ZHCSPF2B December 2021 – December 2024 LM5168 , LM5169
PRODUCTION DATA
- 1
- 1 特性
- 2 應用
- 3 說明
- 4 Device Comparison Table
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 Control Architecture
- 7.3.2 Internal VCC Regulator and Bootstrap Capacitor
- 7.3.3 Internal Soft Start
- 7.3.4 On-Time Generator
- 7.3.5 Current Limit
- 7.3.6 N-Channel Buck Switch and Driver
- 7.3.7 Synchronous Rectifier
- 7.3.8 Enable, Undervoltage Lockout (EN/UVLO)
- 7.3.9 Power Good (PGOOD)
- 7.3.10 Thermal Protection
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Fly-Buck? Converter Application
- 8.2.1 Design Requirements
- 8.2.2
Detailed Design Procedure
- 8.2.2.1 Switching Frequency (RT)
- 8.2.2.2 Transformer Selection
- 8.2.2.3 Output Capacitor Selection
- 8.2.2.4 Secondary Output Diode
- 8.2.2.5 Setting Output Voltage
- 8.2.2.6 Input Capacitor
- 8.2.2.7 Type-3 Ripple Network
- 8.2.2.8 CBST Selection
- 8.2.2.9 Minimum Secondary Output Load
- 8.2.2.10 Example Design Summary
- 8.2.3 Application Curves
- 8.3 Typical Buck Application
- 8.4 Power Supply Recommendations
- 8.5 Layout
- 9 Device and Documentation Support
- 10Revision History
- 11Mechanical, Packaging, and Orderable Information
封裝選項
機械數據 (封裝 | 引腳)
散熱焊盤機械數據 (封裝 | 引腳)
- DDA|8
訂購信息
8.2.2.3 Output Capacitor Selection
The primary output capacitor, COUT1, can be selected using either Equation 14 or Equation 15. For this design, an output voltage ripple of 5 mV and a load transient of 0.2 V is used. From this, a ripple current of 0.34 A at 60-V input, and a peak transformer current of 0.77 A at full load is calculated. The two output capacitor equations give values of 11 μF and 5 μF. Because of the large derating of ceramic capacitors, COUT1 = 1 × 22 μF is used. Keep in mind that the equations give the minimum capacitance value and in no case must the capacitance of COUT1 be less than 2.2 μF. More output capacitance can be used to improve load transient response. Also note that when using type 3 ripple injection, the actual ripple voltage appearing on the output can be kept small.
where
- IPK = peak transformer current from Equation 13
- ΔVO = output voltage load transient
where
- ΔI = ripple current from Equation 12
- Vripple = ripple voltage on primary output
COUT2 is selected using Equation 16. In this case, a ripple voltage on the secondary otuput of 20 mV is chosen. The minimum input voltage must be used in this equation. A value of 10 μF is calculated and 1 × 22 μF for COUT2 is selected. Again, the equation gives the minimum capacitance value and in no case must the capacitance of COUT2 be less than 2.2 μF.
Both output capacitors must be X7R ceramics in a 1206 or 1210 case size, and rated for at least twice the output voltage.