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highpowerZONE Products for the week of October 20, 2008
Cirrus Logic Says…
SA306/SA57: High Current PWM Drivers For Mid-Range Brushless/Brush Dc Motors
Apex Precision Power Family of Motor Control Drivers Deliver 17 A Peak, Cut Board Space Requirements up to 70%
Cirrus Logic Inc. has introduced the Apex Precision Power SA306-IHZ and SA57-IHZ, the industry’s highest-current pulse width modulated (PWM) ICs targeted at the fractional horsepower DC motor drive market. For the first time, designers can choose a single-packaged solution for driving three-phase brushless DC motors, or brush DC motors, in the 9 V to 60 V supply range. The ICs target motor control circuits used in industrial applications, such as factory and office automation, robotic controls, product handlers, as well as aircraft seating and positioning controls in the aerospace and military markets.
Previously, to drive motors requiring current above 3 A continuous, system designers have been faced with developing discrete solutions involving up to 50-60 individual components and requiring up to 70 percent more board space. The SA306-IHZ and SA57-IHZ give customers a simpler, highly reliable IC solution that incorporates ground-breaking performance of up to 5 A of continuous output current (8 A with A Grade versions), and PEAK output of 17 A, all housed in a 64-pin Power Quad package with a footprint measuring less than two centimeters square. Inside the package, the SA306-IHZ and SA57-IHZ deliver cycle-by-cycle current limit, which provides the unique ability to precisely control motor current in real time for each motor phase.
“With the SA3-6-IHZ and SA57-IHZ Cirrus Logic has achieved performance previously only possible with discrete solutions, thus improving reliability, simplifying design and saving space,” said Greg Brennan, vice president, Cirrus Logic Apex Precision Power business unit. “Now under the Apex Precision Power product brand, Cirrus is developing next generation products like the SA306-IHZ and SA57-IHZ with integrated performance and features previously possible only with discrete solutions.”
EN-Genius Says…
The Cirrus Logic acquisition of Apex last year (2007) was a total surprise, at least to me, with no glue logic seeming to link the two companies together. Company cultures were different; management styles were different; Apex was more industrial in its customer base while Cirrus was focused on consumer product OEMs; Apex was high-power Cirrus was audio.
Apex has been the breeding place for some very fine analog engineers but we have been waiting for the birth of new products, from what is now being called the Apex Precision Power Group of Cirrus, to see what direction the new combination might take.
These 3-phase switching amplifiers were in development before the acquisition so they don’t necessarily represent the synergy that might be available. But, logically, we must expect to see the Apex experience with PWM to lead to some Class-D products for the audio-centric Cirrus.
The SA306 for brushless dc motors, and the SA57 for brush dc motors, the former being the more complicated application, are monolithic solutions to problems that typically use 60+ components in discrete implementations. They are PWM drivers integrating 6 power MOSFETs (with Schottky diodes), about 30 low power passives, 3 temperature sensors, and at least 2 power resistors.
The parts offer 5 A continuous load operation (8 A with grade A versions) and 17 A peak operation (10 ms operation). The grade A versions also extend the operating temperature range from -25ºC to +85ºC up to -40ºC to +125ºC. These loads compare to the multitude of 2 A/3 A parts that are available. Supply rails for the new parts can be from 9 V to 60 V (absolute maximum).
A unique feature in these ICs is a cycle-by-cycle current limit control with the current of each of the three upper p-MOSFETs being measured (the lower MOSFETs are n-channel). This allows control of the inrush current, and the resulting back emf, providing the ability to limit the peak current inrush by a factor of about 3:1. Although the body diodes in the MOSFETs provide good reverse recovery characteristics, Cirrus recommends external Schottky flyback diodes to reduce dissipation and heating during commutation of the motor current.
The SA306 can also drive separate brush motors, either two (using a sort of differential drive system with the third channel used communally) or three different motors.
Cirrus has developed a package that has a thermal ground pad of the top surface. This allows for a board-mounted heatsink (about 1.5 inches in length) to be lowered down and tightened on top of the package. This increases the potential dissipation to be increased from about 5 W maximum, with a conventional thermally-enhanced package, to about 9 W, with natural convection from the heatsink, and more than 17 W with an added blower.
The SA306 and SA57 can be controlled by most microcontrollers and DSCs and integrate logic with dead-time generation and shoot-through prevention. Over-current and over-temperature warnings are provided as well as undervoltage lockout. Switching frequencies can be as high as 100 kHz to reduce filter component sizing.
Cirrus is taking a large leap with these products into a market that Apex knows but which is new to the Cirrus sales organization. The training of that sales team, together with the field applications engineers, will spell the degree of success that the products will achieve. The synergy between the original efforts from Apex and the lines of Cirrus will make or break sales. With a mixture of CMOS and DMOS on the same IC the pieces should be doing an optimal job in the different parts of the circuits. I would predict that there will be considerable market success because the parts fill a slot for medium power dc motors that has been a real bitch to implement with discretes, with a large amount of PCB real estate and height. Cirrus pushes the point that you can get a motor spinning within minutes using their demo boards: that is probably the winning line. Add in the value for money compared to discrete implementation, and designers will look at least twice. If the architecture here doesn’t end up as a Class-D woofer solution…
The SA306 and SA57 are in full production in the unique thermally-enhanced QFP-64 with the SA306-IHZ priced at $9.90 and the A grade SA306A-FHZ at $12.85, both in 10-k piece lots. The SA57-IHZ is priced at $7.15 and the A grade SA57A-FHZ at $9.05, also in 10-k piece lots. As noted, demo boards are available.
Data Sheets from the Apex Precision Power home page.
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