Cutting out the middle men

Steve Rogerson looks at Intersil’s latest buck controller that is claimed to cut out an intermediate step-down stage in industrial applications.

Traditional industrial power applications have to go through an intermediate stage to step down from a 48V input to the order of 1V point of load. However, the latest synchronous buck controller from Intersil can, claims the company, bypass the normally 12V intermediate stage and make the drop to the point of load directly.

The launch is part of the company’s attempt to grow the industrial and infrastructure side of its business, which already accounts for nearly two-thirds of its $562m revenue, of which about a fifth is invested back into research and development.

“We see that as critical to drive our business forward,” said senior vice president Mark Downing at the launch of the ISL8117 synchronous step-down PWN controller. “New products are the lifeblood of any company.”

The device has a 40ns minimum on-time that enables the direct step-down conversion from 48V to a 1V point-of-load. This achievement should make it possible for designers to reduce system complexity and cost in industrial, factory automation, medical and communications infrastructure applications.

“Our customers are trying to address higher voltage distribution buses,” said Downing. “They are trying to eliminate the intermediate stage conversion as this will give them two to three per cent gains in efficiency by taking this in a single stage.”

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 conversion that increase footprint and complexity. The ISL8117 controller is said to be a cost-effective and reliable alternative for applications where the Vout to Vin ratio is low. It 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 device’s adjustable switching frequency from 100kHz to 2MHz to optimise power supply cost, size and efficiency.

Though other products can support the 48V input, Downing said that the best competitors could step down to was 3.3V compared with the 1V for this device.

“The ISL8117 buck controller addresses a growing need for direct PoL conversion from very high input voltage such as 48V to 1V output,” said Downing. “The ability to support light load efficiency mode is critical in industrial applications and makes the ISL8117 a much better alternative than existing products based on older technology.”

He said the flexibility this offered was “particularly appealing” and said that while the efficiency gains did vary depending on the input to output range, overall it was very high. The company is claiming efficiencies of up to 98% and a 1.5% output voltage accuracy.

The device is said to reduce footprint and simplify design without compromising performance. Default design values for commonly used functions and the wide Vin to Vout range reduce the number of external components. With this device, engineers can design a complete DC-DC buck converter with ten components, including MOSFETs and passives.

“Adaptive slope compensation ensures we have stability and reduces the number of external components,” said Downing.

The low pin count and layout friendly pin architecture also reduces the number of overlapping traces, further improving power supply performance. The device has 16 pins compared with the normal 20 for this type of product.

Key features and specifications include an input voltage range of 4.5 to 60V covering all standard input rails including 5, 12, 24, 36, 42 and 48V. The voltage output range is configurable from 0.6 to 54V.

“Even though 60V may seem overkill for these types of applications,” said Downing, “in my experience engineers are looking for as much overhead as they can get.”

The programmable 100kHz to 2MHz switching frequency can be synchronised to reduce radiated system noise and avoid beat frequency issues. There is complete fault protection for long-term reliability including over-voltage, under-voltage, over-current and over-temperature.

High current FET drivers and diode emulation mode operation improve efficiency at all load levels. And adjustable soft-start with pre-bias support enables the sequenced start-up of multiple controllers.

The ISL8117 is available now in 4 by 4mm QFN and 6.4 by 5mm HTSSOP packages. Two evaluation boards let designers quickly evaluate device features and performance – the ISL8117EVAL1Z low power (Vin 4.5 to 60V and 3.3Vout, 6A), and the ISL8117EVAL2Z high power (Vin 18 to 60V and 12Vout, 20A).

“Customers can use our device in many varying applications,” said Downing. “To make their life a little easier, we have come out with reference designs that cover low and high power applications.”

He said though that this was just the start and that Intersil was investing heavily in the industrial power area.

“In the coming years, we will see more examples from us at higher voltage requirements to support the industrial and automotive market needs,” he said. “We have a separate automotive group and we collaborate very closely with them to address common markets.”

He said his colleagues in the automotive market were working on buck and buck-boost devices to support 48V battery applications. He acknowledged though that the ISL8117 at 60V was a little short of the margin needed for automotive.

“We will see more dedicated devices coming out to support the automotive market,” he said. “We will though expect this to be used in communications systems.”

For industrial markets, this device has been sampling for the past six months.

“Design-in cycles for industrial and communications can be very long,” he said. “The part is now fully available. You can order it on the web and it is with our distributors.”

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