.      アプリケーション概略図
  4. 改訂履歴
  5. 概要(続き)
  6. Pin Configuration and Functions
    1.     Pin 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
    6. 7.6 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Undervoltage Lockout (UVLO)
      2. 8.3.2  High-Voltage VCC Regulator
      3. 8.3.3  Oscillator
      4. 8.3.4  Slope Compensation
      5. 8.3.5  Error Amplifier
      6. 8.3.6  PWM Comparator
      7. 8.3.7  Soft Start
      8. 8.3.8  HO and LO Drivers
      9. 8.3.9  Bypass Operation (VOUT = VIN)
      10. 8.3.10 Cycle-by-Cycle Current Limit
      11. 8.3.11 Clock Synchronization
      12. 8.3.12 Maximum Duty Cycle
      13. 8.3.13 Thermal Protection
    4. 8.4 Device Functional Modes
      1. 8.4.1 MODE Control (Forced-PWM Mode and Diode-Emulation Mode)
      2. 8.4.2 MODE Control (Skip-Cycle Mode and Pulse-Skipping Mode)
      3. 8.4.3 Hiccup-Mode Overload Protection
      4. 8.4.4 Slave Mode and SYNCOUT
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Feedback Compensation
      2. 9.1.2 Sub-Harmonic Oscillation
      3. 9.1.3 Interleaved Boost Configuration
      4. 9.1.4 DCR Sensing
      5. 9.1.5 Output Overvoltage Protection
      6. 9.1.6 SEPIC Converter Simplified Schematic
      7. 9.1.7 Non-Isolated Synchronous Flyback Converter Simplified Schematic
      8. 9.1.8 Negative to Positive Conversion
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Timing Resistor RT
        2. 9.2.2.2  UVLO Divider RUV2, RUV1
        3. 9.2.2.3  Input Inductor LIN
        4. 9.2.2.4  Current Sense Resistor RS
        5. 9.2.2.5  Current Sense Filter RCSFP, RCSFN, CCS
        6. 9.2.2.6  Slope Compensation Resistor RSLOPE
        7. 9.2.2.7  Output Capacitor COUT
        8. 9.2.2.8  Input Capacitor CIN
        9. 9.2.2.9  VIN Filter RVIN, CVIN
        10. 9.2.2.10 Bootstrap Capacitor CBST and Boost Diode DBST
        11. 9.2.2.11 VCC Capacitor CVCC
        12. 9.2.2.12 Output Voltage Divider RFB1, RFB2
        13. 9.2.2.13 Soft-Start Capacitor CSS
        14. 9.2.2.14 Restart Capacitor CRES
        15. 9.2.2.15 Low-Side Power Switch QL
        16. 9.2.2.16 High-Side Power Switch QH and Additional Parallel Schottky Diode
        17. 9.2.2.17 Snubber Components
        18. 9.2.2.18 Loop Compensation Components CCOMP, RCOMP, CHF
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12デバイスおよびドキュメントのサポート
    1. 12.1 ドキュメントの更新通知を受け取る方法
    2. 12.2 コミュニティ・リソース
    3. 12.3 商標
    4. 12.4 静電気放電に関する注意事項
    5. 12.5 Glossary
  13. 13メカニカル、パッケージ、および注文情報

パッケージ・オプション

メカニカル・データ(パッケージ|ピン)
サーマルパッド・メカニカル・データ
発注情報

Feedback Compensation

The open loop response of a boost regulator is defined as the product of modulator transfer function and feedback transfer function. When plotted on a dB scale, the open loop gain is shown as the sum of modulator gain and feedback gain. The modulator transfer function of a current mode boost regulator including a power stage transfer function with an embedded current loop can be simplified as one pole, one zero, and one right-half-plane (RHP) zero system.

Modulator transfer function is defined as follows:

Equation 16. LM5122ZA eq18_nvs954.gif

where

  • LM5122ZA eq19_nvs954.gif
  • LM5122ZA eq20_nvs954.gif
  • LM5122ZA eq21_nvs954.gif
  • LM5122ZA eq22_nvs954.gif
  • LM5122ZA eq23_nvs954.gif
  • n is the number of the phase.

If the equivalent series resistance (ESR) of COUT (RESR) is small enough and the RHP zero frequency is far away from the target crossover frequency, the modulator transfer function can be further simplified to one pole system, and the voltage loop can be closed with only two loop compensation components, RCOMP and CCOMP, leaving a single pole response at the crossover frequency. A single pole response at the crossover frequency yields a very stable loop with 90 degrees of phase margin.

The feedback transfer function includes the feedback resistor divider and loop compensation of the error amplifier. RCOMP, CCOMP, and optional CHF configure the error amplifier gain and phase characteristics, create a pole at origin, a low frequency zero and a high frequency pole.

Feedback transfer function is defined as follows:

Equation 17. LM5122ZA eq25_nvs954.gif

where

  • LM5122ZA eq26_nvs954.gif
  • LM5122ZA eq27_nvs954.gif
  • LM5122ZA eq28_nvs954.gif

The pole at the origin minimizes the output steady state error. Place the low frequency zero to cancel the load pole of the modulator. The high frequency pole can be used to cancel the zero created by the output capacitor ESR or to decrease noise susceptibility of the error amplifier. By placing the low frequency zero an order of magnitude less than the crossover frequency, the maximum amount of phase boost can be achieved at the crossover frequency. The high frequency pole should be placed beyond the crossover frequency since the addition of CHF adds a pole in the feedback transfer function.

The crossover frequency (open loop bandwidth) is usually selected between one twentieth and one fifth of the fSW. In a simplified formula, the estimated crossover frequency can be defined as:

Equation 18. LM5122ZA eq29_nvs954.gif

where

  • LM5122ZA eq9_nvs954.gif

For higher crossover frequency, RCOMP can be increased, while proportionally decreasing CCOMP. Conversely, decreasing RCOMP while proportionally increasing CCOMP, results in lower bandwidth while keeping the same zero frequency in the feedback transfer function.

The modulator transfer function can be measured by a network analyzer and the feedback transfer function can be configured for the desired open loop transfer function. If the network analyzer is not available, step load transient tests can be performed to verify acceptable performance. The step load goal is minimum overshoot/undershoot with a damped response.