ZHCSY68D October 2008 – April 2025 LM5574-Q1
PRODUCTION DATA
- 1
- 1 特性
- 2 應用
- 3 說明
- 4 Pin Configuration and Functions
- 5 Specifications
- 6 Detailed Description
-
7 Application and Implementation
- 7.1 Application Information
- 7.2
Typical Application
- 7.2.1 Design Requirements
- 7.2.2
Detailed Design Procedure
- 7.2.2.1 Custom Design With WEBENCH? Tools
- 7.2.2.2 External Components
- 7.2.2.3 R3 (RT)
- 7.2.2.4 L1- Inductor
- 7.2.2.5 C3- Ramp Capacitor
- 7.2.2.6 C9 -Output Capacitor
- 7.2.2.7 D1 - Async Diode
- 7.2.2.8 C1- Input Capacitor
- 7.2.2.9 C8 - Vcc Capacitor
- 7.2.2.10 C7 - BST Capacitor
- 7.2.2.11 C4 - SS Capacitor
- 7.2.2.12 R5, R6 - Feedback Resistor
- 7.2.2.13 R1, R2, C2 - SD Pin Components
- 7.2.2.14 R4, C5, C6 - Compensation Components
- 7.2.3 Application Curves
- 7.3 Power Supply Recommendations
- 7.4 Layout
- 8 Device and Documentation Support
- 9 Revision History
- 10Mechanical, Packaging, and Orderable Information
6.4.5 Maximum Duty Cycle and Input Dropout Voltage
There is a forced off-time of 500ns implemented each cycle to make sure of sufficient time for the diode current to be sampled. This forced off-time limits the maximum duty cycle of the buck switch. The maximum duty cycle varies with the operating frequency.
where
- Fs is the oscillator frequency.
Limiting the maximum duty cycle raises the input dropout voltage. The input dropout voltage is the lowest input voltage required to maintain regulation of the output voltage. Use Equation 6 to calculate an approximation of the input dropout voltage.
where
- VD is the voltage drop across the re-circulatory diode.
Operating at high switching frequency raises the minimum input voltage necessary to maintain regulation.