60V step-down controller can eliminate intermediate power buses

May 26, 2015 // By Graham Prophet
Intersil’s ISL8117 is a 60V synchronous buck controller that can simplify power supply and distribution design; allowing for buck conversions such as 48V direct to 1V – through a very low minimum-on-time-specification – it can permit point-of-load supplies to be fed from 48V rails.

Intersil claims 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 (40 nsec minimum on time) enables 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 notes 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 2 MHz to optimise power supply cost, size and efficiency.

Outlining the alternative design options, the company notes that 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 says, 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% conversion efficiency with 1.5% 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.

“The ISL8117 buck controller addresses a growing need for direct POL conversion from very high input voltage such as 48V to 1V output,” said Mark Downing, senior vice president of Infrastructure and Industrial Power Products at Intersil. “The unique ability to support light load efficiency mode is critical in industrial applications and makes the ISL8117 a much better alternative than existing solutions based on older technology.”