SGLS274I September   2008  – November 2023 UCC27423-Q1 , UCC27424-Q1 , UCC27425-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  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 Switching Characteristics
    7. 6.7 Dissipation Ratings
    8. 6.8 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 Input Stage
      2. 7.3.2 Output Stage
      3. 7.3.3 Enable
      4. 7.3.4 Parallel Outputs
      5. 7.3.5 Operational Waveforms and Circuit Layout
      6. 7.3.6 VDD
    4. 7.4 Device Functional Modes
  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 Source and Sink Capabilities During Miller Plateau
        2. 8.2.2.2 Drive Current and Power Requirements
      3. 8.2.3 Application Curves
  10. 9 Power Supply Recommendations
  11. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  12. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  13. 12Revision History
  14. 13Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.2 Drive Current and Power Requirements

The UCC2742x-Q1 family of drivers are capable of delivering 4 A of current to a MOSFET gate for a period of several hundred nanoseconds. High-peak current is required to turn the device ON quickly. Then, to turn the device OFF, the driver is required to sink a similar amount of current to ground. This repeats at the operating frequency of the power device. A MOSFET is used in this discussion because it is the most common type of switching device used in high frequency power conversion equipment.

Reference 1 in the Section 11.2.1 section discuss the current required to drive a power MOSFET and other capacitive-input switching devices. Reference 1 in includes information on the previous generation of bipolar IC gate drivers.

When a driver IC is tested with a discrete, capacitive load, it is a fairly simple matter to calculate the power that is required from the bias supply. The energy that must be transferred from the bias supply to charge the capacitor is given by Equation 2.

Equation 2. GUID-903CAC48-653A-41E8-9C76-CF57715A1F8C-low.gif

where

  • C = load capacitor
  • V = bias voltage (feeding the driver)

There is an equal amount of energy transferred to ground when the capacitor is discharged. This leads to a power loss given by Equation 3.

Equation 3. P = CV2 × f

where

  • f = switching frequency

This power is dissipated in the resistive elements of the circuit. Thus, with no external resistor between the driver and gate, this power is dissipated inside the driver. Half of the total power is dissipated when the capacitor is charged, and the other half is dissipated when the capacitor is discharged. An actual example using the conditions of the previous gate drive waveform should help clarify this.

With VDD = 12 V, CLOAD = 10 nF, and f = 300 kHz, the power loss can be calculated as Equation 4.

Equation 4. P = 10 nF × (12 V)2 × (300 kHz) = 0.432 W

With a 12-V supply, this would equate to a current of Equation 5.

Equation 5. GUID-7090E4A0-8E4E-418C-AD65-BE2C3D14E7A2-low.gif

The actual current measured from the supply was 0.037 A, and is very close to the predicted value. But, consider the IDD current that is due to the IC internal consumption. With no load, the IC current draw is 0.0027 A. Under this condition, the output rise and fall times are faster than with a load. This could lead to an almost insignificant, yet measurable current due to cross-conduction in the output stages of the driver. However, these small current differences are buried in the high-frequency switching spikes, and are beyond the measurement capabilities of a basic lab setup. The measured current with 10-nF load is reasonably close to that expected.

The switching load presented by a power MOSFET can be converted to an equivalent capacitance by examining the gate charge required to switch the device. This gate charge includes the effects of the input capacitance plus the added charge needed to swing the drain of the device between the ON and OFF states. Most manufacturers provide specifications that provide the typical and maximum gate charge, in nC, to switch the device under specified conditions. Using the gate charge Qg, one can determine the power that must be dissipated when charging a capacitor. This is done by using the equivalence Qg = CeffV to provide the power loss in Equation 6.

Equation 6. P = C × V2 × f = V × Qg × f

Equation 6 allows a power designer to calculate the bias power required to drive a specific MOSFET gate at a specific bias voltage.