SLUS352C January   1997  – December 2015 UC1846 , UC2846 , UC3846 , UC3847

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Current Sense Amplifier
      2. 7.3.2 Oscillator
    4. 7.4 Device Functional Modes
      1. 7.4.1 Current Limit
      2. 7.4.2 Shutdown
  8. 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 Design Switching Frequency
        2. 8.2.2.2 Error Amplifier Output Configuration
        3. 8.2.2.3 Parallel Operation Configuration
        4. 8.2.2.4 Design Pulse by Pulse Current Limit Threshold
        5. 8.2.2.5 Soft-Start and Shutdown, Restart Function Design
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Related Links
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

封装选项

请参考 PDF 数据表获取器件具体的封装图。

机械数据 (封装 | 引脚)
  • J|16
  • FK|20
散热焊盘机械数据 (封装 | 引脚)
订购信息

8 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.

8.1 Application Information

The UCx846/7 family of control devices provides all of the necessary features to implement fixed frequency, current mode control schemes while maintaining a minimum external parts count. The superior performance of this technique can be measured in improved line regulation, enhanced load response characteristics, and a simpler, easier to design control loop. Topological advantages include inherent pulse-by-pulse current limiting capability, automatic symmetry correction for push-pull converters. Protection circuitry includes undervoltage lockout and programmable current limit in addition to soft-start capability. A shutdown function is also available which initiates either a complete shutdown with automatic restart or latch the supply off.

8.2 Typical Application

UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 slus352_typapp2.gif Figure 5. Typical Application Diagram

8.2.1 Design Requirements

Table 1 shows the design parameters for this application.

Table 1. Design Parameters

DESIGN PARAMETER TARGET VALUE
Typical efficiency 85%
Switching frequency 880 kHz
Pulse by pulse current limit threshold 1 A

8.2.2 Detailed Design Procedure

This section details the design procedure based on the design requirements.

8.2.2.1 Design Switching Frequency

Output deadtime is determined by the external capacitor, CT, according to the formula:

Equation 2. UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 qu2_lus352.gif

where

  • ID = Oscillator discharge current at 25°C; typically is 7.5.

For large values of RT: τd (μs ) ≈145CT (μF).

Oscillator frequency is approximated by the formula:

Equation 3. UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 qu3_lus352.gif

8.2.2.2 Error Amplifier Output Configuration

UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 error_amp_output_cfg.gif Figure 6. Error Amplifier Output Configuration

8.2.2.3 Parallel Operation Configuration

UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 parallel_op.gif Figure 7. Parallel Operation

8.2.2.4 Design Pulse by Pulse Current Limit Threshold

UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 pulse_by_pulse_curr_limit.gif Figure 8. Pulse by Pulse Current Limiting

8.2.2.5 Soft-Start and Shutdown, Restart Function Design

UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 soft_start_shutdown_restart.gif Figure 9. Soft-Start and Shutdown, Restart Functions

8.2.3 Application Curves

UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 responsive_to_step_load_change.png
t = 0.2 ms/div output response = 20 mV/div
Figure 10. Responsive to a Step Load Change of 1 A
UC1846 UC1847 UC2846 UC2847 UC3846 UC3847 switch_current_showing_fluxbalance.png
Figure 11. Switch Current Showing Flux Balance in UCX846/7