SBAA551 June 2022 ADS8661 , ADS8665 , ADS8671 , ADS8675 , ADS8681 , ADS8685 , ADS8689 , ADS8691 , ADS8695 , ADS8699 , INA823 , INA826 , LM317L , LM337L , MUX509 , TPS2661 , TPS560430
This analog input module front-end design features 8 channels with each channel that can be configured to measure bipolar, universal voltage, and current inputs with a resolution of 16 bits. The module supports a scan rate of 1 ms for all 8 channels. Multiple input voltage ranges are supported with a programmable gain amplifier (PGA). Input ranges supporting up to 20% overrange. Any common-mode voltage (VCM) is effectively rejected. An open-wire detection feature identifies a broken connection to the sensor field transmitter. The design supports the extended industrial operating temperature range of –40°C to 125°C. Table 1-1 summarizes the key parameters of this design.
| Parameter | Value |
|---|---|
| Input channel | 8 |
| Input type | Universal (Current, voltage), bipolar |
| Input mode | Differential or single-ended |
| Differential input signal (maximum) | ±12.288 V |
| Common-mode input signal (maximum) | ±12 V |
| Abs input voltage (each pin) | ±12 V (referred to module ground) |
| Resolution | 16 bit (15+1bit) |
| Sample rate | 8 kSPS |
Voltage input ranges (including 20% overrange) Voltage input ranges (no overrange) Current input ranges | ±10 V ±5 V +10 V +5 V ±2.5 V 0/4...20 mA ±20 mA |
| Input impedance | Voltage mode: > 1 M? Current mode: 250 ? |
| Open-wire detection | Yes |
| 50 or 60 Hz rejection | No |
| Operating temperature | –40°C to 125°C |
All terminals are fully protected against overcurrent up to ±30 mA and overvoltage up to ±33 VDC (permanent). Surges according to IEC61000-4-5 (±1 kV at 42 ?) are effectively suppressed. Measurements on this reference design board demonstrate 16 bits of effective resolution (or ENOB) and 13–14 noise-free bits (NFB), depending on the selected voltage input range. The accuracy at room temperature is < 0.1%. Table 1-2 summarizes the performance specifications for this design.
| Parameter | Performance |
|---|---|
| Overvoltage protection | ±33 V permanent |
| Overcurrent protection | ±30 mA |
| Surge protection | IEC61000-4-5 (±1 kV/42 ?) |
| Mis-wiring protection | Yes, voltage and current input mode |
| Effective number of bits (ENOB) | ≥ 16.3 bit |
| Noise-free bits | ≥ 13.7 bit |
| Accuracy error | < ±0.1% at room temp |
| Common-mode voltage rejection | > 80 dB |