ADS8867 Differential ADC: 7 Checks for Common Mode and Signed Samples
ADS8867 Differential ADC: 7 Checks for Common Mode and Signed Samples
Plan ADS8867 acquisition with bounded differential inputs, external reference drive, conversion timing and checked signed decoding. This is a documentation-based planning guide, not a report of independent hands-on testing.
1. Separate differential range from individual pin voltage
ADS8867 is a sixteen-bit, 100 kSPS true-differential SAR converter. Its differential input range extends from negative VREF to positive VREF, but that does not permit either analog pin to swing freely below ground. Evaluate AINP and AINM individually against the documented input limits. Differential voltage and common-mode voltage must both be valid. Sketch the two input waveforms before selecting an amplifier or connecting a sensor with a floating return. Manufacturer documentation.
2. Understand why common mode changes usable span
The common-mode voltage can vary between ground and VREF, but the full differential span is available at the midpoint, VREF divided by two. As common mode approaches either rail, the allowed individual input voltages constrain the achievable differential excursion. Use the datasheet full-scale input-range table instead of treating common-mode flexibility as unlimited signal range. Test the extreme combinations of signal amplitude and offset, not merely the zero-differential midpoint condition. Manufacturer documentation.
3. Review AVDD, DVDD and REF independently
AVDD operates from 2.7 V to 3.6 V, DVDD from 1.65 V to 3.6 V, and the external reference from 2.5 V to 5 V. The reference can exceed AVDD within this documented architecture; that is not permission to overdrive unrelated pins. Match serial logic to DVDD and verify power sequencing. Keep reference accuracy, temperature drift and noise in the measurement budget rather than assuming sixteen output bits guarantee sixteen accurate bits. Manufacturer documentation.
4. Design reference and input drive for switched capacitors
The SAR conversion process draws dynamic charge from the reference and input network. A reference that is accurate into a static meter may still need suitable buffering and local capacitance for conversion bursts. Likewise, the input driver and RC filter must settle during acquisition to the required error. Review the manufacturer driver examples under their stated conditions. Do not substitute a high-resistance sensor source without calculating and checking its acquisition response. Manufacturer documentation.
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5. Select one documented serial operating mode
The interface supports different wiring and daisy-chain arrangements. Choose a specific timing diagram and implement its CONVST, DIN, SCLK and DOUT relationships consistently. Reserve the required conversion and acquisition intervals instead of assuming that SPI clock rate alone sets valid throughput. No-latency output describes the converter architecture, not permission to read before conversion finishes. Verify pin idle states and timing at startup with a logic analyzer before interpreting long data captures. Manufacturer documentation.
6. Decode the signed transfer characteristic deliberately
The transfer diagram places zero differential input near code 0000, negative full scale at 8000 and positive full scale near 7FFF. Decode the sixteen-bit result as a signed quantity rather than unsigned straight binary. The ideal differential code step spans two times VREF divided by 65536. Test decoding with small positive and negative known differential voltages, checking byte order and sign extension. These arithmetic checks are distinct from calibration or a measured accuracy claim. Manufacturer documentation.
7. Qualify records against known bounded stimuli
Start with a documented differential source and common-mode point, then test positive, negative and near-zero inputs without violating either pin limit. Capture the reference value, supply rails, acquisition timing and raw codes. Check settling after an input step and repeat at the intended sample rate. Preserve saturation flags or software range checks where appropriate. A stable numerical stream can still represent clipping, wrong byte order or inadequate reference drive, so compare it with independent measurements. Manufacturer documentation.
Related reading: ADS8866 SAR ADC: 7 Checks for CONVST Mode and Input Settling.
Catalog note: The exact-part search did not return a matching Epro listing during preparation. Check the current catalog; this guide makes no price, availability or included-accessory claim.