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LTC3833 数据表(PDF) 29 Page - Linear Technology |
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LTC3833 数据表(HTML) 29 Page - Linear Technology |
29 / 50 page LTC3839 29 3839fa APPLICATIONS INFORMATION to INTVCC, it will operate in forced continuous mode at the RT-programmed frequency. If the MODE/PLLIN pin is tied to SGND, the LTC3839 will operate in discontinuous mode at light load and switch into continuous conduction at the RT programmed frequency as load increases. The TG on-time during discontinuous conduction is intentionally slightly extended (approximately 1.2 times the continuous conduction on-time as calculated from VIN, VOUT and f) to create hysteresis at the load-current boundary of continu- ous/discontinuous conduction. If an application requires very low (approaching minimum) on-time, the system may not be able to maintain its full frequency synchronization range. Getting closer to mini- mum on-time, it may even lose phase/frequency lock at no load or light load conditions, under which the SW on-time is effectively longer than TG on-time due to TG/BG dead times. This is discussed further under Minimum On-Time, Minimum Off-Time and Dropout Operation. Minimum On-Time, Minimum Off-Time and Dropout Operation The minimum on-time is the smallest duration that LTC3839’s TG (top gate) pin can be in high or “on” state. It has dependency on the operating conditions of the switching regulator, and is a function of voltages on the VIN and VOUT pins, as well as the value of external resistor RT. A minimum on-time of 30ns can be achieved when the VOUT pin is tied to its minimum value of 0.6V while the VIN is tied to its maximum value of 38V. For larger values of VOUT and/or smaller values of VIN, the minimum achievable on-time will be longer. The valley mode control architecture allows low on-time, making the LTC3839 suitable for high step-down ratio applications. The effective on-time, as determined by the SW node pulse width, can be different from this TG on-time, as it also depends on external components, as well as loading Figure 10. Phase and Frequency Locking Behavior During Transient Conditions PHASE AND FREQUENCY LOCK LOST DUE TO FAST LOAD STEP FREQUENCY RESTORED QUICKLY PHASE AND FREQUENCY LOCK LOST DUE TO FAST LOAD STEP FREQUENCY RESTORED QUICKLY PHASE LOCK RESUMED 3839 F10 PHASE AND FREQUENCY LOCKED ILOAD CLOCK INPUT SW VOUT |
类似零件编号 - LTC3833 |
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类似说明 - LTC3833 |
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