SNVSBJ0A December   2019  – June 2020 LM5170


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Application Circuit
      2.      Channel Current Tracking ISETA Command
  4. Revision History
  5. Description (continued)
  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  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. Channel Enable Commands (EN1, EN2)
        2. Direction Command (DIR)
        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. Soft-Start Control by the SS Pin
        2. Soft Start by MCU Through the ISET Pin
        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. Failure Detection Selection at the SYNCOUT Pin
        2. Nominal Circuit Breaker Function
      17. 8.3.17 Overvoltage Protection (OVPA, OVPB)
        1. HV-V- Port OVP (OVPA)
        2. LV-Port OVP (OVPB)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Multiphase Configurations (SYNCOUT, OPT)
        1. Multiphase in Star Configuration
        2. Configuration of 2, 3, or 4 Phases in Master-Slave Daisy-Chain Configurations
        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. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Typical Key Waveforms
        1. Typical Power-Up Sequence
        2. One to Eight Phase Programming
      2. 9.1.2 Inner Current Loop Small Signal Models
        1. Small Signal Model
        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. Design Requirements
        2. Detailed Design Procedure
          1.  Determining the Duty Cycle
          2.  Oscillator Programming
          3.  Power Inductor, RMS and Peak Currents
          4.  Current Sense (RCS)
          5.  Current Setting Limits (ISETA or ISETD)
          6.  Peak Current Limit
          7.  Power MOSFETS
          8.  Bias Supply
          9.  Boot Strap
          10. RAMP Generators
          11. OVP
          12. Dead Time
          13. IOUT Monitors
          14. UVLO Pin Usage
          15. VIN Pin Configuration
          16. Loop Compensation
          17. Soft Start
          18. ISET Pins
        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

Ramp Generator

Refer to Figure 25 for the circuit block diagram of the ramp generator, gm error amplifier, PWM comparator, and soft-start control circuit. The VINX pin serves as the supply pin for the ramp generator. Each ramp generator consists of an external RC circuit (RRAMP and CRAMP) and an internal pulldown switch controlled by the clock signal.

LM5170 error_amplifier_ramp_generator_soft_start_pwm_comparator_snvsbj0.gifFigure 25. Error Amplifier, Ramp Generator, Soft Start, and PWM Comparator

When the LM5170 is enabled, CRAMP1/2 is charged by the VINX pin through RRAMP1/2 at the beginning of each switching cycle. The internal pulldown FET discharges CRAMP1/2 at the end of the cycle within a 200-ns internal, then the pulldown is released, and CRAMP1/2 repeats the charging and discharging cycles. In general the RAMP RC time constant is much greater than the period of a switching cycle. Therefore, the RAMP pin voltages are sawtooth signals with a slope proportional to the HV-Port voltage. In this way the RAMP signals convey the line voltage info. Being directly used by the PWM comparators to determine the instantaneous switching duty cycles, the RAMP signals fulfill the line voltage feedforward function and enable the LM5170 to have a fast response to line transients.


TI recommends users to select appropriate RRAMP and CRAMP values by the following equation such that the RAMP pins reach the peak value of approximately 5 V each cycle when VIN is at 48 V.

Equation 14. LM5170 eq_14_SNVSAQ6.gif

For instance, if Fsw = 100 kHz, and CRAMP1 = CRAMP2 = 1 nF, a resistor of approximately 96 kΩ should be selected for RRAMP1 and RRAMP2.

Because CRAMP1/2 must be fully discharged every cycle through the 15-Ω channel resistor of the pulldown FET within the 150-ns minimum discharging interval, CRAMP1/2 should be limited to be less than 2.5 nF nominal at room temperature.

There is also a valid RAMP signal detection circuit for each channel to prevent the channel from errantly running into the maximum duty cycle if RAMP goes away. It detects the peak voltage of the RAMP signal. If the peak voltage is less than 0.6 V in consecutive cycles, it is considered an invalid RAMP and the channel will stop switching by turning both HO and LO off until the RAMP signal recovers. This 0.6-V voltage threshold defines the minimum operating voltage of the HV-Port to be approximately 5.76 V.