SNVSBJ0B December   2019  – August 2021 LM5170

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
  7. 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. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Bias Supply (VCC, VCCA)
      2. 8.3.2  Undervoltage Lockout (UVLO) and Master Enable or Disable
      3. 8.3.3  High Voltage Input (VIN, VINX)
      4. 8.3.4  Current Sense Amplifier
      5. 8.3.5  Control Commands
        1. 8.3.5.1 Channel Enable Commands (EN1, EN2)
        2. 8.3.5.2 Direction Command (DIR)
        3. 8.3.5.3 Channel Current Setting Commands (ISETA or ISETD)
      6. 8.3.6  Channel Current Monitor (IOUT1, IOUT2)
      7. 8.3.7  Cycle-by-Cycle Peak Current Limit (IPK)
      8. 8.3.8  Error Amplifier
      9. 8.3.9  Ramp Generator
      10. 8.3.10 Soft Start
        1. 8.3.10.1 Soft-Start Control by the SS Pin
        2. 8.3.10.2 Soft Start by MCU Through the ISET Pin
        3. 8.3.10.3 The SS Pin as the Restart Timer
      11. 8.3.11 Gate Drive Outputs, Dead Time Programming, and Adaptive Dead Time (HO1, HO2, LO1, LO2, DT)
      12. 8.3.12 PWM Comparator
      13. 8.3.13 Oscillator (OSC)
      14. 8.3.14 Synchronization to an External Clock (SYNCIN, SYNCOUT)
      15. 8.3.15 Diode Emulation
      16. 8.3.16 Power MOSFET Failure Detection and Failure Protection (nFAULT, BRKG, BRKS)
        1. 8.3.16.1 Failure Detection Selection at the SYNCOUT Pin
        2. 8.3.16.2 Nominal Circuit Breaker Function
      17. 8.3.17 Overvoltage Protection (OVPA, OVPB)
        1. 8.3.17.1 HV-V- Port OVP (OVPA)
        2. 8.3.17.2 LV-Port OVP (OVPB)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Multiphase Configurations (SYNCOUT, OPT)
        1. 8.4.1.1 Multiphase in Star Configuration
        2. 8.4.1.2 Configuration of 2, 3, or 4 Phases in Master-Slave Daisy-Chain Configurations
        3. 8.4.1.3 Configuration of 6 or 8 Phases in Master-Slave Daisy-Chain Configurations
      2. 8.4.2 Multiphase Total Current Monitoring
    5. 8.5 Programming
      1. 8.5.1 Dynamic Dead Time Adjustment
      2. 8.5.2 Optional UVLO Programming
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Typical Key Waveforms
        1. 9.1.1.1 Typical Power-Up Sequence
        2. 9.1.1.2 One to Eight Phase Programming
      2. 9.1.2 Inner Current Loop Small Signal Models
        1. 9.1.2.1 Small Signal Model
        2. 9.1.2.2 Inner Current Loop Compensation
      3. 9.1.3 Compensating for the Non-Ideal Current Sense Resistor
      4. 9.1.4 Outer Voltage Loop Control
    2. 9.2 Typical Application
      1. 9.2.1 60-A, Dual-Phase, 48-V to 12-V Bidirectional Converter
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1  Determining the Duty Cycle
          2. 9.2.1.2.2  Oscillator Programming
          3. 9.2.1.2.3  Power Inductor, RMS and Peak Currents
          4. 9.2.1.2.4  Current Sense (RCS)
          5. 9.2.1.2.5  Current Setting Limits (ISETA or ISETD)
          6. 9.2.1.2.6  Peak Current Limit
          7. 9.2.1.2.7  Power MOSFETS
          8. 9.2.1.2.8  Bias Supply
          9. 9.2.1.2.9  Bootstrap
          10. 9.2.1.2.10 RAMP Generators
          11. 9.2.1.2.11 OVP
          12. 9.2.1.2.12 Dead Time
          13. 9.2.1.2.13 IOUT Monitors
          14. 9.2.1.2.14 UVLO Pin Usage
          15. 9.2.1.2.15 VIN Pin Configuration
          16. 9.2.1.2.16 Loop Compensation
          17. 9.2.1.2.17 Soft Start
          18. 9.2.1.2.18 ISET Pins
        3. 9.2.1.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Examples
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9.1.2.2 Inner Current Loop Compensation

Equation 24 indicates that the power plant is basically a first-order system. A Type-II compensator as shown in Figure 9-3 is adequate to stabilize the loop for both buck and boost mode operations.

Assuming the output impedance of the gm amplifier is RGM, the gain from the inductor to the output of gm amplifier is determined by Equation 25:

Equation 25. GUID-8458333C-DFEF-4F3C-ACAA-CD0C4B6C98AB-low.gif

where

  • the coefficient 50 is the current sense amplifier gain
  • Gm is the transconductance of the gm error amplifier, which is 1 mA/V
  • ZCOMP(s) is the equivalent impedance of the compensation network seen at the COMP pin (see Equation 26)
Equation 26. GUID-B63D09D5-8780-4A35-915C-1C47A096A1C6-low.gif

Usually CHF is << CCOMP. Thus, Equation 26 can be simplified to Equation 27:

Equation 27. GUID-5CAB94E1-A154-4879-93DA-1E91BEFD6752-low.gif

Because RGM is > 5 MegΩ and the frequency range for loop compensation is usually above a few kHz, the effects of RGM on the loop gain in the interested frequency range becomes negligible. Therefore, substituting Equation 28 into Equation 25, and neglecting RGM, you can get the following:

Equation 28. GUID-945C4F8B-8347-4167-9BC2-92D61145B422-low.gif

The total open-loop gain of the inner current loop is the product of H(s) and G(s):

Equation 29. GUID-D119BD93-0D9D-4C11-8AD7-E55B4242F1AB-low.gif

Or

Equation 30. GUID-1B8DE85F-4B7D-4650-8DC2-AB3B91A1A45F-low.gif

The poles and zeros of the total loop transfer function are determined by:

Equation 31. GUID-B2FCE34D-C52F-4A52-8AC0-2DA0F4673FAB-low.gif
Equation 32. GUID-FBC83470-C2AB-4824-A230-A6AD5E3312F2-low.gif
Equation 33. GUID-CB4F9353-C30E-409B-A660-DB4E0DFDC09D-low.gif
Equation 34. GUID-AFCB6B1C-09C6-4052-9313-B338FCA92670-low.gif

To tailor the total inner current loop gain to cross over at fCO, select the components of the compensation network according to the following guidelines, then fine tune the network for optimal loop performance.

  1. The zero fz is placed at the power stage pole fp2
  2. The pole fp3 is placed at approximately two decade higher then fCO
  3. The total open-loop gain is set to unity at fCO, namely

Equation 35. GUID-331AE67A-8C12-4378-B924-FA24835CD8C8-low.gif

Therefore, the compensation components can be derived from the above equations, as shown in Equation 36.

Equation 36. GUID-814E0ED3-E41B-4194-A3C2-5E803475DED6-low.gif