QT301-IS

ADCs/DACs - Special Purpose Overview

The QT301-IS is a standalone Capacitance-to-Analog Converter (CAC) utilizing a patented charge-transfer method. It detects femtofarad-level capacitance changes and outputs an 8-bit resolution, 100 kHz PWM signal. The device operates on a single supply voltage ranging from 3 V to 5.5 V. Key features include spread-spectrum burst modulation for noise rejection, end-to-end calibration via CAL pins, and sample-on-demand functionality through a Sync input. It requires only one external sampling capacitor (Cs) between 1 nF and 500 nF.

ADCs/DACs - Special Purpose Feature Summary

• Patented charge-transfer conversion with sub-ranging direct-to-analog capability
• 100 kHz PWM output with spread-spectrum acquisition bursts for low noise
• End-to-end calibration (gain/span) stored in internal EEPROM
• Sample-on-demand operation via external Sync pin

ADCs/DACs - Special Purpose Applications

• Fluid level sensors
• Material and proximity sensors
• Position sensing
• Transducer drivers for pressure and humidity
• Moisture detection

ADCs/DACs - Special Purpose Procurement Notes

Verify the -IS suffix indicates the industrial temperature range (-40°C to +85°C). Confirm the package type matches the required footprint, as the datasheet lists both DIP and SOIC options. Check current availability status as the component may be discontinued or subject to lifecycle changes.

ADCs/DACs - Special Purpose Selection Notes

Select based on the required capacitance range (Cx) and sensitivity. The sampling capacitor (Cs) value, adjustable from 1 nF to 500 nF, directly influences gain and response time. Ensure the power supply is stable, as VDD fluctuations affect the PWM output. Use NPO/PPS capacitors for Cs to maintain stability across temperatures.

ADCs/DACs - Special Purpose Part Context

The QT301 is manufactured by QRG Ltd (now QProx) and distributed by Microchip Technology. It is designed for stand-alone instrumentation applications where raw capacitance data is processed externally. Unlike integrated MCUs, it provides unprocessed PWM data suitable for simple RC filtering or timer measurement.

ADCs/DACs - Special Purpose Replacement Considerations

Publicly confirmed substitute part numbers are not available in the provided documentation. Evaluate other CAC ICs from the same manufacturer or competitors based on interface compatibility and capacitance detection range.

ADCs/DACs - Special Purpose FAQ

How is the calibration process performed?

Calibration is triggered by asserting the CAL_DN or CAL_UP pins high for at least 2.5 ms. The device stores the endpoints in internal EEPROM and releases the pin when complete.

What is the function of the Sync pin?

The Sync pin allows the device to synchronize acquisition bursts with external signals, such as mains frequency, to suppress interference. If no sync pulse is received for 100 ms, the device reverts to its default timing.

Can the CAL pins be driven low?

No. Driving either CAL pin low will short-circuit the chip. They must be pulled low via a pulldown resistor and driven high via an open-source output or transistor emitter.