National adds precision amps, filter tools to design environment

Santa Clara, Calif. — National Semiconductor Corp. today expanded its high-performance precision amplifier portfolio with the addition of three high common-mode difference amplifiers. Designed for broad-based industrial, commercial and automotive applications, these new amplifiers meet the requirements for accurate current sensing measurements in products such as battery charging and discharging for notebook computers and cell phones, and fuel injection control.

The LMP8270 and LMP8272 high common-mode amplifiers and LMP8271 high common-mode bidirectional amplifier join National's LMP (linear monolithic precision) product family targeting the precision market.

“National's new line of precision amplifiers delivers remarkable accuracy due to its very low offset voltage and drift. Also, because of their high input common mode voltage range, these parts are perfect for demanding applications, especially where current sensing is needed,” said Erroll Dietz, vice president of National's amplifier product group.

National's bidirectional LMP8271 measures charge and discharge currents at high common mode voltages typically found in precision applications. It uses an external reference voltage to set the voltage defining a zero-current condition. An LMP8271 output voltage greater than the external reference voltage indicates a charging current condition while an output voltage below the external reference voltage identifies a discharging current condition. Accurate bidirectional load current measurements are achieved when monitoring the output with respect to the reference voltage.

National's LMP8270 and LMP8272 are unidirectional, fixed-gain, differential amplifier products. These amplifiers will detect, amplify and filter small differential signals in the presence of high common mode voltages. For the LMP8270 and LMP8271, the gain is fixed at 20. For the LMP8272, the gain is fixed at 14. These parts have a -2 V to 27 V input common mode voltage range and a supply voltage range of 4.5 V to 5.5 V. These devices also function over an extended common mode input voltage (-5 V to +36 V), enabling high-side current sensing where the input voltage range far exceeds the supply voltage range of 5 V.

The very low offset voltage (less than 250 μV) and offset drift (less than 15 μV/°C guaranteed) of the LMP8270/71/72 allow for very accurate small input differential signal conditioning and minimal voltage offset error through the entire temperature range. Additionally, the extended operating temperature range of -40°C to +125&degC allows these amplifiers to be used in extreme conditions, such as those found in automotive and industrial applications.

National's new precision amplifiers are sampling now in limited quantities. Available in SOIC-8 packaging, National's LMP8270 is priced at $1.45, the LMP8271 is priced at $1.57, and the LMP8272 is priced at $1.45, all in 1,000-unit quantities. The LMP8270, LMP8271 and LMP8272 will be available in full production in March 2005.

Click here for additional technical information on the LMP8270.

Click here for additional technical information on the LMP8271.

Click here for additional technical information on the LMP8272.

A large selection of amplifiers and filters are supported by National's Amplifiers Made Simple Webench online design tool and Webench Active Filter Designer online design tool, respectively. To explore these solutions, visit

To learn more about designing with amplifiers, visit National's library of online seminars at

Additionally, National announced its Webench Active Filter Designer, the industry's most powerful online design tool, to speed the creation of sophisticated filters for data acquisition and signal conditioning applications. Designed from the ground up for ease of use, the tool lets engineers design advanced, highly customized filters for all standard filter types: low pass, high pass, band pass and band stop.

“Using the Webench Active Filter Designer, any engineer can create a highly complex theoretical filter in minutes and implement it with highly accurate real world models moments later,” said Phil Gibson, vice president of National Semiconductor's corporate marketing group. “Engineers can sample the amplifiers, download the automatically generated documentation, use the custom assembly diagram, and build a filter tomorrow.”

To view a demonstration showing how to create a 9th order low-pass filter with Bessel response in 30 seconds, visit:

“Today, designers may use the Webench Active Filter Designer to develop more than 200,0000 customized low-pass filters using any of 180 op amps, including our brand new precision offerings,” Dietz said. “National is not just building an 'ideal' structure, but is actually implementing it with real components.”

“National's LMP precision products, such as the ultra-low offset LMP2011 and the LMP8270 high common mode difference amplifier, process minute inputs and now, with advanced filters, any engineer can deliver an extremely precise signal,” said Huibert Verhoeven, senior design manager for National Semiconductor's Precision Amplifier group.

The Webench Active Filter Designer uses a powerful component selection tool, developed by National Semiconductor engineers to rapidly search among the company's portfolio of operational amplifier products (each with hundreds of different electrical parameters) and immediately configure the necessary bill of materials for every design. As with all the tools in National's Webench design environment, the Active Filter Designer and its simulators are available free of charge.

National's Webench Active Filter Designer also contains an embedded expert filter handbook. Visitors are guided through the process of creating a complete filter solution in a logical step-by-step fashion. All of the advanced theory any engineer would need is provided in a simple, integrated flowchart. The user can specify performance by frequency response, group delay or step response. The Filter Designer then creates all of the potential filter options (order and approximation) that meet the user's requirements and presents them as alternatives for comparison. Chebyshev, Bessel, Butterworth and elliptical transfer functions are offered with up to 9th order accuracy. Alternatively, the expert user can specify a set of ideal filters to be compared or even create an advanced filter from scratch.

Performance curves for each of the recommended filters are calculated and presented. The Filter Designer then guides the user through the selected filter implementation, including selection of the best op amp to be used in the design, and selection of each filter stage's topology, including Sallen-key, multiple feedback, and state variable types. Simulation, free samples and automatically generated documentation make the filter a reality.

National's Webench environment is useful for both the expert and the novice. It eliminates the need for a design engineer to perform tedious hand calculations and includes extensive online tutorials in analog design. The tools offer instant access to the latest SPICE models, parametric data and package information, enabling designers to simultaneously compare the performance of multiple devices in multiple applications. Overnight delivery in the United States is available on all of National's products with Webench design tool capability.

For more company information, please visit:

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The Webench Active Filter Designer speeds the creation of sophisticated filters for data acquisition and signal conditioning applications. Filter topologoes include: low pass, high pass, band pass and band stop.

Every six months or so, National Semiconductor adds to the options available in Webench — its increasingly popular online design environment — where engineers can create new products with the click of a mouse. This program results in roughly 3,000 amplifier design turns a month, out of 20,000 total designs monthly.

Phil Gibson walked me through the five-step active filter design process online: Select it, Design it, Analyze it, Build it and Test it. Gibson suggested that even I, who couldn't manage to get my tape recorder to work for the interview without some assistance, could succeed with Webench. “Anyone can implement multi-order, multiple-amplifier, precise active filter circuits, without having any theoretical knowledge of how this is done,” he said.

After checking the program out, which included integrated animated voice-over help tutorials to talk the user through the process, I decided that National Semiconductor does indeed have something special. The Webench design environment appears easy to use. Now, whether or not I could actually design something using it — is a horse of a different color. Nonetheless, the fact that even the remotest possibility existed in my mind, that I might be able to do this was impressive to me.

Today, National Semiconductor is expanding its precision amplifier family offering with three new products — The LMP8270, LMP8271 and LMP8272 high common mode difference amplifiers, which will be available via Webench.

Precision amplifiers are a fairly new playground for National Semiconductor. The company made its foray into the precision amplifier market in October with three devices — the LMP2011, LMP2012 and LMP2014, which are said to improve accuracy in industrial, medical and automotive applications.

National is competing with the likes of Analog Devices Inc., Linear Technology Inc., Maxim Integrated Products Inc., Texas Instruments Inc. and others in the precision amplifier arena.

National hopes to differentiate itself in the precision amplifier market by guaranteeing most precision amplifier electrical specifications — including offset voltage and offset voltage drift over a wide temperature range of -40°C to +125°C.

Extremely critical specifications, such as the temperature drift of the LMP8270, will be guaranteed through production temperature testing. Gaining share in this market is about hitting high performance consistently, especially in extreme environments like automotive applications where component performance can be impacted by elements such as weather, Verhoeven said.

The LMP8270 fixed-gain differential amplifier replaces discrete current sense solutions, which would normally require external resistors that are exactly equal — better than .01% accuracy, Verhoeven said. These costly precision matched pair resistors are integrated in the LMP8270 family. “This is the first time National is integrating highly accurate matched resistor pairs into its amplifiers,” he added.

Products that are driving demand for these high-speed, precision amplifiers include instrumentation, automotive, and computer applications, Verhoeven said.

The company is also including the ability to build complex filters via the addition of its active filter designer software into the Webench online design environment for data acquisition and signal conditioning applications. Filters go hand-in-hand with precision amplifiers since the amplifiers can be used to optimize filter performance by reducing noise and cleaning up the signal with high accuracy and no drift over time, Gibson said.

Previously, Webench users could build basic, low-pass filters. Now, however, designers can build complex filters of many types including Bessel, Chevycheb, Butterworth, and Eliptical architectures — 2nd, 5th, 7th up to an extremely complicated 9th order; any type or range of options is easily configured. National doesn't imagine there are too many users who will want to build anything beyond 9th order filters, Gibson said.

To date, Webench includes power supply design, amplifier and active filter design and audio and wireless design. The next product sector addition to Webench will be data conversion, Gibson said.

National also plans to unveil a new IC process that will be used to build future precision amplifiers, Gibson said. “This new state-of-the-art precision process will be disclosed in detail soon.”

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