ZHCSN51J june   2007  – april 2023 TPS74901

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  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: Other Orderable Devices (non-M3 Suffix)
    6. 6.6  Electrical Characteristics: Orderable Device (M3 Suffix)
    7. 6.7  Typical Characteristics: IOUT = 50 mA (All Other Orderable Devices, Non-M3 Suffix)
    8. 6.8  Typical Characteristics: IOUT = 1 A (All Other Orderable Devices, Non-M3 Suffix)
    9. 6.9  Typical Characteristics: IOUT = 50 mA (M3 Suffix)
    10. 6.10 Typical Characteristics: IOUT = 1 A (M3 Suffix)
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Enable and Shutdown
      2. 7.3.2 Power-Good
      3. 7.3.3 Internal Current Limit
      4. 7.3.4 Thermal Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 Dropout Operation
      3. 7.4.3 Disabled
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Input, Output, and BIAS Capacitor Requirements
      2. 8.1.2 Transient Response
      3. 8.1.3 Dropout Voltage
      4. 8.1.4 Output Noise
      5. 8.1.5 Programmable Soft-Start
      6. 8.1.6 Sequencing Requirements
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Power Dissipation
        2. 8.4.1.2 Thermal Considerations
      2. 8.4.2 Layout Example
  9. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 Evaluation Modules
        2. 9.1.1.2 Spice Models
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 接收文档更新通知
    4. 9.4 支持资源
    5. 9.5 Trademarks
    6. 9.6 静电放电警告
    7. 9.7 术语表
  10. 10Mechanical, Packaging, and Orderable Information

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

8.1.5 Programmable Soft-Start

The TPS74901 features a programmable, monotonic, voltage-controlled soft-start that is set with an external capacitor (CSS). This feature is important for many applications because power-up initialization problems are eliminated when powering FPGAs, DSPs, or other processors. The controlled voltage ramp of the output also reduces peak inrush current during start-up, minimizing start-up transient events to the input power bus.

To achieve a linear and monotonic soft-start, the TPS74901 error amplifier tracks the voltage ramp of the external soft-start capacitor until the voltage exceeds the internal reference. The soft-start ramp time is dependent on the soft-start charging current (ISS), soft-start capacitance (CSS), and the internal reference voltage (VREF), and can be calculated using Equation 2.

Equation 2. GUID-B980DB52-AE46-4EC6-BABA-007A8E971223-low.gif

If large output capacitors are used, the device current limit (ICL) and the output capacitor can set the start-up time. In this case, the start-up time is given by Equation 3:

Equation 3. GUID-0A8E9F66-FD9C-4712-B3EA-831E9A817EB5-low.gif

where:

  • VOUT(NOM) is the nominal set output voltage
  • COUT is the output capacitance
  • ICL(MIN) is the minimum current limit for the device

In applications where monotonic start-up is required, the soft-start time given by Equation 2 must be set to be greater than Equation 3.

The maximum recommended soft-start capacitor is 0.015 µF. Larger soft-start capacitors can be used and do not damage the device; however, the soft-start capacitor discharge circuit can possibly be unable to fully discharge the soft-start capacitor when enabled. Soft-start capacitors larger than 0.015 µF can be a problem in applications where the enable pin must be rapidly pulsed while still requiring the device to soft-start from ground. CSS must be low-leakage; X7R, X5R, or C0G dielectric materials are preferred. See Table 8-1 for suggested soft-start capacitor values.

Table 8-1 Standard Capacitor Values for Programming the Soft-Start Time(1)
CSS SOFT-START TIME
Open 0.1 ms
270 pF 0.5 ms
560 pF 1 ms
2.7 nF 5 ms
5.6 nF 10 ms
0.01 µF 18 ms
(1) GUID-AC018E84-D15D-4144-9485-CA11F042E762-low.gifwhere tSS(s) = soft-start time in seconds.