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Sensor Chips Modulate PWM Signals With Temperature

The manufacturer says . . .

ChipCenter's Alex Mendelsohn says . . .

World's Lowest Voltage PWM Output Temperature Sensor Available in Tiny SOT23 Package from Maxim Sunnyvale, Calif.--Maxim Integrated Products introduced the MAX6676 single-wire PWM output sensor designed to operate with a power supply down to 1.8 V and a 50 µA (typ) current consumption. Available in a tiny 6-pin SOT23 package, this temperature sensor is perfect for industrial, HVAC, process control, and environmental monitoring applications. The MAX6676 encodes temperature data in the PWM output waveform, providing a nominal accuracy of 1.5°C over a single wire, which easily interfaces with a microprocessor or microcontroller I/O port. The device provides an open-drain output and has a nominal output frequency of 1.5 kHz. The MAX6676 operating supply voltage range is from 1.8 V to 5.5 V. The operating temperature range is from -55°C to +150°C. Prices start at $2.75 (2500 up, FOB U.S.A.).

There are actually two products in Maxim's lowest voltage sensor debut—there's the plastic-packaged MAX6676 referred to in the release, and the plastic-packaged MAX6677 not referred to. The '76 has an open-drain output, while the '77 uses a push-pull affair at its output. Also not mentioned in Maxim's press release, both sensors are monolithic BiCMOS chips. With their wide temperature range, they should find application not only in commercial and process-monitoring applications, but also as low-cost temperature monitors for temperature-sensitive microprocessors. Moreover, thanks to their very low current draw, these new sensors should find favor with those of you developing battery-powered products. In use, both new sensors convert ambient temperature levels into ratiometric PWM outputs, with the temperature information proportional to the duty cycle of the output's square wave. That permits the waveform's periods to be measured by an associated microprocessor or microcontroller with a timer or a counter function. While discussing these sensors, you should know that there are also other similar PWM sensor ICs offered by Maxim. There's the MAX6672 and the MAX6673, with open-drain and push-pull outputs, respectively, but in 5-pin SC70 packages. Then there's the MAX6666 and MAX6667 single-wire ratiometric PWM output devices. These sensors, operating at higher voltages, also come in open-drain and push-pull flavors, but typically draw 200 µA from 5 V lines. They're available in 6-pin SOT23 packages, and Maxim's 8-pin µMAX, as well as standard 8-pin SO packages. Now that you know that, note that the new '76 and '77 can be ordered in versions that operate from 3.6 V to 5.5 V, too, as well as the ones called out in the release that work over the touted 1.8 V to 3.6 V range. Driving Capacitive Loads As for the new MAX6677, thanks to its higher power push-pull output stage, it also ensures full CMOS output swings, but can sink and source more current than the single-ended '6676. As such, you can use it to drive capacitive loads such as coax cables or multiple downstream gates, where it will look into loads of up to 100 pF (with less than 1°C of error). In a clever innovation, these chips' low current draw also let you power them from logic. In some applications you can actually eliminate the already-low quiescent current demand just by taking the associated logic line that's powering them low under processor control. That can also keep self-heating under control, ensuring higher accuracy readings. For more details and realistic OEM pricing arrangements, contact Maxim Integrated Products, Inc. 120 San Gabriel Dr. Sunnyvale, CA 94086 Phone: (408) 737-7600        or (800) 998-9872 FAX: (408) 737-7194

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