Power chips

International Rectifier has a new chip set solution for wide range, universal telecommunications input (36V to 75V) and 48V fixed input systems.

Designed for isolated or non-isolated DC-DC converter applications, the chip set enhances system level power supply performance such as bulk 48V conversion for system boards up to 220W or for powering the radio amplifier in base station systems.

“Our new optimized chip set consists of new DirectFET MOSFETs and the new IR2086S controller IC to create complete solutions for two commonly used converter topologies in the networking and communications industry,” said Carl Smith, Marketing Manager for Networking and Telecommunication Products at International Rectifier.

The IR2086S controller IC simplifies isolated DC-DC converter circuits using primary side full-bridge topologies. The IC is specifically optimised for bus converter applications, using a self-oscillating 50% fixed duty cycle. It helps reduce overall board space by up to 50% versus industry-standard quarter-bricks and reduces overall component count by up to 60%.

The IR2086S features an integrated soft-start capacitor that gradually increases duty cycle to 50% over 2000 cycles to limit in-rush current during start up and maintains equal pulse widths for the high- and low-side MOSFETs in the full bridge throughout the start-up sequence. Other features include hiccup current limit protection, ±1.2A gate drive current and adjustable deadtime from 50nsec to 200nsec to protect against shoot-through current and programmable switching frequency up to 500kHz.

To complete the chip set, a designer may choose from four new DirectFET MOSFETs, the 100V IRF6644 and IRF6655 or 40V IRF6613 and IRF6614.The new MOSFETs use IR’s latest trench technology with DirectFET packaging technology, enabling a reduction in key device specifications such as on-resistance and gate charge.

A typical telecom base station power amplifier stage, for example, requires a 28V regulated output from a wide-range (36V to 75V) input. IR’s new DirectFET MOSFET and controller IC chip set can be used to create an efficient (92.5% at full load, 28Vout@/250W) converter using a two-stage approach.

The first stage uses the IRF6655 and IRF6644 in a non-isolated synchronous buck configuration to produce a regulated intermediate voltage, followed by a simple full bridge fixed-ratio bus converter using the IR2086S and IRF6614 on the primary side, and the IRF6644 on the secondary side for self-driven synchronous rectification.

This solution eliminates complex secondary side control schemes that are used in single stage regulated solutions. The 50% nature of the bus converter also allows the use of 100V MOSFETs on the secondary side, rather than 150V or 200V MOSFETs that can reduce efficiency by up to 2%.

The new 100V IRF6644 can also be used to achieve up to 95.7% efficiency at full load of 220W (8Vout @ 27.5A) in stand-alone fixed 48V input bus converter applications, suitable for most networking and high-end computing systems.

Compared to similar circuits using single 100V SO-8 MOSFETs, this is approximately 1% better efficiency, and a 40°C reduction in device temperature. This lower device temperature eliminates the need to parallel additional devices on the primary side for increased current requirements, and in general the IRF6644 enables an approximately 46% increase in output power and balanced temperature between the primary side and secondary side of the converter. The IRF6644 achieves approximately 48% lower on-state resistance versus competing solutions with similar charge parameters.

Key performance figures-of-merit for combined on-state resistance and gate charge are up to 45% better than competing solutions, and the IRF6644 replaces two parallel, lowest charge competing solutions for equivalent on-state resistance. Depending on specific input-to-output voltage ratios, the secondary-side synchronous rectification topology can use IR’s 40V IRF6613 DirectFET MOSFET, for 33% more voltage headroom than a 30V device. When using IR’s 40V device, efficiencies to within 1% of 30V parts can be achieved.

The metal can construction of IR’s patented DirectFET MOSFET packages enables dual-side cooling that effectively doubles the current handling capacity of high frequency DC-DC buck converters powering advanced microprocessors.

Pricing is US $1.10 each for the IRF6644, US $0.48 each for the IRF6655, US $1.47 each for the IRF6613, and US $0.64 each for the IRF6614 and US $2.49 each for the IR2086S, all in 10,000-unit quantities. All of the devices are available now.