MAX271ENG+

Overview

The MAX271ENG+ is a digitally-programmed, dual second-order continuous-time lowpass filter housed in a 20-pin PDIP package. It operates on supply voltages ranging from ±2.375V to ±8V with a typical quiescent current of 6.5mA. The device provides two independent filter sections with programmable cutoff frequencies selectable between 1kHz and 25kHz via 7-bit digital inputs. Unlike switched-capacitor filters, it requires no external clock, eliminating clock noise and achieving a dynamic range exceeding 96dB. A key distinction of the MAX271 variant is the inclusion of an internal track-and-hold circuit.

Feature Summary

• Dual second-order Sallen-Key lowpass filter sections with independently programmable cutoff frequencies
• Integrated track-and-hold circuit for signal acquisition and holding functions
• Continuous-time architecture that eliminates clock noise associated with switched-capacitor designs
• Low-power shutdown mode reducing supply current to less than 15µA

Applications

• Anti-aliasing filtering for analog-to-digital converter interfaces
• Output smoothing for digital-to-analog converters
• Low-noise signal conditioning requiring high dynamic range
• Cascaded configurations for higher-order filter responses

Procurement Notes

Verify the component designation includes the plus suffix to confirm lead-free and RoHS compliance status. Ensure the ordering code matches the ENG variant to secure the specified industrial temperature range and PDIP packaging configuration. Cross-reference the manufacturer's latest documentation for any potential obsolescence notices or lifecycle changes before finalizing procurement plans.

Selection Notes

Select the MAX271ENG+ when a built-in track-and-hold function is required alongside dual filter channels. Choose this part over the MAX270 if direct signal sampling and holding capabilities are necessary within the same integrated circuit. Confirm that the required cutoff frequency range falls within the 1kHz to 25kHz specification limits and that the available digital control interface meets system timing requirements.

Part Context

This component belongs to the MAX270/MAX271 family of digitally-programmed continuous-time filters. The MAX271 variant specifically differentiates itself by integrating a track-and-hold amplifier, whereas the MAX270 provides an uncommitted operational amplifier instead. Both share identical filter core characteristics, power supply requirements, and digital programming interfaces.

Replacement Considerations

The MAX270ENG+ serves as a functional substitute if the track-and-hold feature is unnecessary and an uncommitted op amp is preferred. Verify pin compatibility and ensure the application does not rely on the specific T/H output characteristics unique to the MAX271 series.

FAQ

How is the cutoff frequency programmed?

The cutoff frequency is set using 7-bit data inputs (D0–D6) which select one of 128 discrete frequencies between 1kHz and 25kHz. Programming can be performed via microprocessor control or by hard-wiring the pins.

What is the difference between the MAX271 and MAX270?

The MAX271 includes an internal track-and-hold circuit that can sample and hold the output of either filter section. The MAX270 replaces this with an uncommitted operational amplifier.

Can the filter sections be cascaded?

Yes, the two independent filter sections can be cascaded to create higher-order filter responses, such as a fourth-order response with approximately 80dB/decade rolloff.