Apex Microtechnology of Tucson, Ariz., has long been known for producing power op amps and PWM amplifiers in the form of hybrid assemblies. However, with its introduction of three high-voltage integrated circuits (ICs), the company is beginning to reposition itself as an IC company.
The move toward ICs is meant to lower the cost of the company’s high-power analog technology, making it affordable in many existing and emerging applications. To develop the new ICs, the company is exploiting its proprietary circuitry and the ongoing improvements in high-speed, high-voltage processes. These technical advances make it possible to achieve performance with ICs that was previously available only from discrete designs, hybrids or modules based on open-frame packaging.
Hybrids currently comprise 80% of Apex Microtechnology’s product portfolio. Another 17% of that portfolio consists of power circuits in the open-frame packages, which are akin to the packages commonly used in isolated dc-dc converter “bricks” so popular in telecom applications. The company began developing its open-frame products about two years ago when it became apparent that many customers did not need the hermeticity (i.e., packages that are hermetically sealed) provided by hybrids. Moreover, the lower cost of the open-frame packages made the PWM amplifiers and power op amps feasible in more applications.
By developing these same functions as ICs, which now account for just 3% of the company’s portfolio, the company further reduces product cost. The company refers to this budding product line as “precision ICs” because the components will typically be used by customers to direct fine motion. These chips also are being defined according to their niche within the “high-power analog” component area.
Apex Microtechnology applies the high-power analog description to devices that source or sink greater than 1 A of output current, operate with supply voltages greater than 100 V, feature slew rates above 100 V/µs and operate with quiescent currents below 10 mA. At present, three types of products fall somewhere within these limits—ICs, open-frame modules and hybrids. These product types offer increasing levels of performance in terms of the aforementioned specs (current, voltage and slew rate).
However, the relatively low levels of performance offered by the existing ICs hampers their usefulness in emerging applications. Existing power ICs are limited by current ratings up to 3 A, supply voltages up to 48 V and slew rates up to 100 V/µs. However, by exploiting a new design topology and leveraging the latest IC process technology, Apex Microtechnology is introducing IC components with greater performance, particularly in terms of voltage ratings. Note that the company is taking a “fabless” approach in developing these ICs. In terms of power ratings, Apex’s precision ICs will fall into the 40-W power range, with ballpark costs around $10 per unit.
The first of these new chips are three high-speed, high-voltage op amps—the PA78, PA86 and the PA69 (see the table at the end of this article). Offered in power SOPs and SIPs, these op amps target a growing number of piezo drive applications, which are found wherever ink jet printing is used. These applications require high voltage and high speed because the faster the driver amplifier performs, the faster the ink jet printer will produce its tiny droplets of ink.
The piezo drive applications have been growing rapidly in recent years as the cost of the piezo devices have fallen. In addition to their use in industrial printing of labels, piezo transducers perform positioning of wafers in photolithography equipment, and appear in ultrasonic surgical tools and ultrasonic cleaning systems. In addition, the same op amps developed for these piezo drives can be used in deflection circuits in displays and in gas chromatography instruments.*
The design topology developed to create the new power op amps provides high voltage and high-speed performance but still achieves low quiescent current. For example, the PA78 features a 150-mA (200-mA peak) output current rating and a slew rate of greater than 350 V/µs, yet limits quiescent current (IQ) to 1 mA. To achieve that low current consumption, the amplifier employs dynamic current sources rather than the fixed current sources found in conventional op amp designs. As a result, IQ in the PA78 varies as a function of the input signal. According to Apex Microtechnology, there are no ICs available with equivalent performance, so the new op amps will compete against discrete designs as well as against the company’s hybrid products.
Precision IC op amp product specifications.
|Part Number||Voltage (V)||Current (mA)||Slew rate (V/µs)||Unit price in lots of 10,000|
*For design details on amplifier requirement for piezo drives, see “Power Amplifier Drives Multiple Inkjet Heads,” by Dennis Eddlemon, senior analog design engineer, and Sam Robinson, applications engineer, Apex Microtechnology, Power Electronics Technology, January 2005, available online at powerelectronics.com/mag/power_power_amplifier_drives/index.html.