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60V synchronous buck controller eases power supply design

Posted: 28 May 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Intersil? buck controller? power supply? point-of-load supplies?

Intersil has announced a 60V synchronous buck controller that claims to simplify power supply and distribution design, enabling buck conversions such as 48V direct to 1V through a very low minimum-on-time-specification. The ISL8117 can permit point-of-load supplies to be fed from 48V rails.

Intersil said the device is the first 60V synchronous buck controller able to bypass the intermediate step-down conversion stage traditionally employed in industrial applications. The ISL8117 synchronous step-down PWM controller's low duty cycle (40ns minimum on time) allows the direct step-down conversion from 48V to a 1V point-of-load.


In high voltage applications where a lower output voltage is required, designers have traditionally relied on modules that increase system cost, or two stage DC/DC solutions that increase solution footprint and complexity. Intersil stated that where board space is constrained, and where there is a need to have PoL regulation in close proximity to the load itself, designers have frequently opted for a module solution. The ISL8117 controller offers a cost-effective and reliable alternative for applications where Vout to Vin ratio is low. The ISL8117 uses valley current mode modulation with adaptive slope compensation to enable stable operation for a wide range of Vin and Vout combinations, with no external compensation required. System designers can also use the ISL8117's adjustable frequency up to 2MHz to optimise power supply cost, size and efficiency.

Outlining the alternative design options, the company said an integrated (single-die, on-chip power switch) regulator must use (typically) lateral DMOS transistors; it is not feasible to integrate the more efficient trenchFETs and, "there is a big application space that needs the controller-plus-external FET solution." The device also supports a diode-emulation mode or "skipping" mode at light load, to maintain efficiency. No external current sense resistor is needed, and the lowest on-resistance MOSFETs can be employed. It does not as yet support digital interfaces such as PMBus. The industrial sector is not demanding PMBus at present, Intersil said, but indicates it may produce a device similar to the 8117 with a "digital wrapper" for monitoring and control, when that requirement emerges.

The ISL8117, Intersil adds, reduces solution footprint and simplifies design without compromising performance. Default design values for commonly used functions and the ISL8117's wide Vin and Vout reduce the number of external components compared to competing solutions. With the ISL8117, engineers can design a complete DC/DC buck conversion solution with only 10 components, including MOSFETs and passives, and achieve up to 98 per cent conversion efficiency with 1.5 per cent output voltage accuracy. The ISL8117's low pin count and layout friendly pin architecture also minimises the number of overlapping traces, further improving power supply performance.

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