SNVS300H July   2004  – September 2016 LM5111

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Options
  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 Switching Characteristics
    7. 7.7 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 Undervoltage Lockout
      2. 8.3.2 Output Stage
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 VCC
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Bias Supply Voltage
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
      1. 11.3.1 Drive Power Requirement Calculations in LM5111
      2. 11.3.2 Continuous Current Rating of LM5111
  12. 12Device and Documentation Support
    1. 12.1 Receiving Notification of Documentation Updates
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

High-frequency power supplies often require high-speed, high-current drivers such as the LM5111 family. A leading application is the need to provide a high-power buffer stage between the PWM output of the control IC and the gates of the primary power MOSFET or IGBT switching devices. In other cases, the driver IC is used to drive the power-device gates through a drive transformer. Synchronous rectification supplies are also needed to simultaneously drive multiple devices which presents an extremely large load to the control circuitry.

Driver ICs are used when use of the primary PWM regulator IC to directly drive the switching devices for one or more reasons is not feasible. The PWMIC does not have the brute drive capability required for the intended switching MOSFET, limiting the switching performance in the application. In other cases, there may be a desire to minimize the effect of high-frequency switching noise by placing the high current driver physically close to the load. Also, newer ICs that target the highest operating frequencies do not incorporate onboard gate drivers at all. Their PWM outputs are only intended to drive the high impedance input to a driver such as the UCCx732x. Finally, the control IC is under thermal stress due to power dissipation, and an external driver helps by moving the heat from the controller to an external package.

9.2 Typical Application

LM5111 simplified_app_diagram.gif Figure 12. LM5111 Driving Two Independent MOSFETs

9.2.1 Design Requirements

To select the proper device from the LM5111 family, TI recommends first checking the appropriate logic for the outputs. LM5111 has dual inverting outputs; dual noninverting outputs; inverting channel A and noninverting channel B. Refer to operating modes to select which driver from the family is required in a given application. Moreover, some design considerations must be evaluated first in order to make the most appropriate selection. Among these considerations are VCC and power dissipation.

9.2.2 Detailed Design Procedure

9.2.2.1 VCC

Although quiescent VCC current is very low, total supply current will be higher, depending on OUTA and OUTB current and the programmed oscillator frequency. Total VCC current is the sum of quiescent VCC current and the average OUT current. Knowing the operating frequency and the MOSFET gate charge (Qg), average OUT current can be calculated using Equation 1.

Equation 1. IOUT = Qg × f

where

  • f is frequency

For the best high-speed circuit performance, two VCC bypass capacitors are recommended to prevent noise problems. The use of surface mount components is highly recommended. A 0.1-µF ceramic capacitor should be located closest to the VDD to ground connection. In addition, a larger capacitor (such as 1 µF and above) with relatively low ESR should be connected in parallel, to help deliver the high current peaks to the load. The parallel combination of capacitors should present a low impedance characteristic for the expected current levels in the driver application.

9.2.3 Application Curves

LM5111 20112310.gif
Figure 13. Supply Current vs Frequency
LM5111 20112311.gif
Figure 14. Supply Current vs Capacitive Load