ZHCSHU8F October 2008 – July 2019 LM5575-Q1
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文档支持
- 12机械、封装和可订购信息
7.4.6 Maximum Duty Cycle and Input Dropout Voltage
There is a forced off-time of 500 ns implemented each cycle to ensure 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.
Equation 5. DMAX = 1 – Fs × 500 ns
where
- Fs is the oscillator frequency.
Limiting the maximum duty cycle will raise the input dropout voltage. The input dropout voltage is the lowest input voltage required to maintain regulation of the output voltage. Equation 6 calculates an approximation of the input dropout voltage.
Equation 6. 
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.