ACM2420

The ACM2420's effective resolution (ENOB) varies with output data rate due to the sigma-delta architecture's noise shaping characteristics. At the lowest rate of 5 SPS, you achieve the full 20 ENOB with noise-free resolution of 20 bits. At 10 SPS, ENOB is approximately 19.5 bits. At 100 SPS, expect around 18 ENOB. At the maximum 2 kSPS rate, ENOB is approximately 16 bits. This trade-off between speed and resolution is fundamental to sigma-delta converters. For weigh scale applications requiring maximum precision, use 10-20 SPS. For temperature monitoring where speed is less critical, 5-10 SPS provides optimal results. The integrated digital filter provides excellent 50/60 Hz rejection at lower data rates, making this ADC ideal for power-line-connected equipment.

Select output data rate based on your application's speed vs precision requirements. Use lower rates for maximum precision.

Noise-free resolution is the number of bits that are stable (not toggling due to noise). To calculate: 1) Determine your peak-to-peak noise from the datasheet table based on your selected data rate and PGA gain. For example, at 10 SPS with 1x gain, peak-to-peak noise is approximately 2.5 μV. 2) Calculate the full-scale input range: for a 2.5V reference with 1x gain, FS = 5V (differential +/- 2.5V). 3) Calculate noise-free counts: FS / noise = 5V / 2.5μV = 2,000,000 counts. 4) Convert to bits: log2(2,000,000) = 20.9 bits. 5) Round down to get noise-free resolution: 20 bits. Higher PGA gains reduce the input range proportionally but can improve noise-free resolution for small signals by utilizing more of the ADC's dynamic range.

Use the highest PGA gain that accommodates your signal range to maximize noise-free resolution for small signals.

For RTD (Resistance Temperature Detector) measurement with the ACM2420, use a ratiometric measurement configuration for best accuracy. Connect the RTD in a 3-wire or 4-wire configuration to eliminate lead resistance errors. Use the ACM2420's internal excitation current source (100μA or 200μA) to drive the RTD. Connect the excitation voltage to the ADC reference input (REFIN) to implement ratiometric measurement - this cancels out excitation current variations. Set the PGA gain based on the expected RTD resistance range. For Pt100 RTDs (100Ω at 0°C), use 8x or 16x gain. For Pt1000 RTDs (1000Ω at 0°C), use 1x or 2x gain. Enable the 50/60 Hz filter to reject power line interference. With proper configuration, you can achieve +/- 0.1°C accuracy across the full -200°C to +850°C range.

Use ratiometric measurement with internal excitation current for RTD applications. Select PGA gain based on RTD type and expected temperature range.

Minimizing offset drift requires attention to both hardware and software techniques. Hardware considerations: 1) Use the internal reference voltage which has excellent temperature stability (10 ppm/°C). 2) Ensure good thermal design - keep heat sources away from the ADC and use copper pours for thermal distribution. 3) Use low-drift external components when needed. 4) Implement proper PCB layout with star grounding. Software techniques: 1) Perform offset calibration at startup by shorting inputs and measuring the offset. 2) Implement periodic offset calibration during operation if the system allows brief measurement interruptions. 3) Use chop mode if available, which automatically cancels offset through internal switching. 4) For thermocouple applications, ensure the cold junction compensation sensor is thermally coupled to the input terminals. The ACM2420's inherent offset drift of 0.02 μV/°C is excellent, but proper system design is still essential for maintaining accuracy over temperature.

Implement offset calibration at startup and consider periodic recalibration. Ensure good thermal design and use ratiometric measurement where possible.

Yes, the ACM2420 is excellent for multi-channel thermocouple measurement systems. Its four differential channels can monitor up to 4 thermocouples simultaneously. Key configuration points: 1) Set PGA gain to 32x or 64x to amplify the small thermocouple signals (typically 10-60 mV full scale). 2) Implement cold junction compensation (CJC) using an integrated temperature sensor or external sensor placed near the thermocouple connection terminals. 3) Enable the 50/60 Hz rejection filter to eliminate power line interference. 4) Use the burnout current sources to detect open thermocouple conditions. 5) For best results, use the ACM2420's single-cycle settling mode when switching between channels. The 24-bit resolution provides sufficient dynamic range to resolve 0.1°C temperature changes even with Type K thermocouples. For systems requiring more than 4 channels, multiple ACM2420 devices can share the same SPI bus using separate chip select lines.

Use PGA gain of 32x-64x for thermocouples. Implement cold junction compensation and burnout detection for robust operation.

The ACM2420 and ACM1604 serve different application requirements despite both being AcelaMicro ADCs. The ACM2420 is a sigma-delta converter optimized for high-resolution, low-speed precision measurement with 24-bit resolution and 20 ENOB at low data rates. It's ideal for weigh scales, temperature sensors, and precision instrumentation. The ACM1604 is a SAR converter designed for higher speed applications with 16-bit resolution and 1 MSPS sampling rate, making it better for control loops and data acquisition systems. The ACM2420 features integrated 50/60 Hz rejection and programmable excitation currents for sensor applications. The ACM1604 offers faster channel switching and lower latency. For multi-channel weigh scale systems, choose the ACM2420. For motor control or vibration monitoring, choose the ACM1604. Both offer excellent industrial-grade reliability and automotive qualification options.

Choose ACM2420 for high-precision, low-speed measurement. Choose ACM1604 for moderate-precision, high-speed applications.