Synchronous Buck Controller With Pre-bias Startup, And Optional Clock Synchronization
The LM2747 is a high-speed synchronous buck Regulator controller with a feedback voltage accuracy of 1%. It CAN provide simple down conversion to output voltages as low as 0.6V. Though the control section of the IC is rated for 3 to 6V, the driver section is designed to accept input supply rails as high as 14V. The use of adaptive non-overlapping MOSFET Gate drivers helps avoid potential shoot-through problems while maintaining high efficiency. The IC is designed for the more cost-effective option of driving only N-Channel MOSFETs in both the high-side and low-side positions. It senses the low-side Switch voltage drop for providing a simple, adjustable current limit.
The LM2747 features a fixed-frequency voltage-mode PWM control architecture which is adjustable from 50 kHz to 1 MHz with one external resistor. In addition, the LM2747 also allows the switching frequency to be synchronized to an external Clock signal over the range of 250 kHz to 1 MHz. This wide range of switching frequency gives the power supply designer the flexibility to make better tradeoffs between component size, cost and efficiency.
Features include the ability to startup with a pre-biased load on the output, soft-start, input undervoltage lockout (UVLO) and Power Good (based on both undervoltage and overvoltage detection). In addition, the shutdown pin of the IC CAN be used for providing startup delay, and the soft-start pin CAN be used for implementing precise tracking, for the purpose of sequencing with respect to an external rail.
By National Semiconductor Corporation
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