ZHCSDP0A May 2015 – February 2019 UC1845A-SP
PRODUCTION DATA.
- 1 特性
- 2 應(yīng)用
- 3 說明
- 4 修訂歷史記錄
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
- 8 Detailed Description
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12器件和文檔支持
- 13機(jī)械、封裝和可訂購信息
封裝選項(xiàng)
機(jī)械數(shù)據(jù) (封裝 | 引腳)
散熱焊盤機(jī)械數(shù)據(jù) (封裝 | 引腳)
訂購信息
9.2.2.1 Oscillator
The UC1845A-SP oscillator is programmed as shown in Figure 13. Timing capacitor CT is charged from VREF (5 V) through the timing resistor RT, and discharged by an internal current source. The first step in selecting the oscillator components is to determine the required circuit dead time. Once obtained, Figure 14 is used to pinpoint the nearest standard value of CT for a given dead time. Next, the appropriate RT value is interpolated using the parameters for CT and oscillator frequency. Figure 15 shows the RT/CT combinations versus oscillator frequency. The timing resistor can be calculated from the following formula.
Figure 12. E/A Compensation Circuit for Continuous Boost and Flyback Topologies The UC1845A-SP has an internal divide-by-two flip-flop driven by the oscillator for a 50% maximum duty cycle. Therefore, their oscillators must be set to run at twice the desired power supply switching frequency.
Figure 13. Oscillator Programming 
Figure 14. Dead Time vs CT (RT > 5 kΩ) 
Figure 15. Timing Resistance vs Frequency