Convertor chipset cuts power supply costs

DC/DC convertor offers the performance and simplicity of buck (step-down) regulators for the design of isolated power supplies.

Linear Technology has introduced a family of DC/DC convertors that offers the performance and simplicity of a buck (step-down) regulator for the design of isolated power supplies.

These primary- and secondary-side ICs introduce PolyPhase operation for current sharing and paralleling of two circuits to achieve higher output current.

Other advantages include self-starting capability, which eliminates the need for an extra transformer winding, no-optocoupler design, fast transient response and synchronous rectification for high efficiency operation.

The chipset supports standard output voltages such as 5, 12, 28 and 52V as well as low voltages down to 0.6V.

Furthermore, they allow the use of inexpensive and off-the-shelf magnetics and discrete components.

An example of an application is an isolated power supply with 36-72V input range and outputs of 3.3V at 30A or 1.2V at 100A.

The primary-side controllers, the LTC3705 and LTC3725 are forward drivers.

The LTC3705 is a dual switch driver and the LTC3725 is the simpler version with single-switch operation.

The secondary-side ICs, the LTC3706 and LTC3726, are current mode synchronous rectifiers with a self-starting architecture.

The LTC3706 is suitable for PolyPhase operation whereas the LTC3726 is simpler and ideal for single-phase operation.

To further simplify the design, a proprietary technique is used to multiplex gate drive signals and DC bias power across the isolation barrier through a single, tiny pulse transformer.

The flexible design of the chipset enables both standard and custom footprint isolated power supplies.

Linear Technology offers design assistance for its customers, providing a schematic, bill of materials, simulations, design files and a demo board.

In addition to design support, customers can realise substantial cost savings compared with the cost of a DC/DC module.

The 1000-piece price per unit for the LTC3705, LTC3706, LTC3725 and LTC3726 are $2.63, $3.88, $2.56 and $3.19, respectively.

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