Synchronous buck controller handles extreme step-down ratios

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By Nick Flaherty

STMicroelectronics has launched a synchronous buck controller with an input voltage range from 6V to 75V that can eliminate the need for an intermedia bus.

The L3751 buck controller measures 3.5mm x 4.5mm and is aimed  serves different applications from industrial equipment to battery powered light electric vehicles as well as telecom and networking equipment that use 24V and 48V buses.

The minimum on-time duration of 40ns  supports an extremely low duty cycle thereby permitting a large step-down ratio. This allows powering low-voltage devices directly without intermediate conversion, which helps simplify circuit design and lower bill-of-materials (BOM) costs. The device integrates a 7.5V supply for the gate drivers.

In addition to having a wide supply-voltage range, the L3751 buck controller has 100V-tolerant inputs that allow operation in harsh electrical environments. The switching frequency is adjustable from 100kHz to 1MHz, giving designers flexibility to optimize circuit size, performance, and cost, through selection of the external MOSFETs and passive components.

To enhance efficiency and minimize ripple, the L3751 operates in diode-emulation mode and with pulse skipping at light loads.

The buck controller provides extensive protection functions, including thermal protection, input under-voltage lockout, constant current protection with hiccup mode, and programmable current sensing. There is also an external Enable pin and open-collector power-good indicator.

The L3751 is in production now and available in a QFN20 package with wettable flanks that assist with automated inspection systems. It is priced from $1.36 for orders of 1000 pieces. A 100W evaluation board, the STEVAL-L3751V12 is also available.

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