Analog – Versatile DC-DC switching controllers for high-current applications (ADP1851)Sep 14 2012 - Power [More Power Articles]
Analog Devices has introduced the ADP1851, a wide-input-range synchronous step-down DC-DC controller with voltage tracking and synchronisation capability. The ADP1851 expands ADI’s popular series of configurable controllers following the recently introduced ADP1853. The versatile ADP1851/53 can be configured to work as a voltage-mode controller with input feed-forward or as a current-mode controller, depending on the application and customer preference. The ADP1851/53 are designed for high efficiency, high current, fast, transient point-of-load applications in a broad range of communications networking, industrial, medical, and consumer applications.
The ADP1851/53 can be connected in parallel to achieve higher current delivery – up to 50A depending on the external FETs. The ADP1851 features a synchronisation input eliminating troublesome ‘beat’ frequencies and reducing system input capacitance when multiple devices with phase-shifted synchronisation are used. The ADP1851 also has a tracking capability that enables controlled start-up. Simple, robust sequencing can be implemented using the precision enable and power-good functions. The ADP1851 is available in a 16-lead LFCSP (4mm x 4mm) package while the ADP1853 with clock out is available in a 24-lead (4mm x 4mm) LFCSP package.
In current-mode control, the ADP1851/53 architecture detects the current during the off period to improve noise immunity using the on-resistance of the low-side FET – or a series sense resistor for higher accuracy. Externally adjustable slope compensation is added to optimise performance in current mode. With minor adjustments to external resistor settings, the ADP1851/53 can be configured for voltage-mode control for improved noise performance, using input line feed-forward for ‘excellent’ line rejection. The ADP1851/53 series has a selectable pulse-skip mode to increase efficiency during light load operation. The device also has an accurate current limit, which allows for the sizing selection of external components to optimise valuable PCB space. The ADP1851and ADP1853 are supported by ADI’s online ADIsimPower tools, making the device easy to use and reducing design time, says the company.
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