ADS1278IPAPT

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1. Describe

Based on the single-channel ADS1271, the ADS1274 (quad) and ADS1278IPAPT (octal) are 24-bit delta-sigma (ΔΣ) analog-to-digital converters (ADCs) with data rates up to 144k samples per second (SPS), allowing simultaneous sampling of four or Eight channels. These devices are packaged in the same package, allowing plug-in expansion. Traditionally, industrial delta-sigma ADCs that offer good drift performance use digital filters with large passband drop. Therefore, they have limited signal bandwidth and are best suited for DC measurements. High-resolution ADCs in audio applications provide greater usable bandwidth, but with significantly weaker offset and drift specifications than their industrial counterparts. The ADS1274 and ADS1278IPAPT combine these types of converters to enable high-precision industrial measurements with excellent DC and AC specifications. High order chopper-stabilized modulators achieve very low drift and low in-band noise. An onboard decimation filter suppresses modulator and signal out-of-band noise. These ADCs provide usable signal bandwidth up to 90% of the Nyquist rate with less than 0.005dB ripple. Four operating modes optimize speed, resolution and power. All operations are directly controlled by pins; there are no registers to program. These devices are fully suitable for the extended industrial range (–40°C to +105°C) and are available in the HTQFP-64 PowerPAD™ package.

2. Feature

    1. Simultaneous measurement of four/eight channels

    2. Data rates up to 144kSPS

    3. AC Performance:

        – 70kHz bandwidth

        – 111dB SNR (High Resolution Mode) 

        –108dB Total Harmonic Distortion

    4. DC Accuracy:

        – 0.8μV/°C offset drift

        – 1.3ppm/°C gain drift

    5. Selectable operating modes:

        – High Speed: 144kSPS, 106dB SNR

        – High Resolution: 52kSPS, 111dB SNR

        – Low power consumption: 52kSPS, 31mW/ch

        – Low speed: 10kSPS, 7mW/ch

    6. Linear phase digital filter

    7. SPI™ or frame sync serial interface

    8. Low sampling aperture error

    9. Modulator output option (digital filter bypass)

  10. Analog Power: 5V

  11. Digital Core: 1.8V

  12. I/O power supply: 1.8V to 3.3V

3. Application

    1. Vibration/modal analysis

    2. Multi-channel data acquisition

    3. Acoustic/dynamic strain gauges

    4. Pressure Sensor

4. Pin configuration

5. Function Description

The ADS1278IPAPT is a delta-sigma ADC consisting of 4/8 independent converters that digitize 4/8 input signals in parallel. The converter consists of two main functional blocks that perform ADC conversions: a modulator and a digital filter. The modulator samples the input signal and simultaneously samples the reference voltage to produce a 1s density output stream. The density of the output stream is proportional to the analog input level relative to the reference voltage. The pulse stream is filtered by an internal digital filter that produces the output conversion result. In operation, the input signal is sampled at a high rate by the modulator. The modulator's quantization noise is moved to a higher frequency range and an internal digital filter removes it. Oversampling results in very low noise levels within the signal passband. Because the input signal is sampled at a very high rate, no input signal aliasing occurs until the input signal frequency is at the modulator sampling rate. Due to the high sampling rate of the modulator, this architecture greatly relaxes the requirement for an external antialiasing filter.